| 1. |
- Arnott, S. A., et al.
(författare)
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Selection of prey size and prey species by 1-group cod Gadus morhua: effects of satiation level and prey handling times
- 2000
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 198, s. 225-238
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Tidskriftsartikel (refereegranskat)abstract
- We performed laboratory experiments to investigate feeding behaviour of 1-group Atlantic cod Gadus morhua and compared the results with stomach content records from wild 1-group cod feeding within a shallow bay on the west coast of Sweden. On the basis of the field observations, 3 prey species were investigated: juvenile shore crabs Carcinus maenas, brown shrimps Crangon crangon and 0-group plaice Pleuronectes platessa. When fed single species meals in the laboratory, satiation level was mostly independent of prey size, but cod consumed more plaice than shrimps and more shrimps than crabs. Once satiated on crabs, cod ate plaice if they were subsequently offered, but the reverse was not true. The time taken to ingest crabs was independent of the prey:cod (P:C) length ratio, cod length or stomach fullness, whereas plaice and shrimp ingestion times increased with P:C length ratio, and shrimp times also increased with stomach fullness. Consequently, the profitability of crabs increased up until the maximum edible size, whereas shrimp and plaice profitability peaked at P:C length ratios lower than the maximum edible sizes. For a given prey species, size selection in the field correlated closely with the size-dependent profitability relationships. Species selection had no apparent dependence upon handling-time profitability(, species-dependent satiation level or gastric evacuation rate. Additional factors of probable importance include prey evasiveness, prey abundance, habitat patchiness and abiotic factors such as prevailing light conditions.
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| 2. |
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| 3. |
- Baden, Susanne P., 1952, et al.
(författare)
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Shift in seagrass food web structure over decades is linked to overfishing
- 2012
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 451, s. 61-73
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Tidskriftsartikel (refereegranskat)abstract
- Empirical field studies in seagrass have revealed that overgrowth by filamentous algae which reduces seagrass growth can be explained by a top-down cascading effect caused by declines in top predators, which is enforced by eutrophication. On the Swedish west coast, 60% of the seagrass has disappeared since the 1980s. We hypothesised that overfishing, responsible for a >90% decline in the cod stock, and the 4 to 8 times increase in nutrient load since the 1930s have altered the seagrass structure and function during recent decades. We used quantitative samples from the 1980s and 2000s and analysed the trends in abundance of the 4 feeding guilds: top predatory fish, intermediate predatory fish, crustacean omnivores and mesoherbivores. Since the 1980s, the commercial catch of gadoids on the Swedish west coast has decreased by >90 %, and here we found that the biomass of top predators (gadoids and trout) that forage in seagrass has decreased by approximately 80%. In contrast, the biomass of intermediate predatory fish (gobids and sticklebacks) has increased 8 times during summer and 11 times during autumn, while mesoherbivores (idoteids and gammarids >7 mm) have more or less disappeared from the seagrass bed. We thus found clear evidence that a shift in seagrass food web structure has taken place over the last 3 decades. Combining these findings with our recent empirical results from field cage experiments in the Skagerrak seagrass, where we manipulate top-down and bottom-up regulation, we conclude that lack of grazers in concert with eutrophication most likely contributed to the overgrowth by filamentous algae and disappearance of the seagrass on the Swedish west coast.
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| 4. |
- Baden, Susanne P., 1952, et al.
(författare)
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Vanishing seagrass (Zostera marina, L.) in Swedish coastal waters
- 2003
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Ingår i: Ambio. - 0044-7447. ; 32:5, s. 374-377
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Tidskriftsartikel (refereegranskat)abstract
- Along the Swedish Skagerrak coast eelgrass (Zostera marina) is a dominant phanerogam on shallow soft bottoms. Eelgrass meadows are important biotopes for many crustacean and fish species being either migratory or stationary. During the 1980s, inventories of the shallow coastal areas with eelgrass have been carried out along the Swedish west coast as a basis for coastal zone management. In the present study we revisited 2000 ha of eelgrass meadows in 5 coastal regions along 200 km of the Skagerrak coast. The inventory was made with the same methods (aquascope) as during the 1980s, but increasing the mapping accuracy by using a Global Positioning System (GPS). The results from this study show that the areal extension of Zostera marina has decreased 58% in 10-15 years with great regional variations. The decline was mainly restricted to the shallow parts of the meadow. The causes and ecological consequences are discussed.
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| 5. |
- Bergström, Lena, et al.
(författare)
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Distribution of mesopredatory fish determined by habitat variables in a predator-depleted coastal system
- 2016
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- Shallow nearshore habitats are highly valued for supporting marine ecosystems, but are subject to intense human-induced pressures. Mesopredatory fish are key components in coastal food webs, and alterations in their abundance may have evident effects also on other parts of the ecosystem. The aim of this study was to clarify the relationship between the abundance of coastal mesopredatory fish, defined as mid-trophic level demersal and benthic species with a diet consisting predominantly of invertebrates, and ambient environmental variables in a fjord system influenced by both eutrophication and overfishing. A field survey was conducted over a coastal gradient comprising 300 data points sampled consistently for fish community and environmental data. Results from multivariate and univariate analyses supported each other, demonstrating that mesopredatory fish abundance at species and functional group level was positively related to the cover of structurally complex vegetation and negatively related to eutrophication, as measured by water transparency. Contrary to other studies showing an inverse relationship to piscivore abundance over time, the spatial distribution of mesopredatory fish was not locally regulated by the abundance of piscivorous fish, probably attributed to piscivores being at historically low levels due to previous overfishing. Mesopredatory fish abundance was highest in areas with high habitat quality and positively related to the abundance of piscivores, suggesting a predominance of bottom-up processes. We conclude that, in parallel with ongoing regulations of fishing pressure, measures to restore habitat function and food web productivity are important for the recovery of coastal fish communities in the area.
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| 6. |
- Bergström, Lena, et al.
(författare)
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Relative impacts of fishing and eutrophication on coastal fish assessed by comparing a no-take area with an environmental gradient
- 2019
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 48:6, s. 565-579
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the relative impacts of pressures on coastal ecosystems is central for implementing relevant measures to reach environmental management objectives. Here, survey data on the species and size composition of coastal fish are evaluated in relation to fishing and eutrophication, by comparing a long-standing no-take area to an environmental gradient in the Baltic Sea. The no-take area represents an intermediate eutrophication level, but the species composition resembles that seen at low eutrophication in areas with fishing. The catch biomass of piscivores is 2-3 times higher in the no-take area than in the other areas, while the biomass of Cyprinids, generally benefitted by eutrophication, corresponds to that of areas with low eutrophication. The results support that fishing may generate eutrophication-like effects, and, conversely, that no-take areas may contribute to improving environmental status in impacted areas by enhancing piscivores, which in turn may contribute to further improvement in the food web.
