238-2 Decreased mollusk predation in lower-productivity waters of the Caribbean side of the Isthmus of Panama

Abstract:

The separation of the Atlantic and Pacific Oceans by the Isthmus of Panama during the Mio-Pliocene resulted in shifts in marine biodiversity and ecology. While the Pacific sustained a high primary productivity, Atlantic Caribbean productivity decreased. Many questions remain concerning the effects of the formation of the isthmus, including how these productivity differences affected predator-prey interactions. Dredged modern bivalve and gastropod shells were used to explore predation patterns in mollusk assemblages. This collection of 15,963 specimens was surveyed for frequency of damage associated with successful predatory attempts (complete drill holes) and survived attempts (incomplete drill holes and repair scars). Drill holes dominate among predatory traces (96%). The Pacific exhibits a higher proportion of shell damage (11.0% of specimens) compared to the lower-productivity Caribbean (5.5%), linked to a higher proportion of gastropod drillers (Naticidae and Muricidae) among mollusks in the Pacific (1.8%) compared to the Caribbean (0.7%). Infaunal bivalves exhibit the highest proportion of drill holes among habitats in both waters, and the infaunal naticids appear more commonly than the epifaunal muricids. Repair scars are more common among epifaunal bivalves. Semi-infaunal gastropods exhibit a higher proportion of damage than epifaunal ones in the Pacific, but less in the Caribbean. In both waters, suspension-feeding bivalves and carnivorous gastropods were most frequently drilled. While prey sizes are the same, drill-hole diameter (predator size) and predator-prey size ratios are significantly larger on the Pacific side. These results suggest that environmental shifts associated with closure of the isthmus may have impacted regional mollusk predation.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.