Tropicalization of temperate reef fish communities depends on urchin
herbivory and thermal response diversity
AbstractGlobal declines in structurally complex habitats are reshaping both land
and seascapes in directions that may change how biological communities
respond to warming. Here, we test whether the widespread loss of kelp
habitats through overgrazing by sea urchins changes fish community
structure in directions that systematically alter warming sensitivity.
We use simulations and comparisons of communities from 5996 sites across
19 ecoregions to test for thermal diversity shifts related to habitat.
We find that the realized thermal affinities and ranges of fishes from
kelp and urchin barrens differ, but only in regions with high initial
response diversity. Fish communities in warm-temperate barrens host
relatively more warm-affinity species than neighbouring kelp beds,
highlighting that urchin herbivory can exacerbate tropicalization
processes. By contrast, relatively cool-affinity species colonize
cool-temperate barrens and explain apparent lags with ocean warming in
these locations. Evidently, urchins are agents of ecological change with
implications for climate resilience.