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| 7. |
- Boström, C., et al.
(författare)
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Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems: Implications for coastal management and conservation
- 2014
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Ingår i: Aquatic conservation. - : Wiley. - 1052-7613. ; 24:3, s. 410-434
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Forskningsöversikt (refereegranskat)abstract
- This paper focuses on the marine foundation eelgrass species, Zostera marina, along a gradient from the northern Baltic Sea to the north-east Atlantic. This vast region supports a minimum of 1480km2 eelgrass (maximum >2100km2), which corresponds to more than four times the previously quantified area of eelgrass in Western Europe. Eelgrass meadows in the low salinity Baltic Sea support the highest diversity (4-6 spp.) of angiosperms overall, but eelgrass productivity is low (<2g dw m-2 d-1) and meadows are isolated and genetically impoverished. Higher salinity areas support monospecific meadows, with higher productivity (3-10g dw m-2 d-1) and greater genetic connectivity. The salinity gradient further imposes functional differences in biodiversity and food webs, in particular a decline in number, but increase in biomass of mesograzers in the Baltic. Significant declines in eelgrass depth limits and areal cover are documented, particularly in regions experiencing high human pressure. The failure of eelgrass to re-establish itself in affected areas, despite nutrient reductions and improved water quality, signals complex recovery trajectories and calls for much greater conservation effort to protect existing meadows. The knowledge base for Nordic eelgrass meadows is broad and sufficient to establish monitoring objectives across nine national borders. Nevertheless, ensuring awareness of their vulnerability remains challenging. Given the areal extent of Nordic eelgrass systems and the ecosystem services they provide, it is crucial to further develop incentives for protecting them. © 2014 The Authors.
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| 8. |
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| 9. |
- Emanuelsson, Andreas, et al.
(författare)
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Accounting for overfishing in life cycle assessment: new impact categories for biotic resource use
- 2014
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Ingår i: International Journal of Life Cycle Assessment. - : Springer Science and Business Media LLC. - 0948-3349 .- 1614-7502. ; 19:5, s. 1156-1168
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Tidskriftsartikel (refereegranskat)abstract
- Overfishing is a relevant issue to include in all life cycle assessments (LCAs) involving wild caught fish, as overfishing of fish stocks clearly targets the LCA safeguard objects of natural resources and natural ecosystems. Yet no robust method for assessing overfishing has been available. We propose lost potential yield (LPY) as a midpoint impact category to quantify overfishing, comparing the outcome of current with target fisheries management. This category primarily reflects the impact on biotic resource availability, but also serves as a proxy for ecosystem impacts within each stock. LPY represents average lost catches owing to ongoing overfishing, assessed by simplified biomass projections covering different fishing mortality scenarios. It is based on the maximum sustainable yield concept and complemented by two alternative methods, overfishing though fishing mortality (OF) and overfishedness of biomass (OB), that are less data-demanding. Characterization factors are provided for 31 European commercial fish stocks in 2010, representing 74 % of European and 7 % of global landings. However, large spatial and temporal variations were observed, requiring novel approaches for the LCA practitioner. The methodology is considered compliant with the International Reference Life Cycle Data System (ILCD) standard in most relevant aspects, although harmonization through normalization and endpoint characterization is only briefly discussed. Seafood LCAs including any of the three approaches can be a powerful communicative tool for the food industry, seafood certification programmes, and for fisheries management.
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| 10. |
- Engelsen, Anna, 1964, et al.
(författare)
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Benthic trophic status and nutrient fluxes in shallow-water sediments
- 2008
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714. ; 78:4, s. 783-795
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Tidskriftsartikel (refereegranskat)abstract
- Proliferation of fast-growing ephemeral macroalgae in shallow-water embayments constitutes a large-scale environmental change of coastal marine ecosystems. Since inorganic nutrients essential for the initiation and maintenance of macroalgal growth may be supplied from the underlying sediment, we investigated the coupling between benthic inorganic nutrient (mainly N and P) fluxes and sediment properties in 6 bays representing a wide gradient of sediment characteristics (grain size, organic matter content, solid phase C and N). The initial characterization of bays was made in June and also included measurements of oxygen flux and microphytobenthic and macrofaunal biomass. In September, still within the growth season of the macroalgae, complementary experiments with sediment-water incubations for benthic flux measurements of oxygen and nutrients focused on trophic status (balance between auto- and heterotrophy) as a controlling factor for rates of measured benthic nutrient fluxes. Generally, sediments rendered autotrophic by microphytobenthic photosynthesis removed nutrients from the overlying water, while heterotrophic sediments supplied nutrients to the overlying bottom water. Estimations of the green-algal nutrient demand suggested that late in the growth season, net heterotrophic sediments could cover 20% of the N-demand and 70% of the P demand. As the benthic trophic status is a functional variable more closely coupled to nutrient fluxes than the comparably conservative structural parameter organic matter content, we suggest that the trophic status is a more viable parameter to classify sediments and predict benthic nutrient fluxes in shallow-water environments.
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| 11. |
- Engelsen, Anna, 1964, et al.
(författare)
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Grazing effects by Nereis diversicolor on development and growth of green algal mats
- 2008
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Ingår i: Journal of Sea Research. - : Elsevier BV. - 1385-1101. ; 59:4, s. 228-236
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Tidskriftsartikel (refereegranskat)abstract
- Nereis diversicolor is generally considered to be a predator and deposit feeder, but have also been found to graze on benthic algae in shallow coastal areas. In this study we investigated the grazing effects on the development and growth of green algae, Ova spp. Algal growth was studied in an experiment including two levels of sediment thickness; 100 mm sediment including macrofauna and 5 mm sediment without macrofauna, and three treatments of varying algal biomass; sediment with propagules, sediment with low algal biomass (120 g dry weight (dwt) m(-2)) and sediment with high algal biomass (240 g dwt m(-2)). In the 100 mm sediment, with a natural population of macrofauna, N. diversicolor was the dominating (60% of total biomass) species. After three weeks of experimentation the result showed that N. diversicolor was able to prevent initial algal growth, affect growth capacity and also partly reduce full-grown algal mats. The weight of N. diversicolor was significantly higher for polychaetes in treatments with algae added compared to non-algal treatments. There were also indications that a rich nutrient supply per algae biomass counteracted the grazing capacity of N. diversicolor. (c) 2008 Elsevier B.V. All rights reserved.
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| 12. |
- Hedvall, Ola, et al.
