| 1. |
- Gullström, Martin, et al.
(författare)
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Övervakning av makrovegetation i Bottniska viken– en vägledning
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- SammanfattningVi rekommenderar att dyktransekter enligt den nationella undersökningstypenförVegetationsklädda bottnar, ostkust (Naturvårdsverket 2004) används vidövervakning av makrovegetation. Metoden ger möjlighet till hög taxonomisknoggrannhet och kan svara upp mot i stort sett alla förvaltningsuppdrag. Denfungerar bra för att beskriva djuputbredning och täckningsgrad av arter.Skattningarna kan även omräknas till täckningsindex. Tyvärr finns det ingenfullständig metodbeskrivning. För att säkerställa kvalitén i nationella databaseroch underlätta upphandling av inventeringsuppdrag för myndigheterna bör entydlig metodbeskrivning omgående tas fram. Av samma orsaker behövs ävenmetodikkurser anordnas och i kombination med kontinuerlig interkalibrering avtäckningsgradsskattning och artbestämning kan en ackreditering av utföraregenomföras.När det gäller att designa ett miljöövervakningsprogram så bör syftet medövervakningen först definieras. Att övervaka klimatförändringen, övergödningeneller följa upp ekologisk status i vattenförekomster styr hur programmet sättsupp. Ett brett program med transekter spridda från inner till ytter skärgård dvs. iskärgårdsgradienten och en metod som har bra taxonomisk (och rumslig)upplösning ger möjlighet att nyttja data för fler syften.Vår rekommendation när det gäller att designa ett övervakningsprogram för attfölja upp storskaliga förändringar är att inte lägga stationerna alltför nära lokalautsläppskällor. Om stationerna ska användas som referens till recipienter ska dedock inte placeras för långt ut, så att de enbart beskriver förhållanden längst ut iskärgårdsgradienten.Vi rekommenderar att programmet bör följa upp flera responsvariabler t.ex.djuputbredning av arter, täckningsgrad, och diversitet. På detta sätt ökar chansenatt programmet fångar upp framtida, okända förändringar. Det är också enförutsättning för att nyttja transekterna för fler förvaltningssyften.Bottensubstrat är en av de faktorer som har störst betydelse förmakrovegetationens sammansättning och täckningsgrad. Det är viktigt att tahänsyn till detta när framtida analyser av data görs. Det är troligtvis en mycketviktig faktor när det gäller att stratifiera placering och bestämma antalet stationervid uppbyggnad av ett övervakningsprogram. I Bottniska viken är det mycketvanligt med transekter med blandade substrat eller att transekterna relativt snabbtövergår från hårdbotten till mjukbotten eftersom kusten är på många ställenflack. Detta är probelmatiskt för övervakning av ekologisk status kopplat tilldjuputbredning av arter.Våra analyser av djuputbredning och täckningsindex inom fyra skärgårdsområdenvisar att man med fördel kan stratifiera sina provpunkter utifrånvågexponering. Syftet med undersökningen bestämmer dock var i skärgårdendessa lokaler bör ligga.
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| 2. |
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| 3. |
- Andersson, Mathias H, 1976-, et al.
(författare)
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Importance of Using Multiple Sampling Methodologies for Estimating of Fish Community Composition in Offshore Wind Power Construction Areas of the Baltic Sea
- 2007
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 36:8, s. 634-636
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Tidskriftsartikel (refereegranskat)abstract
- It is standard procedure that an Environmental Impact Assessment (EIA) is conducted before larger constructions are built. To adequately describe the impact, methods used in an EIA should be carefully adapted considering both the character of the constructions under development and the environment that will be affected. Various sampling techniques are applied to estimate fish abundances and species composition. Methods used, including trawling, seine and gill netting, angling, echo-sound sampling, fishery data, video recordings, dredging, and visual counts using SCUBA, will all give different estimates of fish community composition.
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| 4. |
- Eklöf, J.S., et al.
