| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 95 === The feeding habit of a coral reef fish is generally adaptable. While the environment is ever changing, the fish with a higher feeding plasticity would be less affected by changes of available foods. It is also more capable of immigrating into a newly developed habitat with suitable food substitutions. The substrate in the small embayment, the intake bay of the third nuclear power plant at Kenting, was previously dominated by Acropora corals. The recent outbreak of sea-anemones has eliminated branching corals in some areas. It also occurred that more Plectroglyphidodon dickii had immigrated into these sea-anemone dominated habitats than its cogener P. johnstonianus. In this study, the reef area in the embayment was divided into two different zones, zone A dominated by branching corals and zone B, by sea-anemone. In order to study whether the distribution pattern was underlain by the food availability and feeding habit plasticity, both stomach content and stable isotope analyses were used to delineate feeding habits of these two damselfishes at two different zones.
Both analyses showed that coral polyps were the major food source for P. johnstonianus from both zones (70.0%). The major food sources for P. dickii from zone A were algae (33.4%) and coral polyps (22.3%) while in zone B it mainly took algae (35.8%) and sea anemones (28.2%). ANCOVA analysis showed that, for P. dickii, difference between sample sites was significant in δ13C values, but not in δ15N values, indicating that P. dickii might have accessed different sources of organic carbon. This is consistent with the finding from stomach content analysis that the fish had taken different foods in the two zones. Meanwhile, differences in both δ13C and δ15N values between P. dickii and algae are higher than per-trophic level increase, indicating that algae might not be as important as the stomach content showed. Instead, in addition to coral polyps and sea-anemones, polychaete and sipuncula are possibly its major food source. Overall, P. dickii used sea-anemones to substitute coral polyps in the diet in the sea-anemone dominated habitat, thus showing a higher feeding plasticity than P. johnstonianus. This may help explain the recent dramatic occurrence of P. dickii in the newly developed habitat.
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