238-4 Exploring Body Size, Predation Pressure, and Shell Biomass in Central America’s Neogene Corbulidae Community Following the Formation of the Isthmus of Panama

Abstract:

The Isthmus of Panama formed through the Miocene to Late Pliocene, severing the connection between the Atlantic and Pacific Oceans and causing significant disruption to Caribbean marine ecosystems. During the final stages of Isthmus emergence, the Caribbean Sea experienced increases in salinity and carbonate deposition, as well as decreases in nutrient availability and primary productivity due to reduced upwelling. Although these changes to the physical environment are well-documented, and there have been several studies on their impact on the benthic marine communities of the Caribbean, the connection between reduced planktonic productivity and its impacts on specific bivalve communities and trophic groups is still understudied. The abundant equatorial bivalve mollusks belonging to the family Corbulidae would have been directly affected by a decrease in productivity, as they are suspension-feeding bivalves. Corbulidae are very abundant in the Neogene marine record of the Isthmus of Panama, making them an excellent focus for this research. This research focuses on a collection of corbulid bivalves from the southwestern Caribbean that range in age from ~11 Ma to 7 Ka. We examine fossil corbulids that were previously collected by the Panama Paleontology Project (PPP) in the 1990s-2000s. These samples were previously collected as bulk samples, sieved, identified to genus, and counted. In order to generate automated size measurements, each corbulid was photographed with the umbo directed upwards on a flat black surface, with a scale bar, using StackShot to create a stacked image. Digital images of shells were measured using AutoMorph, a morphometric software that uses stack images to quantify 2- and 3-dimensional traits, i.e., height, length, and depth for each shell, providing approximate measurements of shell biomass. Automorph compilations of body size measurements from different time periods will allow testing the hypothesis that decreases in primary productivity in the Caribbean drove a decrease in overall body size and a decrease in abundance of corbulid bivalves in the Caribbean post-isthmian closure. Abundance counts of both the corbulid bivalves, as well as predatory gastropods (e.g., naticids and muricids), will also test the hypothesis that the proportion of Caribbean primary consumers to predators increased after the isthmus formed, resulting in lower incidence of predation in the Caribbean in the later Neogene.

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