Carbonate processing by intertidal gastropoda on Jamaican limestone shores

At least eight species of Littorinidae occur sympatrically on a limestone p latform on the northern coast of Jamaica with little evidence of competitiv e displacement. Most of these, plus a cobble shore gastropod (Planaxis nucl eus), were studied with respect to the amount of carbonate each removes fro m the shore while feeding. The feces of P. nucleus contain 92.8% carbonate. On the platform, Nodilittorina riisei fecal pellets contained 88.7% carbon ate, N. ziczac 74.9%, N. angustior 67.0%, N. dilatata 88.3%, Tectarius anto nii 91.3%, Cenchritis muricatus collected from the rocky substratum 74.8%, and C. muricatus collected from the maritime shrub Rhachicallis americana 1 8.6%. Although the rock-dwelling Littorinidae ingest different quantities o f carbonate, there is no clear relationship between the amount of carbonate ingested and the position each species occupies on shore. Fecal pellet cou nts were made for all species. The mean numbers of pellets recovered from t he rectums were: P. nucleus (48.7), N. riisei (8.56), N. ziczac (26.1), N. angustior (14.1), N. dilatata (22.2), T. antonii (22.8), and C. muricatus ( 35.3), The mean size and weight of pellets for each species were: A nucleus (1.73 mm(2), 0.040 mg), N. riisei (1.21 mm(2), 0.028 mg), N. ziczac (1.43 mm(2), 0.066 mg), N. angustior (0.959 mm(2), 0.024 mg), N. dilarara (1.76 m m(2), 0.052 mg), T. antonii (3.23 mm(2), 0.118 mg), and C muricatus (4.45 m m(2), 0.112 mg), The bioerosive impact of each species was assessed by calc ulating the amount of carbonate removed from the shore per individual and p er species based on density and an estimated 48-h defecation cycle. Impacts were expressed in terms of both a single defecation cycle and annually. Co llectively, the Littorinidae are estimated to remove at least 2,850 kg of c arbonate from the approximately 500 x 24-m limestone platform annually.