UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Crabs of the species Dardanus pedunculatus form a symbiotic relationship with Calliactis tricolor anemones on Moorea, French Polynesia. Crabs actively collect anemones for protection against octopus predation, while simultaneously giving the anemones a better habitat, defense against predators, and food as a result of the crab’s messy eating. In a laboratory setting, crabs will compete for anemones with larger crabs winning competitions. This paper examined crabs’ field collection patterns, and found that larger crabs collect more anemones, cover a greater percentage of their dorsal side with anemones, and carry a larger volume of anemones than smaller individuals. An experiment was designed to determine collection preference when unimpeded by field restrictions, and found that larger crabs show similar collection patterns as in the field, while smaller crabs cover a greater percentage of their dorsal side with anemones than in the field. This implies that abundance of anemones limits collection for this population, and that smaller crabs are being out-competed for anemones in the field. Additional behavioral experiments were designed to determine individual anemone preference patterns. Crabs show no preference for anemones they had been associated with in the field, but did show a significant preference for larger anemones. Gaining a better understanding of this symbiosis adds to the much-needed literature on the fragile coral reef ecosystem.