Chemical defense in tropical green algae, order Caulerpales

Abstract

Forty marine algae of the order Caulerpales were chemically investigated. Virtually all produce toxic secondary metabolites of a unique and unprecedented class. These metabolites are generally Linear terpenoids, but unusual structural features such as aldehydes and bis-enol acetate functional groups make these compounds uruque. The conlpounds are t o n c or deterrent toward microorganisms, sea urchin larvae, and herbivous fishes, and when incorporated into diets at naturally occurring concentrations cause mortality in juvenile conch. Concentrations of bioactive metabolites were found to show httle variation in different plant parts such as blades, shpes and holdfasts. Young growlng tips and reproductive structures contained higher concentrahons than mature plant tissues on a dry weight and ash-free dry weight basis. Chemical variation, both qualitahve and quantitative, was observed in different populations of the same species. In the cases examined, algae growing in areas known to have the highest herbivory produced the greatest concentrations and varieties of secondary metabolites. Based upon these observations and pnor feeding preference data, we conclude that chemical defense IS a major factor In the sumval of marine algae within this order.

Chemical mediation of interactions among marine organisms

“…85 Other green algae such as Penicillus, Udotea, Rhipocephalus, and Caulerpa also often produce higher concentrations or different types of secondary metabolites in populations from herbivore-rich reef habitats than in populations from herbivore-poor areas such as reef fiats or seagrass beds. 118 " 119 Shallow and deep water populations of the brown alga Stypopodium zonale produced different secondary metabolites. 120 The red alga Portieria hornemanni is well known to vary in its composition of halogenated monoterpenes among different collection sites in the tropical Pacific; 91 ' 121 this variation does not appear to be environmentally mediated.…”

Palatability of Macroalgae that Use Different Types of Chemical Defenses

“…Ulva spp. extracts and caulerpenyne are toxic to larval and adult stages of many marine invertebrates and vertebrates (Paul and Fenical, 1986;Lemee et al, 1993;Pedrotti et al, 1996;Nelson et al, 2003). Ulvoid extracts have reduced the growth and germination of seagrass epiphytes and macroalgal zygotes (Nelson et al, 2003).…”

“…Ulvoid extracts have reduced the growth and germination of seagrass epiphytes and macroalgal zygotes (Nelson et al, 2003). Caulerpenyne is also toxic to bacterial and fungal pathogens (Paul and Fenical, 1986). Although studies often test for toxicity by bathing organisms in algal extracts, which may not accurately assess potential for deterring settlement or feeding, these studies demonstrate that bloom-forming and invasive species have the potential to impair or kill organisms if they release metabolites into the water column.…”

“…Caulerpenyne was semipurified from C. sertularioides crude extract with flash column chromatography (Paul and Fenical, 1986). It was found in the 95:5 hexane/ethyl acetate fraction of a florisil column, and nuclear magnetic resonance indicated ∼90% purity.…”

“…Their extracts deter feeding in artificial assays (Paul and Van Alstyne, 1992). Algae also produce higher concentrations or additional defensive compounds in areas subject to high herbivore pressure (Paul and Fenical, 1986). In addition, algae in the order Ulvales and Cladophorales, such as Ulva, Enteromorpha, and Cladophora spp., are less palatable than other algae in the field and in live algal and artificial feeding trials toward some temperate herbivores (Paul and Hay, 1986;Van Alstyne et al, 2001;Van Alstyne and Houser, 2003), although less is known about their secondary chemistry.…”