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Coral Reef Habitats and Fish Connectivity: Implications for coastal management and fishery
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coral reefs have one of the highest levels of biodiversity of all ecosystems in the world and are important for both human livelihood and food security throughout many tropical countries. However, due to increased anthropogenic pressure on marine ecosystems, especially during the last couple of decades, coral reefs have become critically over-fished, and many reefs are now in a degraded state and are facing additional future threats due to further over-exploitation, chemical pollution, sedimentation, and effects of climate change.

The main aim of this PhD thesis was to understand effects of anthropogenic disturbances on tropical coastal ecosystems and fish connectivity for coastal management purposes. Therefore, linkages between anthropogenic disturbance and corals were investigated (Paper I), as well as interactions between coral reef habitat and associated fish assemblage (Paper II). Furthermore, connectivity between coral reefs and other tropical coastal ecosystems was explored (Paper III), as well as fish migration to reproduction sites (Paper IV), and evaluations of spatial ecology methods (Paper V).

The result showed that coral reefs that are already exposed to disturbances, such as freshwater and nutrient run-offs, may be more sensitive to climate change, in terms of increased sea surface temperatures (Paper I). In addition, there were also clear linkages between coral reef quality, in terms of coral coverage, and fish assemblages, which displayed high spatial variability and suggesting patchy recovery after the 1997/1998 bleaching and subsequent coral mass mortality event (Paper II). This highlights the importance of understanding effects of disturbances on corals, especially in terms of synergistic effects between increased water temperatures and other coastal stressors such as decreased salinity and increased nutrients; and the indirect effects of habitat degradation on the fish community.

Linkages between fish and different coastal habitats were further explored. The results showed that coral reefs were strongly connected with mangrove and seagrass beds, through ontogenetic migration of fish (Paper III). Migrations to spawning sites of groupers were related to lunar activities when thousands of fish gather for reproduction purposes during new moon, which increases the risk of over-exploitation (Paper IV). The results emphasises the importance of protecting key areas such as nursing grounds and reproduction sites. Furthermore, acoustic telemetry has become an increasingly common method in studies of fish movement, and the results showed that efficiency of acoustic arrays may increase depending on deployment strategies and habitat characteristics (Paper V).

In conclusion, the results from this PhD thesis emphasises the importance of protecting coral reef habitats, as well as identifying related susceptible tropical coastal areas, such as nursing grounds and reproduction sites. Indeed, a better scientific understanding of coral reef ecology and indirect and direct effects on fish assemblages are needed for efficient and accurate coastal management decisions.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2016. , 80 p.
Keyword [en]
anthropogenic disturbance, coral reef habitat, fish community, coastal ecosystems, conservation management, spatial ecology, seascape perspective, holistic approach
National Category
Biological Sciences
Research subject
Marine Ecotoxicology
Identifiers
URN: urn:nbn:se:su:diva-125595ISBN: 978-91-7649-337-3 (print)OAI: oai:DiVA.org:su-125595DiVA: diva2:894231
Public defence
2016-03-11, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.

Available from: 2016-02-17 Created: 2016-01-14 Last updated: 2017-02-20Bibliographically approved
List of papers
1. Effects of elevated water temperature, reduced salinity and nutrient enrichment on the metabolism of the coral Turbinaria mesenterina
Open this publication in new window or tab >>Effects of elevated water temperature, reduced salinity and nutrient enrichment on the metabolism of the coral Turbinaria mesenterina
2010 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 88, no 4, 482-487 p.Article in journal (Refereed) Published
Abstract [en]

