Distribution and Abundance of an Isolated Population of Terebra Gouldi (Gastropoda: Terebridae) on a Hawaiian Subtidal Sand Flat

Species of the carnivorous gastropod genus Terebra are common members of tropical subtidal sand associations. Despite superficially uniform sand habitats, these species occupy well—defined population centers. The distributional pattern of Terebra gouldi Deshayes, an endemic Hawaiian species, and the physical and biological factors influencing this pattern, were studied on a subtidal sand flat surrounding Ahu O Laka Island in Kaneohe Bay, Hawaii. The species was not widely distributed around this sand flat, but rather was concentrated in two sub—populations located on the windward and leeward sides of the island, where densities were as high as 15 animals per m 2 . Of more than 40 associated infaunal species, only the prey, Ptychodera flava, appeared to have an important effect on T. gouldi distribution. There was no preference by T. gouldi for a specific sand particle size, or for a specific degree of sediment sorting. Substratum factors determining subtidal distribution through an influence on crawling, burrowing, and prey capture included the presence of attached vegetation, hard compacted sand, and limestone platform. Factors preventing dispersal of the species into intertidal areas are also discussed. Two hypotheses are advanced to explain observed intra—population density gradients. These are chemoreceptive locomotory activity in response to prey, and life history factors including recruitment of young in high density adult population centers, followed by gradual dispersal of maturing animals.