(författare)
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Sea urchin overgrazing of seagrasses: A review of current knowledge on causes, consequences and management
- 2008
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 79:4, s. 569-580
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Tidskriftsartikel (refereegranskat)abstract
- Sea urchins are one of the most common seagrass macro-grazers in contemporary seagrass systems. Occasionally their grazing rates exceed seagrass growth rates, a phenomenon sometimes referred to as overgrazing. Because of a reported increasing frequency of overgrazing events, concomitant with loss of seagrass-associated ecosystem services, it has been suggested that overgrazing is one of the key threats to tropical and subtropical seagrasses. In light of this, we review the current knowledge on causes, consequences. and management of sea urchin overgrazing of seagrasses. Initially we argue that the definition of overgrazing must include scale and impairment of ecosystem services, since this is the de facto definition used in the literature, and will highlight the potential societal costs of seagrass overgrazing. A review of 16 identified cases suggests that urchin overgrazing is a global phenomenon, ranging from temperate to tropical coastal waters and involving at least 11 seagrass and 7 urchin species. Even though most overgrazing events Seem to affect areas of <0.5 km(2), and recovery often occurs within a few years, overgrazing can have a range of large, long-term indirect effects such as loss of associated fauna and decreased sediment stabilization. A range of drivers behind overgrazing have been suggested, including bottom-up (nutrient enrichment). top-down (reduced predation control due to e.g. overfishing), "side-in" mechanisms (e.g. changes in water temperature) and natural population fluctuations. Based on recent studies, there seems to be fairly strong support for the top-down and bottom-up hypotheses. However, many potential drivers often co-occur and interact, especially in areas with high anthropogenic pressure, suggesting that multiple disturbances-by simultaneously reducing predation control, increasing urchin recruitment and reducing the resistance of seagrasses-could pave the way for overgrazing. In management, the most common response to overgrazing has been to remove urchins, but limited knowledge of direct and indirect effects makes it difficult to assess the applicability and sustainability of this method. Based on the wide knowledge gaps, which severely limits management, we suggest that future research should focus on (1) identification and quantification of ecosystem and societal scale effects of overgrazing; (2) assessment of the relative importance and interactions of different drivers; and (3) development of a holistic proactive and reactive long-term management agenda.
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| 5. |
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| 6. |
- Eklöf, Johan, 1978, et al.
(författare)
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Sjögräsängar - hotade av både övergödning och överfiske?
- 2009
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Ingår i: HavsUtsikt: Om svensk havsforskning och havets resurser. - 1104-0513. ; 1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Sjögräsängar är viktiga som barnkammare för många fiskarter, men är hotade av människan genom bland annat övergödning. Nu visar resultat från forskning utförd av svenska forskare i Sverige och i Östafrika på att även överfiske av stora rovfiskar skulle kunna ge negativa effekter på sjögräset. Detta visar hur viktigt det är att man inom förvaltningen använder sig av en kombination av åtgärder när sjögräsängarna ska räddas.
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| 7. |
- Eklöf, Johan, 1978, et al.
(författare)
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The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii
- 2008
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Ingår i: Aquatic Botany. - : Elsevier BV. - 0304-3770. ; 89, s. 337-340
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Tidskriftsartikel (refereegranskat)abstract
- Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (I times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37-41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% x 3) compared to the one of low-intensity/low-frequency (25% x I) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing. (C) 2008 Elsevier B.V. All rights reserved.
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| 8. |
- Gullström, Martin, 1968, et al.
(författare)
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Assessment of changes in the seagrass-dominated submerged vegetation of tropical Chwaka Bay (Zanzibar) using satellite remote sensing
- 2006
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Ingår i: Estuarine Coastal and Shelf Science. - : Elsevier BV. - 0272-7714. ; 67:3, s. 399-408
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Tidskriftsartikel (refereegranskat)abstract
- Spatial and temporal dynamics of submerged aquatic vegetation (SAV) cover were studied in the relatively pristine and seagrass-dominated area of Chwaka Bay, Zanzibar (Tanzania) by using satellite remote sensing. Through complementary field work the potential of the technique for change detection was verified. The general changes in SAV cover were examined using Landsat images from 1986, 1987, 1998, 2001 and 2003. Two of these images, from 1987 (Landsat TM) and 2003 (Landsat ETM+), were specifically analysed to create a map of the change in SAV cover. Overall, the general distribution of SAV stayed fairly stable over the period investigated, but the result also showed regions where significant alterations, both losses and gains, had occurred between the two years. Based on our findings and anecdotal information from local fishermen and seaweed farmers potential causative factors are discussed. It was concluded that a repeated mapping with satellite remote sensing is a suitable tool to monitor changes of seagrass and seaweed distribution in shallow tropical environments. (c) 2005 Elsevier Ltd. All rights reserved.
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| 9. |
- Gullström, Martin, et al.
