Scale-specific drivers of kelp forest communities
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Identifying spatial scales of variation in natural communities and the processes driving them is critical for obtaining a predictive understanding of biodiversity. In this study, we focused on diverse communities inhabiting productive kelp forests on shallow subtidal rocky reefs in southern California, USA. We combined long-term community surveys from 86 sites with detailed environmental data to determine what structures assemblages of fishes, invertebrates and algae at multiple spatial scales. We identified the spatial scales of variation in species composition using a hierarchical analysis based on eigenfunctions, and assessed how sea surface temperature (SST), water column chlorophyll, giant kelp biomass, wave exposure and potential propagule delivery strength contributed to community variation at each scale. Spatial effects occurring at multiple scales explained 60% of the variation in fish assemblages and 52% of the variation in the assemblages of invertebrates and algae. Most variation occurred over broad spatial scales (> 200 km) consistent with spatial heterogeneity in SST and potential propagule delivery strength, while the latter also explained community variation at medium scales (65–200 km). Small scale (1–65 km) community variation was substantial but not linked to any of the measured drivers. Conclusions were consistent for both reef fishes and benthic invertebrates and algae, despite sharp differences in their adult mobility. Our results demonstrate the scale dependence of environmental drivers on kelp forest communities, showing that most species were strongly sorted along oceanographic conditions over various spatial scales. Such spatial effects must be integrated into models assessing the response of marine ecosystems to climate change.
KeywordsMulti-scale patterns Spatial ecology Scale dependence Connectivity Kelp forests
The authors are thankful to Daniel Borcard for stimulating discussions on multiscale analyses and for providing useful comments on an early version of this manuscript. This research was supported by the National Aeronautics and Space Administration Biodiversity and Ecological Forecasting program (NASA Grant NNX14AR62A), the Bureau of Ocean and Energy Management Ecosystem Studies program (BOEM award MC15AC00006) and NOAA in support of the Santa Barbara Channel Biodiversity Observation Network and the US National Science Foundation in support of the Santa Barbara Coastal Long Term Ecological Research program.
Author contribution statement
TL, DR, AR and RM designed the study, TL, AR, DS, LK, TB and RS processed the data and TL performed statistical analyses. TL wrote the first draft of the manuscript, and all authors contributed substantially to revisions.
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