Data from Persistent kelp forests during a massive decline reveal the importance of land-sea connectivity [Dataset]

The different datasets present data on the benthic community assemblage in remnant habitat patches of bull kelp in 9 sites in Northern California, US, and related environmental variables driving its composition. For the study we used a combination of in situ field surveys (years 2020 to 2022), remote sensing data (years 2016 to 2022), and a laboratory grazing experiment with urchins (Strongylocentrotus purpuratus). We found that, in addition to the two dominant states (kelp forest vs. urchin barren), there is a third community state dominated by understory canopy-forming macroalgae that stays subsurface. Moreover, bull kelp abundance and cover were positively associated with freshwater flow and proximity to freshwater sources, and bull kelp persistence was positively associated with sand cover, all of which seem to diminish sea urchin abundance and negative effects of sea urchin herbivory on bull kelp. This was also shown in the laboratory experiment where sea urchin herbivory rates on bull kelp decreased with decreasing salinity. Overall, these results suggest that freshwater influence in shallow coastal environments could prevent loss of bull kelp and show that land-sea connections should be considered for species-specific management and conservation actions