(författare)
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Active habitat selection by megalopae and juvenile shore crabs Carcinus maenas: a laboratory study in an annular flume
- 1998
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. ; 376, s. 89-100
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Tidskriftsartikel (refereegranskat)abstract
- We studied megalopae (postlarvae) and young juveniles of the shore crab (Carcinus maenas L.) in laboratory experiments to examine four potentially important processes for juvenile distribution and recruitment: (1) hydrodynamic processes and passive deposition of megalopae, (2) active habitat selection of megalopae, (3) habitat specific predation rates, and (4) active habitat selection by juveniles. In an annular flume, simulating natural current velocities in nursery areas on the Swedish west coast, we assessed the distribution of dead megalopae, Live megalopae, live megalopae with predators (juvenile conspecifics and brown shrimp, Crangon crangon), and first instar crabs, in four simultaneously presented habitats: blue mussels (Mytilus edulis), eelgrass (Zostera marina), filamentous green algae (Cladophora sp. and Chaetomorpha linum) and bare sand. In a second experiment we studied the distribution of Live megalopae between four different ephemeral macroalgae with different structural complexity (Ulva lactuca, Enteromorpha sp., Cladophora sp. and Ectocarpus siliculosus). Dead megalopae were evenly distributed between the four habitats, whereas all other treatments showed significantly lower proportions of megalopae and juvenile crabs in the sand habitat (0-2%) compared to the structurally complex habitats (24-40%). The distribution between mussels, eelgrass and filamentous algae of live megalopae in absence of predators did not differ significantly from the hydrodynamical null hypothesis, i.e. distribution of dead megalopae. However, predation increased the proportion of megalopae significantly in the filamentous algae, providing the best refuge from predation of these habitats. First instar crabs showed a significantly different distribution compared to megalopae, with higher proportion in the algal habitat, whereas juvenile predatory crabs were found in significantly higher proportion among mussels. Megalopae selected all four different macroalgae species over open sand, but a significantly lower proportion were found in the algae with the highest structural complexity (Ectocarpus siliculosus; 14%) compared to the other algal species (26-30%). These results indicate that passive deposition have Little influence on the small scale (< 10 s of meters) distribution of shore crab megalopae during normal current velocities, but that active habitat selection by megalopae is the major process responsible for the non-random distribution of megalopae and juvenile shore crabs. The results further suggest that the initial distribution of megalopae between nursery habitats is quickly modified by habitat specific predation rates and size-specific movements and habitat choices by juveniles. The correlation between the habitat choice of megalopae and juvenile crabs, and the refuge value of the examined habitats suggests that habitat specific predation rates is a major selective force behind the behavior of active habitat selection in this species.
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| 13. |
- Kalogirou, S., et al.
(författare)
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Bycatch Dynamics from a Small-Scale Shrimp Trap Fishery in the Mediterranean Sea
- 2022
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Ingår i: Diversity. - : MDPI AG. - 1424-2818. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- Small-scale fisheries (SSFs) in the Mediterranean and Black seas play a significant social and economic role, representing 84% of the fishing fleet (70,000 vessels), 26% of total revenue (USD 633 million) and 60% of total employment (150,000 people), with the Food and Agriculture Organization (FAO) recently taking important initiatives to sustain livelihoods. Effective management of important natural fisheries resources that sustain livelihoods requires a holistic approach account-ing for all parts of the catch. Quantitative data on seasonal catch dynamics together with classification of bycatch species to IUCN vulnerability status and associated revenues from retained incidental catch were used to reveal the effect of a small-scale shrimp trap fishery on bycatch. We use three main quantitative variables (i.e., density, biomass and number of bycatch species) and show a positive correlation between bycatch and the seasonal catch dynamics of the target species during late spring and summer. On the contrary, discards were proportionally lower during winter, with the majority of discarded fish species not considered endangered. Six retained species in spring– summer and five discarded species in winter were found to modulate the structure of species’ as-semblage. Out of 55 bycatch species, 26 were retained and 29 discarded. Only four species were considered threatened, all of which were caught in very low numbers (<2 individuals), while the majority of the retained species was not considered endangered. The rapid sorting time (<1 min/per trap) pointed towards a decreased effect on certain discarded crustacean species and a significant reduction in total bycatch with timely haul time (from 71 to 47%). The results of this study can be used when considering future mitigation measures for this fishery, while the methodology used can provide insights into the management of similar trap fisheries worldwide when taking into account the sustainability of SSFs and the regional vulnerability status of bycatch species.
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| 14. |
- Kalogirou, Stefan, 1981, et al.
(författare)
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Diversity, structure and function of fish assemblages associated with Posidonia oceanica beds in an area of the eastern Mediterranean Sea and the role of non-indigenous species
- 2010
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Ingår i: Journal of Fish Biology. - 0022-1112. ; 77:10, s. 2338-2357
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Tidskriftsartikel (refereegranskat)abstract
- Temporal and spatial variation in density, biomass and body size of littoral fish species associated with nearshore Posidonia oceanica meadows was studied over an annual cycle in an area of the eastern Mediterranean Sea. A total of 109 350 littoral fishes were collected, belonging to 34 families and 88 species. Density of fishes peaked during the summer due to high numbers of juveniles. Season was a significant factor determining density, although number of species and biomass did not show any obvious seasonal pattern. Throughout the study, schooling planktivorous fish species such as the picarel Spicara smaris, the bogue Boops boops and the damselfish Chromis chromis were dominant, both in terms of density (80%) and biomass (70%). Temporal variation in density and body size of fishes was used to assess the seasonal and ontogenetic habitat use of each species, with their affinity to seagrass assessed by comparing their respective distribution on sand. Four functional guilds were created (juvenile migrants, seagrass residents, seasonal migrants and occasional visitors) to describe the habitat use of P. oceanica meadows by each species. Several species associated with P. oceanica meadows used this habitat mainly as juveniles during summer, although many others were present concurrently as adults and as juveniles. Among the species encountered, 11 were non-indigenous of Indo-Pacific origin, of which three used seagrasses mainly as juveniles and four as residents. The non-indigenous silverstripe blaasop Lagocephalus sceleratus ranked among the 10 most dominant species in terms of biomass (2%) and was classified as a seagrass resident.
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| 15. |
- Kalogirou, Stefan, 1981, et al.
