65
tures might lead to a decreasing mixed layer depth, which
would expose the community to higher radiations (Villafañe
et al. 2013). Shallower mixed layers combined with stronger
solar radiance as future condition might also result in cellular
stress. Chlorophyll a can decline in phytoplankton cells as
response to light stress. The cells can contract and move their
chloroplasts, which leads to a temporary photoinhibition of
photosynthesis (Kiefer 1973). Diatoms are more prone to
ozone-related negative solar UV-B radiation, which can
affect aquatic systems, thus generally likely dominating
future communities (Häder et al. 2007).
Ocean acidification might lead to a shift in nutrient
requirements and C:N:P stoichiometry, thus influencing biogeochemical cycles (Bellerby et al. 2008). In addition,
decreasing pH influences micronutrient bioavailability such
as leading to decreased concentrations of iron bioavailability
and increase phytoplankton iron stress (Shi et al. 2010).
Besides phytoplankton being influenced by nutrients and
other environmental factors, they themselves influence the
climate and environment they are living in. One example is
the role of phytoplankton in the formation of former ice ages.
Iron-rich dust was transported to the Southern Ocean, where
water masses were rich of nutrients such as nitrate and phosphate but lacked iron. This natural iron fertilization of phytoplankton in the Subantarctic could partly explain atmospheric
carbon dioxide changes over the last 1.1 million years.
Measurements of foraminifera-bound nitrogen isotopes from
sediment cores taken in the Subantarctic Atlantic indicated
dust flux, productivity and the degree of nitrate consumption
as characterizing factors for peak glacial times and millennial cold events. Triggering blooms and changes in the
Southern Ocean’s food web and biological pump can be seen
as the cause of the full emergence of ice age conditions.
However, the main drivers for the initial carbon dioxide
decrease were most likely physical processes, such as surface water stratification, wind changes and changes in sea ice
extent (Martínez-Garcia et al. 2009, 2014; Jaccard et al.
2013).
Another example for phytoplankton impacts on the climate is dimethylsulfide (DMS). DMS is the degradation
product of dimethylsulfoniopropionate (DMSP), which is
produced by phytoplankton as an osmoprotectant and
degraded by marine bacteria (Yoch 2002). The main DMSP
producing phytoplankton belong to the groups of dinoflagellates and prymnesiophytes, but also include some diatoms
and Chrysophyceae species (Keller et al. 1989). Important
phytoplankton include Phaeocystis sp., Emiliania huxleyi,
Prorocentrum sp. and Gymnodinium sp. (Yoch 2002). Since
atmospheric DMS is an important sulfur source for the global
environment and its oxidation causes reflection of solar radiation, it can have a cooling effect on the Earth’s temperature
(for further reading, see Yoch 2002; Stefels et al. 2007; Lana
et al. 2012).
Effects like these make phytoplankton blooms interesting
candidates to actively help reversing the effects of climate
change, for example by trying to trigger carbon sequestering
blooms (Bakker et al. 2005). However, large scale blooms
may have unforeseen ecological effects, such as becoming
toxic (Silver et al. 2010).
Harmful Algal Blooms
Harmful algal blooms (HABs) refer to blooms of diatoms,
dinoflagellates, raphidophytes, haptophytes, cyanobacteria,
and certain macroalgae perceived as harmful due a negative
impact on the environment or public health. Some have the
capability to express toxins under certain circumstances.
Other blooms are harmful not due to toxins but because the
build-up of high biomass leads to disruption of food webs
and development of anoxic zones (Kudela et al. 2017).
Apart from ecological effects, HABs can affect human
health upon exposure to poisoned seawater, food or marine
aerosols and can have severe socio-economic impacts
(Pierce et al. 2003; Fleming et al. 2007). Most frequent
HAB related illness worldwide is Ciguatera Fish Poisoning
(CFP), which occurs manly in the tropics and subtropics.
A variety of dinoflagellate species can produce toxins,
such as the Gambierdiscus toxicus species complex, which
can produce the toxins maitotoxin and ciguatoxin (Murata
et al. 1992).
Other illnesses are Paralytic Shellfish Poisoning (PSP)
and Diarrhetic Shellfish Poisoning (DSP), which can occur
worldwide (Berdalet et al. 2016). Prorocentrum lima can
produce a variety of toxins, i.a. DSP causative okadaic acid
(Murakami et al. 1982). HABs can have extensive ecological
effects, such as mass mortality of whales suffering from PSP
by feeding on mackerels poisoned with saxitoxins from
dinoflagellates or enhanced fish kills (Geraci et al. 1989;
Glibert et al. 2001; Nash et al. 2017).
Furthermore, some diatoms can also express toxins.
Several species of the genus Pseudo-nitzschia are, for example, capable of producing domoic acid (Rao et al. 1988).
HABs can have widespread occurrences. They can occur
at coastlines all over the world and have been reported
throughout history from Canada, Japan, Scotland, Australia,
and many other places (e.g., White 1977; Murakami et al.
1982; Bruno et al. 1989; Nash et al. 2017). Although toxic
blooms are a natural phenomenon, they can also be a reaction to environmental shifts and the production of toxins can
be connected to environmental conditions (Etheridge and
Roesler 2005). Experiments with toxin producing
Alexandrium sp. showed that increasing radiance and temperature significantly enhanced toxin production (Lim et al.
2006). Nutrient changes in particular can have distinct effects
in triggering toxin production. Iron fertilization can lead to
formation of a toxic Pseudo-nitzschia spp. bloom and natural
iron fertilization might have the same effect (Silver et al.
