Sea level rise can severely reduce biodiversity and community net production on rocky shores

Sea level rise (SLR), driven by anthropogenic climate change, can be a major threat to coastal ecosystems. Among the most biologically diverse but SLR-threatened coastal ecosystems are rocky shores, especially in regions with a small tidal range. Nonetheless, the impacts of SLR on rocky shore biodiversity, community structure and ecosystem functions have rarely been studied. Here, we use the biogenic intertidal ecosystem, Mediterranean vermetid reefs on the Israeli coast, as case study for testing the potential impact of SLR on reef communities, with surveys, 3D topographic mapping plus SLR simulations, and a manipulative community translocation experiment. We show that: (1) biodiversity is much lower on very shallow, permanently submerged, horizontal rocky surfaces compared to that on intertidal reef platforms, (2) the extensive intertidal platforms will permanently drown under even modest SLR scenarios, (3) the rich intertidal community will transform, when permanently submerged, either to a very different but still rich community when protected from grazing by highly abundant invasive fish (rabbitfish), or to a much poorer turf community when exposed to such fish grazing, and (4) the reef community net production will drastically drop under permanent submersion. Because the main ecosystem engineer of the vermetid reefs, Dendropoma anguliferum (Monterosato, 1878), is nearly extinct in the southeast Levant, it is unlikely that new reefs will be formed higher on the shore in the future, presumably resulting in extensive coastal ecological shifts. Considerable coastal community shifts are forecasted for many regions globally due to SLR, as many shorelines are predicted to suffer from "coastal squeeze". Hence, similar manipulative experiments are encouraged in other regions to test for generality vs. context dependency in SLR ecological impacts. We suggest that in cases where essential/unique intertidal habitats like vermetid reefs are expected to vanish by SLR, constructing carefully-planned, ecologically friendly, artificial alternatives should be considered.