(författare)
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Feeding ecology of indigenous and non-indigenous fish species within the family Sphyraenidae
- 2012
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 80:7, s. 2528-2548
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Tidskriftsartikel (refereegranskat)abstract
- The feeding ecology of two common indigenous (Sphyraena viridensis and Sphyraena sphyraena) and one abundant non-indigenous sphyraenid species, Sphyraena chrysotaenia, of Indo-Pacific Ocean origin, was investigated in an area of the eastern Mediterranean Sea. The stomach contents of 738 individuals of varying size, collected during the period December 2008 to August 2009, were examined. The dietary analyses revealed that all three species were specialized piscivores with a diet consisting of >90% fish, both by number and mass. Concurrent sampling of the fish assemblage made it possible to calculate selectivity as well as diet breadth and overlap of these strict piscivores. Even though several prey species were found in the stomachs of the three predators examined, selectivity towards Atherina boyeri was highly significant. For all species examined, >70% of the diet by mass was made up by three indigenous species of commercial value: Spicara smaris, Boops boops and A. boyeri. Diet breadth and size of prey increased with increasing body size for all predators. With increased body size, the diet overlap between indigenous and non-indigenous species decreased. This could be attributed to increased diet breadth and the specific life-history characteristics of indigenous species developing into larger individuals. During winter, the condition factor of the non-indigenous species was significantly lower than that of the indigenous, indicating that winter conditions in the Mediterranean Sea may limit its further expansion north and westward. With this study, the gap in knowledge of the feeding preferences of the most abundant piscivorous species found in coastal areas of the study region is filled. Additionally, the results indicate that non-indigenous species familial affiliation to indigenous ones does not facilitate invasion success.
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| 16. |
- Kalogirou, Stefan, 1981, et al.
(författare)
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Non-indigenous species in Mediterranean fish assemblages: Contrasting feeding guilds of Posidonia oceanica meadows and sandy habitats
- 2012
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 96:1, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative sampling in combination with classification of fish species into six major feeding guilds revealed the position and contribution of non-indigenous species (NIS) in the food web of Posidonia oceanica and sandy habitats in an area of the eastern Mediterranean. In P. oceanica beds and on sandy bottoms 10 and five species, respectively, were non-indigenous fish of Indo-Pacific origin. The proportional contribution of NIS individuals on P. oceanica beds was lower than that of sandy bottoms (12.7 vs. 20.4%) a pattern that also followed for biomass (13.6 vs. 23.4%), indicating that low diverse systems may be more liable to introductions than species-rich communities. The two habitats had similar fish feeding guilds, but the biomass contribution from NIS varied within each guild, indicating different degrees of impact on the available resources. This study showed that only few non-indigenous fish species contributed to the differences in biomass between habitats. No support could be found in postulating that taxonomic affiliation could predict invasion success. Size was considered highly important due to habitat shift of species with increased size. Two of the aspects considered in this study, the chance of establishing vs. the chance of being very dominant will depend upon competitive abilities strongly coupled to size and grounds for habitat shift. However, success of establishment will also depend on appropriate food resources in the recipient community as well as competitive abilities and level of competition in the food web within habitats
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| 17. |
- Kalogirou, S., et al.
(författare)
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Shrimp trap selectivity in a Mediterranean small-scale-fishery
- 2019
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836. ; 211, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- Small-scale shrimp trap fisheries, which have received very little attention in areas with limited potential for economic diversification, could offer a sustainable and socially beneficial option for profitable businesses in these regions. This study explores the effect of mesh size on selectivity of the commercially important narwal shrimp, Plesionika narval, in the Mediterranean Sea. Three different mesh sizes (8 × 8, 12 × 12 and 12 × 25 mm) were tested in fishing trials, with a theoretical Minimum Landing Size (MLS) using a defined maturity size of 12 mm to support interpretation of the results. Using the retention rates and the estimations on population fractions above and below MLS, we show that the use of the smallest- and largest-sized meshes would not support sustainable or efficient fishery. The results demonstrate a significant decrease in capture probability of undersized narwal shrimps with increased mesh size. The medium-sized mesh traps prove to be the best compromise for the fishery with high catch efficiency of commercial size shrimp and a low capture probability of undersized individuals. The results outlined in this article could be used to develop management plans for small-scale trap fisheries as a basis for developing viable enterprises in remote coastal communities. © 2018 Elsevier B.V.
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| 18. |
- Kalogirou, S., et al.
(författare)
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Spatial and temporal distribution of narwal shrimp Plesionika narval (Decapoda, Pandalidae) in the Aegean Sea (eastern Mediterranean Sea)
- 2017
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Ingår i: Regional Studies in Marine Science. - : Elsevier BV. - 2352-4855. ; 16, s. 240-248
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Tidskriftsartikel (refereegranskat)abstract
- In the Aegean Sea the trap fishery for narwal shrimp, Plesionika narval, contributes to social and cultural cohesion of local fishery communities. Spatial and temporal distribution patterns of narwal shrimp was studied during an annual cycle, including catch per unit effort (CPUE), sex ratio and proportion of ovigerous females in the population. Shrimps were sampled at five localities within the depth range of 10 to 170 m. Catch per unit effort increased during the summer period at all depths, when seawater temperature increase. Differences in CPUE were observed between depths, with highest catches at depths below 70 m. The proportion of females decreased significantly with depth, a pattern especially evident during the summer period (May to August), indicating a migration of females to shallower waters. Significant higher abundance of ovigerous females was observed during the period May to October, concurrently with a vertical migration of females to warmer waters. To further support this pattern, the proportion of ovigerous individuals among females increased with decreased depth at all seasons. We suggest that the findings of our study have significant implications to current and future management of narwal shrimp in the Mediterranean Sea. © 2017 Elsevier B.V.
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| 19. |
- Moksnes, Per-Olav, 1965, et al.
(författare)
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Cannibal-prey dynamics in young juveniles and postlarvae of the blue crab
- 1997
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Ingår i: Journal of Experimental Marine Biology and Ecology. ; 215:2, s. 157-187
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Tidskriftsartikel (refereegranskat)abstract
- Although cannibalism can act as a density-dependent regulator of population size in terrestrial systems, little is known of its effects in the marine environment. Herein we investigate the influence of cannibalism upon the early life history stages of the blue crab, Callinectes sapidus Rathbun, emphasizing cannibalism between juveniles and postlarvae (i.e. megalopae) of the same year class. In laboratory mesocosms we examined various factors modulating cannibal-prey dynamics, specifically: (1) the effects of habitat and presence of conspecifics on postlarval metamorphosis rate; (2) the effect of metamorphosis rate on the mortality of postlarvae from both intra- and inter-cohort cannibalism; (3) the effects of habitat and predator density on the functional response of young juvenile blue crab predators to varying densities of postlarval prey, and (4) the effects of prey size and habitat on predation mortality. Inter-cohort cannibalism caused significant mortality in every crab size and habitat type combination, and was lower in grass than sand for all prey smaller than fifth instar. Cannibalism between postlarvae was associated with metamorphosis and was density-dependent in sand, but not present in grass. Metamorphosis rates of postlarvae were inversely density-dependent in sand, but density-independent and higher in grass, indicating that habitat and intra-cohort agonism likely affects postlarval metamorphosis rates. Inter-cohort cannibalism was negatively correlated with metamorphosis rates of postlarvae. The functional response of young juvenile cannibalistic blue crabs differed significantly between sand and grass habitats, and between medium and high predator densities. Juvenile crabs displayed a type II, inversely density-dependent functional response in sand, resulting in very high mortality at low densities of postlarval prey. In grass, the crabs displayed a weak type III, density dependent response, yielding significantly lower mortality at low prey densities. Thus, habitat complexity changes the form of the functional response in cannibal-prey interactions and grass provides a relative habitat refuge from cannibalism. Doubling the number of predators in grass decreased the consumption rates per predator significantly and eliminated the density-dependence, indicating that intraspecific density can qualitatively change the form of the functional response. In the crab size experiment, only prey smaller than fifth instars received a habitat refuge from cannibalism in grass, whereas fifth instars received a relative size refuge in sand. Our results demonstrate that intra-year class cannibalism can cause mortality upon settling megalopae and first juvenile instars that is dependent on prey density. We expect inter-cohort cannibalism to cause local extinction of cohorts settling in sand, especially at low settlement densities, and high mortality at moderate settlement densities in grass. Satiation of predators at high settlement densities in grass suggests that episodic settlement can overwhelm predators locally. Furthermore, density-dependent mutual interference within large cohorts in the grass beds likely reduces their predation efficiency? indicating that aggregation of conspecific predators in grass habitats does not necessary lead to an increase in predation pressure. Finally, a relative size-refuge from inter-cohort cannibalism for fifth instar crabs supports an ontogenetic habitat shift around this crab size, which may be influenced by density-dependent agonistic behavior within cohorts. We suggest that intra-year class cannibalism is a major process regulating both survival and dispersal in megalopae and juvenile blue crabs. (C) 1997 Elsevier Science B.V.
