PROTECTION OF SYMBIOTIC CNIDARIANS BY THEIR HERMIT-CRAB HOSTS - EVIDENCE FOR MUTUALISM

Symbioses involving sea anemones (Calliactis sp.) and hydroids (Hydrac tinia sp. or Podocoryne sp.) living with hermit crabs usually have bee n classified as mutualisms (i.e., both partners benefit). Several bene fits have been reported for the crabs, but none has been demonstrated for the cnidarians. This paper examines the ability of two species of hermit crab (from different geographical regions) to protect their cni darian symbionts from predation. Experiments demonstrated that Pagurus pollicaris provided protection for anemones and hydroids against sea stars (Echinaster spinulosus), while Dardanus venosus protected Callia ctis from fireworms (Hermodice carunculata). These results provide the first evidence that these symbioses are mutualistic.