Projecting future distribution of the seagrass Zostera noltii under global warming and sea level rise

In future decades, coastal ecosystems are expected to be exposed to increased risk of experiencing adverse consequences related to climate change, exacerbated by human induced pressures. The seagrass Zostera noltii forms meadows mainly within the intertidal zone, leading it to be particularly vulnerable to seawater temperature increase and sea level rise (SLR). Considering the presently declining situation and the predicted scenarios of increasing seawater temperature and SLR by the end of the 21st century, we assessed the response of Z. noltii to climate change (i) accounting for changes in seawater temperature at its entire biogeographical range level; and (ii) under SLR scenarios at estuary level (Oka estuary, Basque Country, south-eastern Bay of Biscay). Objectives were addressed coupling habitat suitability models with climate change simulations. By the end of the 21st century, seawater temperature increase will trigger a northward distributional shift of 888 km in the suitable habitat of the species, and a retreat of southernmost populations. The loss of southernmost populations due to climate change may imply future conservation problems. In contrast, SLR and derived changes in current velocities are expected to induce the landward migration of the species in the Oka estuary, increasing the available suitable intertidal areas (14-18%) to limits imposed by anthropogenic barriers. This modelling approach could lead to an advanced understanding of the species' response to climate change effects; moreover, the information generated might support conservation actions towards the sites where the habitat would remain suitable for the species under climate change.