Feeding preferences of the surgeonfish Zebrasoma flavescens in relation to chemical defenses of tropical algae

Abstract

Seaweed preferences of the tropical herbivorous surgeonfish Zebrasorna flavescens were examined in aquarium assays on Guam, in order to examine the role of secondary metabolites in determining its preferences. Of 55 species of macrophytes examined (49 algae, 5 cyanobactena, l seagrass), only 7 species were highly preferred. Seaweed extracts were examined by thin-layer chromatography (TLC) and proton nuclear magnetic resonance (NMR) spectroscopy to determine the presence or absence of secondary metabolites. Extracts from the non-preferred seaweeds and several pure major metabolites from these seaweeds were tested as feeding deterrents by applying them to the surface of Enterornorpha clathrata, a preferred alga. Extracts that contained secondary metabolites and were the most deterrent were from Bryopsis pennata, Chlorodesmis fastigiata, Desmia hornernanni, Microcoleus lyngbyaceus, Liagora farinosa, and Dictyota bartayresii. The deterrent pure metabolites were malygamide A (from M. lyngbyaceus), chlorodesmin (from C. fastigiata), pachydictyol A (from D. bartayresii), ochtodene (from D. hornernanni), and a fatty acid metabolite isolated from L. farinosa. Several extracts which did not contain metabolites based on our chemical analyses were also significantly deterrent including those from Codiurn geppii, Padina tenuis, Galaxaura oblongata, and Halyrnenia durvlllaei. Extracts from Caulerpa racernosa, Avrainvillea obscura, and Asparagopsis taxiformis contained secondary metabolites yet were non-deterrent. The pure metabolites caulerpin, caulerpenyne, and avrainvilleol from C, racernosa and A. obscura were also non-deterrent. Secondary metabolites appear to account for the low palatabhty of many of the seaweeds examined. However, not all secondary metabolites were effective deterrents toward this herbivore.

Feeding preference of the sea urchin Lytechinus variegatus (Lamarck, 1816) on seaweeds

“…In C. racemosa it was observed that, although it produces high concentrations of sesquiterpenes (1 to 2% of dry weight), this seaweed is easily consumed by fish (PAUL; HAY, 1986;MEYER;PAUL, 1992). Also, the major metabolite caulerpenine does not inhibit most fishes (WYLIE;PAUL, 1988;MEYER;PAUL, 1992), although it is able to influence other herbivores, such as some gastropods FENICAL, 1986). In the present study, it was observed that C. racemosa was consumed in high amounts both with alive and triturated specimens.…”

Palatability of Macroalgae that Use Different Types of Chemical Defenses

“…For instance, Caulerpa spp. were avoided by the surgeonfish Zebrasoma flavescens (C. prolifera, C. racemosa, Caulerpa serrulata, C. sertularioides; Wylie and Paul, 1988) and the sea urchins Paracentrotus lividus (Caulerpa taxifolia; Lemee et al, 1996), and Lytechinus variegatus (C. prolifera, Lowe, 1974;Vadas et al, 1982). In contrast, many reef fish, including parrotfish, surgeonfish, and rabbitfish, consumed Caulerpa spp.…”

“…Alternatively, Cladophora spp. were avoided by parrotfish and some surgeonfish (Paul and Hay, 1986), yet were consumed by Z. flavescens (Wylie and Paul, 1988) and the amphipod Amphithoe longimana (Hay et al, 1987a). Ulva spp.…”

“…Although sea urchins (McConnell et al, 1982) and a few reef fish (Targett et al, 1986;Paul et al, 1987) have been deterred by caulerpenyne, most reef fish were not deterred by Caulerpa spp. extracts or caulerpenyne (Paul et al, 1987;Wylie and Paul, 1988;Paul et al, 1990.…”

“…Rhizophytic algae in the order Bryopsidales, including Caulerpa, Halimeda, Udotea, Penicillus, and Rhipocephalus spp., are less palatable than other species commonly found in reef habitats (Paul and Hay, 1986;Wylie and Paul, 1988;Meyer et al, 1994). Their extracts deter feeding in artificial assays (Paul and Van Alstyne, 1992).…”