Water quality is declining in many coastal areas, which has caused coral degradation worldwide. In addition, reduced water quality may aggravate the impacts of seawater temperature. In this study the effects of increased temperature (31 degrees C), nitrate enrichment (+5 mu M NO3-), low salinity (20) and combinations of these stressors were investigated compared to ambient water (25 degrees C, 30, 0.3 mu M NO3-) on the metabolism and survival of the coral Turbinaria mesenterina from the Tonkin Gulf, Vietnam. The results showed that all specimens exposed to a combination of all three stressors (i.e. high temperature + high nitrate + low salinity) died after 24 h exposure, while those that had been exposed to high nitrate + low salinity at ambient temperature did not show any effects on the metabolism or survival. Furthermore, corals exposed to low salinity + high temperature displayed a decrease in gross primary production/respiration (GP/R) ratio and the mortality rate was 50%. In addition, all corals exposed to increased temperature, alone or in combination with another stressor, displayed a GP/R-24h ratio below 1.0, suggesting that they depend on stored energy to cover their metabolic requirements. The results showed that corals may tolerate short-term exposure to stressors such as low salinity + high nitrate concentration in ambient temperature, while additional increased temperature lead to rapid mortality, hence suggesting a synergistic effect. Thus, the effect of climate change might be more severe in nearshore coastal areas where corals already are exposed to several disturbances.

Keyword
temperature increase, salinity, nutrients, corals, metabolism, stress
National Category
Biological Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-49476 (URN)10.1016/j.ecss.2010.05.008 (DOI)000279860800006 ()
Note

authorCount :3

Available from: 2010-12-14 Created: 2010-12-14 Last updated: 2017-12-11Bibliographically approved
2. Spatial variability in habitat structure and heterogenic coral reef fish assemblages inside a small-scale marine reserve after a coral mass mortality event
Open this publication in new window or tab >>Spatial variability in habitat structure and heterogenic coral reef fish assemblages inside a small-scale marine reserve after a coral mass mortality event
2015 (English)In: Ocean and Coastal Management, ISSN 0964-5691, E-ISSN 1873-524X, Vol. 114, 32-41 p.Article in journal (Refereed) Published
Abstract [en]

Coral reefs at the inner granitic islands in the Seychelles were heavily affected by the worldwide bleaching event in 1998, which led to subsequent coral mortality and widespread phase shifts to macroalgae dominated reefs. In this study, five sites within a small, but well enforced marine reserve at Cousin Island, were investigate using various methods to explore differences in coral habitat quality, coral recruitment, fish assemblages, key invertebrate grazers, and rugosity. The objective of the study was to collect a broad set of scientific data, which could be useful to describe linkage between coral reef and fish assemblages after a large-scale disturbance, as well as for future management decisions regarding marine resources, in terms of MPA protection and recovery abilities. The results showed high spatial variation in coral coverage between sites (from 1.5% to 43.2%), which were higher than previously reported, as well as high variation in dispersal of coral recruits. Furthermore, there were large heterogenic differences in fish densities and composition, which were directly linked to coral habitat quality, e.g. total fish abundance was 15 times higher on sites with high coral coverage in comparison to sites with low coral cover. In summary, this study demonstrates that coral reef habitat and fish assemblage may display high spatial variability and heterogenic differences after large-scale disturbances and suggests that potential recovery from coral mass mortality may occur in a non-linear and patchy procedure, which in turn may depend on underlying stocastical processes that affect coral recruitment and survivorship.

Keyword
Marine protected areas, Coral reef, Habitat quality, Fish community, Management, Seychelles
National Category
Earth and Related Environmental Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-120908 (URN)10.1016/j.ocecoaman.2015.06.003 (DOI)000359502100004 ()
Available from: 2015-09-24 Created: 2015-09-18 Last updated: 2017-12-01Bibliographically approved
3. Ecological connectivity and niche differentiation between two closely related fish species in the mangrove−seagrass−coral reef continuum
Open this publication in new window or tab >>Ecological connectivity and niche differentiation between two closely related fish species in the mangrove−seagrass−coral reef continuum
2013 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 477, 201-215 p.Article in journal (Refereed) Published
Abstract [en]

