Co-Occurrence of Chemical and Structural Defenses in the Gorgonian Corals of Guam
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MARINE ECOLOGY PROGRESS SERIES Vol. 239: 105–114, 2002 Published August 23 Mar Ecol Prog Ser Co-occurrence of chemical and structural defenses in the gorgonian corals of Guam Melany P. Puglisi1,*, Valerie J. Paul3, Jason Biggs3, Marc Slattery1, 2 1Department of Pharmacognosy, School of Pharmacy, University of Mississippi, University, Mississippi 38677, USA 2National Center for the Development of Natural Products, Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, Mississippi 38677, USA 3University of Guam Marine Laboratory, Mangilao 96913, Guam ABSTRACT: Chemical and structural defense mechanisms have been reported to co-occur in algae and some soft corals. This study addressed the co-occurrence of chemical and structural defense mechanisms in 7 of the common gorgonian species found around Guam, specifically focusing on pat- terns of within-colony variation of these 2 modes of defense. Lipophilic crude extract and sclerite con- centrations were compared among the base, mid-axis and tip of multiple colonies of each species. Crude extract concentrations differed significantly among parts of Annella mollis, A. reticulata, Suber- gorgia suberosa, and Viminella sp. colonies. Sclerite concentrations differed significantly within colonies of Astrogorgia sp. and Villogorgia sp. Crude extracts and sclerites from the mid-axes and tips of the colonies were assayed in the field against natural assemblages of reef fishes. Extracts from the tips of 6 of the 7 species were unpalatable to fishes. Of these 6 species, extracts from the mid-axes of A. mollis, A. reticulata and S. suberosa, all of the family Subergorgiidae, deterred fish feeding. Chemical and structural defenses co-occurred in representatives of the families Plexauriidae (Astro- gorgia sp. and Villogorgia sp.) and Subergorgiidae (A. mollis and S. suberosa). Only 1 gorgonian coral, Viminella sp., appeared to rely primarily upon structural defenses rather than chemical defenses. To determine if size and shape were factors associated with sclerite structural defenses, a second set of feeding assays was conducted with powdered and whole sclerites from the unpalatable species. Fishes avoided the powdered sclerites from 4 of the 5 species when offered at natural con- centrations, suggesting that other properties remaining after the structural integrity of the sclerites was destroyed optimize the calcite skeletal elements for a defensive role. KEY WORDS: Extracts · Sclerites · Chemical Ecology · Annella spp. · Subergorgia suberosa · Rumphella sp. · Villogorgia sp. · Viminella sp. · Astrogorgia sp. · Guam Resale or republication not permitted without written consent of the publisher INTRODUCTION 1992, van Alstyne et al. 1994, Slattery 1999, Koh et al. 2000, Puglisi et al. 2000). Production of multiple de- Chemical (i.e. secondary metabolites) and structural fense mechanisms by sessile marine organisms may be defense mechanisms (i.e. CaCO3) have been reported to their advantage, allowing them to overcome preda- to co-occur in algae (Paul & Hay 1986, Pennings & Paul tion pressures from the high diversity of tropical con- 1992, Hay et al. 1994, Schupp & Paul 1994, Pennings et sumers (Paul & Hay 1986, Hay et al. 1994, Schupp & al. 1996) and octocorals (Gerhart et al. 1988, Harvell et Paul 1994, Pennings et al. 1996). Schupp & Paul (1994) al. 1988, Harvell & Fenical 1989, van Alstyne & Paul observed differences in the effects of diterpenoid sec- ondary metabolites from the green alga Halimeda *Present address: Scripps Institution of Oceanography, Mail macroloba and aragonite (the CaCO3 form found in H. Code 0204, UCSD, La Jolla, California 92093, USA. macroloba) when offered at natural concentrations to E-mail: [email protected] different herbivorous fishes in laboratory feeding assays. © Inter-Research 2002 · www.int-res.com 106 Mar Ecol Prog Ser 239: 105–114, 2002 Scarus sordidus and Ctenochaetus striatus avoided the Qualitative and quantitative variation of chemical diterpenes but not the aragonite, while Naso lituratus and structural components within colonies occurs in and Siganus spinus avoided the aragonite but not the some species of soft corals (Harvell & Fenical 1989, van diterpenes (Schupp & Paul 1994). A limited number of Alstyne & Paul 1992, Kim et al. 2000, Puglisi et al. 2000). comparative studies have been conducted among dif- In an early study of the chemical and structural com- ferent species in the same phylum other than calcified ponents of Pseudopterogorgia spp., metabolites were algae (Paul & Hay 1986). Studies such as these are reported to be concentrated at the tips of colonies important to determine whether general patterns of whereas sclerites were more