(författare)
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Assessment of vegetation changes in seagrass communities of tropical Chwaka Bay (Zanzibar) using satellite remote sensing
- 2006
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 67:3, s. 399-408
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Tidskriftsartikel (refereegranskat)abstract
- Spatial and temporal dynamics of submerged aquatic vegetation (SAV) cover were studied in the relatively pristine and seagrass-dominated area of Chwaka Bay, Zanzibar (Tanzania) by using satellite remote sensing. Through complementary field work the potential of the technique for change detection was verified. The general changes in SAV cover were examined using Landsat images from 1986, 1987, 1998, 2001 and 2003. Two of these images, from 1987 (Landsat TM) and 2003 (Landsat ETM+), were specifically analysed to create a map of the change in SAV cover. Overall, the general distribution of SAV stayed fairly stable over the period investigated, but the result also showed regions where significant alterations, both losses and gains, had occurred between the two years. Based on our findings and anecdotal information from local fishermen and seaweed farmers potential causative factors are discussed. It was concluded that a repeated mapping with satellite remote sensing is a suitable tool to monitor changes of seagrass and seaweed distribution in shallow tropical environments.
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| 10. |
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| 11. |
- Gullström, Martin, 1968, et al.
(författare)
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Seagrass structural complexity and landscape configuration as determinants of tropical fish assemblage composition
- 2008
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 363, s. 241-255
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Tidskriftsartikel (refereegranskat)abstract
- Seagrass meadows are regularly used by fish as resident, transient, or nursery habitat. However, there is a long-standing debate on how spatial variability of seagrass fish assemblages is determined. We examined the influence of seagrass structural complexity, physical water conditions, and proximity of neighboring shallow-water habitats on tropical fish assemblage composition in a shallow seagrass-dominated embayment at Zanzibar Island in the western Indian Ocean. Sampling of fish assemblages was carried out in seagrass meadows dominated by Enhalus acoroides or Thalassia hemprichii (3 localities each), 1 mixed meadow, and 1 unvegetated area. Overall, the density and biomass of fish were dominated by juvenile and subadult herbivores, either stationary seagrass residents or fish associated with coral reef and seagrass habitats. In terms of number of fish species, the majority were either carnivorous or omnivorous, and mainly coral-seagrass-associated. Multiple regression analysis indicated that canopy height was the foremost predictor for density, biomass, and species richness of juvenile fish, whereas adult and subadult fish densities were predicted by water depth. Moreover, distance-based correlation analyses revealed that fish assemblage structure was significantly correlated with the distance to neighboring mangrove and coral-reef habitats, shoot density, and (although weaker) canopy height. Based on these findings, attributes of seagrass structure and the location of a seagrass habitat within the seascape context appear to be important determinants of spatial patterns and variability of seagrass fish assemblages. This kind of information is important for spatial coastal management and for the selection of marine protected areas.
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| 12. |
- Moksnes, Per-Olav, 1965, et al.
(författare)
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Trophic cascades in a temperate seagrass community
- 2008
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 117:5, s. 763-777
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Tidskriftsartikel (refereegranskat)abstract
- We assessed the relative importance of bottom-up and top-down processes in structuring an eelgrass community in Sweden, a system impacted both by eutrophication and overfishing. Using artificial seagrass as substrate, we manipulated nutrient levels and predator abundance in a full-factorial cage-experiment. The results revealed a seagrass community dominated by strong top-down processes controlling the aggregate biomass of mesograzers and macroalgae. In the absence of predators the large amphipod Gammarus locusta became very abundant resulting in a leaf community with low biomass of algae and smaller mobile fauna. One enclosed gobid fish predator reduced the abundance of adult G. locusta by > 90%, causing a three to six times increase in the biomass of algae, smaller mesograzers and meiofauna. Numerous small predators in uncaged habitats reduced the biomass of G. locusta and other mesograzers by > 95% in comparison to the fish treatment, further increasing the biomass of epiphytic algae and meiofauna. Although water column nutrient enrichment caused a temporal bloom of the filamentous macroalgae Ulva spp., no significant nutrient-effects were found on the algal community at the end of the experiment. The only lasting nutrient-effect was a significant increase in the biomass of G. locusta, but only in the absence of ambient predators. These results demonstrate that mesograzers can respond to enhanced food supply, increase their biomass and control the algal growth when predation rates are low. However, in the assessed system, high predation rates appear to make mesograzers functionally extinct, causing a community-wide trophic cascade that promotes the growth of ephemeral algae. This top-down effect could penetrate down, despite a complex food-web because the interaction strength in the community was strongly skewed towards two functionally dominant algal and grazer species that were vulnerable to consumption. These results indicate that overexploitation of gadoid fish may be linked to increased macroalgal blooms and loss of eelgrass in the area through a trophic cascade affecting the abundance of mesograzers.
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| 13. |
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| 14. |
- Molander, Sverker, 1957, et al.
