DIFFERENCES IN PREDATION RATES AMONG BIVALVE TAXA

Drilling intensity by predatory gastropods on their bivalve prey is influenced by intrinsic characteristics of the bivalve prey as well as differences in environments. We examined traces of predatory drilling on over 100,000 bivalve shells over the past 11 MA and quantified the drilling intensity for the most common taxonomic groups. Drilling intensities were unchanged within taxonomic groups despite dramatic environmental change in the time period studied. In contrast, there were highly significant differences in drilling intensity among taxa associated with differences in life habits, shell morphology, and size of the prey. Pectinids have consistently low rates of drilling through time and among different habitats (Mdn 0.50%) associated with their free-swimming and byssally attached life habits, whereas cemented epifaunal bivalves are heavily drilled (Mdn 21.71%). There are also striking differences related to size in infaunal taxa. Small bivalves, including corbulids, lucinids, and venerids display consistently high rates of drilling (Mdns 21.53, 31.19, and 10.53% respectively), while large lucinids and venerids suffer lower drilling predation (Mdns 12.70 and 5.56% respectively). These results illustrate the importance of considering drilling rates among different prey types when inferring changes in predation through time and space, and support the need for studies of predation to occur at the assemblage level.