Biodiversity enhances coral growth, tissue survivorship and suppression of macroalgae

Abstract

Coral reefs are declining dramatically and losing species richness, but the impact of declining biodiversity on coral well-being remains inadequately understood. Here, we demonstrate that lower coral species richness alone can suppress the growth and survivorship of multiple species of corals (Porites cylindrica, Pocillopora damicornis and Acropora millepora) under field conditions on a degraded, macroalgae-dominated reef. Our findings highlight the positive role of biodiversity in the function of coral reefs, and suggest that the loss of coral species richness may trigger negative feedback that causes further ecosystem decline.

Figure 1:. Coral monoculture and polyculture plots in the field (a) where growth was commonly enhanced in polyculture vs. monocultures.

a, Monoculture and polyculture plots at the beginning of the experiment (month zero; Image Credit: C.S. Clements). a inset, Histogram of the frequency of coral species richness in 36 × 36 cm quadrats (N = 113) from field surveys. Coral growth (mean % ± SE; N = 12 plots treatment⁻¹) at four months for: b, Porites cylindrica, Pocillopora damicornis, and Acropora millepora in monocultures vs. polycultures, c, the combined growth of Porites, Pocillopora, and Acropora in monocultures vs. polycultures, d, Acropora millepora (the best performing monoculture) vs. the combined change of Porites, Pocillopora, and Acropora in polycultures. e, f, and g mirror b, c, and d, but at sixteen months. P-values from linear mixed effect models. Dots show values for individual data points, with the total number of corals assessed per treatment indicated below each bar.

Figure 2:. Coral tissue mortality and macroalgal cover in polyculture vs. monoculture.

a, Percent tissue mortality (mean % ± SE) at four months for Porites cylindrica, Pocillopora damicornis, and Acropora millepora in monocultures vs. polycultures. b, As above, but at sixteen months. P-values from Fisher-Pitman permutation tests (10000 permutations). Dots represent mean values for each independent plot (N = 12 plots treatment⁻¹). c, Percent cover of upright macroalgae (mean ± SE) at four months and d, biomass of upright macroalgae at sixteen months for monocultures of Porites cylindrica, Pocillopora damicornis, and Acropora millepora and polycultures containing all three species. Letters indicate significant groupings (P < 0.05) via ANOVA and Tukey post-hoc tests using a permutation approach (5000 permutations). Dots represent mean values per plot (N = 12 plots⁻¹ treatment⁻¹).