IS THERE A LINK BETWEEN PARASITISM, KLEPTOPARASITISM, AND PREDATION IN MARINE BIVALVES? A CASE STUDY FROM THE PLIO-PLEISTOCENE OF NORTHEASTERN FLORIDA

Shallow water marine communities are intertwined by complex ecological interactions. Biomineralized fauna record such interactions and provide reliable evidence of ecological interactions in deep time. This study examines bivalves of the family Mactridae from the Plio-Pleistocene Nashua Formation. Shells were examined for three biotic interactions: predation by drilling predators, kleptoparasitism by spionid polychaetes, and parasitism by digenean trematodes. Three research questions were tested: 1) what were the dominant drilling predators of mactrids, 2) was there stereotypy in trace emplacement, and 3) was there a link between parasitism, kleptoparasitism, and predation within individuals?

10.1 liters of Plio-Pleistocene spoils from the Big Horse Ranch Quarry near Hastings, Florida were sieved and 15 bivalve families have been identified. Preliminary results based on 708 disarticulated valves of mactrids suggest the presence of two highly plastic species, the extinct Mulinia congesta (n=542) and the extant M. lateralis (n=18). 35 drilled valves were recovered with 29 attributable to Oichnus paraboloides. Sector analysis of drill holes indicates that the umbo-dorsal region was selectively drilled, suggesting that naticid gastropods were the dominant drillers. 19 shells with spionid mudblisters were identified, of which a majority were situated in the posterior region of the shell. 66 trematode traces were identified within 12 valves of M. congesta (10 were right valves). No stereotypy in trace location within individual valves was observed. No parasitic or kleptoparasitic traces were observed within drilled valves. Furthermore, no evidence of trematode induced traces were found within spionid infested shells and vice versa.

These initial results suggest that neither trematode nor spionid infestations make mactrids more susceptible to drilling predators. The lack of correlation between the occurrences of spionid and trematode traces suggest that neither influence each other in mactrids. The absence of trematode traces in M. lateralis may indicate the inability of parasites to adapt to the new host, though this could be due to low sample size. This study provides more observations to an expanding record of shell malformations attributable to trematode parasitism.