Desiccation amelioration and climate risk on rocky shores

A large fraction of global biodiversity resides within biogenic habitats
that ameliorate physical stresses. In most cases, details of how physical
conditions within facilitative habitats respond to external climate
forcing remain unknown, hampering climate change predictions for many of
the world’s species. Using intertidal mussel beds as a model system, we
characterize relationships among external climate conditions and
within-microhabitat heat and desiccation conditions. We use these data,
along with physiological tolerances of two common inhabitant taxa (the
isopod Cirolana harfordi and the porcelain crab Petrolisthes cinctipes),
to examine the magnitude of climate risk inside and outside biogenic
habitat, applying an empirically derived model of evaporation to simulate
mortality risk under a high-emissions climate-warming scenario. We found
that biogenic microhabitat conditions responded so weakly to external
climate parameters that mortality risk was largely unaffected by climate
warming. We also found that desiccation outside the biogenic habitat drove
substantial mortality in both species at temperatures 4.4 to 8.6 ºC below
their hydrated thermal tolerances. This finding emphasizes the importance
of warming-exacerbated desiccation to climate-change risk and the role of
biogenic habitats in buffering this less-appreciated stressor. Our results
suggests that, when biogenic habitats remain intact, climate
warming may have weak direct effects on organisms within them.
Instead, risk to such taxa is likely to be indirect and tightly coupled
with the fate of habitat-forming populations. Our findings emphasize that
conserving and/or restoring biogenic habitats that offer climate
refugia could support biodiversity conservation in the face of climate
warming.