Phytoplankton Responses to Marine Climate Change – An Introduction
tures might lead to a decreasing mixed layer depth, which
would expose the community to higher radiations (Villafañe
et al. 2013). Shallower mixed layers combined with stronger
solar radiance as future condition might also result in cellular
stress. Chlorophyll a can decline in phytoplankton cells as
response to light stress. The cells can contract and move their
chloroplasts, which leads to a temporary photoinhibition of
photosynthesis (Kiefer 1973). Diatoms are more prone to
ozone-related negative solar UV-B radiation, which can
affect aquatic systems, thus generally likely dominating
future communities (Häder et al. 2007).
Ocean acidification might lead to a shift in nutrient
requirements and C:N:P stoichiometry, thus influencing biogeochemical cycles (Bellerby et al. 2008). In addition,
decreasing pH influences micronutrient bioavailability such
as leading to decreased concentrations of iron bioavailability
and increase phytoplankton iron stress (Shi et al. 2010).
Besides phytoplankton being influenced by nutrients and
other environmental factors, they themselves influence the
climate and environment they are living in. One example is
the role of phytoplankton in the formation of former ice ages.
Iron-rich dust was transported to the Southern Ocean, where
water masses were rich of nutrients such as nitrate and phosphate but lacked iron. This natural iron fertilization of phytoplankton in the Subantarctic could partly explain atmospheric
carbon dioxide changes over the last 1.1 million years.
Measurements of foraminifera-bound nitrogen isotopes from
sediment cores taken in the Subantarctic Atlantic indicated
dust flux, productivity and the degree of nitrate consumption
as characterizing factors for peak glacial times and millennial cold events. Triggering blooms and changes in the
Southern Ocean’s food web and biological pump can be seen
as the cause of the full emergence of ice age conditions.
However, the main drivers for the initial carbon dioxide
decrease were most likely physical processes, such as surface water stratification, wind changes and changes in sea ice
extent (Martínez-Garcia et al. 2009, 2014; Jaccard et al.
2013).
Another example for phytoplankton impacts on the climate is dimethylsulfide (DMS). DMS is the degradation
product of dimethylsulfoniopropionate (DMSP), which is
produced by phytoplankton as an osmoprotectant and
degraded by marine bacteria (Yoch 2002). The main DMSP
producing phytoplankton belong to the groups of dinoflagellates and prymnesiophytes, but also include some diatoms
and Chrysophyceae species (Keller et al. 1989). Important
phytoplankton include Phaeocystis sp., Emiliania huxleyi,
Prorocentrum sp. and Gymnodinium sp. (Yoch 2002). Since
atmospheric DMS is an important sulfur source for the global
environment and its oxidation causes reflection of solar radiation, it can have a cooling effect on the Earth’s temperature
(for further reading, see Yoch 2002; Stefels et al. 2007; Lana
et al. 2012).
Effects like these make phytoplankton blooms interesting
candidates to actively help reversing the effects of climate
change, for example by trying to trigger carbon sequestering
blooms (Bakker et al. 2005). However, large scale blooms
may have unforeseen ecological effects, such as becoming
toxic (Silver et al. 2010).
Harmful Algal Blooms
Harmful algal blooms (HABs) refer to blooms of diatoms,
dinoflagellates, raphidophytes, haptophytes, cyanobacteria,
and certain macroalgae perceived as harmful due a negative
impact on the environment or public health. Some have the
capability to express toxins under certain circumstances.
Other blooms are harmful not due to toxins but because the
build-up of high biomass leads to disruption of food webs
and development of anoxic zones (Kudela et al. 2017).
Apart from ecological effects, HABs can affect human
health upon exposure to poisoned seawater, food or marine
aerosols and can have severe socio-economic impacts
(Pierce et al. 2003; Fleming et al. 2007). Most frequent
HAB related illness worldwide is Ciguatera Fish Poisoning
(CFP), which occurs manly in the tropics and subtropics.
A variety of dinoflagellate species can produce toxins,
such as the Gambierdiscus toxicus species complex, which
can produce the toxins maitotoxin and ciguatoxin (Murata
et al. 1992).
Other illnesses are Paralytic Shellfish Poisoning (PSP)
and Diarrhetic Shellfish Poisoning (DSP), which can occur
worldwide (Berdalet et al. 2016). Prorocentrum lima can
produce a variety of toxins, i.a. DSP causative okadaic acid
(Murakami et al. 1982). HABs can have extensive ecological
effects, such as mass mortality of whales suffering from PSP
by feeding on mackerels poisoned with saxitoxins from
dinoflagellates or enhanced fish kills (Geraci et al. 1989;
Glibert et al. 2001; Nash et al. 2017).
Furthermore, some diatoms can also express toxins.
Several species of the genus Pseudo-nitzschia are, for example, capable of producing domoic acid (Rao et al. 1988).
HABs can have widespread occurrences. They can occur
at coastlines all over the world and have been reported
throughout history from Canada, Japan, Scotland, Australia,
and many other places (e.g., White 1977; Murakami et al.
1982; Bruno et al. 1989; Nash et al. 2017). Although toxic
blooms are a natural phenomenon, they can also be a reaction to environmental shifts and the production of toxins can
be connected to environmental conditions (Etheridge and
Roesler 2005). Experiments with toxin producing
Alexandrium sp. showed that increasing radiance and temperature significantly enhanced toxin production (Lim et al.
2006). Nutrient changes in particular can have distinct effects
in triggering toxin production. Iron fertilization can lead to
formation of a toxic Pseudo-nitzschia spp. bloom and natural
iron fertilization might have the same effect (Silver et al.
Phytoplankton Responses to Marine Climate Change – An Introduction