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Biodiversity increases ecosystem functions despite multiple stressors on coral reefs

Abstract

Positive relationships between biodiversity and ecosystem functioning (BEF) highlight the importance of conserving biodiversity to maintain key ecosystem functions and associated services. Although natural systems are rapidly losing biodiversity due to numerous human-caused stressors, our understanding of how multiple stressors influence BEF relationships comes largely from small, experimental studies. Here, using remote assemblages of coral reef fishes, we demonstrate strong, non-saturating relationships of biodiversity with two ecosystem functions: biomass and productivity. These positive relationships were robust both to an extreme heatwave that triggered coral bleaching and to invasive rats which disrupt nutrient subsidies from native seabirds. Despite having only minor effects on BEF relationships, both stressors still decreased ecosystem functioning via other pathways. The extreme heatwave reduced biodiversity, which, due to the strong BEF relationships, ultimately diminished both ecosystem functions. Conversely, the loss of cross-system nutrient subsidies directly decreased biomass. These results demonstrate multiple ways by which human-caused stressors can reduce ecosystem functioning, despite robust BEF relationships, in natural high-diversity assemblages.

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Fig. 1: Relationships between biodiversity, ecosystem function and human disturbances on remote coral reefs.
Fig. 2: Effect of human disturbances on BEF relationships on remote coral reefs.
Fig. 3: Links between human-caused stressors, reef characteristics, biodiversity and ecosystem function.
Fig. 4: Hypothesized and observed effects of human-caused stressors on biodiversity and ecosystem function (EF).

Data availability

The data that support the findings of this study are available on GitHub (github.com/cbenkwitt/bef-reefs).

Code availability

The code that supports the findings of this study is available on GitHub (github.com/cbenkwitt/bef-reefs).

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Acknowledgements

We thank the United Kingdom Foreign and Commonwealth Office and the British Indian Ocean Territory Administration for granting us permission to undertake this research. This project was funded by the Australian Research Council, Royal Society and the Bertarelli Foundation and contributed to the Bertarelli Programme in Marine Science. We thank R. Morais for help with productivity calculations and R. Evans, C. Mora and J. Robinson for constructive feedback on the manuscript. Fish illustrations are from Tracey Saxby, Integration and Application Network, University of Maryland Center for Environmental Science (ian.umces.edu/imagelibrary/).

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C.E.B. and N.A.J.G. conceived this study; C.E.B., N.A.J.G. and S.K.W. collected the data; C.E.B. conducted the analyses; C.E.B. wrote the manuscript with input from N.A.J.G. and S.K.W.

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Correspondence to Cassandra E. Benkwitt.

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Extended data

Extended Data Fig. 1 Estimated effects of biodiversity and human disturbance on biomass of fishes on remote coral reefs.

Models were run using observed species richness (dark blue) and estimated species richness (light blue). Points represent scaled estimates (mean-centered and scaled by one standard deviation) from linear mixed-effects models, thick lines represent 75% confidence intervals, and thin lines represent 95% CIs. For non-scaled estimates of all explanatory variables, see Supplementary Tables 1 and 2.

Extended Data Fig. 2 Estimated effects of biodiversity and human disturbance on productivity of fishes on remote coral reefs.

Models were run using a, observed species richness and b, estimated species richness. Productivity was calculated in four ways, assuming: no difference in Kmax between rat-free versus rat-infested islands (‘0%’), 10% higher Kmax around rat-free islands, 25% higher Kmax around rat-free islands, and 45% higher Kmax around rat-free islands (see Methods). Separate models were run for each productivity estimate, and colours represent these different models. Points represent scaled estimates from linear mixed-effects models, thick lines represent 75% confidence intervals, and thin lines represent 95% CIs. For non-scaled estimates of all explanatory variables from models assuming no difference in Kmax, see Supplementary Tables 1 and 2.

Extended Data Fig. 3 Estimated effects of human disturbance on biodiversity on remote coral reefs.

Models were run using observed species richness (dark blue) and estimated species richness (light blue) as response variables. Points represent scaled estimates from linear mixed-effects models, thick lines represent 75% confidence intervals, and thin lines represent 95% CIs. For non-scaled estimates of all explanatory variables, see Supplementary Table 1.

Supplementary information

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Supplementary Tables 1–4.

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Benkwitt, C.E., Wilson, S.K. & Graham, N.A.J. Biodiversity increases ecosystem functions despite multiple stressors on coral reefs. Nat Ecol Evol 4, 919–926 (2020). https://doi.org/10.1038/s41559-020-1203-9

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