COLLAPSE OF PARASITIC INTERACTIONS IN THE ANTHROPOCENE OF THE NORTHERN ADRIATIC, ITALY

Parasites are natural in all ecosystems and healthy parasites reflect a healthy ecosystem. Gymnophallid trematodes are parasites with a complex life cycle that induce pits in their intermediate hosts. Even if these pits represent the parasites' sole fossil record, they might aid in evaluating the status of a modern ecosystem by comparing its present-day status against that which was present before major phases of human impact (i.e., define parasitic baselines). This approach is, in turn, informative for near-future ecosystem management. For example, recent anthropogenic perturbation in ecosystems can impact ecosystem structure and parasite transmission, affecting the parasite population and indicating environmental stress. We quantified dynamics of trematode (i.e., prevalence, pits size, and pits aggregation) on specimens of the economically relevant and shoreface dominant bivalve Chamelea gallina retrieved from the late Holocene succession (around 3000 cal BP) and the modern seabed of the Po-Adriatic System (Italy). We examined 193 trematode-infested valves and measured 838 trematode-induced pits to address these questions. Of these, 715 were from Holocene core samples, and 123 were from modern death assemblages. Gaussian finite mixture modeling of pit size distributions shows two size components of unequal variance for the two evaluated time bins. This suggests no extinction but the persistence of two trematode taxa infesting the C. gallina over the last three thousand years. However, trematode prevalence decreased by nearly an order of magnitude in the last three thousand years. Also, the average number of pits, median size, and parasite pit aggregation decreased significantly over time. This generalized decrease likely decreased trematode parasites' effective population size, suggesting a potential collapse of trematode-C. gallina parasite-host interactions during increasing human influence in the northern Adriatic Sea.