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Habitat structure, degradation and management effects on coral reef fish communities
Stockholm University, Faculty of Science, Department of Zoology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coral reefs are among the most diverse and productive ecosystems on earth, and are critical to the survival of tropical marine ecosystems and sustenance of local human populations. However, coral reefs are quite vulnerable to disturbances, both natural and anthropogenic. This thesis looks at how coral reef communities have responded to climactic disturbances, particularly the 1997-98 El Niño Southern Oscillation (ENSO) and subsequent coral bleaching and mortality that affected much of the Indian Ocean, including the coastal waters of Tanzania, where the study was conducted. In particular, it investigates the effects of coral bleaching, habitat degradation and reef spatial arrangement on reef fish assemblages.

Habitat structural complexity and spatial arrangement of reefs had an effect on reef fish communities. Fish communities showed patterns in distribution among habitats and between patch and continuous reefs. Fishes preferred live to bleached/dead or eroded coral, but trophic groups reacted differently to patch and continuous reefs. There were slight changes in fish abundance and significant changes in fish diversity on experimental, bleached branching Acropora coral plots over a period of one year. While fish abundance on one site increased shortly after a bleaching event, 6 years later fish abundance had decreased significantly. Conversely, coral reef communities in northern Tanzania had changed little over an 8-year period, with minor changes associated with the 1997-98 ENSO and the presence or absence of fisheries management. The coral reefs in the region were found to show high variability in community structure and responses of associated fish and invertebrate communities.

The findings of this thesis indicate the importance of habitat structure and spatial arrangement of reefs, the detrimental effects of coral bleaching, and the possibility that some reefs and some (generalist) reef fish taxa may exhibit resilience to climate change.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2011. , 46 p.
Keyword [en]
fish assemblages, climate change, coral degradation, Indian Ocean, patch reefs, coral bleaching, resilience
National Category
Ecology Zoology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-62187ISBN: 978-91-7447-360-5 (print)OAI: oai:DiVA.org:su-62187DiVA: diva2:440169
Public defence
2011-10-07, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Available from: 2011-09-15 Created: 2011-09-12 Last updated: 2011-09-13Bibliographically approved
List of papers
1. Long-term effects of the 1998 coral bleaching event on reef fish assemblages
Open this publication in new window or tab >>Long-term effects of the 1998 coral bleaching event on reef fish assemblages
2006 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 315, 237-247 p.Article in journal (Refereed) Published
Abstract [en]

Coral bleaching events constitute compound disturbances often resulting in coral death as well as successive degradation of the reef framework. The 1997/1998 El Niño Southern Oscillation (ENSO) was the most severe on record and affected coral reefs worldwide. The present study examined the response of fish assemblages in plots of transplanted coral before and after the 1998 bleaching. Multidimensional scaling ordinations (MDS) demonstrate significant changes in assemblage composition related to habitat alteration. Within-site variability increased with disturbance, the increase being most apparent following substrate erosion. The differences in long-term responses as opposed to short-term responses were striking. Six mo after coral death, total abundance as well as taxonomic richness had increased at one of the sites, but not the other, whereas 6 yr later, both measures had decreased significantly at both sites. Functional groups, with documented affiliations with coral, were significantly influenced by the habitat alteration. Herbivore abundance increased as an immediate response to bleaching, but was subsequently decimated in eroded habitat. The loss of structural complexity had major detrimental effects on the entire fish community. In conclusion, we present evidence of severe and long-lasting secondary impacts of a catastrophic bleaching event, with no apparent recovery. The discrepancies between short-term and long-term responses underline the importance of long-term monitoring of fish assemblages following habitat alteration.

Keyword
Habitat structure, Disturbance, Coral degradation, Community ecology, Herbivores, Corallivores, Multivariate analyses, Global warming
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-25795 (URN)10.3354/meps315237 (DOI)
Available from: 2009-03-05 Created: 2009-02-25 Last updated: 2011-09-13Bibliographically approved
2. Coral bleaching and habitat effects on colonisation of reef fish assemblages: an experimental study
Open this publication in new window or tab >>Coral bleaching and habitat effects on colonisation of reef fish assemblages: an experimental study
Show others...
2011 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 94, no 1, 16-23 p.Article in journal (Refereed) Published
Abstract [en]

Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management.

Keyword
coral reefs, fish communities, habitat degradation, disturbance, field experiment, resilience
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-25796 (URN)10.1016/j.ecss.2011.04.012 (DOI)000294150400002 ()
Available from: 2009-03-05 Created: 2009-02-25 Last updated: 2012-01-17Bibliographically approved
3. Fish assemblages in relation to quality, structure and configuration of staghorn coral reefs at Mafia and Zanzibar islands, Tanzania
Open this publication in new window or tab >>Fish assemblages in relation to quality, structure and configuration of staghorn coral reefs at Mafia and Zanzibar islands, Tanzania
Show others...
(English)Manuscript (Other academic)
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-25797 (URN)
Available from: 2009-03-05 Created: 2009-02-25 Last updated: 2011-09-13Bibliographically approved
4. Fish and sea urchin community patterns and habitat effects on Tanzanian coral reefs
Open this publication in new window or tab >>Fish and sea urchin community patterns and habitat effects on Tanzanian coral reefs
(English)Manuscript (preprint) (Other academic)
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-62186 (URN)
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2011-09-13Bibliographically approved
5. Changes in northern Tanzania coral reefs during a period of increased fisheries management and climatic disturbance
Open this publication in new window or tab >>Changes in northern Tanzania coral reefs during a period of increased fisheries management and climatic disturbance
Show others...
2009 (English)In: Aquatic conservation, ISSN 1052-7613, E-ISSN 1099-0755, Vol. 19, no 7, 758-771 p.Article in journal (Refereed) Published
Abstract [en]

1. Surveys of coral reefs in northern Tanzania were conducted in 2004/5 with the aim of comparing them over an∼8-year period during a time of increased efforts at fisheries management and the 1998 El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) coral mortality event that caused 45% mortality in northern Tanzania and much of the Indian Ocean.

2. Changes associated with both management, its absence, and the ENSO were found but changes were generally small and ecological measures indicated stability or improvements over this period, particularly when compared with reports from much of the northern Indian Ocean.

3. Fisheries management in two areas increased the biomass of fish and benthic communities. A small fisheries closure (0.3 km2) displayed little change in the coral community but ecological conditions declined as measured by sea urchins and fish abundances. This change may be associated with its small size because similar changes were not measured in the large closure (28 km2).

4. The few sites without any increased management were still degraded and one site had experienced a population explosion of a pest sea urchin, Echinometra mathaei.

5. The lack of significant changes across this disturbance indicates that these reefs are moderately resilient to climate change and, therefore, a high priority for future conservation actions.

Keyword
1998 ENSO, climate change, coral bleaching, fisheries closures, Indian Ocean, marine protected areas
National Category
Zoology Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-25798 (URN)10.1002/aqc.1020 (DOI)000271778200004 ()
Available from: 2009-03-05 Created: 2009-02-25 Last updated: 2011-09-13Bibliographically approved

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