博士 / 國立中興大學 / 生命科學系所 / 97 / Kenting’s coral reefs face serious threats from natural disturbances and human impacts, such as typhoons, coral bleaching, overfishing, habitat loss, sedimentation, sewage discharge, eutrophication, and oil pollution over the past few decade. The combination of these factors resulted in reduced coral cover, increased abundance of macroalgae, a reduction in fish abundance, sea anemone outbreaks, and occasionally, phase shifts from coral to macroalga or sea anemone dominated reefs. This thesis is the first study to explore the attributes of community structure and functioning of Kenting coral reefs.
Comparing the trophic structure and other community attributes by the Ecopath approach between marine protected area (MPA) and non MPA (nMPA) reefs revealed the trophic transfer efficiency, flow and matter cycling, resilience ability to resist the natural disturbance were greater at MPA reefs. However, fishing pressures reduced biomass of fish and other heterotrophic benthic communities, while sewage discharge led to increase growth rate and biomass in macrophytes, resulting in greater net primary production unused in the system. The analysis also revealed that MPA reefs did not only protect organisms from human activities, but also maintain community structure and normal function close to that of more pristine ecosystem. It also revealed that human activities most greatly contributed to degradation of coral reefs in Kenting. Some of the indices derived from the Ecopath approach may serve as good tools for exploring the status of coral reefs. For example, the relative ascendency ratio increased; indicating that large macrophytes underwent increases in biomass, productivity, and P/R ratios in response to eutrophication. The mean trophic level of catch, Finn’s cycling index (FCI), and average path length (APL) decreased as a result of overfishing.
The Kenting coral reefs were categorized as a very limited MPA reef by a global network of MPAs study. The fishery status also revealed an overfishing of coral reefs after considering studies of long term ecological research in Kenting (Kenting-LTER) and data from fishery analyses. Comparisons with other coral reefs by Ecopath approach revealed that Nanwan Bay was similar to the unprotected Bolinao and Mahahual reefs which were characterized by high fishery catches, small fish biomass, lower mean trophic level of the catch, and extremely small cycling matter and trophic transfer efficiency. It also suggested that coral reefs of Nanwan Bay should be given overfished status, thus enhancing future protection to improve upon this currently limited MPA situation.
The Kenting-LTER study and mixed trophic impacts analysis by the Ecopath approach revealed the most likely causes of coral degradation, algal increases, and sea anemone outbreaks in Nanwan Bay were sewage discharges and overfishing. The mesocosm experiments found that green alga, Codium edule, and sea anemone, Mesactinia genesis, coexisted with the live or dead coral, Acropora muricata, under low nutrients and grazing pressure. Combined nitrogen and phosphorus additions under low grazing pressure markedly increased the photosynthetic efficiencies of zooxanthellae in A. muricata, the coverage of C. edule, and the asexual reproduction of M. genesis, resulting in space competition. The hierarchy of competitive superiority under nutrient enrichment was in the order of C. edule > M. genesis > A. muricata, resulting in coral inhibited by sea anemones and algae. Coral death left more substrates open for macroalgal or sea anemone colonization, might not be prerequisites for the decline if disease, bleaching, and sedimentation follow nutrient-stimulated ecological disruption in this system.
This thesis suggested that MPAs are one of best way to maintain the community structure and function of coral reef ecosystem. The set up of MPA reefs is necessary for habitat protection. However, it also revealed that enforcement and efficiency of protection are inadequate within Kenting National Park. Nanwan bay demonstrated degradation from severe human impacts, suggesting either the need for reduced fishing or the establishment of more or larger MPAs in Kenting. Fishing should be forbidden within MPAs. Government agencies can design certain fishing areas for recreation or commercial fishing and setup more buffer areas between fishing and recreation areas and MPAs, according to scientific studies and the needs of the local residents and economy of Kenting. There are too many non-point pollution sources in Kenting, a serious reduction in sewage will be essential so that interactions within coral reefs communities are not permanently altered. For a degraded coral reef, the best way to promote recovery is to reduce disturbance from human activities. Human intervention in ecological affairs such as removal of invasive sea anemones or transport of control species which will change the balance of these ecosystems is not recommended.
| Identifer | oai:union.ndltd.org:TW/097NCHU5105069 |
| Date | January 2009 |
| Creators | Pi-Jen Liu, 劉弼仁 |
| Contributors | 林幸助 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 89 |
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