Associate Professor University of California, Los Angeles, United States
Background/Question/Methods Ecologists have long known that biodiversity can promote the functioning of ecosystems for decades. However, we still have little ability to predict whether biodiversity maintains ecosystem productivity overtime against climate extremes, besides unclear stabilizing effects of biodiversity across scales in natural ecosystems; and thus, the scale-dependence of stabilizing effects of biodiversity remains poorly understood. An unpredicted extreme heatwave has swept the North Pacific Ocean during the weak 2014/2015 El Niño and allowed us to assess its impacts on the stabilizing effects of biodiversity in marine ecosystems. First, we calculated their diversity and the temporal stability (1/CV) of biomass among functional groups (i.e., fish, mobile invertebrates, sessile invertebrates, and understory algae) across spatial extents (i.e., from local to broad spatial extents) and organizational levels (i.e., from populations to communities), using the annual biomass for kelp forest species from the Santa Barbara Coastal Long Term Ecological Research program (2001-2020). And then, we implemented the calculations before (2007-2013) versus after (2014-2020) the heatwave to examine the heatwave effects. In particular, we were interested in changes in the diversity-stability relationships (DSRs) and their distinct underlying mechanisms before versus after the heatwave across these scales.
Results/Conclusions We found that the extreme heatwave did not significantly (P > 0.05) decrease marine biodiversity and production. However, our analyses demonstrated that population stability was ~15 % decreased after the heatwave. By decreasing species asynchrony and spatial asynchrony, the heatwave also decreased community stability at both local and broad scales by ~20 % and ~30 %, respectively. Moreover, the extreme heatwave altered the strengths of DSRs in marine ecosystems, in which changes of DSRs were primarily dependent on functional groups. Specifically, the extreme heatwave amplified the DSRs of both mobile invertebrates and understory algae while it dampened the DSRs of fish groups but had no effects on that of sessile invertebrates. These results highlight the irreplaceable significance of biodiversity maintaining productivity dynamics across scales in marine ecosystems, especially under extreme warming, leading to urgent biodiversity conservations under the future unpredictable climate extremes.