Seasonal regulation of herbivory and nutrient effects on macroalgal recruitment and succession in a Florida coral reef.

Alain Duran,Ligia Collado-Vides,Deron E Burkepile

doi:10.7717/peerj.2643

Alain Duran, Ligia Collado-Vides + Show 1 more

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https://doi.org/10.7717/peerj.2643

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Abstract

Herbivory and nutrient enrichment are drivers of benthic dynamics of coral reef macroalgae; however, their impact may vary seasonally. In this study we evaluated the effects of herbivore pressure, nutrient availability and potential propagule supply on seasonal recruitment and succession of macroalgal communities on a Florida coral reef. Recruitment tiles, replaced every three months, and succession tiles, kept in the field for nine months, were established in an ongoing factorial nutrient enrichment-herbivore exclusion experiment. The ongoing experiment had already created very different algal communities across the different herbivory and nutrient treatments. We tracked algal recruitment, species richness, and species abundance through time. Our results show seasonal variation in the effect of herbivory and nutrient availability on recruitment of coral reef macroalgae. In the spring, when there was higher macroalgal species richness and abundance of recruits, herbivory appeared to have more control on macroalgal community structure than did nutrients. In contrast, there was no effect of either herbivory or nutrient enrichment on macroalgal communities on recruitment tiles in cooler seasons. The abundance of recruits on tiles was positively correlated with the abundance of algal in the ongoing, established experiment, suggesting that propagule abundance is likely a strong influence on algal recruitment and early succession. Results of the present study suggest that abundant herbivorous fishes control recruitment and succession of macroalgae, particularly in the warm season when macroalgal growth is higher. However, herbivory appears less impactful on algal recruitment and community dynamics in cooler seasons. Ultimately, our data suggest that the timing of coral mortality (e.g., summer vs. winter mortality) and freeing of benthic space may strongly influence the dynamics of algae that colonize open space.

Highlights

‘‘Grazing ecosystems’’ are characterized by an herbivore-based food web where over 50% of primary production is processed by aquatic or terrestrial grazers (McNauthon, 1985; Douglas, McNaughton & Tracy, 1998; Burkepile, 2013)
We saw no temporal changes in biomass or density of total and herbivorous fish as no significant differences were found among seasons (One-factor ANOVA, p > 0.05 in all cases, Appendix S3)
Macroalgal species richness on recruitment tiles increased across seasons, averaging 9.73 ± 0.63 species per tile in fall, 12.13 ± 0.79 in winter, and 14.40 ± 1.19 in spring

Summary

Introduction

‘‘Grazing ecosystems’’ are characterized by an herbivore-based food web where over 50% of primary production is processed by aquatic or terrestrial grazers (McNauthon, 1985; Douglas, McNaughton & Tracy, 1998; Burkepile, 2013). Increases in water temperature and light availability can promote macroalgal growth and trigger reproduction in some species (Clifton, 2008; Collado-Vides et al, 2011) Both Dictyota pulchella and Sargassum spp. show a peak of abundance during the summer and a loss of biomass in the coolest seasons (Lirman & Biber, 2000; Renken et al, 2010). In reefs in the Florida Keys, both extreme warm water (Eakin et al, 2010) and cold water (Lirman et al, 2011) anomalies can lead to coral mortality Given that these disturbances open up free space for macroalgal colonization during different times of the year with different abiotic conditions, different species of algae may become dominant and drive different successional trajectories depending on the timing of these disturbances and the initiation of algal succession.

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