Host-use and selection of differently colored sea anemones by the symbiotic crab Allopetrolisthes spinifrons

Adults of the reddish green symbiotic crab Allopetrolisthes spinifrons obtain different degrees of camouflage from the red, green, reddish green, and blue sea anemones Phymactis clematis, and the orange Phymanthea pluvia on which they are commonly found. Previous studies have indicated that the distribution of the crab on sea anemones may be influenced by the host's coloration. During the present study, we tested whether adult crabs dwell more commonly on those sea anemones that offer a higher degree of camouflage, and whether "behavioral preferences" can explain crab distribution on sea anemone species and color morphs in the field. We examined the frequency of occurrence of adult crabs on 200 sea anemones of each color morph, and crab distribution was compared to that expected by the relative abundance of different anemone hosts in the field. Adult crabs occurred more frequently than expected by chance on sea anemones most similar to their own color (reddish green), and occurred less frequently than expected by chance on sea anemones where homochromy was reduced (e.g. blue). Multiple host selection experiments conducted under laboratory conditions demonstrated that adult crabs avoid blue sea anemones compared to other host color morphs offered for colonization, but no preference was observed among red, green, reddish green, and orange sea anemones. These results suggest that "behavioral preference" play a role in determining the field distribution of A. spinifrons adult crabs in the field. The lack of preference for reddish green sea anemones in the laboratory, but its high frequency of occupancy by adult crabs in the intertidal, further suggests that factors other than homochromy-related preferences (e.g. sea anemones habitat) might affect crab distribution in the field. Alternative host selection experiments revealed that the specific host from which crabs were collected (source host) affected the host-choice behavior of crabs, indicating that previous experience is important in choice of sea anemone hosts. (C) 2002 Elsevier Science B.V. All rights reserved.