Some physical properties of shelter that influence den preference in spiny lobsters

Several properties of shelter were analyzed for their importance in den selection by the California spiny lobster Panulirus interruptus (Randall). Field surveys indicated that dens of spiny lobsters usually had more than one entrance and that entrances were much smaller than the inner diameter of a den. Dens always had top cover and a back wall, but they did not always have side walls. In laboratory experiments lobsters completely avoided transparent artificial shelters in favor of opaque ones of the same size and shape. No preference was exhibited by lobsters for opaque shelter when transparent shelter was shaded. Den preference was found to depend more on presence of shaded cover than on den walls. Single, isolated shelter having front and rear entrances was preferred to shelter having only one entrance, though this preference was lacking when a second shelter was attached laterally. A function of lobster antennae in defensive behavior is suggested based on their positioning as observed in laboratory trials. Antennae were held posteriorly, possibly to guard the abdomen and telson, when residency was established in shelter having openings both at front and back ends. Antennae were directed anteriorly, outside the shelter, when residency was established in shelter having only one entrance. Shade, shelter, antennae posturing, and conspecific attraction are discussed relative to their probable roles in predatory defense in this species.