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| 20. |
- Moksnes, Per-Olav, 1965, et al.
(författare)
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Predation on postlarvae and juveniles of the shore crab Carcinus maenas: importance of shelter, size and cannibalism
- 1998
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Ingår i: Marine Ecology-Progress Series. ; 166, s. 211-225
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Tidskriftsartikel (refereegranskat)abstract
- Settlement and early juvenile stages are considered a bottleneck in the Life history of many epibenthic organisms because of high predation mortality. Nursery habitats may play an important role in mitigating settlement and post-settlement mortality by providing refuge from predation. We examined these relationships in postlarvae and early juvenile stages of the shore crab Carcinus maenas L. in laboratory and field tethering experiments. We studied habitat and size related habitat mortality using postlarvae and young juvenile crabs as prey, and various predators, including juvenile conspecifics, in several habitats common in shallow (0 to 1 m) soft bottom nursery areas on the Swedish west coast. Settling mortality was high in open sand (80 to 90%), whereas a significant habitat refuge was obtained in mussel beds, eelgrass and filamentous green algae, the latter yielding the lowest mortality (13 to 14%). Small differences in structural complexity of ephemeral macroalgae dramatically affected predation mortality of first instar crabs, with a significant refuge obtained only in algae of medium complexity. Predation rate on tethered crabs in the field was high (52 to 67%) only on the smallest crabs (<5 mm carapace width, CW), which obtained a significant refuge in the eelgrass habitat compared to open sand. Mortality for larger crabs (5 to 25 mm CW) was low (<10%) and similar in sand and eelgrass habitats. Our results indicate that predation is an important process that can create a bottleneck for juvenile shore crab populations during settlement and early juvenile stages, mediated by the availability of nursery habitats. Postlarvae obtained refuge from predation in several different habitats, suggesting that the recruitment of juvenile shore crabs will be less affected by temporal and spatial variation of any single habitat type. The strong size refuge for crabs larger than 4 mm CW indicates that key predators are small. We suggest that cannibalistic juveniles, which caused predation rates similar to or higher than all other investigated predators, are dominant predators on settling postlarvae and young juvenile crabs in nursery areas. We further propose that habitat- and size-specific predation by small epibenthic predators are an important selective force in habitat selection by postlarvae and ontogenetic shifts in habitat use by juveniles.
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| 21. |
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| 22. |
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| 23. |
- Osterling, M., et al.
(författare)
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Effects of filamentous green algal mats on benthic macrofaunal functional feeding groups
- 2001
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Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981. ; 263:2, s. 159-183
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Tidskriftsartikel (refereegranskat)abstract
- A field experiment investigating the structuring effect of filamentous green algae on macrofaunal abundance, including functional feeding groups, was performed in a shallow (1 m) soft bottom bay on the Swedish West Coast. Temporal macrofaunal changes were investigated at three occasions under simulated moderate algal disturbance, using algal filled net-bags attached over the sediment. The moderate algal disturbance was also compared to a simulated high algal disturbance where cages were filled with algae. Abundance of suspension feeders and surface detrivores decreased significantly in the sediment after 3 weeks of exposure to high algal disturbance in cages compared to control sediment, but did not change in abundance from moderate disturbance under algal net-bags after this time. However, total macrofauna, suspension feeders and surface detrivores had significant lower abundance in the sediment under algal net-bags compared to controls, when all three occasions were included. Total abundance per unit area in the algae and its underlying sediment was significantly higher in the net-bag treatment compared to total macrofauna. in algal cages and controls. This was mainly due to high abundance among algae. Burrowing detrivores and predators had higher abundance among algae in the net-bags compared to algae in the cages. High abundance of macrofauna recorded among algae in the net-bag treatment could be due to filtering of larvae, post settlement redistribution or vertical migrations. In a laboratory experiment, juvenile Cerastoderma spp. and Corophium volutator migrated vertically into filamentous algae from sediment covered by an algal mat. C. volutator and adult Cerastoderma edule also had the ability to perform small-scale horizontal migrations from algae covered sediment. Suspension feeding bivalves are major contributors to production of the infauna in shallow soft bottoms, are important food for epibenthic predators and may functionally stabilise shallow marine soft bottoms. Decreases in recruitment and abundance of such an important functional group may thereby alter function and trophic relationships on shallow soft bottoms. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 24. |
- Pihl, Leif, 1951, et al.
