Geographic variation of parasitic and predatory traces on mollusks in the northern Adriatic Sea, Italy: implications for the stratigraphic paleobiology of biotic interactions

Abstract

Parasitic trematode worms leave characteristic pits in their bivalve mollusk hosts and represent an ideal system for analyzing parasite-host interactions through space and time with statistically meaningful sample sizes. Previous work in Late Pleistocene–Holocene sequences from the Po plain revealed significant long-term fluctuations in trematode prevalence values: higher prevalence in retrogradational environments (TST) and negligible prevalence in progradational environments (HST). Here we expand upon this work by investigating traces of parasitism, kleptoparasitism, and predation on mollusk death assemblages from two domains along the northern Adriatic coastline. The domain north of the Po delta (TST-like) and the southern domain (including the Po delta; HST-like) comprise environments comparable to those recovered in late Holocene (<6 Kyr) subsurface progradational deposits. We collected 17,299 specimens representing 111 species from 11 locations on the northern Adriatic coast of Italy. Our results reveal high predation pressure, a high diversity of host taxa, and widespread presence of trematode infestation in starved, oligotrophic, environmentally more stable (i.e., TST-like) settings north of the Po delta. Immediately south of the Po delta, in settings with strong and variable sedimentary input, almost no infestation is recorded. The reappearance of infestation is evident in the southern portion of the study area (i.e., Cattolica-Montemarciano), relatively far from the highly stressed environments south of the Po River. There is no significant difference in trematode prevalence values between fossil and modern samples. The distribution of spionid traces (an indicator of stressed environments) was nearly the opposite of that displayed by trematodes. Drilling frequency is highest in TST-like environments and is not correlated with diversity indices. These results suggest that temporal trends of trematode prevalence (and possibly also other biotic interactions) in sedimentary successions are controlled by environmental changes driven by glacio-eustatic dynamics, and reaffirm the importance of interpreting temporal trends in the context of spatial variation.

Surges in trematode prevalence linked to centennial-scale flooding events in the Adriatic

“…Similarly, significantly higher trematode prevalence was documented in host taxa from sediment-starved northern Adriatic strandline death assemblages, relative to that documented from comparable assemblages from the Po delta shoreline 25 . These two coastal regimes serve respectively as modern analogues for Holocene transgressive and prograding settings 26 .…”

Climate variation during the Holocene influenced the skeletal properties of Chamelea gallina shells in the North Adriatic Sea (Italy)

“…The third sub-fossil horizon (code "CE") was collected from core 240-S8 (Cervia 441 6'N, 12˚20'E) ( Fig 1). All investigated horizons came from shoreface depositional environments characterized by sandy substrates and estimated water depth between~5 and 10 m. Paleoenvironmental, paleobathymetric and paleogeographic reconstructions of the Po-Adriatic system during the Holocene are detailed in previous studies [19,[27][28][29] (for details see S1…”

Incorporating Information on Varying Sedimentation Rates Into Paleontological Analyses

“…(1) Environmental preferences of taxa: Taxa can track shifting environments through time, first and last taxon occurrences in a stratigraphic column thus do not necessarily reflect global taxon origination or extinction, but rather reflect local or regional ecologically relevant colonization or extirpation due to changing conditions such as water depth or substrate consistency (Scarponi et al 2013;Huntley and Scarponi 2015;Nawrot et al 2018;Dominici et al 2018;Jarochowska et al 2018).…”