A significant number of halogenated low molecular weight metabolites have exhibited an impressive array of biological properties ranging from antimicrobial to insecticidal activities. Studies on the natural products chemistry of the red seaweeds were recently stimulated by the discovery of the acyclic monoterpene halomon, which exhibits selective antitumor activity in the National Cancer Institute's human tumor and disease oriented in vitro screen.The present review is a taxonomy based compilation of the available literature on the halogenated volatile metabolites (C 1 -C 10 ) produced by red seaweeds, with a short description of the reported ecological and pharmaceutical activities. The review begins with a presentation of simple halogenated hydrocarbons and phenols, showing their wide occurrence in rhodophyta, along with a description of simple halogenated lipids in some of the most frequently investigated red algae species and finally focuses on the chemical composition of individual red algae species.

In order to combat the human immunodeficiency virus (HIV), diverse strategies have been developed to research on compounds which can be developed as therapeutic agents. Screening of natural products derived from numerous species has afforded metabolites with significant antiviral activity against the HIV. The marine environment representing approximately half of the global biodiversity offers an enormous resource for novel compounds. Currently more than 150 natural products with promising levels of anti-HIV activity have been isolated following bioassay guided protocols from aqueous or organic extracts of marine organisms. Some of the most characteristic marinemetabolites that have exhibited significant anti-HIV activity on different biochemical assays designed for chemotherapeutic strategies are: Cyanovirin-N, a protein from a blue green alga; various sulfated polysaccharides extracted from seaweeds (i.e. Nothogenia fastigiata, Aghardhiella tenera); the peptides tachyplesin and polyphemusin, which are highly abundant in hemocyte debris of the horseshoe crabs Tachypleus tridentatus and Limulus polyphemus; sponge metabolites such as avarol, avarone, ilimaquinone and several phloroglucinols; and a number of metabolites from marine fungi such as equisetin, phomasetin and integric acid. Considering that number of unique metabolites that have been isolated from a small extent of the ocean's biological and chemical diversity, the oceans represent a virtually untapped resource for the discovery of novel bioactive compounds.

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Marine Sponges, Chemical Defense, Antifouling The defense roles and the antifouling activity of the organic extracts and the major metabolites of the sponges Ircinia oros, I. variabilis and I. spinosula were investigated. The antifeedant activity was tested in experimental aquaria on the generalist predator fish Thalassoma pavo as well as in coastal ecosystems rich in fishes. Some of the major metabolites exhibited high levels of antifeedant activity. The antifouling activity was tested in laboratory assays, against representatives of the major groups of fouling organisms (marine bacteria, marine fungi, diatoms, macroalgae and mussels). All extracts showed promising levels of activity. As was expected, no single extract was active in all tests and some fractions that were effective against one organism showed little or no activity against the others. The high but variable level of antifouling activity in combination with the absence of toxicity (tested on the development of oyster and sea urchin larvae) shows the potential of these metabolites to become ingredients in environmentally friendly antifouling preparations.

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