Kuempel CD and Altieri AH (2017), The emergent role of small-bodied herbivores in...

ECB-ART-45107

Sci Rep 2017 Jan 05;7:39670. doi: 10.1038/srep39670.

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The emergent role of small-bodied herbivores in pre-empting phase shifts on degraded coral reefs.

Kuempel CD , Altieri AH .

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Natural and anthropogenic stressors can cause phase shifts from coral-dominated to algal-dominated states. In the Caribbean, over-fishing of large herbivorous fish and disease among the long-spined urchin, Diadema, have facilitated algal growth on degraded reefs. We found that diminutive species of urchin and parrotfish, which escaped die-offs and fishing pressure, can achieve abundances comparable to total herbivore biomass on healthier, protected reefs, and exert sufficient grazing function to pre-empt macroalgal dominance following mass coral mortality. Grazing was highest on the most degraded reefs, and was driven by small herbivores that made up >93% of the average herbivore biomass (per m2). We suggest that previously marginal species can achieve a degree of functional redundancy, and that their compensatory herbivory may play an important role in ecosystem resilience. Management strategies should consider the potential role of these additional herbivore functional groups in safeguarding natural controls of algal growth in times of increased uncertainty for the world''s reefs.

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Genes referenced: LOC105441782 LOC115924199 LOC115925415

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	Figure 1. Associations between dominant benthic covers on coral reefs.(a) Relationship between average percent of macroalgal cover and average percent of live coral cover (n = 12) (b) Relationship between average percent of macroalgal cover and average percent of dead coral cover (n = 12) on surveyed reefs in the Bocas del Toro Archipelago.
	Figure 2. Distribution of total herbivore biomass across body-size classes and dominant herbivore species (n = 3315).(a) Average (±SEM) biomass of the diminutive urchin (E. viridis) and striped parrotfish (S. iseri) versus all other herbivores with inset photograph from STRI Point study site depicting typical E. viridis activity on a dead coral head during the day (Photo credit: C.D.K.), (b) average relative body size (±SEM) comparison of herbivorous parrotfish and urchins found at our study sites and (c) total biomass pooled across sites within each body-size class. The sample size (n) is denoted in each figure, respectively.
	Figure 3. Response of five genera of macroalgae to herbivory (n = 30).(a) Average (±SEM) final percent cover as a function of caging treatment and (b) average (±SEM) change in percent cover as a function of caging treatment and macroalgal genus during the 22-day transplant experiment.
	Figure 4. Mean algal biomass (±SEM) on experimental tiles under factorial nutrient enrichment (ambient, enriched) and herbivore exclusion (full cage, cage control, open) treatments (n = 44).
	Figure 5. Grazing impacts as a function of herbivore body size.Final mean algal biomass (±SEM) as a function of caging treatment (n = 48): jumbo mesh excluded large herbivores but allowed access for small herbivores including the reef urchin E. viridis and striped parrot fish S. iseri, small mesh excluded all herbivorous fish and urchin, and the jumbo mesh control, small mesh control, and open treatments allowed access to all herbivores.
	Figure 6. Herbivory intensity[(Mean caged biomass-Mean open biomass)/Mean caged biomass] by site, depicting sites with significant herbivory (≥50% of algae present was consumed; right of dashed line) and sites with non-significant herbivory (left of dashed line; n = 12).

References [+] :

Adam, Herbivory, connectivity, and ecosystem resilience: response of a coral reef to a large-scale perturbation. 2011, Pubmed