Saccostrea cucullata (Von Born, 1778): food availibility in a mangrove creek (Gazi, Kenya)
Bollen, A. (1993). Saccostrea cucullata (Von Born, 1778): food availibility in a mangrove creek (Gazi, Kenya), in: Chardon, M. et al. Third Belgian Congress of Zoology, 5-6 November 1993. Belgian Journal of Zoology, 123(Suppl. 1): pp. 6-7 In: Chardon, M.; Goffinet, G. (Ed.) (1993). Third Belgian Congress of Zoology, 5-6 November 1993. Belgian Journal of Zoology, 123(Suppl. 1). University of Liège: Liège. 109 pp., more In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276; e-ISSN 2295-0451, more |   |
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| Abstract | In this study is checked whether morphological differences of the mangrove oyster Saccostrea cucullata (von Born, 1778) can be explained by its food supply. In the first part the theoretical amount of food available for Saccostrea cucullata in Gazi (Kenya) is determined, in the form of zooplankton, phytoplankton, particulate organic matter (POC and chlorophyll a) and dissolved organic carbon (DOC). By means of ANOV A we showed that there are few significant differences in the amount of three of these four variables (zooplankton, phytoplankton, particulate organic matter) as a function of the tide. This means that any differences in food availability for Saccostrea cucullata are a result of the difference in immersion time, caused by the different heights above chart datum at which the oysters grow. Zooplankton and DOC seem to be abundant in Gazi bay, POC and total seston show the same amount as in other coastal areas, and phytoplankton and chlorophyll a are present in very low concentrations. Carbon isotope analysis showed that Saccostrea cucullata filters detritus from mangrove leaves and from seagrasses, but stomach analysis also gave certainty about intake of diatoms and dinoflagellates. The maximal daily ration of Saccostrea cucullata in Gazi creek appears to be highest for DOC, followed by POC and finally zooplankton and phytoplankton. In the second part of this study we tested the hypothesis that the theoretical amount of available food, as derived from the height above chart datum, is related to the morphological differences of the oysters within the oyster culture in Gazi bay, expressed in lengths and dry weights of the organs. First we showed with ANOV A that formaline has almost no influence on the sizes and the weights of oyster organs. Our results also show that all measured organs are linearly correlated with the shell length, but that the height above chart datum does not show any linear correlation with the shell length. One of the most important findings of this study is that there are no apparent differences in organ sizes of Saccostrea cucullata whether it is growing high or low above chart datum, while there is a large difference in potential feeding time, with always about the same food availability. |
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