SPATIAL VARIATION IN PREDATORY AND NONPREDATORY BIOEROSION IN SELECTED BIVALVES FROM THE PLIO-PLEISTOCENE OF THE U.S. COASTAL PLAIN
Two different samples of Chione elevata (1753 and 2121 specimens) from the Caloosahatchee at La Belle both had drilling frequencies (DF) of 10%, though bioerosion differed slightly but significantly between the samples (37% vs 40% of specimens were bioeroded). Anadara aequicostata from three localities of the Waccamaw yielded DF of 0, 17% and 18%, and the percent of bioeroded specimens was 8%, 27%, and 12%. With the exception of bioerosion at the Shallotte locality (27%), none of the differences between localities for either DF or bioerosion is statistically significant. Likewise, DF and percent of specimens that were bioeroded were consistent between the Waccamaw and James City for individual species. Greater variation in degree of bioerosion occurs within taxa at different latitudes. In all cases, drilling frequencies were greater in North Carolina than in Florida: 39% vs 24% for Lirophora latilirata (difference not significant); 9% vs 4% for Carditamera; 13% vs 4% for arcoids. The results support a previously documented pattern of greater drilling in the Carolina Province than in the Gulf Province. In contrast, percent of specimens with nonpredatory bioerosion was significantly greater in Florida than in North Carolina for Carditamera (47% vs 4%) and arcoids (54% vs 15%), though Lirophora latilirata from the two latitudes had equivalent amounts of bioerosion (3 4%). Higher percentages of bioerosion in Florida may represent greater productivity.