| 1. |
- Eggertsen, Maria, et al.
(författare)
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Seascape Configuration and Fine-Scale Habitat Complexity Shape Parrotfish Distribution and Function across a Coral Reef Lagoon
- 2020
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Ingår i: Diversity. - : MDPI AG. - 1424-2818. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- Structural complexity spanning fine to broad spatial scales can influence the distribution and activity of key organisms within marine ecosystems. However, the relative importance of hard (e.g., corals) and/or soft (e.g., macroalgae) structural complexity for marine organisms is often unclear. This study shows how both broad-scale (seascape configuration of coral structure) and fine-scale habitat complexity (structure height, number of holes, and presence of macroalgae) can influence the abundance and spatial ecology of reef fish. Underwater visual census of fish, surveys of habitats, remote underwater videos, and behavioral observations by following individual fish were used to quantify fine-scale habitat characteristics (e.g., complexity, coral structure height, macroalgae presence) and the abundance, size structure, and behavior (rates of herbivory, tortuosity ratios and total distance travelled) of abundant parrotfish. Both seascape configuration and macroalgae influenced the patterns of fish abundance and rates of herbivory. However, these relationships varied with trophic groups and ontogenetic stages. Abundance of adult and intermediate-phase parrotfishes was positively influenced by densely aggregated coral structures, whereas juvenile abundance was positively influenced by the presence of macroalgae. Foraging path and bite rates of an abundant parrotfish, Chlorurus spilurus, were not influenced by coral structure configuration or height, but the presence of macroalgae increased the bite rates of all juvenile parrotfish. Our results suggest that a combination of seascape configuration, fine-scale habitat complexity, and microhabitat selectivity influence reef fish community structure and foraging behavior, thus altering herbivory. However, these relationships can differ among functional groups of fish and life-history stages. Information on these fish–habitat interactions is critical for identifying habitats that facilitate ecological functions and ensures the successful management and conservation of essential habitats.
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| 2. |
- Eggertsen, Maria, 1981-, et al.
(författare)
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Seascape configuration and microhabitat condition shapes parrotfish distribution and function across a coral reef lagoon
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Structural complexity spanning fine to coarse spatial scales can influence the distribution and activity of key organisms within marine ecosystems. The current study shows how both broad-scale (seascape configuration of coral structure) and fine-scale habitat complexity (structural height, number of holes, and macroalgae) can influence the abundance and spatial ecology of reef fishes in a shallow tropical lagoon. Visual surveys, remote underwater video, and field observations were used to quantify habitat characteristics and the abundance, size structure and behavior (rates of herbivory, tortuosity ratios and total distance travelled) of abundant reef fishes. Both seascape configuration and macroalgae influenced patterns of fish abundance and rates of herbivory. However, these relationships varied with fish trophic groups and ontogenetic stages. High levels of hard complexity increased abundance of adult and intermediate-phase parrotfishes, whereas juvenile abundance was positively influenced by the presence of macroalgae, irrespective of the spatial configuration of coral structure in the seascape. Foraging path patterns (directed vs. convoluted) and bite rates of an abundant excavating parrotfish, Chlorurus spilurus, was not influenced by coral structure configuration in the seascape (dense/sparse) or coral structure height (high/low), but the presence of macroalgae increased the bite rates of all juvenile parrotfishes (including C. spilurus). Our results suggest a combination of microhabitat selectivity, fine-scale habitat complexity, and seascape configuration influence reef fish community structure and foraging behaviour, with consequences for the important ecological function of herbivory.
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| 3. |
- Fulton, Christopher J., et al.
(författare)
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Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes
- 2020
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Ingår i: Fish and Fisheries. - : Wiley. - 1467-2960 .- 1467-2979. ; 21:4, s. 700-717
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Tidskriftsartikel (refereegranskat)abstract
- Canopy-forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life-history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta-analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal-associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life-history stage. Major overlap (40%-43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal-associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal-associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal-associated fish and fisheries.
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| 4. |
- Wilson, Shaun K., et al.