We aim to understand ontogenetic shifts in habitat use and feeding patterns by 2 fish species, Lutjanus fulviflamma and L. ehrenbergii, within a tropical seascape in East Africa. Stomach contents and stable isotope signatures of muscle tissues (δ13C and δ15N) were compared between and within species. Fish of all life stages and potential food items were sampled from mangrove creeks, seagrass beds, and coral reefs around Mafia Island, Tanzania. Due to similarities in morphology between species, correct species identity was confirmed using genetic barcoding (mtDNA, partial sequence of cytochrome oxidase subunit I [COI]). Stable isotope analysis in R  (based on mixing models) confirmed that δ13C and δ15N values in L. fulviflamma and L. ehrenbergii reflected those of prey items caught in different habitats. Diets and mean δ13C and δ15N values of muscle tissue differed between life stages of fish, indicating ontogenetic changes in habitat and diet. L. fulviflamma and L. ehrenbergii differed in diet and δ13C and δ15N values of muscle tissue, although they overlapped in habitat use, suggesting food resource partitioning between the 2 species. Furthermore, diet overlap indexes were low between subadult species in mangrove and seagrass or coral habitats. L. fulviflamma displayed a diet shift with decreasing importance of small crustaceans in juveniles and an increasing importance of prey fishes in subadults and adults. L. ehrenbergii showed the opposite pattern. The study verifies feeding interlinkage within the mangrove-seagrass-coral reef continuum in Mafia Island by providing strong evidence of ontogenetic migration. Understanding these connections will enhance our ability to manage tropical seascapes, and highlights the need to include multiple habitats in marine protected areas.

Keyword
Stable isotopes, Stomach content, Ontogenetic shifts, Connectivity, Resource partitioning, Coral reef, Seagrass, Mangrove
National Category
Ecology
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-75190 (URN)10.3354/meps10171 (DOI)
Available from: 2012-04-16 Created: 2012-04-11 Last updated: 2017-12-07Bibliographically approved
4. Dynamics of Camouflage (Epinephelus Polyphekadion) and Brown Marbled Grouper (Epinephelus Fuscoguttatus) Spawning Aggregations at a Remote Reef Site, Seychelles
Open this publication in new window or tab >>Dynamics of Camouflage (Epinephelus Polyphekadion) and Brown Marbled Grouper (Epinephelus Fuscoguttatus) Spawning Aggregations at a Remote Reef Site, Seychelles
2008 (English)In: Bulletin of marine science, ISSN 0007-4977, E-ISSN 1553-6955, Vol. 83, no 2, 415-431 p.Article in journal (Refereed) Published
Abstract [en]

Aggregations of camouflage, Epinephelus polyphekadion (Bleeker, 1849), and brown marbled grouper, Epinephelus fuscoguttatus (Forsskål, 1775), were found to overlap spatially and temporally at a reef pass site located in the outer island group of the archipelagic Seychelles. Over three spawning seasons, we investigated the spatial and temporal dynamics of aggregations using a combination of underwater visual census (UVC) surveys and trends in reproductive parameters, notably gonadosomatic index. Interannual variation in aggregation formation was evident for both species, but was more variable in camouflage grouper. Aggregations lasted between 2–3 wks, with peak abundances attained a few days prior to the new moon, soon after which aggregations quickly dispersed. Spawning within aggregations was confirmed using direct (observations of hydrated oocytes) and indirect (gonadosomatic indices, behavior, color changes) signs. Spawning seasons were estimated at between 2 and 3-mo long, occurring between November and February, with interannual variation in onset and termination. Tagged camouflage grouper exhibited site fidelity on scales of weeks to months, and one individual returned to the aggregation the following year. The aggregations are known to fishers and are commercially exploited. Fisher knowledge was found to be a reliable source of information for locating aggregations.

National Category
Biological Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-125585 (URN)000259711700009 ()
Available from: 2016-01-14 Created: 2016-01-14 Last updated: 2017-11-30Bibliographically approved
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