Abstract
Diet composition and food sources of five species of chiton coexisting in the same biotope on a rockyboulder reef were studied using a combination of two methods: gut contents analysis and analysis of marker fatty acids composition in the digestive tract tissue. Despite the common food supply, there was considerable interspecific selection in consumption. In the gut contents of Ischnochiton hakodadensis, Tonicella granulata and Mopalia retifera, diatoms as well as fragments of red calcareous algae (Corallinaceae) and other macrophytes dominated. Harpacticoid and amphipod crustaceans were most frequent in the digestive tract of the chiton Placiphorella borealijaponica. The meiobenthic prey of Lepidozona albrechti was mostly harpacticoids, nematodes, ostracods, acarins and foraminiferans. In large L. albrechti, juvenile cirripedes constituted up to 95% of the gut contents. For all the investigated chitons, the fatty acid composition of total lipids in the digestive tract was determined for the first time. The species I. hakodadensis, T. granulata and M. retifera were characterized by a 16:0/16:1n-7 ratio � 1 and an 18:1n-9/18:1n-7 ratio � 1 along with a low content of the acid 22:6n-3. In contrast, the content of the acid 22:6n-3 in the lipids of the other two chiton species (L. albrechti and P. borealijaponica) was higher and the 16:0/16:1n-7 ratio � 1 and the 18:1n-9/18:1n-7 ratio � 1. The marker fatty acid distributions suggested that diatoms prevailed in the diet of I. hakodadensis, T. granulata and M. retifera, i.e. the three chiton species were mainly herbivorous. This was in agreement with the gut content data, and differentiated them from the other two chitons L. albrechti and P. borealijaponica which were carnivorous, as indicated by analysis of both marker fatty acid composition and gut contents. The share of macrophytes and insignificant bacterial contribution to the chiton diets as well as the possibility of shifts in the feeding strategy of chitons were discussed.
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