Substrate selection of the caprellid Caprella dilatata (Crustacea, Amphipoda)

Abstract

The diversity of space and the variability of environmental conditions that affect habitat quality for organisms, are determining factors in the selection of an ideal habitat. The present study aimed to understand the substrate selectivity of a caprellid amphipod, Caprella dilatata, in natural environments along the southern Brazilian coast and in laboratory conditions. A total of 31 biological substrates sheltering invertebrates were collected across various localities. C. dilatata was recorded in 11 substrate samples, and was a dominant species only in finely branched and softly surfaced algal substrate, ascidian and bryozoan colonies, and the surfaces of buoys and ropes. Laboratory experiments for substrate selection by C. dilatata were performed under two conditions: two-algal substrates and four-algal substrates. The phytals of Gracilaria cervicornis, Pterocladia capillacea, Sargassum cymosum and Ulva fasciata were selected for the experiments due to their contrasting degrees of ramification. In the first experiment (two-algal substrates), caprellids were transferred to three aquaria containing varied combinations of two algal substrates with a total of nine combinations. For the second experiment (four-algal substrates), all species of algae were combined together in each aquarium. Amphipods obtained for laboratory experiments always showed an exoskeleton color very close to that of the original algal substrate. Caprellids showed a strong preference for the original algal substrate. Despite the cosmopolitan morphology of C. dilatata for selection of the substrate, the individuals were mostly found in structurally complex substrates, and the experiments show the importance of camouflage for these caprellids.