HOW EFFECTIVE ARE THE ECOLOGICAL INNOVATIONS AGAINST DRILLING PREDATION - INSIGHT FROM RECENT BIVALVE ASSEMBLAGE OF THE NORTHERN RED SEA

Drilling predation is often used as a model system to evaluate evolutionary and ecological effects of biotic interaction on the composition of molluscan communities. Using such data, it is also possible to assess quantitatively specific predictions that postulate the effectiveness of ecological traits against predation in present-day environments. The high frequency of drilling (DF) in a diverse Recent bivalve assemblage from shallow water environments of the northern Red Sea enables us to test such evolutionary hypotheses, predicting low DF in large bivalves, infauna and siphonate groups, lower DF in byssally attached than in other epifaunal bivalves, and high DF in shallow habitats. We evaluate these predictions based on >15,000 bivalve specimens using three different methods to calculate DF namely, 1) per-species perstation DF, 2) per-species DF by pooling all stations, and 3) per-station DF by pooling all species.

Among morphological attributes, we found size and shape of a species to be a good predictor of drilling frequency. However, substrate affinity shows a pattern contrary to our prediction, because infaunal groups show the highest DF. Although we did not find any significant correlation between predator abundance and DF, the dominance of naticid gastropods and low abundance of muricid gastropods can explain the difference between DF of infauna and epifauna. Siphonate bivalves tend to have lower drilling frequency compared to non-siphonate bivalves. Attachment type does not always show a predictable pattern in deterring drilling predation; however, byssally attached bivalves sometimes show a slightly lower drilling frequency compared to cemented bivalves. Although water depth fails to show any significant effect on DF, it might be affected by the relatively narrow depth range of the studied stations. We did not find significant variation in DF between groups with different habitat; however, DF seems to show a difference between groups with different feeding mode. Our study demonstrates that many of the ecological traits (such as infaunalization, predator avoidance by choosing deeper habitat) that are claimed to be anti-predatory, do not offer effective defense against drilling predation in today's environment—a result consistent with the idea of ever escalating predator-prey dynamics.