Coral Reef: A Research to Understand the Ecological Decline of Coral Reef
Project location: WORLDWIDE
Project start date: February 2002 - Project end date: May 2002
Project number: 2001-07
Beneficiary: The Wildlife Conservation Society Marine Program
Summary of Prof. McClanahan's Research:
The WCS Coral Reef Conservation Program works to determine the effects of marine parks, global climate change, fishing, and indigenous management on coral reef ecology and to develop methods to support the restoration and long-term conservation of coral reef ecosystems. The support of The Nando Peretti Foundation has been instrumental in recent successes of the project, including new work in Kenya and Belize to synthesize scientific investigations with improved management practices. The specific objectives of the project are to:
Fisheries management impacts: Data were collected in southern Kenya on coral reef ecosystems and fisheries to assess the influence of the 1998 coral bleaching and mortality event. Dr. McClanahan compared benthic cover, sea urchin and fish abundance in unfished marine parks and fished reefs and the reef-associated fisheries three years before and after 1998. Hard and soft coral decreased while coralline algae increased in both management areas. Turf increased in marine parks and sponge and fleshy algae increased in the fished reefs. Sea urchin grazer biomass was unchanged over this period and the fish community changed less than benthic cover. In general, butterflyfish, damselfish and wrasses were negatively influenced while surgeonfish and a few uncommon families were positively influenced by the substratum change. There was a 17% increase in fishing effort as measured by fishermen per day at each landing site and the total demersal catch declined by 8% and the catch per man declined by 21% after 1998. The decline in the total catch and CPUE combined with the increase in effort suggest an over exploited fishery and this makes it difficult to distinguish changes caused by coral mortality versus those caused by fishing effort.
Climate change impact: Reef corals are likely to have four gross responses to anomalous warm-water. These are 1) to not bleach and live (mortality <10%), 2) not bleach and die (mortality >20%), 3) bleach and live, and 4) bleach and die. Dr. McClanahan examined the frequency of these four possible responses for 18 common coral taxa in the Mombasa Marine National Park over the unusually warm1998 El Niño where there was an average of 41.2 + 34.7 (+ S.D.) mortality for the 18 taxa. We made field observations on the intensity of bleaching and mortality during five sampling periods based on 6803 colonies and also calculated mortality based on 180 m of line-intercept transects completed four months before and near the end of the bleaching episode. There was no clear relationship between the intensity of the bleaching response and either direct or transect-based estimates of mortality for the 18 taxa. The morphology of the taxa did not influence the bleaching response but branching taxa had higher mortality than massive and submassive taxa. Bleaching and mortality are the most common responses to warm water as only Pavona did not bleach or die and only two taxa, Cyphastrea and Millepora, did not significantly bleach but died. Of the 15 taxa that bleached, five taxa, Astreopora, Favia, Favites, Goniopora and Leptoria did not die. Mortality of the branching taxa was detected reasonably by direct field observation but some taxa were underestimated compared to line transects. Mortality of encrusting and massive taxa including Echinopora, Galaxea, Hydnophora, Montipora, Platygyra, and massive Porites were poorly detected with direct observations but proved to have modest to high mortality (20-80%) based on line transects. There is no single response to warm water in these common corals but these data, collected during an extreme warm-water anomaly, indicate that bleaching is most frequently a sign of morbidity, particularly for branching taxa.
Pollution impact: Although high bioerosion rates of carbonate substrates by endolithic organisms (borers) have been attributed to the effects of increased nutrients and reduced herbivory, these factors have not been experimentally manipulated simultaneously. Dr. McClanahan used a combination of herbivore-exclusion cages and an inorganic fertilizer to manipulate herbivore abundance and nutrient availability. Dr. McClanahan measured the effect of these treatments on bioerosion rates by microborers in experimental substrates made from Strombus gigas shells at Glovers Atoll Reef, Belize. Microborers in each treatment were identified and their density calculated using scanning electron microscopy of their boring casts. Dr.McClanahan found that the dominant microborer was the green alga Phaeophila sp., common in all treatments. Fertilized cages were most differentiated by the differential dominance of cyanobacteria, while fungi differentiated unfertilized treatments with the grazed and fertilized treatment being intermediate between these two groups. The highest bioerosion rates and most unique microborer community was found on the herbivore-reduction and fertilized treatment while the inclusion of macro-grazers resulted in lower erosion rates and all fertilized treatments were significantly higher than both non-fertilized treatments. Bioerosion rates in non-fertilized treatments were lowest and did not differ statistically. Our results indicate that fertilization increased bioerosion by a factor of 10 while herbivory reduced rates by a factor of 2, but only when fertilized. Eutrophication of reefs, therefore, has the potential to increase rates of bioerosion by microborers even in the presence of grazing.
During previous reporting periods Dr. McClanahan has described meetings with a group fishermen in the Diani, Kwale District region who agreed to eliminate the use of beach seines in their landing sites. This management has continued in all sites in the Diani area after some problems with compliance. During the last meeting in June in the library of the Coast District Fisheries Department, the results of the catch-monitoring program were presented. During the meeting it was found that some late-night seine netting has returned from fishermen from a site south of the study area in an area called Gazi creek. It was decided that efforts to detect late-night seining should increase and should be reported to the Fisheries Department. It was also decided that Dr. McClanahan should begin a fisheries catch-monitoring program in Gazi and to invite the leaders in this group to join the regular meetings in order to discuss ways to reduce this conflict. In August Dr.McClanahan began fish catch monitoring in Gazi Creek and this has been maintained until the present without any conflicts. Dr.McClanahan plans to hold a meeting early in 2003 to discuss these findings and find ways to reduce cross-landing conflicts. Fishers and the Fisheries Department remain supportive of this gear restriction and this represents a major advance in fisheries management on the Kenyan coast. Catches rose quickly after the removal of seine nets but have been constant over the past nine months.
Summary of Prof. Backer's Research
The primary objective of this research program is to inform conservation of coral reef ecosystems through field- and laboratory-based investigations of how coral reefs respond to environmental stresses, such as climate change. With the generous support of the Nando Peretti Foundation, Dr. Andrew Baker of the Wildlife Conservation Society and his team of research scientists are providing the scientific and conservation communities with new understanding of the way that reef systems function and the steps that need to be taken to ensure their long-term conservation. Specific objectives of the workplan for this year are to: