California Sea Grant College Program

It is difficult to assess ecosystem biodiversity, yet essential to do so. Trematodes are particularly promising bioindicators, being connected to surrounding biodiversity and easily sampled in their first intermediate host snails. This investigation's primary goal was to evaluate the hypothesis that these parasites reflect free-living animal diversity and abundance.

We quantified bird assemblages at several sites within an estuary to find that bird diversity and abundance positively correlated with that of trematodes in hom snails, Cerithidea californica.

We quantified assemblages of fishes, benthic invertebrates, and trematodes in hom snails at 32 sites in three California estuaries, finding that trematode diversity and abundance may indicate that of large benthic invertebrates and the diversity of small benthic invertebrates. Trematodes did not appear to indicate fish assemblages, but this likely was because typical surveys inadequately quantify fishes at that scale.

At larger scales (habitats in three estuaries in California and Baja California), we documented that trematode prevalence in hom snails correlated with the densities of fishes, crabs, burrowing shrimp, and snails, but did not significantly correlate with bivalves and polychaetes. Trematode assemblages on the whole changed in space congruently with combined fish and benthic invertebrate host assemblages. These results were strongest for trematodes in the most wide-spread snail size classes.

To assess the bioindicator promise of trematodes in non-estuarine ecosystems, we analyzed data from two published studies, one in the Chilean rocky intertidal zone, and another from an African rift lake. In both cases, we found that trematode prevalence was positively related to some element of surrounding diversity.

To facilitate the use of a trematode assemblage with promise for use as a bioindicator, I provide descriptions and an annotated key to identify eight species of trematodes that infect the common East Asian mud snail, Batillaria attramentaria.

On the whole, these findings support the idea that trematodes in snails indicate several types of free-living assemblages, and additionally provide an inexpensive bioindicator tool for surveillance of broader community change. In a time when the importance of biodiversity monitoring is escalating, we should seriously consider the widespread use of trematodes as bioindicators.