Macroalgae reduce growth of juvenile corals but protect them from parrotfish damage

Abstract

Inhibition of early life stages of corals by benthic algae is a critical bottleneck to the recovery and resilience of corals. Increasingly frequent and severe disturbances are causing largescale coral mortality, usually followed by colonisation and dominance by benthic algae. The capacity of corals to re-establish in such algal-dominated habitats will depend on the effects of the algae on growth and survivorship of juvenile corals. We experimentally evaluated the competition between juvenile corals Porites astreoides and algae and the effects of algae on the exposure of juvenile corals to damage by parrotfishes (family Scaridae) in a Colombian Caribbean reef. We also explored whether those effects were consistent among climatic seasons (upwelling and non-upwelling). Benthic algae had negative and positive effects on the juvenile corals. The removal of algal turfs and fleshy macroalgae enhanced coral growth. Unexpectedly, removal of algae from around the juvenile corals increased predation upon the corals by parrotfishes. When algae were removed, at least 50% of the corals were grazed by parrotfishes, but no bites were observed on corals with intact algae. Coral growth and parrotfish damage were not affected by season. However, damage by parrotfishes neither lessened survivorship nor resulted in negative growth for any of the grazed coral colonies. The beneficial effects of algae in protecting the juvenile corals from parrotfish damage seem to be outweighed by the negative effects of the algae on coral-algal competition. Understanding such complexities in the interactions between algae and early life stages of corals can provide insight into the roles of algae in coral reef resilience.

Coral responses to macroalgal reduction and fisheries closure on Caribbean patch reefs

“…Given that incidence of predation were not quantified in this study, these conclusions remain speculative, but studies in old non-Caribbean reserves have reported that corallivory causes retarded recovery after disturbances . Nonetheless, the patterns observed here and the findings of a recent study (Venera-Ponton et al 2011) suggest that coralalgal inter actions are considerably more complicated and that additional factors are involved than proposed by the common coral-algal competition hypo theses.…”

“…Consequently, other factors such as recruitment limits, temperature anomalies, disease, and predation pressure could be more important than macro algae in determining these species' health and survival (Vu et al 2009, Venera-Ponton et al 2011). Many of the small-scale experimental manipulations show immediate responses on the order of days to weeks (Smith et al 2006, Liu et al 2009), which we suggest are largely a result of experimental conditions that are atypical of field conditions.…”

“…Yet, laboratory and small-scale experiments create experimental artifacts and environmental conditions that do not emulate conditions experienced by the species and, therefore, need to be interpreted and extrapolated to natural systems with caution. Similarly, experiments that restrict scale or multiple realistic interactions may overlook factors critical to the health and survival of corals (Venera-Ponton et al 2011 Denotes 6 most abundant macroalgal herbivore species that were pooled to calculate total herbivore density (ind. m ) of herbivorous fishes (pooled densities of Scaridae and Acanthuridae species) over time and treatment.…”

“…Results of statistical tests are given in Table 3 effects have used either caging experiments, aquariums, or transplanted or placed algae in direct or close contact with corals and generally over short time periods (Jompa & McCook 2002, Nugues & Bak 2006, Smith et al 2006, Tit ly a nov et al 2007, Foster et al 2008, Liu et al 2009, Rasher & Hay 2010. Longterm field experiments have found fewer negative interactions (Venera-Ponton et al 2011), and often specific to species (Nugues & Bak 2006) or limited to physical shading or abrasion rather than indirect and lethal interactions (Box & Mumby 2007).…”

“…Strong effects of coral-algal competition may be greater on smaller colonies or juvenile colonies (Raymundo & Maypa 2004, Box & Mumby 2007, Idjadi et al 2010, Venera-Ponton et al 2011). Similar to our results, Vu et al (2009), using small but not juvenile corals, did not detect negative effects of 3 common macroalgal species on coral growth in their short-term study.…”