Estimating Effects of Sea Level Rise on Benthic Biodiversity and Ecosystem Functioning in a Large Meso-Tidal Coastal Lagoon

SIMPLE SUMMARY: Estuaries are among the world’s most productive ecosystems, but due to their location between land and open sea, they are affected by many anthropogenic pressures, including the consequences of climate change. A rising sea level is one major consequence, which will affect both humans and ecosystems, especially in estuaries with extensive intertidal habitats. There is, however, a lack of knowledge regarding the ecological implications of losing intertidal habitats. Therefore, we investigated how seafloor macrofauna communities and their contribution to ecosystem functioning may change due to rising sea levels. Based on a spatially extensive dataset on macrofauna and environmental variables, we identified three main community groups representing intertidal, shallow subtidal, and deep subtidal habitats. Functional trait analysis indicated low functional redundancy for a key intertidal suspension-feeding bivalve (Austrovenus stutchburyi) and the lack of a shallow subtidal functional replacement should intertidal habitats become inundated (i.e., become shallow subtidal habitats). These findings thus strongly suggest that sea level rise and the associated environmental changes will modify the seafloor macrofauna communities in estuaries, and subsequently, the ecosystem functions that they influence will be altered. ABSTRACT: Estuaries are among the world’s most productive ecosystems, but due to their geographic location, they are at the forefront of anthropogenic pressures. Sea level rise (SLR) is one major consequence of climate change that poses a threat to estuaries with extensive intertidal habitats. The ecological implications of intertidal habitat loss have been largely overlooked despite their likely significance. We aimed to address this knowledge gap by investigating how benthic macroinvertebrate communities and their contributions to ecosystem function are likely to respond to SLR. Based on a spatially extensive dataset (119 sites) from a large coastal lagoon, depth, sediment chlorophyll concentrations, mud content, and average current speed were identified as the main drivers of community compositional turnover. Shifts in benthic community structure and associated functional implications were then evaluated using depth as a proxy for SLR. Three main macrofaunal groups representing intertidal, shallow subtidal, and deep subtidal habitats were identified. Functional trait analysis indicated low functional redundancy for a key intertidal suspension-feeding bivalve (Austrovenus stutchburyi) and the lack of a shallow subtidal functional replacement should intertidal habitats become inundated. These findings strongly suggest SLR and the associated environmental changes will alter estuarine macroinvertebrate communities, with implications for future ecosystem function and resilience.