The relationship between seaweed diet and purple fluid production in Aplysia dactylomela Rang, 1828 (Gastropoda : Opisthobranchia) From Northeast, Brazil

Abstract

Aplysia dactylomela is a large marine opisthobranch gastropod, which inhabits shallow tropical shoreline regions, eats red and green algae, and releases a purple ink when disturbed. Many functions have been proposed for this secretion and although there is no consensus on this, some of its constituents are believed to be derived from the red algal diet, it may provide the snail with a substantial survival advantage. A. californica only produces ink when it ingests red seaweeds. In some locations of the Northeastern Coast of Brazil, A. dactylomela is seen feeding only on green seaweeds, and yet it releases the ink. The aim of this work is to investigate this contradiction by studying the feeding habits of A. dactylomela and assessing the relationship between the algal diet and the purple ink. Feeding habits were investigated by field observation and by analysis of gut contents. Purple ink production was monitored by histologic analysis of the ink gland from sea hares kept in water tanks, fed with either red or green seaweeds. Composition and protein profile of the purple ink also were studied. Homologies between seaweed components and the purple ink were sought for by immunodiffusion techniques. Our findings are that the sea hare A. dactylomela, likewise other Aplysia species, needs to consume red seaweeds to be able to secrete the purple ink. The proteins of the ink seem to be synthesized by the sea hare itself and are not obtained directly from the diet, as is the case for the ink pigments