Impact of herbivore identity on algal succession and coral growth on a Caribbean reef.

Deron E Burkepile,Mark E Hay,Geoffrey Clayton Trussell

doi:10.1371/journal.pone.0008963

Deron E Burkepile, Mark E Hay + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0008963

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Abstract

BackgroundHerbivory is an important top-down force on coral reefs that regulates macroalgal abundance, mediates competitive interactions between macroalgae and corals, and provides resilience following disturbances such as hurricanes and coral bleaching. However, reductions in herbivore diversity and abundance via disease or over-fishing may harm corals directly and may indirectly increase coral susceptibility to other disturbances.Methodology and Principal FindingsIn two experiments over two years, we enclosed equivalent densities and masses of either single-species or mixed-species of herbivorous fishes in replicate, 4 m2 cages at a depth of 17 m on a reef in the Florida Keys, USA to evaluate the effects of herbivore identity and species richness on colonization and development of macroalgal communities and the cascading effects of algae on coral growth. In Year 1, we used the redband parrotfish (Sparisoma aurofrenatum) and the ocean surgeonfish (Acanthurus bahianus); in Year 2, we used the redband parrotfish and the princess parrotfish (Scarus taeniopterus). On new substrates, rapid grazing by ocean surgeonfish and princess parrotfish kept communities in an early successional stage dominated by short, filamentous algae and crustose coralline algae that did not suppress coral growth. In contrast, feeding by redband parrotfish allowed an accumulation of tall filaments and later successional macroalgae that suppressed coral growth. These patterns contrast with patterns from established communities not undergoing primary succession; on established substrates redband parrotfish significantly reduced upright macroalgal cover while ocean surgeonfish and princess parrotfish allowed significant increases in late successional macroalgae.SignificanceThis study further highlights the importance of biodiversity in affecting ecosystem function in that different species of herbivorous fishes had very different impacts on reef communities depending on the developmental stage of the community. The species-specific effects of herbivorous fishes suggest that a species-rich herbivore fauna can be critical in providing the resilience that reefs need for recovery from common disturbances such as coral bleaching and storm damage.

Highlights

On coral reefs large herbivores such as fishes and sea urchins can remove .90% of the daily seaweed production and maintain a ‘‘grazing lawn’’ of small, highly productive, algal turfs that supports a large portion of the secondary production on reefs [1,2,3]
Herbivore diversity could be especially critical on Caribbean coral reefs because these reefs are species poor compared to reefs in many other regions [21] and because herbivorous fishes are heavily exploited in many areas of the Caribbean [22]
For communities undergoing primary succession in our experiments, we showed strong speciesspecific effects of herbivores with both ocean surgeonfish and princess parrotfish limiting the abundance of late-successional algae and facilitating early successional species such as filamentous algal turfs

Summary

Introduction

On coral reefs large herbivores such as fishes and sea urchins can remove .90% of the daily seaweed production and maintain a ‘‘grazing lawn’’ of small, highly productive, algal turfs that supports a large portion of the secondary production on reefs [1,2,3]. Observational studies of herbivorous fishes in the Caribbean show important among-species differences in diet selection, bioerosion rates, and foraging behavior [27,28,29,30,31] suggesting that different species may produce different direct and indirect effects on reef community structure. Observational studies of herbivorous fishes are important for documenting feeding behavior and patterns, they cannot assess unambiguously the complex, direct and indirect effects of herbivore identity and richness on algal communities and coral fitness. These direct and indirect effects can be evaluated only by using controlled experimentation [32], albeit with limitations. The lack of a richness effect contrasts significantly with previously documented effects of these same fishes in these same cages on established algal communities where both herbivore identity and herbivore richness effects were strong [16]

Results

Discussion

Materials and Methods