Resistance of rocky intertidal communities to oceanic climate fluctuations

Shifts in intertidal communities with sea star wasting disease and climate fluctuations Our analysis did detect a shift in rocky intertidal communities in relation to the years since sea star wasting disease, which caused sea star biomass to decline by 60–90% [9]. We found that SSWD accounted for 15.9% of variation in community structure in the mid zone (Table 2b) and was correlated to an increase in mussels (Fig 8, Table 3b), and a decrease in diversity (Fig 11e, Table 5b). These findings are consistent with the keystone predation hypothesis [73,74] that suggests P. ochraceus increases diversity by consuming mussels, thereby freeing space for other taxa in the intertidal zone thus increasing diversity. In the high zone, diversity showed an unexpected opposite trend with sea star wasting disease (Fig 11i, Table 5c). Upon further inspection, however, this seemed to be driven by low diversity estimates in the early part of the study (2006–2008) while no increase was evident since the outbreak in 2014. This suggests this trend is not related to the disease but instead may be due to low taxonomic resolution in the Table 5. Linear model results testing the trends in taxon diversity (Shannon Index) with mean Pacific Decadal Oscillation index (mean PDO), mean North Pacific Gyre Oscillation index (mean NPGO), mean El Niño Southern Oscillation index (mean ENSO), mean and standard deviation of the Biologically Effective Upwelling Transport Index index (mean and sd BEUTI, respectively), mean daily sea surface temperature (Mean SST), mean daily max-

imum air temperature (Max Air Temp), and years since the sea star wasting disease epidemic (Yr Since SSWD). Model terms meeting the Bonferroni cutoff of P < 0.002 are in bold, and for these we subsequently tested the bivariate correlation of each significant term with diversity (bold indicates a bivariate correlation > 0.10). Term Chisq Df Pr(>Chisq) Bivariate R2 a) High zone Mean PDO 10.21 1 <0.001 0.042 Mean NPGO 0.19 1 0.660 ENSO 5.29 1 0.021 BEUTI 6.15 1 0.013 SD BEUTI 2.24 1 0.134 Max Air Temp 17.49 1 <0.001 0.029 Mean SST 2.39 1 0.122 Yr Since SSWD 2.71 1 0.099 b) Mid zone Mean PDO 1.18 1 0.277 Mean NPGO 87.94 1 <0.001 0.040 ENSO 38.28 1 <0.001 0.029 BEUTI 5.22 1 0.022 SD BEUTI 0.06 1 0.805 Max Air Temp 0.69 1 0.406 Mean SST 9.02 1 0.003 Yr Since SSWD 76.56 1 <0.001 0.006 c) Low zone Mean PDO 6.50 1 0.011 Mean NPGO 17.51 1 <0.001 0.030 ENSO 4.01 1 0.045 BEUTI 9.97 1 0.002 0.001 SD BEUTI 5.26 1 0.022 Max Air Temp 0.16 1 0.688 Mean SST 18.36 1 <0.001 0.065 Yr Since SSWD 68.03 1 <0.001 0.229 https://doi.org/10.1371/journal.pone.0297697.t005 PLOS ONE Resistance of rocky intertidal communities PLOS ONE | https://doi.org/10.1371/journal.pone.0297697 May 29, 2024 25 / 34