57
cingulum divides the cells into two parts and houses one
transverse flagellum and the sulcus houses a second longitudinal flagellum. Dinoflagellates can be auto-, mixo-, and heterotrophs (e.g., Carvalho et al. 2008; McMinn and Martin
2013). Several species can cause so-called “red-tides” and
harmful algae blooms (Loeblich 1976; Taylor et al. 2008).
Haptophytes belong to flagellates and consist of different
groups and genera. They include, for example, coccolithophorids and the potentially toxic algae genus Prymnesium,
which includes some cytotoxin, ichthyotoxin, neurotoxin,
and haemolytic toxin producing species (Seoane et al. 2017).
Motile haptophytes possess two flagella and a haptonema.
The haptonema is a characteristic cell organelle and resembles a third flagellum. In contrast to the other two flagella, it
is not used for swimming but to capture particles and to
attach to surfaces (Hibberd 1976; Kawachi et al. 1991;
Jordan and Chamberlain 1997; Andersen 2004).
Primary Production and Essential Elements
Due to its broad distribution and abundance in the ocean,
phytoplankton is the fundamental primary producer and
serves as a food source at the base of oceanic food webs. It is
part of the microbial loop due to its interaction with bacteria
and its decomposition by viral lysis and bacteria.
In general, phytoplankton is dependent on the availability
of nutrients, light, and other prevalent conditions such as
regional and seasonal changes both physically (temperature,
salinity, currents, mixing of water layers, precipitation) as
well as biologically (e.g., parasites, grazing of potential
predators) (Falkowski and Oliver 2007; Racault et al. 2012,
further reading: Mackas et al. 1985; Fenchel 1988; Reid
et al. 1990).
Phytoplankton uses photosynthesis as energy source and,
doing so, contributes with 48% noticeably to global carbon
fixation by taking up and incorporating carbon from carbon
dioxide. Another important environmental function of phytoplankton is the production of oxygen during photosynthesis
(Field et al. 1998). Since photosynthesis requires light, active
phytoplankton can only be found in the euphotic zone of the
ocean (Fig. 2). Depth of the euphotic zone may differ enormously depending on the presence of biological and nonbiological substances absorbing and scattering light within
the water column. However, phytoplankton itself often narrows the euphotic zone (Lorenzen 1972).
Phytoplankton as primary producers are part of the biological carbon pump, since they take up carbon dioxide
(CO 2 ) from the atmosphere and bind the carbon in their cells,
which are then taken up by higher trophic levels or become
part of sinking particles and remineralisation. Time scales
for the carbon to re-enter the cycle and to be reused can vary
from days, over weeks and years up to several millennia,
especially for carbon reaching the sediment surface (Emerson
and Hedges 1988; Shen and Benner 2018). Sinking particles
that originate from fragmentation, aggregation or egestion
after consumption by higher trophic levels such as zooplankton can either be consumed again or be decomposed by
microbial processes. At the same time, active vertical migration by the organisms distributes the carbon further within
different water layers and therefore has a significant impact
on the oceanic carbon cycle and productivity (Azam 1998;
Buesseler et al. 2007). As consequence, phytoplankton are
subject to high fluctuations and show seasonality as well as a
spatial heterogeneity.
To produce biomass, phytoplankton need certain nutrients, the most important being carbon (C), nitrogen (N) and
phosphorous (P). For marine primary production, Redfield
(1958) calculated the ratio in which these essential nutrients
are required as C:N:P = 106:16:1.
Important sources of nitrogen are nitrate and ammonium.
Ammonium can be taken up effectively by phytoplankton
and provides up to 35% of nitrogen assimilated depending
on species and location (Eppley et al. 1971, 1979). Nitrate
uptake as nitrogen source requires a higher amount of energy.
Thus, ammonium uptake is generally preferred (Thompson
et al. 1989). Furthermore, nitrate uptake is relatively slow.
Phytoplankton show a great metabolic diversity. For example
some phytoplankton species are incapable of nitrate uptake,
whereas other species even prefer the uptake of nitrate to
ammonium. Ammonium can, in high concentrations, even
suppress growth (Glibert et al. 2016; Van Oostende et al.
2017). Nitrogen can be taken up faster by amino acids and
fastest via ammonium (Dortch 1982), though only some
phytoplankton species are able to take up amino acids
(Wheeler et al. 1974).
In competitive environments, however, organic nitrogen
such as urea can serve as valuable source to phytoplankton
(Bradley et al. 2010). The availability of nitrogen in different
forms can also have an influence on the respective species
composition (Glibert et al. 2016; Van Oostende et al. 2017).
Phosphorus is also essential for phytoplankton and is usually taken up via phosphate, which frequently acts as limiting
nutrient (Perry 1976). Both nitrogen and phosphorus can act
as limiting nutrients for primary production (Smith 2006).
Some phytoplankton species are capable of reducing their
phosphorus demand by producing substitute lipids instead of
phospholipids (Van Mooy et al. 2009). Marine diatoms,
which can make up large fractions of phytoplankton communities, are furthermore dependent on silicate to form their
characteristic external shell (Harvey 1939; Paasche 1973a, b;
Treguer et al. 1995; Turner et al. 1998).
