6 Marine Macro- and Microalgae: An Overview
phycosphere, which is the ecologically and physiologically integrated neighborhood inhabited by the
alga (Brodie et al. 2017). Epibiosis (surface colonization of one organism, by other organisms, epibionts)
occurs on all immersed surfaces, including those of micro- and macroalgae. Epibiotic interactions (e.g.,
alga-alga, alga-bacterium, alga-virus) play key roles in nutrient acquisition and recycling, metabolic flux,
energy flow, and developmental processes. Together with herbivory, epibiosis represents one of the most
important interactions for algae and has been shown to shape entire marine communities (Brodie et al.
2017).
A very important contribution to our knowledge of the evolution of life on earth was the
endosymbiotic theory by Lynn Margulis (1981) according to which single-cell creatures without
complex internal structures achieved evolutionary success through increasing cellular complexity. This
complexity emerged through symbiosis between organisms of different species, the most effective forms
occurring when two cell types merged, each contributing to the creation of a harmonious living whole,
the eukaryotic cell.
This theory assumes a monophyletic origin of eukaryotes from a common ancestor (progenote),
which through various symbiosis events acquired the various organelles typical of eukaryotes. A large
evolutionary radiation happened very early at the cellular level, resulting in celled organisms that differed
in their cell structure. Some variants acquired chloroplast and become photoautotrophic. Others did not
and remained heterotrophic.
Chloroplasts, flagella, and mitochondria have descended from free-living prokaryotes; the
chloroplasts derived from cyanophytes and the latter from true bacteria. When the Earth’s atmosphere
already had oxygen, a primitive phagotrophic eukaryote with amoeboid movements incorporated an
aerobic bacterium. It was not digested, and started functioning as a respiratory organelle (mitochondrion).
As a result, the primitive eukaryote became aerobic. Later, this aerobic eukaryote incorporated another
prokaryotic saprophyte, mobile by microtubules in a 9 + 2 arrangement. The incorporation was not
total and the flagellum started acting as the host locomotion organelle, evolving later into the typical
flagellum of eukaryotes. At about 1500 Ma ago, some of these heterotrophic flagellates incorporated a
cyanobacterium (Palmer 2003; Keeling 2004) which was not digested and turned into a photosynthetic
organelle (chloroplast), giving rise to the first photoautotrophic eukaryotes which subsequently gave rise
to the various groups of algae and land plants.
Three major eukaryotic photosynthetic groups (possessing primary plastids) have descended from
a common prokaryotic ancestor, whereas the remaining algal groups have acquired their plastids via
secondary or even tertiary endosymbiosis. The three major algal lineages with primary plastids are the
Glaucophyta, the Rhodophyta, and the Chlorophyta. Multicellular green algae then successfully invaded
the land environment and originated mosses, ferns, and vascular plants. Other algae underwent processes
of secondary endosymbiosis (Keeling 2004), for example, green algae evolved into Euglenophyta and
red originated the Chromalveolata, a diverse group of algae whose chloroplasts possess chlorophyll a and
c, including the Cryptophyta, the Haptophyta (coccolitophoroids), the Ochrophyta (=Heterokontophyta),
and the dinoflagellates.
In this view, green algae and higher plants form a group having a common ancestor with the red
algae, and the chloroplasts of brown algae resulted from a secondary endosymbiosis with a red alga.
Although our understanding of the evolution of algae has improved in the last years, first by phylogenetic
analyses of nuclear ribosomal sequence data (mainly 18S), and more recently by analyses of multi-gene
and chloroplast genomic data, the phylogenetic relationships are still not well established (Fang et al.
2017).
Classification
The classification of living organisms has undergone a major evolution over time as a result of an increased
phylogenetic knowledge. In this text we will follow the higher classification, proposed by Ruggiero et al.
