PREDATION ON THE MODERN ECHINOID MEOMA VENTRICOSA IN A TROPICAL MARINE ENVIRONMENT

Although predation is arguably one of the most widely studied biotic interactions, the importance and effects of predation in modern echinoid communities remains relatively understudied. Modern echinoids are preyed upon by many organisms, producing diverse traces that can be preserved in the fossil record. Therefore, echinoids are a viable target group to expand our understanding of the evolutionary role of predation beyond mollusks.

To determine the role of predation on taphonomic biases and echinoid preservation potential, drilling predation rates were quantified using the irregular echinoid Meoma ventricosa from shallow nearshore tropical marine habitats (San Salvador Isl., Bahamas). The drilling frequency of the accumulating shallow subsurface echinoid death assemblage was unusually high, and 97% of tests had traces of lethal predation, with drill holes primarily located on the oral surface (81%). Drilled tests were smaller on average than in situ live M. ventricosa (t-test p<<0.01), which may indicate a size refuge for M. ventricosa. The predator can be constrained to a single species, Cassis tuberosa, identified through in situ field and experimental observations. Repeated sampling of a single echinoid population indicates that predators consumed an average of 1.4 M. ventricosa per day. Observed echinoid drill holes made by C. tuberosa are distinctive and therefore, recognizable in fossil material. We propose that drilling predation in this instance, creates a taphonomic bias towards higher numbers of drilled specimens in the fossil record. Cassis preys upon M. ventricosa in the shallow sediment subsurface, likely increasing the preservation potential of M. ventricosa and other similar prey species by concentrating drilled tests in the sediment, and providing an additional entrance for sediment infilling.

A more thorough understanding of the ecological interactions between echinoids and their predators in modern settings, particularly those producing traces, could improve our ability to investigate echinoid predation in the fossil record and quantify predation intensity using fossil echinoid tests.