(författare)
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The contribution of macroalgae-associated fishes to small-scale tropical reef fisheries
- 2022
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Ingår i: Fish and Fisheries. - : Wiley. - 1467-2960 .- 1467-2979. ; 23:4, s. 847-861
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Tidskriftsartikel (refereegranskat)abstract
- Macroalgae-dominated reefs are a prominent habitat in tropical seascapes that support a diversity of fishes, including fishery target species. To what extent, then, do macroalgal habitats contribute to small-scale tropical reef fisheries? To address this question we: (1) Quantified the macroalgae-associated fish component in catches from 133 small-scale fisheries, (2) Compared life-history traits relevant to fishing (e.g. growth, longevity) in macroalgal and coral-associated fishes, (3) Examined how macroalgae-associated species can influence catch diversity, trophic level and vulnerability and (4) Explored how tropical fisheries change with the expansion of macroalgal habitats using a case study of fishery-independent data for Seychelles. Fish that utilised macroalgal habitats comprise 24% of the catch, but very few fished species relied entirely on macroalgal or coral habitats post-settlement. Macroalgal and coral-associated fishes had similar life-history traits, although vulnerability to fishing declined with increasing contribution of macroalgae association to the catch, whilst mean trophic level and diversity peaked when macroalgal-associated fish accounted for 20%–30% of catches. The Seychelles case study revealed similar total fish biomass on macroalgal and coral reefs, although the biomass of primary target species increased as macroalgae cover expanded. Our findings reinforce that multiple habitat types are needed to support tropical fishery stability and sustainability. Whilst coral habitats have been the focus of tropical fisheries management, we show the potential for macroalgae-associated fish to support catch size and diversity in ways that reduce vulnerability to overfishing. This is pertinent to seascapes where repeated disturbances are facilitating the replacement of coral reef with macroalgal habitats.
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| 5. |
- Berkström, Charlotte, et al.
(författare)
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The arrangement of nurseries within a tropical seascape structure fish communities on nearby reefs
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ecosystems are linked by the movement of organisms across habitat boundaries and the arrangement of habitat patches can affect species abundance and composition. In tropical seascapes many coral reef fishes settle in adjacent habitats and undergo ontogenetic migrations to coral reefs as they grow. Few studies have attempted to measure at what distances from nursery habitats these fish migrations (connectivity) cease to exist and how the abundance, biomass and proportion of nursery species change on coral reefs along distance gradients away from nursery areas. The present study examines seascape arrangement, including distances between habitats, and its consequences on connectivity within a tropical seascape in Mozambique using a seascape ecology approach. Fish and habitat surveys were undertaken in 2016/2017 and a thematic habitat map was created in ArcGIS, where cover and distances between habitat patches were calculated. Distance to mangroves, seagrasses and channels were significant for most nursery species and both abundance, biomass and proportion of nursery species were highest in the south of the archipelago, where mangroves were present and decreased with distance to nurseries (mangroves and seagrasses). Some nursery species were absent on reef sites furthest from nursery habitats (80km) and at 8km from seagrass habitats the proportion of nursery/non-nursery species as well as abundance and biomass of seagrass nursery species drastically changed, indicating a threshold distance at which migrations may cease. A similar pattern was found between 3 and 6 km from channels. Threshold distances were found where ontogenetic movement from nurseries to reefs appeared to cease and these distances differed between fish families. Isolation and arrangement of nursery habitats were also found to structure adult fish communities on reefs, highlighting the importance of considering the matrix (sand and deep water) as barriers for fish migration.
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| 6. |
- Berkström, Charlotte, et al.
(författare)
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Thresholds in seascape connectivity : the spatial arrangement of nursery habitats structure fish communities on nearby reefs
- 2020
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Ingår i: Ecography. - : Wiley. - 0906-7590 .- 1600-0587. ; 43:6, s. 882-896
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystems are linked by the movement of organisms across habitat boundaries and the arrangement of habitat patches can affect species abundance and composition. In tropical seascapes many coral reef fishes settle in adjacent habitats and undergo ontogenetic habitat shifts to coral reefs as they grow. Few studies have attempted to measure at what distances from nursery habitats these fish migrations (connectivity) cease to exist and how the abundance, biomass and proportion of nursery species change on coral reefs along distance gradients away from nursery areas. The present study examines seascape spatial arrangement, including distances between habitats, and its consequences on connectivity within a tropical seascape in Mozambique using a seascape ecology approach. Fish and habitat surveys were undertaken in 2016/2017 and a thematic habitat map was created in ArcGIS, where cover and distances between habitat patches were calculated. Distance to mangroves and seagrasses were significant predictors for abundance and biomass of most nursery species. The proportions of nursery species were highest in the south of the archipelago, where mangroves were present and decreased with distance to nurseries (mangroves and seagrasses). Some nursery species were absent on reef sites farthest from nursery habitats, at 80 km from mangroves and at 12 km from seagrass habitats. The proportion of nursery/non-nursery snapper and parrotfish species, as well as abundance and biomass of seagrass nursery species abruptly declined at 8 km from seagrass habitats, indicating a threshold distance at which migrations may cease. Additionally, reefs isolated by large stretches of sand and deep water had very low abundances of several nursery species despite being within moderate distances from nursery habitats. This highlights the importance of considering the matrix (sand and deep water) as barriers for fish migration.
