The growth performances of two mangrove crabs, Chiromanthes bidens and Parasesarma plicata under different leaf litter diets

Abstract

The growth performance of adult individuals of the detritivorous mangrove grapsid crabs Chiromanthes bidens and Parasesarma plicata common in the Mai Po Marshes, Hong Kong, was followed in a long-term laboratory rearing experiment (10 months). Individual crabs’ moulting frequency, growth increment and mortality when fed four kinds of leaf litter available in their natural habitats, viz. brown (two weeks of decomposition) and yellow (fresh litter) Kandelia candel, and brown and yellow Avicennia marina were followed. The survival period was strongly related to litter type when the data from both crab species were pooled, being longest for crabs fed with brown Avicennia marina, followed by brown Kandelia candel > yellow Avicennia marina > yellow Kandelia candel. A higher proportion of crabs moulted twice when yellow Avicennia marina was supplied, but more crabs moulted for a third time when fed with brown Avicennia marina. The growth increment of the two species of crabs after moulting was found to be significantly related to their pre-moult size (ANOVA, P<0.05), but effects of the four treatments were non-significant. Increment of Chiromanthes bidens was significantly greater than that of Parasesarma plicata under the brown Kandelia candel treatment. Litter treatment has no effect on the time taken for the crabs to moult, only in the case of the yellow Avicennia marina treatment did Parasesarma plicata take a longer time to moult a second time.