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S.M. Coelho et al.
6.1 What Are Algae?
The term “algae” does not have a precise taxonomic meaning and different authors
have used this term to refer collectively to different groups of photosynthetic organisms. It is, therefore, important that we begin this chapter by defining what we
mean by this term. Here we define algae as all photosynthetic eukaryotes other than
the embryophytes (or land plants; Keeling 2004). This definition does not include
photosynthetic prokaryotes. Nonetheless, it still covers a very broad range of taxa
because it includes all the groups of organisms from across the eukaryotic tree that
have acquired, by one means or another, a chloroplast. Note that, despite being
referred to as land plants, the embryophytes include some species that have returned
to the marine environment, such as seagrasses. We do not define these organisms as
algae, although they are discussed briefly later in the chapter.
The logic behind treating such a diverse collection of organisms as a group is
based on the origin of their plastids. The plastids of all eukaryotic algae are all
thought to be derived, either directly or indirectly, from a single primary endosymbiotic event that occurred in a common ancestor of the green, red and glaucophyte
algae (see below).
6.2 Why Algae Are Interesting
Algal research is motivated by a number of different aspects of the biology, ecology
and evolutionary history of this group of organisms. Many unicellular marine algae
are constituents of the phytoplankton and these organisms make important contributions to global geochemical cycles. Phytoplankton algae are also key primary
producers in marine food chains. Along with these essentially positive roles, algae
can also have a dark side, for example when toxins are produced by algal blooms.
In coastal ecosystems, red, green and brown macroalgae are usually the most obvious components, sometimes forming dense forests that cover an impressive area
of the seabed. These organisms represent a major component of coastal ecosystems,
being classified as ecosystem engineers (Coleman and Williams 2002). For instance,
large kelp forests not only act as sites of primary production, but also contribute
significantly to secondary production by marine food webs and provide habitats to
numerous animal and algal species (Duggins et al. 1989). The phylogenetic diversity
of the algae is also a major point of interest. Many algae occupy key phylogenetic
positions in the tree of life and can provide important insights into many of the
more ancient events that occurred during the evolution of the eukaryotes. This phylogenetic diversity is also of interest with respect to the general biology of these
organisms. As a result of their very divergent evolutionary histories the different
major groups of algae often exhibit innovations in terms of their metabolisms, cell
biology, morphology, life histories, etc. These diverse characteristics are of interest
both from a fundamental point of view and as a potential source of novel molecules
and procedures for a wide range of biotechnological applications.
In recent years, the application of genomic approaches has led to significant
advances in many areas of algal research. In many instances the application of
S.M. Coelho et al.
6.1 What Are Algae?
The term “algae” does not have a precise taxonomic meaning and different authors
have used this term to refer collectively to different groups of photosynthetic organisms. It is, therefore, important that we begin this chapter by defining what we
mean by this term. Here we define algae as all photosynthetic eukaryotes other than
the embryophytes (or land plants; Keeling 2004). This definition does not include
photosynthetic prokaryotes. Nonetheless, it still covers a very broad range of taxa
because it includes all the groups of organisms from across the eukaryotic tree that
have acquired, by one means or another, a chloroplast. Note that, despite being
referred to as land plants, the embryophytes include some species that have returned
to the marine environment, such as seagrasses. We do not define these organisms as
algae, although they are discussed briefly later in the chapter.
The logic behind treating such a diverse collection of organisms as a group is
based on the origin of their plastids. The plastids of all eukaryotic algae are all
thought to be derived, either directly or indirectly, from a single primary endosymbiotic event that occurred in a common ancestor of the green, red and glaucophyte
algae (see below).
6.2 Why Algae Are Interesting
Algal research is motivated by a number of different aspects of the biology, ecology
and evolutionary history of this group of organisms. Many unicellular marine algae
are constituents of the phytoplankton and these organisms make important contributions to global geochemical cycles. Phytoplankton algae are also key primary
producers in marine food chains. Along with these essentially positive roles, algae
can also have a dark side, for example when toxins are produced by algal blooms.
In coastal ecosystems, red, green and brown macroalgae are usually the most obvious components, sometimes forming dense forests that cover an impressive area
of the seabed. These organisms represent a major component of coastal ecosystems,
being classified as ecosystem engineers (Coleman and Williams 2002). For instance,
large kelp forests not only act as sites of primary production, but also contribute
significantly to secondary production by marine food webs and provide habitats to
numerous animal and algal species (Duggins et al. 1989). The phylogenetic diversity
of the algae is also a major point of interest. Many algae occupy key phylogenetic
positions in the tree of life and can provide important insights into many of the
more ancient events that occurred during the evolution of the eukaryotes. This phylogenetic diversity is also of interest with respect to the general biology of these
organisms. As a result of their very divergent evolutionary histories the different
major groups of algae often exhibit innovations in terms of their metabolisms, cell
biology, morphology, life histories, etc. These diverse characteristics are of interest
both from a fundamental point of view and as a potential source of novel molecules
and procedures for a wide range of biotechnological applications.
In recent years, the application of genomic approaches has led to significant
advances in many areas of algal research. In many instances the application of