Journal of Chemical Ecology, Vol. 29, No. 6, June 2003 (  C 2003) QUANTITATIVE ASSESSMENT OF NATURAL TOXICITY IN SPONGES: TOXICITY BIOASSAY VERSUS COMPOUND QUANTIFICATION RUTH MART ´ I, 1∗ ANGELO FONTANA, 2 MAR ´ IA-J. URIZ, 1 and GUIDO CIMINO 2 1 Centre d’Estudis Avanc ¸ats de Blanes (CSIC) Carretera d’Acc´ es a la Cala Sant Francesc, 14 E-17300 Blanes, Girona, Spain 2 Instituto di Chimica Biomolecolare (CNR) Via Campi Flegrei, 34 80078 Pozzuoli, Napoli, Italy (Received March 7, 2002; accepted January 28, 2003) Abstract—Microtox  assay was used to assess the natural toxicity of two sponges, Dysidea avara and Ircinia variabilis. The activity of crude extracts and major metabolites were compared. Methanol extract of D. avara was more toxic than that of acetone and was as toxic as pure avarol, thus suggesting that the toxicity of the sponge was mainly due to this metabolite. We also quanti- fied palinurin, the major metabolite of I. variabilis, in specimens from several habitats. With the same methanol extracts used for palinurin quantification, we ran the Microtox  assay and found a positive significant regression between toxicity and concentration of this metabolite. Pure palinurin was tested at the same concentration present in the extract, and the toxicity recorded was higher than that of the methanol extract. As with avarol from D. avara, palinurin is the main secondary metabolite that confers toxicity to I. variabilis. The results confirm that the standardized Microtox  assay is an accurate and reproducible tool for assessing the toxicity of crude extracts and pure metabolites of marine organisms. These results also suggest that methanol is more suitable than ace- tone for the detection of species toxicity by Microtox  . The method is faster and easier to perform than chemical quantification even when the sponge chemistry is known, and is appropriate for studies on variation in natural toxicity over a range of environmental conditions. Key Words—Natural toxicity, sesterpene, avarol, palinurin, secondary metabo- lites, crude extracts, bioactivity, bioassays, Microtox  , chemical quantification, sponges, Dysidea avara, Ircinia variabilis. ∗ To whom correspondence should be addressed. E-mail: ruth@ceab.csic.es 1307 0098-0331/03/0600-1307/0 C  2003 Plenum Publishing Corporation