Species-specific effects of herbivorous fishes on the establishment of the macroalga Lobophora on coral reefs

<p>Herbivory is a key ecosystem function that influences ecosystem trajectories. However, interactions between plants and herbivores are species-specific and change throughout the plants’ lifetime. On coral reefs, herbivorous fishes reduce competition between corals and macroalgae through their grazing activity, thereby regulating the ecosystem state. Grazing vulnerability of marine algae generally decreases with increasing algal size. Therefore, the removal of newly settled recruits by herbivorous fish is likely important in preventing macroalgal blooms and reducing competition with corals. We studied the grazing susceptibility of recruits of the brown macroalga <i>Lobophora</i> to multiple fish species through a combination of feeding observations and manipulative <i>in situ</i> and <i>ex situ</i> experiments. Further, we recorded short-term <i>Lobophora</i> growth patterns and adult survival over 9 wk. <i>Lobophora</i> recruits were more susceptible to herbivory than adults, likely owing to their smaller size. However, recruit mortality was driven by only 3 of the studied species: <i>Acanthurus nigrofuscus</i>, <i>Scarus niger</i> and <i>Chlorurus spilurus,</i> whereas other common herbivores did not remove any <i>Lobophora</i> recruits. Our data also suggest variable growth and recruitment among months. These findings point to a possible increase in grazing resistance with age for <i>Lobophora</i>. As such, a decrease in grazing pressure by key fish species controlling <i>Lobophora</i> recruits could permit <i>Lobophora</i> to establish more grazing-tolerant adult populations. </p>