The concurrent ecological role of eelgrass beds and on-bottom oyster farms driving community structure in two bays of Atlantic Canada.

Abstract

Marine sediments support distinct complements of epifaunal and infaunal assemblages, that often end up associated with the habitats created by ecosystem engineers. While human activity has caused the decline of many of these engineers, like seagrasses, it also accounts for the farming and growth of others, like oysters. This study assessed the contribution of natural eelgrass beds (Zostera marina), on-bottom Eastern oyster aquaculture (Crassostrea virginica), and bare sediments to the abundance and richness of epifaunal and infaunal communities in two bays of Prince Edward Island, Atlantic Canada. Our working hypothesis was that structured habitats (eelgrass and oyster leases) sustain richer or otherwise distinct communities relative to bare sediments. To test it, we sampled epifauna through multiple trapping surveys and then examined infaunal communities in the three habitats. Epifaunal surveys showed that eelgrass beds and oyster leases supported richer and more abundant communities than bare sediments. Multivariate analyses also showed that samples from the first two habitats differed from bare sediments in composition and abundance. Meanwhile, infaunal communities were denser but less diverse in bare sediments, with MDS plots evidencing clear among-habitat differences. These results supported our hypothesis and the notion that structurally complex habitats foster richer epifaunal and infaunal communities, likely by providing diverse shelter and resources. Despite their transitional nature, on-bottom oyster leases contributed to local community structure much like natural eelgrass beds, playing a concurrent ecological role. Hence, they provide services well beyond the economic benefits that they are best known for.