Ecological and socioeconomic impacts in Seychelles of the 1998 coral bleaching event.


Newcastle University


Anna C. Liljevik


A dissertation submitted to the Department of Marine Sciences and Coastal Management, University of Newcastle upon Tyne, UK, as requirement in partial fulfilment of the Degree of Master of Science in Tropical Coastal Management


August 1999


Academic supervisor: Dr Alasdair J Edwards



Abstract

In 1998, widespread coral bleaching occurred in Seychelles and many other parts of the Indian Ocean. The event coincided with unprecedented positive seawater temperature anomalies, often reaching temperatures as high as 3 to 5º C above normal. Reports of post-bleaching mortality ranged from 50 to 95% throughout the Seychelles, with branching species being the most affected. With the objective of investigating some of the short-term ecological and socio-economic impacts of the bleaching event, a six-week field study was carried out in Seychelles from 13 May to 24 June 1999. During this time, data were gathered on reef fish abundance and biomass, taxonomic composition of live coral cover and coral recruits, and tourists' perceptions of the reefs in Seychelles.

This study supports the hypothesis that fast-growing branching corals of the families Acroporidae and Pocilloporidae are less tolerant to temperature stress in the Indo-Pacific. Coral recruitment appeared to be very slow at all of the sites studied, although the observed low abundance of juvenile corals could be a result of the survey methodology that was used. Temporal comparisons of pre- and post-bleaching reef fish biomass, revealed that corallivores had decreased significantly in biomass, while the overall biomass of other trophic groups remained unchanged. One herbivorous territorial damselfish, Plectroglyphidodon lacrymatus, increased significantly in biomass, while biomass of the algal grazing parrotfishes, Scarus sordidus and Scarus niger had not changed. Interspecific competition for a common food source was proposed as a possible explanation for the variable response among herbivorous species. The changes that occurred in planktivore biomass varied between sites and species, and were likely the result of local biotic or abiotic factors, rather than coral mortality. Tourist questionnaire surveys revealed that the most disappointing reef attributes were a lack of (1) variety of corals, (2) colourful corals and (3) abundance of corals and fishes. Despite this, 72% of the visitors believed that they would return to Seychelles in the future.


E-mail

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