Saccostrea cucullata (von Born, 1778): voedselaanwezigheid in een mangrovekreek (Gazi, Kenya) = Saccostrea cucullata (von Born, 1778): food availability in a mangrove creek (Gazi, Kenya)
Bollen, A. (1993). Saccostrea cucullata (von Born, 1778): voedselaanwezigheid in een mangrovekreek (Gazi, Kenya) = Saccostrea cucullata (von Born, 1778): food availability in a mangrove creek (Gazi, Kenya). MSc Thesis. Vrije Universiteit Brussel: Brussel. 105 pp.
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| Keywords |
Availability > Food availability
Saccostrea cucullata [sic] [WoRMS]
ISW, Kenya, Gazi Bay [Marine Regions]
Brackish water |
| Author keywords |
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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 ANOVA we showed that there are few significant differences in the ration 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 (resp. 4,5x104 to 8,0x105 ind./l, and 5,44 to 5,94 mg/l), POC and total seston show the same amount as in other coastal are as (resp. 0,373 to 1,376 mg/l, and 12,55 to 20,55 mg/l), and phytoplankton and chlorophyll a are present in very low concentrations (resp. 1,7x103 to 1,9x105 cells/l, and 0,055 to 0,298 µg/l). 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 findings on DOC-concentrations do not exclude the intake of DOC by Saccostrea cucullata. The daily ration of Saccostrea cucullata in Gazi creek, respectively on the highest and the lowest level, appear to be highest for DOC (5,5 and 211,9 %), followed by POC (1,3 and 49,1 %) and finally zooplankton (0,07 and 2,5 %) and phytoplankton (0,004 and 0,2 %). In the second part of this study we tested (by means of ANOVA and linear regression) the hypothesis that the theoretical amount of food available, 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 ANOVA 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. |
| Dataset |
- Bollen A.; Polk P.; Faculteit Wetenschappen; Laboratorium voor Ecologie en Systematiek. VUB: Belgium; (2016): Zooplankton and phytoplankton densities in the oyster farms of Gazi Creek (Kenya) sampled in October 1992., more
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