PREDATION ON REGULAR AND IRREGULAR ECHINOIDS BY CASSID GASTROPODS ON SAN SALVADOR ISLAND, THE BAHAMAS

This project examines the tests of multiple species of echinoids from a tropical marine environment in order to determine the frequency and behavior of predatory gastropods. Cassid gastropods are known drilling predators of echinoids, cutting out an irregular sub-circular hole in the test. Echinoid tests were collected and analyzed for drill holes from two localities on the island of San Salvador, The Bahamas. The first collection site was Sand Dollar Beach, located south of Rocky Point on the northwest side of the island at coordinates 24°06’22” north and 74°31’09” west. This locality was systematically surveyed every 3 days for a month along a 150 by 150 meter transect that ranged from beach shallow water (<3 meters) in order to collect specimens of Meoma ventricosa and Leodia sexiesperforata. The second collection site was at Fernandez Bay, located south of the Cockburn Town on the west side of the island at coordinates 24°02’07” N, 74°31’32” W. Specimens Tripneustes ventricosus and Echinometra sp. were collected from this locality along a 20 by 1000 meter north-south transect that ranged from shallow water (<1m) to onshore environments. Total specimens collected from Sand Dollar Beach were 63 for Meoma ventricosa and 67 for Leodia sexiesperforata. The calculated rate of new kills at Sand Dollar Beach to be 2.2 per day for M. ventricosa and 3.6 per day for L. sexiesperforata. The only known live Cassid at this locality is Cassis tuberosa, however the shell of Cypraecassis testiculus was found in the area. Overall drilling frequency for M. ventricosa is 96.8% and 85.5% for L. sexiesperforata. Landmark analysis indicated that the predatory gastropods showed no drilling stereotypy as the position of the drill hole lacked any noticeable pattern. However, the oral side of the test was preferentially drilled by gastropods (80.3% for M. ventricosa and 96.2% for L. sexiesperforata) in both echinoid species. Specimens collected at Fernandez Bay were used to analyze stereotypy of drill hole location on the test. Total number of specimens collected at this locality was 84 for Echinometra sp. and 21 for Tripneustes ventricosus. Out of the 105 collected specimens, 44 tests possessed drill holes. The shells of Cassis testiculus and Phalium granulatum were collected onshore, however no live predatory gastropods were obtained in this locality.