Apart from these crucial elements, a range of trace metals
is required for phytoplankton growth. Morel and Price (2003)
made a first attempt to calculate a stoichiometry for essential
trace metals including iron, manganese, zinc, copper, cobalt,
Phytoplankton Responses to Marine Climate Change – An Introduction
cingulum divides the cells into two parts and houses one
transverse flagellum and the sulcus houses a second longitudinal flagellum. Dinoflagellates can be auto-, mixo-, and heterotrophs (e.g., Carvalho et al. 2008; McMinn and Martin
2013). Several species can cause so-called “red-tides” and
harmful algae blooms (Loeblich 1976; Taylor et al. 2008).
Haptophytes belong to flagellates and consist of different
groups and genera. They include, for example, coccolithophorids and the potentially toxic algae genus Prymnesium,
which includes some cytotoxin, ichthyotoxin, neurotoxin,
and haemolytic toxin producing species (Seoane et al. 2017).
Motile haptophytes possess two flagella and a haptonema.
The haptonema is a characteristic cell organelle and resembles a third flagellum. In contrast to the other two flagella, it
is not used for swimming but to capture particles and to
attach to surfaces (Hibberd 1976; Kawachi et al. 1991;
Jordan and Chamberlain 1997; Andersen 2004).
Primary Production and Essential Elements
Due to its broad distribution and abundance in the ocean,
phytoplankton is the fundamental primary producer and
serves as a food source at the base of oceanic food webs. It is
part of the microbial loop due to its interaction with bacteria
and its decomposition by viral lysis and bacteria.
In general, phytoplankton is dependent on the availability
of nutrients, light, and other prevalent conditions such as
regional and seasonal changes both physically (temperature,
salinity, currents, mixing of water layers, precipitation) as
well as biologically (e.g., parasites, grazing of potential
predators) (Falkowski and Oliver 2007; Racault et al. 2012,
further reading: Mackas et al. 1985; Fenchel 1988; Reid
et al. 1990).
Phytoplankton uses photosynthesis as energy source and,
doing so, contributes with 48% noticeably to global carbon
fixation by taking up and incorporating carbon from carbon
dioxide. Another important environmental function of phytoplankton is the production of oxygen during photosynthesis
(Field et al. 1998). Since photosynthesis requires light, active
phytoplankton can only be found in the euphotic zone of the
ocean (Fig. 2). Depth of the euphotic zone may differ enormously depending on the presence of biological and nonbiological substances absorbing and scattering light within
the water column. However, phytoplankton itself often narrows the euphotic zone (Lorenzen 1972).
Phytoplankton as primary producers are part of the biological carbon pump, since they take up carbon dioxide
(CO 2 ) from the atmosphere and bind the carbon in their cells,
which are then taken up by higher trophic levels or become
part of sinking particles and remineralisation. Time scales
for the carbon to re-enter the cycle and to be reused can vary
from days, over weeks and years up to several millennia,
especially for carbon reaching the sediment surface (Emerson
and Hedges 1988; Shen and Benner 2018). Sinking particles
that originate from fragmentation, aggregation or egestion
after consumption by higher trophic levels such as zooplankton can either be consumed again or be decomposed by
microbial processes. At the same time, active vertical migration by the organisms distributes the carbon further within
different water layers and therefore has a significant impact
on the oceanic carbon cycle and productivity (Azam 1998;
Buesseler et al. 2007). As consequence, phytoplankton are
subject to high fluctuations and show seasonality as well as a
spatial heterogeneity.
To produce biomass, phytoplankton need certain nutrients, the most important being carbon (C), nitrogen (N) and
phosphorous (P). For marine primary production, Redfield
(1958) calculated the ratio in which these essential nutrients
are required as C:N:P = 106:16:1.
Important sources of nitrogen are nitrate and ammonium.
Ammonium can be taken up effectively by phytoplankton
and provides up to 35% of nitrogen assimilated depending
on species and location (Eppley et al. 1971, 1979). Nitrate
uptake as nitrogen source requires a higher amount of energy.
Thus, ammonium uptake is generally preferred (Thompson
et al. 1989). Furthermore, nitrate uptake is relatively slow.
Phytoplankton show a great metabolic diversity. For example
some phytoplankton species are incapable of nitrate uptake,
whereas other species even prefer the uptake of nitrate to
ammonium. Ammonium can, in high concentrations, even
suppress growth (Glibert et al. 2016; Van Oostende et al.
2017). Nitrogen can be taken up faster by amino acids and
fastest via ammonium (Dortch 1982), though only some
phytoplankton species are able to take up amino acids
(Wheeler et al. 1974).
In competitive environments, however, organic nitrogen
such as urea can serve as valuable source to phytoplankton
(Bradley et al. 2010). The availability of nitrogen in different
forms can also have an influence on the respective species
composition (Glibert et al. 2016; Van Oostende et al. 2017).
Phosphorus is also essential for phytoplankton and is usually taken up via phosphate, which frequently acts as limiting
nutrient (Perry 1976). Both nitrogen and phosphorus can act
as limiting nutrients for primary production (Smith 2006).
Some phytoplankton species are capable of reducing their
phosphorus demand by producing substitute lipids instead of
phospholipids (Van Mooy et al. 2009). Marine diatoms,
which can make up large fractions of phytoplankton communities, are furthermore dependent on silicate to form their
characteristic external shell (Harvey 1939; Paasche 1973a, b;
Treguer et al. 1995; Turner et al. 1998).
Apart from these crucial elements, a range of trace metals
is required for phytoplankton growth. Morel and Price (2003)
made a first attempt to calculate a stoichiometry for essential
trace metals including iron, manganese, zinc, copper, cobalt,
Phytoplankton Responses to Marine Climate Change – An Introduction