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| 7. |
- Eggertsen, Linda, et al.
(författare)
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Effects of tidal current-induced flow on reef fish behaviour and function on a subtropical rocky reef
- 2016
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 559, s. 175-192
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Tidskriftsartikel (refereegranskat)abstract
- Tidal currents are important features in reef environments with high tidal range. Such current-influenced areas can be attractive for fish due to transport of nutrients and food items. Biological sampling, however, is difficult in these environments and it remains poorly understood to what degree strong currents actually shape tropical and subtropical reef fish communities. We used remote underwater video to investigate effects of flow velocity on fish across the tidal cycle at a rocky reef in southern Mozambique. Fish were recorded during flow velocities ranging from 0 to 1.44 m s(-1). Current flow velocity had no significant effect on the benthic fish assemblage, while increasing flow velocity had a negative effect on pelagic fish abundance and influenced trophic group composition. Limits for tolerated flow velocity on the pelagic assemblage were species-specific, with the highest resistance for larger predatory fish using subcarangiform swimming. Flow velocity had significant positive effects on size of Caranx spp., showing that smaller individuals had lower tolerance to flow than larger conspecifics. Planktivorous pomacentrids and monodactylids were very abundant in flows up to 0.5 m s(-1), suggesting that the area functions as an important foraging ground for planktivorous fish up to this flow velocity, while abundance of barracudas Sphyraena spp. was higher in moderate currents compared to slack water. For the benthic assemblage, benthic structures seemed to provide sufficient flow refuge for fish throughout the tidal cycle, highlighting the importance of structural complexity for benthic fish in this environment. Fish assemblages on reefs subjected to strong tidal currents might therefore be sensitive to habitat modifications. The ecological importance of tidal currents should be considered in marine management.
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| 8. |
- Eggertsen, Linda, 1981-
(författare)
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Identification and implications of fish nurseries in tropical and subtropical seascapes
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many species of reef fish reside in specific nursery habitats as juveniles. Seagrass meadows, and mangroves are examples of well-recognized nursery habitats, but only recently canopy-forming seaweeds have been found to provide important habitats for some fish species in the tropics. Availability of nurseries can have effects on the abundance and spatial distribution of adult fish, which is why it is important to recognize key nursery habitats for proper management. Information on reef fish nurseries is largely lacking in the South Western Atlantic (SWA), while information in the Western Indian Ocean (WIO) and elsewhere is more extensive. However, more information on the consequences of nursery availability on adult fish populations is needed. This thesis studies nursery habitat use of reef fish on tropical and subtropical reefs in the SWA and in seagrass and reef systems in the WIO. The hypothesis that seagrass and canopy-forming macroalgae meadows function as a nursery habitat for reef fish is tested in the SWA. The aim of this thesis is also to understand distribution patterns of fish arising from the arrangement of the seascape, using a seascape ecology approach, linking patterns to non-reef nursery habitat use (mangroves and seagrass systems). Results showed that spatial and temporal patterns of juvenile reef fish abundance were weak on rocky, subtropical reefs in the SWA (Paper I), while there was a stronger preference for certain habitats on SWA tropical biogenic reefs, especially seaweed beds dominated by Sargassum (Paper II). The widely accepted paradigm that seagrass meadows function as nursery habitats for reef fish was not supported by the results from the study site in the tropical SWA (Paper II). This may be related to habitat availability in the seascape. In the SWA, seagrass meadows are spatially small, fragmented and less complex, compared to in the WIO, where they display high structural complexity and cover large areas. At the WIO study site (Bazaruto Archipelago), the juvenile fish assemblage in the seagrass meadows encompassed a number of reef fish species from a range of trophic groups and families, as well as resident seagrass species (Paper III). Key variables and extent of spatial scales that structure ontogenetic migrations were identified in both seagrass and reef habitats. Fish distribution patterns in the seagrass seascape was strongly influenced by seascape configuration and distance to adjacent habitats, highlighting that not all seagrass meadows are equally productive as nursery habitats. Variables important for distribution patterns of fish were identified, which in most cases were species-specific, and related to life history and functional traits of species. Effects of two small protected areas on the fish assemblage was also linked to geographical placement of reserves in the seascape. Likewise, the adult fish community composition on the reefs was found to be structured by the spatial arrangement of nursery habitats in the seascape, and presence of stretches of sand acting as isolating barriers (Paper IV). Nursery fish species were less abundant on reefs far from nurseries, resulting in differences in community and functional group composition along distance gradients in the seascape. Depending on functional traits of the nursery fish assemblage, seagrass and mangroves can enhance certain ecological functions on reefs. Both community structure and ecosystem functioning may therefore change depending on nursery habitat availability, highlighting the need to adopt a holistic seascape approach in management.
