Complex species interaction in tropical backreef communities

A complex interaction between the sea urchin, Tripneustes ventricosus, and snail, Cerithium litteratum, has emerged in lagoonal backreefs of Jamaica. These two species are spatially correlated in most of the habitats that were examined. In field and laboratory observations, urchins pick up and cover their tests with as many as 40 live snails continuously for up to two days. I examined whether urchins cover to avoid predation, and whether growth and survival of snails is negatively affected by this behavior. The presence of predators prompted urchins to collect ten times as many snails, which gained 47% less tissue weight and 75% less shell lip thickness than snails unassociated with urchins. However, the survival rate of snails positioned on urchins was three times greater than that of free snails on sandy backreef substratum. Results of this study imply a biomass gain versus survival trade-off, and provide insights into complex interactions.