Herbivory on coral reefs: algal susceptibility to herbivorous fishes

Abstract

The susceptibility of several tropical algal species to fish grazing was studied on the Belizean barrier reef off the Caribbean coast of Central America. Short-term transplant experiments indicate that plant species vary markedly in their rates of biomass loss to grazing by a shallow-water guild of herbivorous fishes. Algal species transplanted from habitats with low grazing pressure are highly susceptible to grazing, while species occurring in habitats with high herbivore densities are highly resistant to grazing. Algal species show differential susceptibility to grazing by two major components of the tropical herbivore guild, Acanthurus (surgeonfishes) and Sparisoma (parrotfishes).Variability in plant susceptibility to grazing by herbivorous fishes was not clearly correlated with morphological or chemical characteristics that have been previously suggested as plant defenses against herbivory. Plants found to be highly resistant to fish grazing, such as Halimeda, exhibit both morphological characteristics and secondary chemical compounds which do appear to reduce herbivory. In contrast, species of Caulerpa, Sargassum, Turbinaria, and Padina, which also possess alleged morphological and/or chemical defenses, are nevertheless highly susceptible to fish grazing.

Spatial and temporal variations in grazing pressure by herbivorous fishes: Tobacco Reef, Belize

“…Other studies have indicated that many algal species characteristic of habitats with high grazing intensities are resistant to herbivorous fish grazing and, conversely, algae in habitats with low grazing intensity are susceptible to herbivory (Hay 1981b, 1984, Littler et al 1983, Lewis 1985, 1986. For example, the coralline-coral-Dictyota zone (Macintyre et al 1987) is the zone in which we measured the highest levels of herbivory.…”

“…A mixed assay allowed us to determine grazing intensity with respect to the variety of herbivore groups observed to be active in this area. For example, previous studies (Lewis 1985) have shown that T. turbinata, S. polyceratium, T. testudinum and P. jamaicensis are preferred and primarily consumed by parrotfish (Sparisoma and Scarus spp.). In contrast the red algal species, A. spicifera, L. papillosa and L. intricata, are preferred and primarily consumed by acanthurid species (Acanthurus bahianus, A. coeruleus and A. chirugus) (Lewis 1985).…”

“…For example, previous studies (Lewis 1985) have shown that T. turbinata, S. polyceratium, T. testudinum and P. jamaicensis are preferred and primarily consumed by parrotfish (Sparisoma and Scarus spp.). In contrast the red algal species, A. spicifera, L. papillosa and L. intricata, are preferred and primarily consumed by acanthurid species (Acanthurus bahianus, A. coeruleus and A. chirugus) (Lewis 1985). Another herbivore, Diadema antillarum, was not considered in this study because it had undergone a massive die-off throughout the Caribbean (Lessios et al 1983) and was never common on this back-reef sediment apron of Tobacco Reef.…”

Chemical defense in the seaweed Dictyopteris delicatula: differential effects against reef fishes and amphipods

“…After 5.5 h, they were collected and the amount of each blade consumed was estimated by measuring its remaining length to the nearest 0.5 cm (see Hay et al 1987b for elaboration of this method). This method primarily assays for grazing by parrotfishes (Lewis 1985, Hay et al 1987b, 1988a.…”

Effects of herbivores and water quality on Sargassum distribution on the central Great Barrier Reef:cross-shelf transplants

“…On many reefs, high rates of herbivory maintain algal turfs with low biomass and high productivity (Hatcher & Larkum 1983, Russ 1987, Carpenter 1988, Hatcher 1988, Steneck 1988, Klumpp & McKinnon 1989, 1992, Klumpp & Polunin 1990. Numerous studies using experimental transplants and/or herbivore exclusion (cages) have shown herbivory to affect the distribution or abundance of various algal groups at various scales, from damselfish territories (Hixon & Brostoff 1981 in Hawaii; Sammarco 1983 on GBR), zones or habitats within reefs (Hay 1981a, b, 1984a, b, 1985, Sammarco 1982a, Hay et al 1983, Littler et al 1983a, b, Hay & Taylor 1985, Lewis 1985, Lewis & Wainwright 1985, Carpenter 1986, Lewis et al 1987, Morrison 1988, all on Caribbean reefs) to whole patch reefs (Sammarco 1982b). Mass mortalit~es of Diadema urchins on over-fished reefs in the Cartbbean led to very 1.arge scale shifts from coral to algal dominance (Hughes et al 1987, Hughes 1989, Carpenter 1990.…”