Consequences of kelp forest ecosystem shifts and predictors of persistence through multiple stressors

Abstract

Ecological communities can be stable over multiple generations, or rapidly shift into structurally and functionally different configurations. In kelp forest ecosystems, overgrazing by sea urchins can abruptly shift forests into alternative states that are void of macroalgae and primarily dominated by actively grazing sea urchins. Beginning in 2014, a sea urchin outbreak along the central coast of California resulted in a patchy mosaic of remnant forests interspersed with sea urchin barrens. In this study, we used a 14-year subtidal monitoring dataset of invertebrates, algae, and fishes to explore changes in community structure associated with the loss of forests. We found that the spatial mosaic of barrens and forests resulted in a region-wide shift in community structure. However, the magnitude of kelp forest loss and taxonomic-level consequences were spatially heterogeneous. Taxonomic diversity declined across the region, but there were no declines in richness for any group, suggesting compositional redistribution. Baseline ecological and environmental conditions, and sea urchin behaviour, explained the persistence of forests through multiple stressors. These results indicate that spatial heterogeneity in preexisting ecological and environmental conditions can explain patterns of community change.

Syncopation and synchrony: Phenological dynamics of Pyropia nereocystis (Bangiophyceae) in central California

“…Attributing causal relationships across heterogenous environments without adequately describing spatial and temporal variability may be premature, as abiotic and biotic factors likely interact inconspicuously (e.g., Dayton, 1985). This may especially be true within the central California region, where abiotic and biotic characteristics can be spatially and temporally heterogeneous (Blanchette et al, 2008;Carroll, 2009;Fiedler & Mantua, 2017;Gentemann et al, 2017;Hare & Mantua, 2000;Smith et al, 2024;Young et al, 2016).…”