Introduction to the Marine Algae: Overview 15
whole system due to its ability to fix calcium carbonate (highly abundant in the water surrounding the
coral reefs), depositing calcite (CaCO 3 ) in their cell wall (Littler 1976). Many reefs are essentially formed
by these organisms. The fragmentation of these calcareous algae, by drilling organisms and scrappers,
increases the amount of sediment and calcium carbonate that occurs on the reef floor. The genus Halimeda,
for example, is responsible for about 77% of the sediments that make up some tropical reefs (Littler and
Littler 1988).
The reefs are characterized by a huge quantity and diversity of animal life being among the more
productive marine systems (Dawes 1998). The herbivores (mainly fish, sea urchins, and mollusks)
dominate and keep algal growth under control. Without this intense grazing pressure algae would develop
rapidly, covering the available substrate and inhibiting the colonization of the area by corals (Paddack
and Cowen 2006).
Chemical defenses
Algae, as many other organisms, have a set of metabolic pathways that produce molecules essential for
its basic operation. They also produce other, non-essential, molecules. Primary metabolites are those
essential compounds without which the organism cannot survive (e.g., aminoacids, cofactors, lipids,
sugars, pigments) and secondary compounds (also known as secondary metabolites or natural products)
are the ones that are not involved in the development and maintenance of the organism. The latter have
a limited biological distribution (often occur only in a given species) and are normally produced in
response to an ecological intervention (Maschek and Baker 2009), for example, excessive solar radiation,
epiphytism, or herbivory (Williams et al. 1989). Scheuer (1990) proposed that all secondary metabolites
evolved from primary ones and that their action in algae is mainly protective.
Life in intertidal environments involves periods of emersion in which there is direct exposure to solar
ultraviolet radiation (UV), with significant adverse effects on algal tissue (Holzinger and Lutz 2006).
Seaweeds subjected to these conditions have defense mechanisms involving the action of metabolites
such as phenols and pigments. Some mechanisms include: (i) changes in the amount and composition
of carotenoids and xanthophylls (Goss and Torsten 2010); (ii) the mobilization of non-enzymatic
antioxidants such as phenols (Bischof et al. 2006); and (iii) the synthesis of compounds which absorb UV
such as aminoacids (Solovchenko and Merzlyak 2008).
The competition for space and resources is very intense in marine environments (McClintock
and Baker 2001) and macroalgae are an ideal substrate for the attachment and growth of endo- and
epibionts (Lane and Kubanek 2009). Some associations between algae and guests are mutual but most are
competitive and the algae can be subjected to a number of infections caused by various microorganisms
(Harvell et al. 1999). The effect of pathogens and herbivores can even cause the destruction of algae
populations, causing imbalances in the associated communities and ecosystems (Potin 2009). Survival
in an environment with these constraints led the algae to develop metabolic strategies and physiological
mechanisms that enable them to eliminate or impede the deleterious action of herbivores and parasites
(Armstrong et al. 2001). Among these mechanisms allelopathy, the chemical inhibition of growth of other
organisms, has been the object of much attention in recent years (Hellio et al. 2000; Pereira and Gama
2009). One of the best examples of allelopathy is the production of chemicals by crustose corallines to
destroy zoospores of other species, preventing their attachment and the subsequent overgrowth of upright
epiphytes (Gross 2003). Kim et al. (2004) reported the destruction of spores of 14 species of macroalgae
by allelopathic substances produced by the crustose Lithophyllum yessoense.
As the epibionts have a very diverse nature, the algae have to produce different metabolites for
different guests. For a product to be a chemical inhibitor of the growth of other organisms and therefore
constitute a natural and effective antiepibiont (antifouling), it must ensure the algal thallus resistance
against colonization by epibiontic organisms. This is only possible through a continuous production and
release of the metabolite (Jormalainen and Honkanen 2009). Each type of antiepibiont has a specific
target and therefore prevents the colonization of the algal thallus by a specific organism. The revisions
of Amsler et al. (2009), Jormalainen and Honkanen (2009), and Pereira and Gama (2009) on the work
performed, respectively, in polar, tropical, and temperate regions, show that the production of secondary
whole system due to its ability to fix calcium carbonate (highly abundant in the water surrounding the
coral reefs), depositing calcite (CaCO 3 ) in their cell wall (Littler 1976). Many reefs are essentially formed
by these organisms. The fragmentation of these calcareous algae, by drilling organisms and scrappers,
increases the amount of sediment and calcium carbonate that occurs on the reef floor. The genus Halimeda,
for example, is responsible for about 77% of the sediments that make up some tropical reefs (Littler and
Littler 1988).