concentrated in the mid- defense exist among related groups of organisms. axes and bases, suggesting a potential tradeoff in re- Gorgonians, like other sessile marine organisms, source allocation between chemical and structural produce a variety of secondary metabolites (Faulkner components (Harvell & Fenical 1989). Van Alstyne & 2000a,b and references therein). These metabolites are Paul (1992) observed similar patterns for the soft corals concentrated in the coenenchyme (polyp bearing con- Sinularia polydactyla and Sinularia sp. where higher nective tissue surrounding the gorgonian skeleton) concentrations of metabolites where found in the termi- which also contains small calcite skeletal elements nal branches of colonies. Kim et al. (2000) recently re- called sclerites (Bayer 1955). Feeding studies with ported the crude extracts from the tips of healthy Gor- crude extracts and secondary metabolites from sea gonia spp. colonies to be more resistant to the fungal fans and whips have demonstrated that many species pathogen Aspergillus sydowii than extracts from other of gorgonians are chemically defended (Pawlik et al. parts of the colony. This activity was correlated with 1987, Harvell et al. 1988, 1993, 1996, Fenical & Pawlik higher crude extract concentrations in the tips of the 1991, Pawlik & Fenical 1992, Maia et al. 1999, Slattery colonies. However, 2 independent studies of G. ven- 1999, Koh et al. 2000, Puglisi et al. 2000). However, talina by van Alstyne & Paul (1992) and Slattery (1999), broad surveys of the common species of gorgonians in found no within-colony variation of crude extract and the Caribbean and Guam show that the production of sclerite concentrations in the upper portions of the chemical defenses is not ubiquitous in this group of colonies. In a recent study, feeding assays with crude animals (Pawlik et al. 1987, Puglisi 2001). extracts and sclerites from the Pacific gorgonians An- Sclerites are the microscopic components of a meso- nella mollis and A. reticulata showed that crude ex- skeleton that prevent damage to the tissues caused by tracts from the tips of colonies deterred fish feeding, heavy wave action and currents (Esford & Lewis 1990, while similar concentrations of extracts from the mid- Lewis & von Wallis 1991). Sclerites differ considerably axes were not always effective deterrents (Puglisi et al. in size, shape and color among species of octocorals and 2000). Crude extract concentrations did not differ be- are used as a taxonomic delineation (Bayer 1955). The tween mid-axes and tips for either species, thus sug- few feeding studies conducted with gorgonian sclerites gesting that quantitative differences in the concentra- have demonstrated that the Caribbean gorgonians tion of the crude extract does not reflect differences in Briareum asbestinum (Harvell et al. 1993, West 1997, the active components. 1998), Gorgonia ventalina (van Alstyne & Paul 1992, In addition to providing an advantage to the organism Cronin et al. 1995, Slattery 1999), Leptogorgia virgulata by affording multiple defenses against a multitude of (Gerhart et al. 1988), Pseudopterogorgia acerosa (Har- predators, the components of a multiple defense system vell et al. 1988) and the Singapore gorgonians Cteno- may act additively or synergistically (Gerhart et al. 1988, cella pectinata, Ctenocella sp. and Echinogorgia sp. Hay et al. 1994, Hay 1996). The components are additive (Koh et al. 2000) are structurally as well as a chemically if the combined effect is equal to the sum of the expected defended. In a broad survey of Caribbean species, the activities predicted by the dose response curve of the in- extracts from species with small sclerites were usually dividual components. They are synergistic if the com- found to be unpalatable to fishes (Pawlik et al. 1987, bined effect of the components is greater than the sum Harvell & Fenical 1989). The importance of the size, predicted by the dose response curves of the individual shape and density of sclerites in the coenenchyme to components (Berenbaum 1989). One advantage of syn- palatability has only been addressed for B. asbestinum ergism to the host organism is that multiple components (West et al. 1993, West 1998). Short, densely packed of the defense system can be maintained within the sclerites in colonies at shallow depths deterred fishes, tissues in a non-toxic state. Evidence for synergism be- while longer, larger, more loosely associated sclerites in tween chemical defenses and CaCO3 in feeding studies colonies at deeper depths did not (West et al. 1993, has been reported for the green alga Halimeda goreauii West 1998). In addition, simulated predator damage to (Hay et al. 1994) and the gorgonian Leptogorgia virgu- colonies resulted in the induction of the smaller scle- lata (Gerhart et al. 1988,