Tropical Chemically Defended Macroalgae

The majority of natural products from tropical macroalgae are terpenoids (mainly sesqui- and diterpenoids), followed by acetogenins (acetate-derived compounds), and metabolites of mixed biosynthetic origin (such as meroditerpenes), frequently composed of terpenoid and aromatic portions (Blunt et al. 2007 and previous reviews see Chap. 1). 

Chlorophyta or green algae comprise one of the major groups of algae and include several exclusively marine orders and genera from tropical regions. Natural products chemistry research has identified more than 300 secondary metabolites from Chlorophyta, with most being sesquiterpenoid and diterpenoid compounds 

Chemical defenses of marine macroalgae have been extensively studied during the past 20 years (Paul and Puglisi 2004), ranging from species collected in Antarctic polar waters (e.g., Amsler et al. 2005 see Chap. 4) to those from the 

5 Tropical Macroalgal Chemical Defenses and Community Structure 

Many herbivorous fishes are found on coral reefs (Horn 1989 Choat 1991) and their grazing activities are commonly the dominant factor affecting the distribution and abundance of macroalgae (e.g., Morrison 1988 Hixon and Brostoff 1996 Marques et al. 2006) as well as the structure and function of marine communities and ecosystems in general (Duffy and Hay 2001). For example, the exclusion of 

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These associational defenses are examples of a mechanism that is to date underexplored in tropical regions and that probably represents one of the most important cascading effects of chemically defended macroalgae on community structure. Thus, chemically defended macroalgae can act as local biodiversity centers, by increasing the coexistence of species under their chemical defense umbrellas. 

Wikstrom et al. 2006). We need similar studies to assess the impact of chemically defended macroalgae on the structure and dynamics of tropical marine benthic communities. 

Table 2.1 Chemically defended tropical macroalgae, with geographic distribution, ecological role attributed, and references Genus and studied...

The Invasive Potential of Chemically Defended Tropical Macroalgae... 

Tropical seaweeds are often well defended owing to high levels of predation by fishes on tropical reefs 18,37 however, coldwater seaweeds also use chemical protection, mainly against sea urchins and crabs. A number of macroalgae from the Antarctic subcontinent possess chemical extracts that are deterrent to sea stars,38,39 amphipods,39,40 or fish,39 while Arctic algae have been screened for deterrency toward sea urchins and amphipods.41 Chemical defenses have also been detected in seagrasses, notably in the Mediterranean Posidonia oceanica whose extracts deter feeding by sea urchins and fish 42... 

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