(författare)
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Distribution of green algal mats throughout shallow soft bottoms of the Swedish Skagerrak archipelago in relation to nutrient sources and wave exposure
- 1999
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Ingår i: Journal of Sea Research. ; 41:4, s. 281-294
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Tidskriftsartikel (refereegranskat)abstract
- Distribution and biomass of green algal mats were studied in marine shallow (0-1 m) soft-bottom areas on the Swedish west coast from 1994 to 1996, by combining aerial photography surveys with ground truth sampling. Filamentous green algae, dominated by species of the genera Cladophora and Enteromorpha, were generally present throughout the study area during July and August, and largely absent in late April and early May. These algae occurred at 60 to 90% of the locations investigated during the summer, and were estimated to cover between 30 and 50% of the total area of shallow soft bottoms of the Swedish Skagerrak archipelago. The distributional patterns were similar during the three years of the investigation and appeared unrelated to annual local nutrient inputs from point sources and river discharge. We postulate that the apparent lack of such a relationship is due to an altered state of nutrient dynamics throughout the archipelago. Mechanisms are likely to involve long-term, diffuse elevations in nutrient levels in coastal waters of the Skagerrak and the Kattegat over several decades leading to current eutrophic conditions, exceeding nutrient requirements for abundant filamentous algal growth. Patterns of algal abundance in our study were largely related to physical factors such as exposure to wind, waves and water exchange under conditions where nutrient loads among embayments seemed to be unlimited. Further, our results show that sediments covered by algal mats had higher carbon and nitrogen contents than unvegetated sediments. We hypothesise that sustained high nutrient loads, manifested in extensive biomass of filamentous algae during summer months, are re-mineralised via decay and sedimentation in the benthic realm. Hence, accumulated carbon and nutrients in the sediment could, in turn, constitute the basic pool for future algal mat production overlying soft bottoms in areas where tidal exchange is limited. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 25. |
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| 26. |
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| 27. |
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| 28. |
- Pihl, Leif, 1951, et al.
(författare)
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Relating plaice (Pleuronectes platessa) recruitment to deteriorating habitat quality: effects of macroalgal blooms in coastal nursery grounds
- 2005
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X. ; 62:5, s. 1184-1193
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Tidskriftsartikel (refereegranskat)abstract
- Concentration of juveniles of marine fishes in nurseries may act as a bottleneck during the life cycle, where quantity and quality of nurseries determine population size. Macroalgal blooms have become a common phenomenon in eutrophic shallow waters worldwide, and matforming algae may now cover many essential nursery habitats. In this investigation, the aim was to assess the quantitative effect of algal mats on the recruitment of plaice (Pleuronectes platessa) from nurseries in the Swedish Skagerrak archipelago. A model was constructed using data on nursery size, settling density, and mortality of plaice combined with data on algal distribution. Recruitment of 0-group plaice from nurseries could be reduced by 30%-40% due to algae. The largest negative effect occurred during high settlement, reducing the important influence of strong year classes on stock size. The model predicted a reduction of juveniles due to algae of 45-46 x 10(6) individuals at high settlement. This amounts to 68% of the output at medium settlement and equals the amount of plaice produced during 5 years of low settlement. Up to 75% of the total reduction could occur in one quarter of the study area. With limiting resources, management actions should not be generally applied but rather be concentrated to optimize the cost-benefit of measures taken.
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| 29. |
- Pihl, Leif, 1951, et al.
(författare)
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Shift in fish assemblage structure due to loss of seagrass Zostera marina habitats in Sweden
- 2006
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Ingår i: Estuarine Coastal and Shelf Science. - London : Elsevier BV. - 0272-7714 .- 1096-0015. ; 67:1-2, s. 123-132
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Tidskriftsartikel (refereegranskat)abstract
- The areal extent of Zostera marina in the archipelago of the Swedish Skagerrak has decreased by 60% over two decades. To investigate the effects of Z. marina loss on the local fish assemblages, the fish fauna was compared between existing seagrass beds and sites where seagrass had vanished. A field study was carried out at four shallow locations in the outer archipelago of the coast in June 2004. Within each location two sites were sampled, one with an existing Z. marina bed and another where Z. marina had disappeared. Fish were sampled semi-quantitatively with a beach seine. Samples were taken during both day and night and captured fish were examined to species, enumerated and measured in the field, and released thereafter. The number of fish species was found to be significantly higher in Z. marina habitats compared to areas where seagrass was missing, and density and biomass of fish were generally lower in areas dominated by bare sediment compared to those in the seagrass habitats. Several species and groups of fishes (i.e., gadoids, labrids, syngnathids) were absent or occurred in low densities at sites where Z. marina was missing. For example, juvenile 0-group cod density was reduced by 96% at sites where Z. marina had disappeared. Such a reduction in recruitment of cod is in the same order of magnitude as the combined effect of seal predation and mortality due to by-catches in the eel fyke-net fishery estimated for the archipelago of the Swedish Skagerrak. Hence, the results clearly indicate a shift in the fish assemblage, including a loss of taxa at the family level as a result of degradation in habitat-forming vegetation. (c) 2005 Elsevier Ltd. All rights reserved.
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| 30. |
- Pihl, Leif, 1951, et al.
(författare)
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Spatial distribution patterns of newly settled plaice (Pleuronectes platessa L.) along the Swedish Skagerrak archipelago
- 2000
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Ingår i: Journal of Sea Research. - 1385-1101. ; 44:1-2, s. 65-80
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Tidskriftsartikel (refereegranskat)abstract
- Spatial distribution patterns of newly settled plaice (Pleuronectes platessa) were investigated along a 200 km coastline of the Swedish Skagerrak archipelago. Juvenile plaice were sampled quantitatively with a drop-trap in 32 small (0.02-0.04 km(2)) nursery bays over a 13-day period in mid-May 1998. The investigated area was divided into Four geographical regions along the coast, each with an inner and an outer archipelago zone. In each of the resulting sight sub-areas two randomly allocated pairs of closely situated (500-1000 m) bays were sampled, so that variation in post-settlement densities of plaid could be tested over different scales from hundreds of metres to tens of kilometres. Plaice density varied significantly on a regional scale, with order-of-magnitude higher densities in the northern (22.3 ind. m(-2)) than southern (2.3 ind. m(-2)) bays. Further, bays situated in the outer archipelago had significantly higher densities of juvenile plaid than bays in the inner archipelago. However, considerable variation was also found on a smaller spatial scale, with significant differences in plaice density within pairs of bays. The seasonal development in growth and mortality of juvenile plaice was studied in a sub-sample of bays characterised by high, medium and low post-settlement densities in May. Three bays from each group were revisited in July and August. Growth rates showed negative, and mortality rates positive, density-dependent relationships with plaice density. The observed patterns in settlement densities of plaice reflected the potential for variation in larval supply, local habitat characteristics and predation, over the spatial scales investigated. In addition, we outline the processes likely to produce density-dependent relationships in growth and mortality rates of juvenile plaice. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 31. |
- Pihl, Leif, 1951, et al.
