Microzooplankton as a food source for the Pacific oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>: seasonal variation in gut contents and food availability |
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Authors: | Takashi Kamiyama |
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Institution: | (1) National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruichi, Hatsukaichi Hiroshima, 739-0452, Japan |
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Abstract: | In this study I investigated the seasonal occurrence of microzooplankton in the gut of the Pacific oyster Crassostrea gigas. Gut contents consisted of various microzooplankton, including tintinnid ciliates, dinoflagellates (Dinophysis spp.), copepods, copepod nauplii, bivalve larvae, and rotifers. Monthly variations in the abundance of protists (tintinnids
and Dinophysis spp.) in the gut contents were significantly correlated with the variation in their abundances in the surrounding seawater,
whereas this relationship was not significant with metazoans (copepods, copepod nauplii, and bivalve larvae). In laboratory
experiments, oysters actively fed on ciliates. When oysters fed on ciliates labeled with a stable nitrogen isotope (15N), the 15N:total N ratio of the oyster tissues was significantly higher than that for oysters under a no-food condition, suggesting
that oysters assimilate nitrogen of the ciliates into their body tissues. Based on these results, I conclude that microzooplankton
forms an important food source for oysters, especially when other food sources such as phytoplankton are not abundant. |
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