Doherty Marine Biology Postdoctoral Scholar Bowdoin College, Maine, United States
Abstract: Spatio-temporal heterogeneity of habitat structure can impact community assemblage by creating new niches for species to inhabit a single ecosystem. The effects of spatial and temporal variation are often confounded; therefore, their independent and interactive effects on habitat structure are often unknown. We surveyed eelgrass (Zostera marina) epifaunal communities and eelgrass structure at six sites across two regions within the Gulf of Maine, repeating the surveys monthly during the growing season 2022. The variation in epifaunal communities throughout the growing season was approximately the same as the variation between regions. Temporal variation in epifaunal communities in the south was driven by Littorina littorea in June and Cribrilina mutabilis in July, while gammarid amphipods drove northern epifaunal communities in July. Species composition differed by region; invasive faunal epiphytes heavily drove southern epifaunal communities, while northern communities contained native epifauna. We predict that faunal epiphytes may lead to a difference in structure as they are not typically grazed, unlike algal epiphytes, and will shade eelgrass. Northern shoot density and shoot height were 44.6% and 64.3% greater than southern meadows, respectively. Southern shoot density and height did not change, while northern shoot height increased by 38.5% during the summer. Changes in shoot height were negatively correlated strongly with the Shannon index. These results indicate that spatio-temporal variation has differential impacts across trophic levels. Furthermore, management of seagrass population should monitor the presence of faunal epiphytes as they may pose a large threat to eelgrass conservation.
