What to do when there is nothing to do: the ecology of Jamaican intertidalLittorinidae (Gastropoda : Prosobranchia) in repose

The littorine gastropods Cenchritis muricatus, Nodilittorina mespillum, N. angustior, N. dilatata, N. riisei, N. ziczac and Tectarius antonii from a n atural limestone platform on the north coast of Jamaica were evaluated acco rding to several ecological parameters in an effort to define their respect ive niches on this shore. Distributions along transects perpendicular to th e shore demonstrated that distance from the sea is one, albeit not always c onsistent, ecological criterion which serves to delineate these species. N. riisei generally occupies that region of the shore frequently wetted by wa ve splash, N. mespillum is usually found within frequently refreshed tidepo ols and C. muricatus always occupies the highest regions of the shore most distant from the sea. There is, however, considerable overlap between these and other species and, along much of the rock platform, N. angustior, N. d ilatata, T. antonii and C. muricatus are sympatric. N. dilatata has the bro adest range on this low profile limestone platform. A comparison of body te mperatures and substratum temperatures taken from adjacent rock surfaces re vealed that the body temperatures of T. antonii generally reflect that of t he ambient environment. On the other hand, C. muricatus, N. dilatata, N. ri isei and N. angustior seem to thermoregulate, maintaining body temperatures above ambient at temperatures below 29 degrees C and below ambient at temp eratures above 33 degrees C. Data were also compiled for most species with respect to resting posture (whether hanging suspended or resting aperture-d own), resting site (whether within the shelter of a crevice or upon an expo sed rock surface), shell orientation and the relative frequency (presence o r absence) of a mucous holdfast. Size-frequency analyses indicate that N. r iisei and N. angustior re-populate the shore from the meroplankton at least sometime between January and March.