Ecostructuring of marine nematode communities by submarine groundwater discharge

Inputs of submarine groundwater discharge (SGD) to the coastal ocean may alter local and regional-scale biology. Here, we report on nematode assemblages along the north shore of Long Island, NY. We test if nematode communities differed between sites impacted by mixed fresh-saline SGD and where SGD is exclusively saline. Diversity of nematodes was low at sites impacted by fresh SGD and communities were dominated by a few opportunistic genera. Moreover, a set of typical freshwater nematode genera restricted to impacted sites was observed. Their presence in the marine coastal zone is exceptional and underlines the structuring role that fresh SGD plays in the local ecosystem. Saline SGD structured nematode assemblages differently compared to sites impacted by fresh SGD. The number of nematode genera was markedly higher at saline SGD sites, with a different community structure. This study highlights the importance to which inputs of fresh SGD may have on local ecosystem diversity in marine coastal environments. •Fresh submarine groundwater discharge has significant impact on local diversity.•Presence of recirculated, saline SGD structured nematode assemblages differently than sites impacted by fresh SGD.•Presence of freshwater nematodes in a marine zone, underlines the structuring role of SGD in the local ecosystem.•Fresh SGD can locally alter all trophic levels, from bacteria, through primary producers and up to higher consumers.