(författare)
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Structure and diversity of fish assemblages on rocky and soft bottom shores on the Swedish west coast
- 2002
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Ingår i: Journal of Fish Biology. - 0022-1112. ; 61, s. 148-166
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Tidskriftsartikel (refereegranskat)abstract
- Density and biomass of fishes, from shallow rocky and soft bottom habitats on the Swedish west coast, showed large seasonal variation with low values in winter and spring and with peaks in June. Season was also the most important factor determining the fish assemblage structure. Within season, however, there was a clear separation in assemblage structure between rocky-and soft-bottom habitats. There were significantly higher total fish abundances and biomasses during night compared with day catches. On soft bottoms density and biomass of fishes decreased with increasing depth, but no such pattern was seen in rocky habitats indicating that the distribution of fishes was related to vegetation cover. Altogether, 53 fish species were recorded of which 30 were common to both habitats. Species richness was similar on rocky and soft bottoms. Of the 10 most abundant species found in rocky habitats four belonged to the Labridae and three to the Gadidae. The fish assemblage on soft bottoms were of a more mixed nature with representatives among the 10 dominants from six families (Clupeidae, Cottidae, Gadidae, Gobiidae, Labridae and Pleuronectidae). When ranking the 10 dominant fish species on rocky bottoms according to biomass c. 50% of the mass was Labridae, 19% Gadidae and 13% Cottidae. In soft bottom habitats, fish biomass was mainly distributed between six families. Pleuronectidae and Gadidae were dominant and each made up 25% of the biomass,,whereas Labridae only contributed 4% of the fish mass. It is concluded that the fish assemblage in rocky habitats is dominated by permanent non-commercial species (63% of biomass), whereas soft bottoms mainly function as nurseries for juvenile fishes and as feeding grounds for seasonal migrants of commercial species (80% of biomass). (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.
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| 32. |
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| 33. |
- Rönnbäck, P., et al.
(författare)
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Ecosystem goods and services from Swedish coastal habitats: Identification, valuation, and implications of ecosystem shifts
- 2007
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Ingår i: Ambio. - 0044-7447. ; 36:7, s. 534-544
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Tidskriftsartikel (refereegranskat)abstract
- Coastal areas are exposed to a variety of threats due to high population densities and rapid economic development. How will this affect human welfare and our dependence on nature's capacity to provide ecosystem goods and services? This paper is original in evaluating this concern for major habitats (macroalgae, seagrasses, blue mussel beds, and unvegetated soft bottoms) in a temperate coastal setting. More than 40 categories of goods and services are classified into provisional, regulating, and cultural services. A wide variety of Swedish examples is described for each category, including accounts of economic values and the relative importance of different habitats. For example, distinguishing characteristics would be the exceptional importance of blue mussels for mitigation of eutrophication, sandy soft bottoms for recreational uses, and seagrasses and macroalgae for fisheries production and control of wave and current energy. Net changes in the provision of goods and services are evaluated for three cases of observed coastal ecosystem shifts: i) seagrass beds into unvegetated substrate; ii) unvegetated shallow soft bottoms into filamentous algal mat dominance; and iii) macroalgae into mussel beds on hard substrate. The results are discussed in a management context including accounts of biodiversity, interconnectedness of ecosystems, and potential of economic valuation.
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| 34. |
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| 35. |
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| 36. |
- Stål, Johan, 1974, et al.
(författare)
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Coastal habitat support to fish and fisheries in Sweden : Integrating ecosystem functions into fisheries management
- 2008
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Ingår i: Ocean and Coastal Management. - : Elsevier BV. - 0964-5691 .- 1873-524X. ; 51:09-aug, s. 594-600
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Tidskriftsartikel (refereegranskat)abstract
- This study adopts an interdisciplinary approach, where ecological data on habitat structure and fish populations are combined with results from economic valuation case studies to assess effects of habitat disturbance. The focus is on three major habitats (soft sediment bottoms, seagrass beds and rocky bottoms with macroalgae), five fish species (cod, plaice, eel, mackerel and sea trout) and three types of fisheries (commercial, subsistence and recreational fisheries). The results have important implications for coastal zone management, demonstrating both ecologically and economically how coastal habitats support fisheries.
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| 37. |
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| 38. |
- Stål, Johan, 1974, et al.
(författare)
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Food utilisation by coastal fish assemblages in rocky and soft bottoms on the Swedish west coast: Inference for identification of essential fish habitats
- 2007
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Ingår i: Estuarine Coastal and Shelf Science. - : Elsevier BV. - 0272-7714. ; 71:3-4, s. 593-607
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Tidskriftsartikel (refereegranskat)abstract
- The concept of essential fish habitats (EFHs) is widely accepted for conservational and management purposes. EFHs are often considered as high quality habitats for fisheries species and subsequently of high values for society. In this study, fish and Substrate-Associated Prey (SAP) were sampled during the productive summer season 1998 (fish) and 2003 and 2004 (SAP) in shallow coastal rocky- and soft-bottom habitats on the Swedish west coast. The aim was to study the spatial and monthly variation of SAP as well as abundance and biomass of fish, and to examine if food items found in the diet of the fish assemblage were derived from SAP. We also examined if the diet of Ctenolabrus rupestris, a resident and abundant fish species in the shallow coastal habitats, and the diet of four seasonally abundant and commercially important fish species (Gadus morhua, Pleuronectes platessa, Salmo trutta and Scomber scombrus) were derived from SAP. There were significantly higher mean species number and abundance of the SAP assemblage on rocky compared to soft bottoms and the highest values were found on the rocky bottoms in August and in the shallowest (0-3 m) depth strata. There were no significant differences in number of fish species caught in the two habitats, although mean number of fish and mean biomass were significantly higher on rocky bottoms. Both habitats showed the same seasonal variation and the highest values of number of fish species, abundance and biomass were observed in June. On rocky bottoms, gastropods and amphipods were the most frequent food items in the diet of the entire fish assemblage and these items were also the most abundant SAP in this habitat. The dominant food items of the soft-bottom fish assemblage were decapods and fish, which were not common SAP. However, except for S. scombrus, the diet of the selected fish species showed a strong association to the SAP availability. Gadus morhua displayed the strongest association to SAP on rocky bottoms and P. platessa and C. rupestris to SAP on soft bottoms. Further, for C. rupestris, multivariate statistical analysis showed a significant association to the SAP assemblage on both rocky and soft bottoms. These results provide vital new information for the management and conservation of Essential Fish Habitats on the Swedish west coast. (c) 2006 Published by Elsevier Ltd.
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| 39. |
- Sundbäck, Kristina, 1949, et al.
(författare)
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Importance of benthic nutrient regeneration during initiation of macroalgal blooms in shallow bays
- 2003
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 246, s. 115-126
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Tidskriftsartikel (refereegranskat)abstract
- Fast growing ephemeral algae are increasingly observed in shallow coastal waters worldwide. This is generally considered a symptom of coastal eutrophication. It has been suggested that the reoccurrence of macroalgal mats, despite ongoing efforts to decrease nutrient loadings, may be explained by the fact that sheltered bays function as self-regenerating systems through benthic regeneration of nutrients. The importance of benthic nutrient regeneration during the initiation of the growth of filamentous green algal mats was investigated in 2 shallow-water bays on the west coast of Sweden. Nutrient regeneration was assessed in situ and in the laboratory, using sediment-water light/dark incubations and pore water distribution patterns. Benthic efflux of inorganic nutrients could supply up to 55 to 100% of the estimated nitrogen demand and 30 to 70% of the phosphorus requirements for the initial macroalgal growth from May to June. However, the availability of the pore water nutrient pool was influenced by the amount and functional type of infauna, and by competition from microphytobenthos. Because of the internal nutrient source of the embayments, it is suggested that there may be a significant time lag between a decreased nutrient supply to coastal waters and improved conditions of shallow water embayments.
