Abstract

Seagrass meadows are productive marine ecosystems that stabilize sediments and provide food and shelter for a diverse associated community. The recognition of these important habitats in the geological record is problematic, because marine angiosperms rarely fossilize. Thus, the presence of paleo-seagrass vegetation often has to be inferred from the occurrence of associated organisms with a higher potential for fossilization, such as mollusks. Because most mollusk taxa are not restricted to seagrass meadows, the species composition and feeding ecology of fossil mollusk faunas need to be considered when distinguishing paleo-seagrass meadows from other marine habitats. In this study the utility of faunal composition and feeding ecology of gastropods as an indicator of seagrass vegetation was tested using present-day ecosystems. Bulk-sediment samples containing gastropod death assemblages from shallow-water seagrass meadows and unvegetated sandflats from San Salvador Island, Bahamas were collected in July 2012. Vegetation varied across localities in terms of density and number of seagrass species. Twenty-four standardized (n  =  200) samples of gastropods were compared in terms of species composition and relative abundance of feeding guilds. Multivariate analyses indicate that species composition is an effective tool for distinguishing between gastropod assemblages from vegetated versus unvegetated areas. To a lesser extent, species composition differs among vegetation zones on sandflats with seagrass cover. Feeding guild composition based on species richness also differs on seagrass-vegetated and unvegetated sandflats. The results suggest that gastropod assemblages are a useful proxy for seagrass meadows in the fossil record.

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