Herbivory effects on benthic algal composition and growth on a coral reef flat in the Egyptian Red Sea

Abstract

; mean ± SE) compared to sea urchins (3.4 ± 0.2 ind. m −2 ), they were 5-fold more efficient in reducing algal dry mass and 22-fold more efficient in reducing autotrophic production of nitrogen. A significant shift from benthic turf to macroalgae (mostly Padina sp. and Hydroclathrus clathrathus) was observed when grazers were excluded. These algae may serve as early warning indicators for overfishing. Findings suggest that herbivorous fish act as an important top-down factor controlling both benthic algal biomass and composition at the study location. Results also indicate the potential of rapid benthic community change at the study site if herbivory is impeded.

In-Situ Effects of Simulated Overfishing and Eutrophication on Benthic Coral Reef Algae Growth, Succession, and Composition in the Central Red Sea

“…In contrast to a recent study by Jessen and Wild [55] in the Egyptian Red Sea, who found frondose brown algae within 4 wks after the start of a similar experiment, this algal group was not observed during the present study. Other studies from other oceans found frondose brown algae also within 4 months on their tiles [11]–[13], [50], [51], [86], though some of the examined substrates were likely affected by preconditioning.…”

“…However, C and N data analyses provide a more neutral method than other biomass measures because values are independent of algal species and their calcified structures, if any, and permit greater comparability between studies, albeit data available are scarce. Only one recent study from the Egyptian Red Sea [55] showed N removal rates and their maxima were similar to the results found here. The consistently lower organic C/N ratio in the caged treatments indicates that herbivore preferentially graze on N rich algae [91]–[93], which did not accumulate outside the cages.…”

Coral Reef Resilience, Tipping Points and the Strength of Herbivory

“…Herbivory alters the death rate of algae, and of course an herbivory threshold should also vary with factors that influence algal birth rates, such as the potential of the reef ecosystem to support rapid colonization and/or subsequent growth of fleshy algae. The latter will depend on the combination of particular algal species present as well as nutrification or other factors that enhance algal growth, and it may vary substantially within and among geographic regions2238. For example, Moorea, which is in a very nutrient-poor region of the Indo Pacific, may have a tipping point at a lower intensity of herbivory than reefs located in more nutrient-rich locations.…”

“…If herbivore populations are reduced by fishing, then macroalgae may be able to escape top down control on the reef, especially following a disturbance that kills coral on a landscape scale such that herbivory pressure functionally becomes diluted25. While numerous small scale experiments where herbivorous fishes were excluded resulted in the proliferation of macroalgae in the absence of herbivory29343536373839, we generally lack knowledge of the level of herbivory that would be sufficient to control fleshy seaweeds at the landscape scale (but see Graham et al 15…”

An experimental evaluation of macroalgal consumption and selectivity by nominally herbivorous fishes on subtropical rocky reefs

“…These species are known to be extremely important in shaping hard bottom benthic communities at various scales due to their grazing activity (Lewis and Wainwright, 1985;Carpenter, 1986;Polunin, 1988;Jesse and Wild, 2013). Indeed, a number of field and experimental studies have demonstrated the capacity of nominally herbivorous fishes to influence the distribution, standing crop, productivity and community structure of different algal groups on tropical reefs (Hatcher and Larkum, 1983;Carpenter, 1986;Klumpp and Polunin, 1990;Choat, 1991) and subtropical and temperate environments (Choat, 1982;Ojeda and Muñoz, 1999;Mendes et al, 2009;Taylor and Schiel, 2010).…”