(2015), in two superkingdoms (Prokaryota and Eukaryota) and seven kingdoms, namely the prokaryotic
Archaea (Archaebacteria) and Bacteria (Eubacteria), and the eukaryotic Protozoa, Chromista, Fungi,
Plantae, and Animalia. This classification is neither phylogenetic nor evolutionary but instead represents
phycosphere, which is the ecologically and physiologically integrated neighborhood inhabited by the
alga (Brodie et al. 2017). Epibiosis (surface colonization of one organism, by other organisms, epibionts)
occurs on all immersed surfaces, including those of micro- and macroalgae. Epibiotic interactions (e.g.,
alga-alga, alga-bacterium, alga-virus) play key roles in nutrient acquisition and recycling, metabolic flux,
energy flow, and developmental processes. Together with herbivory, epibiosis represents one of the most
important interactions for algae and has been shown to shape entire marine communities (Brodie et al.
2017).
A very important contribution to our knowledge of the evolution of life on earth was the
endosymbiotic theory by Lynn Margulis (1981) according to which single-cell creatures without
complex internal structures achieved evolutionary success through increasing cellular complexity. This
complexity emerged through symbiosis between organisms of different species, the most effective forms
occurring when two cell types merged, each contributing to the creation of a harmonious living whole,
the eukaryotic cell.
This theory assumes a monophyletic origin of eukaryotes from a common ancestor (progenote),
which through various symbiosis events acquired the various organelles typical of eukaryotes. A large
evolutionary radiation happened very early at the cellular level, resulting in celled organisms that differed
in their cell structure. Some variants acquired chloroplast and become photoautotrophic. Others did not
and remained heterotrophic.
Chloroplasts, flagella, and mitochondria have descended from free-living prokaryotes; the
chloroplasts derived from cyanophytes and the latter from true bacteria. When the Earth’s atmosphere
already had oxygen, a primitive phagotrophic eukaryote with amoeboid movements incorporated an
aerobic bacterium. It was not digested, and started functioning as a respiratory organelle (mitochondrion).
As a result, the primitive eukaryote became aerobic. Later, this aerobic eukaryote incorporated another
prokaryotic saprophyte, mobile by microtubules in a 9 + 2 arrangement. The incorporation was not
total and the flagellum started acting as the host locomotion organelle, evolving later into the typical
flagellum of eukaryotes. At about 1500 Ma ago, some of these heterotrophic flagellates incorporated a
cyanobacterium (Palmer 2003; Keeling 2004) which was not digested and turned into a photosynthetic
organelle (chloroplast), giving rise to the first photoautotrophic eukaryotes which subsequently gave rise
to the various groups of algae and land plants.
Three major eukaryotic photosynthetic groups (possessing primary plastids) have descended from
a common prokaryotic ancestor, whereas the remaining algal groups have acquired their plastids via
secondary or even tertiary endosymbiosis. The three major algal lineages with primary plastids are the
Glaucophyta, the Rhodophyta, and the Chlorophyta. Multicellular green algae then successfully invaded
the land environment and originated mosses, ferns, and vascular plants. Other algae underwent processes
of secondary endosymbiosis (Keeling 2004), for example, green algae evolved into Euglenophyta and
red originated the Chromalveolata, a diverse group of algae whose chloroplasts possess chlorophyll a and
c, including the Cryptophyta, the Haptophyta (coccolitophoroids), the Ochrophyta (=Heterokontophyta),
and the dinoflagellates.
In this view, green algae and higher plants form a group having a common ancestor with the red
algae, and the chloroplasts of brown algae resulted from a secondary endosymbiosis with a red alga.
Although our understanding of the evolution of algae has improved in the last years, first by phylogenetic
analyses of nuclear ribosomal sequence data (mainly 18S), and more recently by analyses of multi-gene
and chloroplast genomic data, the phylogenetic relationships are still not well established (Fang et al.
2017).
Classification
The classification of living organisms has undergone a major evolution over time as a result of an increased
phylogenetic knowledge. In this text we will follow the higher classification, proposed by Ruggiero et al.
(2015), in two superkingdoms (Prokaryota and Eukaryota) and seven kingdoms, namely the prokaryotic
Archaea (Archaebacteria) and Bacteria (Eubacteria), and the eukaryotic Protozoa, Chromista, Fungi,
Plantae, and Animalia. This classification is neither phylogenetic nor evolutionary but instead represents