Parasites and Holocene sea-level rise: Recurrent upsurges in trematode infestation linked to repeated flooding events in the Adriatic Sea

Theacceleratingincreaseinglobaltemperatureandconcomitantsealevelrisemayresultinanincreasedprevalence (i.e.infestationfrequency)ofmanypathogensandparasites.UsingtheHolocenebrackishdepositsofthePoPlain, we evaluate this issue from a historical perspective by documenting temporal changes in trematode infestation of mollusk hosts during high-frequency (102-103 yrs) sea-level fluctuations that took place over the most recent millennia. During that time interval, the dominant bivalve species, Abra segmentum, was frequently infested by trematodes. Median body size was significantly larger in infested individuals (p = 2.21*10-34), likely reflecting accumulation of parasites with ontogenetic age. Prevalence estimates were significantly elevated (p < 0.01) in samples of A. segmentum associated with flooding surfaces and significantly depressed (p < 0.01) in intervening samples.Incontrast,temporaltrendsinhostbodysize,hostavailability,salinity,diversity,turnover,andcommunity structure did not correlate significantly with parasite prevalence. The results reported here reinforce the recently proposedhypothesisthatincreasingtrematodeprevalenceislinkedtofloodingevents,apatternnowdocumentedin shallowmarineandestuarinesettingsontwocontinents,inbothmodernandfossiltaxa.Consequently,theongoing anthropogenic warming and sea-level rise is expected to trigger a significant upsurge in trematode prevalence, resulting in suppressed fecundity of common benthic organisms and negative impacts on marine ecosystems and ecosystem services.