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| 40. |
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| 41. |
- Troell, M., et al.
(författare)
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Regime shifts and ecosystem services in Swedish coastal soft bottom habitats: when resilience is undesirable
- 2005
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Ingår i: Ecology and Society. - Ottawa, Ont. : Ecological Society of America. - 1708-3087. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Ecosystems can undergo regime shifts where they suddenly change from one state into another. This can have important implications for formulation of management strategies, if system characteristics develop that are undesirable from a human perspective, and that have a high resistance to restoration efforts. This paper identifies some of the ecological and economic consequences of increased abundance of filamentous algae on shallow soft bottoms along the Swedish west coast. It is suggested that a successive increase in the sediment nutrient pool has undermined the resilience of these shallow systems. After the regime shift has occurred, self-generation properties evolve keeping the system locked in a high-density algae state. The structural and functional characteristics of the new system state differ significantly from the original one, resulting in less valuable ecosystem goods and services generated for society. In Sweden, loss of value results from the reduced capacity for mitigating further coastal eutrophication, reduced habitat quality for commercial fishery species, and the loss of aesthetic and recreational values.
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| 42. |
- Wennhage, Håkan, 1965, et al.
(författare)
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Distribution and quality of plaice (Pleuronectes platessa) nursery grounds on the Swedish west coast
- 2007
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Ingår i: Journal of Sea Research. - : Elsevier BV. - 1385-1101. ; 57:2-3, s. 218-229
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Tidskriftsartikel (refereegranskat)abstract
- Plaice (Pleuronectes platessa) has spatially restricted nursery grounds located in shallow soft bottom areas, where the nursery areas only make up a small fraction of the species distribution range. The importance of different coastal areas for recruitment is expected to depend on the quality and size of the nursery grounds. This paper describes the geographical extension of plaice nursery grounds at a regional level along the Swedish west coast. Densities of juvenile plaice were used as the response variable of habitat quality and were compiled based on records from autumn sampling in the various regions. Different aspects of nursery ground quality were related to the density of 0-group plaice, to evaluate the contribution of different factors to the geographical pattern observed. Larval supply was found to be the most important component of nursery quality showing a close relationship with the density of juvenile plaice on a regional scale. The relative contribution of plaice recruits from Swedish nursery grounds to the Skagerrak/Kattegat stock was evaluated using historical data. Swedish nursery grounds were estimated to contribute 77% of the recruits to the adult stock in the area. (c) 2006 Elsevier B.V. All rights reserved.
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| 43. |
- Wennhage, Håkan, 1965, et al.
(författare)
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Fish feeding guilds in shallow rocky and soft bottom areas on the Swedish west coast
- 2002
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Ingår i: Journal of Fish Biology. - 0022-1112. ; 61, s. 207-228
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Tidskriftsartikel (refereegranskat)abstract
- Multivariate analyses of the diet relationships within fish assemblages resulted in the recognition of five major feeding guilds in shallow (0-9m) rocky- and soft-bottom habitats on the Swedish west coast. The two habitats had similar guilds that could be broadly described as piscivores, decapod feeders, copepod feeders and amphipod and mollusc feeders. The last guild on the rocky bottom was more strictly one of amphipod feeders, whereas the last guild on soft bottoms consisted of infauna feeders (mainly polychaetes and bivalves). A comparison of the diet of the entire fish assemblages showed that amphipods and gastropods were more prevalent as prey taxa on rocky bottoms, whereas bivalves and teleosts were more common on soft bottoms. A large proportion (12 out of 27 species) of the fish species investigated was found in both habitats. These fish species generally seemed to rely on the same major prey groups in the two habitats, but also included prey taxa characteristic for the habitat in which they resided. Sea trout Sahno trutta, mackerel Scombrus scombrus, saithe Pollachius virens, whiting Merlangius merlangus and cod Gadus niorhua were found to be the major piscivores in both the investigated habitats. Herring Clupea harengus and members of the family gobiidae were the most prevalent prey species for piscivores within the rocky- as well as the soft-bottom fish assemblage. A comparison of feeding modes suggested that the fish assemblage on rocky bottoms predominantly (60% of the food items) relied on food found in vegetation. On soft bottoms, the average distribution of food categories among fish species was 44% benthic, 35% pelagic and 21 % vegetation-associated food items. (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.
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| 44. |
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| 45. |
- Wennhage, Håkan, 1965, et al.
(författare)
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Settlement patterns of newly settled plaice (Pleuronectes platessa) in a non-tidal Swedish fjord in relation to larval supply and benthic predators
- 2001
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Ingår i: Marine Biology. - 0025-3162. ; 139:5, s. 877-889
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Tidskriftsartikel (refereegranskat)abstract
- In demersal fish species with a pelagic larval stage, settlement patterns may be a consequence of variations in larval supply, habitat selection at settlement, and processes acting between the time of settlement and the time of benthic sampling. This study describes temporal (1994-1998) and spatial variation in plaice (Pleuronectes platessa L.) settlement densities in four semi-isolated nursery areas with similar habitat characteristics, in the non-tidal Gullmarsfjord on the west coast of Sweden. Juvenile abundance varied by a factor of ten, both among years and among nursery grounds. For the 3 years when larval sampling was undertaken (1994-1996) and all nursery areas, there was a significant positive relationship between larval supply and juvenile abundance (linear regression: r(2) = 0.45, n = 24, P < 0.001). On the southern side of the fjord, a significant positive relationship between larval and juvenile abundance was found in one area (r(2) = 0.62, n = 6, P < 0.05). The absolute mortality rate of plaice after settlement was related to the initial settlement density (r(2) = 0.95, n = 20. P < 0.001), and to the abundance of predatory shrimps Crangon crangon (r(2) = 0.44, n = 20, P < 0.01). Plaice otoliths were found in 6% of the shrimp stomachs analysed from an area with high density (13.3 m(-2)) of newly settled plaice. The present study suggests that the density of juvenile plaice was limited by larval supply to the nursery grounds. Consistency in the relative abundance of juveniles among nursery grounds between years also suggested that some nursery areas may be in the settlement shadow of others. The irregular nature of the coastline in combination with larval depletion could thereby cause small-scale (10(3)-10(4) m) variation in settlement densities of the same order of magnitude as the inter-annual variability in recruitment to individual nursery grounds.
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