The reefs are characterized by a huge quantity and diversity of animal life being among the more
productive marine systems (Dawes 1998). The herbivores (mainly fish, sea urchins, and mollusks)
dominate and keep algal growth under control. Without this intense grazing pressure algae would develop
rapidly, covering the available substrate and inhibiting the colonization of the area by corals (Paddack
and Cowen 2006).
Chemical defenses
Algae, as many other organisms, have a set of metabolic pathways that produce molecules essential for
its basic operation. They also produce other, non-essential, molecules. Primary metabolites are those
essential compounds without which the organism cannot survive (e.g., aminoacids, cofactors, lipids,
sugars, pigments) and secondary compounds (also known as secondary metabolites or natural products)
are the ones that are not involved in the development and maintenance of the organism. The latter have
a limited biological distribution (often occur only in a given species) and are normally produced in
response to an ecological intervention (Maschek and Baker 2009), for example, excessive solar radiation,
epiphytism, or herbivory (Williams et al. 1989). Scheuer (1990) proposed that all secondary metabolites
evolved from primary ones and that their action in algae is mainly protective.
Life in intertidal environments involves periods of emersion in which there is direct exposure to solar
ultraviolet radiation (UV), with significant adverse effects on algal tissue (Holzinger and Lutz 2006).
Seaweeds subjected to these conditions have defense mechanisms involving the action of metabolites
such as phenols and pigments. Some mechanisms include: (i) changes in the amount and composition
of carotenoids and xanthophylls (Goss and Torsten 2010); (ii) the mobilization of non-enzymatic
antioxidants such as phenols (Bischof et al. 2006); and (iii) the synthesis of compounds which absorb UV
such as aminoacids (Solovchenko and Merzlyak 2008).
The competition for space and resources is very intense in marine environments (McClintock
and Baker 2001) and macroalgae are an ideal substrate for the attachment and growth of endo- and
epibionts (Lane and Kubanek 2009). Some associations between algae and guests are mutual but most are
competitive and the algae can be subjected to a number of infections caused by various microorganisms
(Harvell et al. 1999). The effect of pathogens and herbivores can even cause the destruction of algae
populations, causing imbalances in the associated communities and ecosystems (Potin 2009). Survival
in an environment with these constraints led the algae to develop metabolic strategies and physiological
mechanisms that enable them to eliminate or impede the deleterious action of herbivores and parasites
(Armstrong et al. 2001). Among these mechanisms allelopathy, the chemical inhibition of growth of other
organisms, has been the object of much attention in recent years (Hellio et al. 2000; Pereira and Gama
2009). One of the best examples of allelopathy is the production of chemicals by crustose corallines to
destroy zoospores of other species, preventing their attachment and the subsequent overgrowth of upright
epiphytes (Gross 2003). Kim et al. (2004) reported the destruction of spores of 14 species of macroalgae
by allelopathic substances produced by the crustose Lithophyllum yessoense.
As the epibionts have a very diverse nature, the algae have to produce different metabolites for
different guests. For a product to be a chemical inhibitor of the growth of other organisms and therefore
constitute a natural and effective antiepibiont (antifouling), it must ensure the algal thallus resistance
against colonization by epibiontic organisms. This is only possible through a continuous production and
release of the metabolite (Jormalainen and Honkanen 2009). Each type of antiepibiont has a specific
target and therefore prevents the colonization of the algal thallus by a specific organism. The revisions
of Amsler et al. (2009), Jormalainen and Honkanen (2009), and Pereira and Gama (2009) on the work
performed, respectively, in polar, tropical, and temperate regions, show that the production of secondary