Bioassays with Marine and Freshwater Macroorganisms

Abstract

The general methods for extraction, purification, and identification of marine secondary metabolites are similar to, or involve slight modifications of, those used with terrestrial organisms. Marine methodologies for small organic molecules have been reviewed by Norris and Fenical (1985), and those for phlorotannins by Ragan and Glombitza (1986). Many compounds, such as those involved in prey detection, predator detection, and home site selection are less well understood chemically, and general reviews for methodologies dealing with the chemistry of these types of compounds are not available. With the exception of the phlorotannins, the large majority of known secondary metabolites from marine organisms are lipid soluble (Faulkner 1996, and earlier reviews cited therein). This produces significant experimental advantages because known quantities of lipid-soluble metabolites can be dissolved in volatile organic solvents such as diethyl ether and coated at desired concentrations onto surfaces (for tests as settlement cues or antifouling agents); onto palatable prey that have been blotted dry; or onto finely powdered, dried algal or animal tissue that can then be imbedded in a gel matrix (for tests as defenses against consumers see McConnell et al. 1982; Targett et al. 1986; Hay et al. 1987a, 1987b, 1994; Paul 1987, 1992; Henrikson & Pawlik 1995; Schmitt et al. 1995). After the solvent evaporates, these hydrophobic compounds adhere to the treatment surfaces or foods and do not dissolve when immersed in seawater while being used in settlement or feeding assays. Comparisons of feeding or settlement on treatments versus controls (treated with solvent only) allow for a determination of the effects of the compound alone. Modifications of these basic procedures have been applied widely in both field and laboratory investigations.