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| 9. |
- Eggertsen, Linda, 1981-, et al.
(författare)
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Identifying reef fish nursery habitats on subtropical rocky reefs in the Southwestern Atlantic
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Availability of nursery habitats can potentially limit adult populations of reef fish. Suitable nursery habitats are often shallow and located close to shore, and in many cases overlap with anthropogenic stressors and human activities. For proper management of reef fish communities it is therefore important to identify these habitats and minimize conflicts of habitat use in time and space. To identify potential spatial and temporal patterns of nursery habitat use, the reef fish communities on subtropical rocky reefs in the South western Atlantic were surveyed with under water visual census. Surveys were performed in summer and winter months during two years, along a depth gradient on marginal reefs and in seasonal Sargassum macroalgal beds. No clear patterns in total juvenile abundance and distribution were distinguished between seasons, although some families occurred in significantly higher abundances in summer months (Haemulidae and Sparidae). There were large variances in juvenile abundance between the two surveyed summers, with low total abundance in the summer of 2017, which could be linked to weak upwelling in the area and hampered growth of Sargassum. Similar to in other locations globally, climatic events that affect biomass of Sargassum may hence have large effects on fish recruitment also in the South western Atlantic. In general, shallow areas in sheltered bays had higher abundances of juvenile fish, especially when Sargassum was present in these locations. Spatial patterns of acanthurids and labrid scarinae, were more homogenous compared to those of tropical reefs in the South western Atlantic, where Sargassum beds harbor significantly more juveniles than other habitats. We suggest that fish in sub-tropical rocky reef environments in the South western Atlantic have access to less habitat diversity and complex substrate to use as nursery areas, and thus shallow, sheltered and vegetated habitats are critical for many species. Additionally, those habitats are also the most threatened by human uses demanding proper management.
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| 10. |
- Eggertsen, Linda, et al.
(författare)
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Seascape Configuration Leads to Spatially Uneven Delivery of Parrotfish Herbivory across a Western Indian Ocean Seascape
- 2020
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Ingår i: Diversity. - : MDPI AG. - 1424-2818. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- Spatial configuration of habitat types in multihabitat seascapes influence ecological function through links of biotic and abiotic processes. These connections, for example export of organic matter or fishes as mobile links, define ecosystem functionality across broader spatial scales. Herbivory is an important ecological process linked to ecosystem resilience, but it is not clear how herbivory relates to seascape configuration. We studied how herbivory and bioerosion by 3 species of parrotfish were distributed in a multi-habitat tropical seascape in the Western Indian Ocean (WIO). We surveyed the abundance of three species with different life histories-Leptoscarus vaigiensis (seagrass species), Scarus ghobban (juvenile-seagrass/adults-reefs) and Scarus rubroviolaceus (reef species) -in seagrass meadows and on reefs and recorded their selectivity of feeding substrate in the two habitats. Herbivory rates for L. vaigiensis and S. ghobban and bioerosion for S. rubroviolaceus were then modelled using bite rates for different size classes and abundance and biomass data along seascape gradients (distance to alternative habitat types such as land, mangrove and seagrass). Bioerosion by S. rubroviolaceus was greatest on reefs far from seagrass meadows, while herbivory rates by S. ghobban on reefs displayed the opposite pattern. Herbivory in seagrass meadows was greatest in meadows close to shore, where L. vaigiensis targeted seagrass leaves and S. ghobban the epiphytes growing on them. Our study shows that ecological functions performed by fish are not equally distributed in the seascape and are influenced by fish life history and the spatial configuration of habitats in the seascape. This has implications for the resilience of the system, in terms of spatial heterogeneity of herbivory and bioerosion and should be considered in marine spatial planning and fisheries management.
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