Interaction of herbivory and seasonality on the dynamics of Caribbean macroalgae
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Many Caribbean coral reefs are undergoing a phase shift from coral to macroalgal dominance. Understanding the processes driving changes in algal abundance and community structure requires clarification of the relative effects of top-down (e.g., herbivory) and bottom-up processes (e.g., light, temperature, and nutrients). To date, a number of studies have examined the relative effects of grazing versus nutrification but interactions between herbivory and natural, seasonal fluctuations in temperature and light have not been investigated. This study considered the dynamics of three Caribbean macroalgal species [Lobophora variegata (Lamouroux), Dictyota pulchella (Hörnig and Schnetter), and Halimeda opuntia (Linnaeus)] and algal turf. A field experiment was established to measure species-specific algal dynamics (changes in abundance) over 13 months in the presence and absence of herbivory. Both herbivory and seasonal changes were important processes controlling macroalgal and turf abundance. Water temperature and light had a key role on D. pulchella; this species’ abundance significantly increased in the summer, when water temperature and light were the highest, and decreased during winter. Surprisingly, herbivory did not seem to control D. pulchella directly. However, herbivory was the most important process controlling the abundance of L. variegata,H. opuntia, and turf. The abundance of both algal species was correlated with seasonal changes in the environment, but was depleted outside cages throughout the year. The abundance of H. opuntia was positively correlated with temperature and light, but there was no statistical interaction between drivers. The statistical interaction between temperature and light was significant for the abundance of L. variegata and turf, but algal abundance declined as both factors increased. Overall, macroalgal and turf cover were mainly controlled by herbivory, while community structure (which species contributed to the overall cover) was largely influenced by seasonal changes in temperature and light.
KeywordsDictyota pulchella Lobophora variegata Halimeda opuntia Macroalgal dynamics Herbivory Seasonality
This study was funded by a Khaled bin Sultan Living Oceans Foundation and a Wildlife Conservation Society Research Leadership Program Fellowships (R. F.), and supported by an ARC Laureate Fellowship, and EU FORCE project (P. J. M.). R. F. was funded by a Comision Nacional de Ciencia y Tecnologia (CoNaCyT) of Mexico, an ORSAS University of Exeter and a University of Queensland scholarships, M. G. R. was funded by the Fondo Nacional de Ciencia, Tecnología e Inovación (FONACIT) of Venezuela. We thank volunteers for field assistance, and the staff at the Glovers Reef Marine Station for invaluable field support. We thank the Smithsonian Research Station at Carrie Bow Caye, Belize, for providing the solar insolation data and the Fisheries Department of Belize for issuing the research permit. Comments by three anonymous referees greatly improved the manuscript.
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