(författare)
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Socio-technical-ecological evaluations of the potential to implement renewable energy sources in coastal areas of tropical developing countries – an East African case study
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The suggested project aims at evaluating the potential for a successful implementation of renewableenergy sources in the coastal zone of tropical developing countries integrating results from differentscientific disciplines (ecology, social science and technology) into a useful support for developmentpolicy. Its emphasis will be on remote areas where poor infrastructures raise the demand forindependent electricity supplies. Moreover, the project intends to identify key-issues and sociotechnicalpathways for a future integration of suitable renewable energy sources in such areas.The research will be based on analyses of the relationships between technical, ecological andsocial systems and focus on applying adequate technology in a socially and ecologically feasible way.The energy sources considered will be selected from local natural flowing resources, i.e. mainly tidal,stream, and wave energies.With funding from Sida (SAREC Planning Grant) and Adlerbertska Forskningsstiftelsen, a planningstudy was carried out during October – November 2007, including the subsequent parts:1) meetings with representatives from several concerned institutions in Mozambique and inTanzania2) field visit to remote rural areas in southern Tanzania where hydrographical and coastmorphological features were documented3) meetings with village representatives in remote rural southern Tanzania in order to collectinformation about living standards, energy demands and development intentionsCompiled results from the three parts are presented in this report and will constitute a baseline for theforthcoming application of Sida Project grant, to be handed in April 2008. When taking part of theresults it is important to keep in mind that the suggested project does not intend to construct any actualpower plants, or pilot plants, but to study the prerequisites and consequences, technical, natural as wellas societal in order to evaluate if and how a future implementation of these recent technologies couldbe carried out in a feasible and sustainable way.This report is written with a plain perspective and contains no abstract. As the proceedings of the studywill be the basis for a research application in progress, conclusions will instead be developed withinthat context.
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| 15. |
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| 16. |
- Mwandya, Augustine, 1969-
(författare)
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Fish community patterns in Tanzanian mangrove creeks
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human beings have exploited the biota of mangrove systems for centuries and fish continue to be one of the main products harvested from these habitats. The assumption of mangroves functioning as recruitment areas for juvenile fish from neighbouring habitats such as seagrass beds and coral reefs is a common argument for conservation and management of mangrove ecosystems. Yet, mangrove systems are increasingly in decline worldwide primarily because of destructive anthropogenic activities. In the present thesis, fish assemblages in various mangrove creeks in Tanzania were investigated. Specifically, it dealt with the distribution, abundance and trophic structure of fishes in space and time as predicted by habitat characteristics and environmental conditions occurring naturally and following human-induced changes of clearing for construction of ponds for salt production and fish farming. In addition, the variation in population density and genetic connectivity of the economically important striped mullet (Mugil cephalus) was examined. In undisturbed creeks the fish abundance and assemblage composition showed inconsistent spatial patterns within and among different creeks that appear to be strongly influenced by species-specific responses to dominant bottom substrate types and to some extent to water depth and clarity. Seasonality had little impact on most fish assemblage variables. The genetic analysis showed mixed demes of Mugil cephalus and significant separation between Zanzibar Island and Tanzania mainland. Anthropogenic effects were found on the structural and functional organisation of fish assemblages resulting in lower densities, species numbers, diversity and number of trophic groups in the reservoirs compared to less disturbed sites. These changes in fish assemblage composition seem to be caused by an increase in salinity and water temperature as well as by the loss of refuge and feeding grounds. The findings in this thesis will contribute to coastal management planning for conservation and suggests integration of various activities (like fish farming and salt production) in order to maximise the economical use of deforested areas.
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| 17. |
- Nyqvist, Anna, 1961, et al.
(författare)
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Dynamics of Seagrass Meadows on the Swedish Skagerrak Coast
- 2009
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Ingår i: Ambio. - : Royal Swedish Academy of Sciences. - 0044-7447 .- 1654-7209. ; 38:2, s. 85-88
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Tidskriftsartikel (refereegranskat)abstract
- Seagrasses have declined in many places around the world, and the Swedish Skagerrak coast is no exception. Between the 1980s and 2000, the cover of eelgrass (Zostera marina L.) on the Swedish Skagerrak coast decreased about 60%. In the present study, the sites that were investigated in the 1980s and 2000 were revisited (1655 ha) in 2003 and 2004 to investigate long and short term temporal and spatial differences in eelgrass coverage. The distribution of eelgrass was mapped from a small boat using an aquascope and a GPS receiver. No variation in total (about 150 km) or regional (about 20 km) eelgrass cover was found between 2000 and 2004, but there were substantial changes (both losses and gains) in meadow size on a local (less than about 2 km) scale. The results have implications for management of shallow soft bottoms, particularly because it was shown that even though no eelgrass is found in a single survey in a specific area, there could be eelgrass growing there in the following years.
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