2.2 Zooxanthellae in Corals
29
maximum can lead to a breakdown of the symbiosis (Mieog et al. 2009) and thus the
loss of symbiotic algae from the host (Muller-Parker et al. 2015).
The photosynthetic pigments of the symbiotic algae are responsible for the color
of the coral (Jones 1997; Falkowski and Dubinsky 1981; Dove et al. 2001; Fine and
Loya 2002) and this can vary from white, yellow, brown and olive to red, green, blue
and purple (Holden 1999).
Corals stress out when environmental conditions are altered and this leads to
the expulsion of the Symbiodinium spp (or a decrease in the photosynthetic pigment
concentration within the zooxanthellae) (Holden 1999). Environmental perturbations
(such as an increase in seawater temperature) lead to global climate change and induce
dysfunction and collapse of symbiosis leading to zooxanthellae loss or so-called
‘bleaching’; which causes visible paling of coral colonies, and this phenomenon has
led to severe worldwide decline of coral reefs (Brown and Howard 1985; Guzman
and Jimenez 1992; Gardener et al. 2003; Baker et al. 2008; Weis 2008; Bielmyer
et al. 2010; Ganot et al. 2011; Bielmyer-Fraser et al. 2018).
‘Bleaching’ refers to the change of coloration, revealing the white skeleton, and
is considered the initial response to a stress of the host and/or the photosynthetic
symbiont (Jones 1997; Perez et al. 2001; Baker et al. 2008; Muller-Parker et al.
2015). The extent of bleaching depends on the type of stress and the duration of
it. Corals may recover from bleaching, depending on the intensity and duration of
the stress, but if the algal symbiont communities are not restored relatively quickly
(typically 2–4 weeks); corals may die (Mieog et al. 2009; Bielmyer et al. 2010;
Bielmyer-Fraser et al. 2018).
2.3 Coral Nutrition
Reef building corals exhibit mixotrophy, relying on both the photoautotrophic products of their endosymbiotic algae and the nutrients acquired through heterotrophic
predation (Goreau et al. 1971; Muscatine and Porter 1977; Hughes and Grottoli 2013).
Mixotrophy results in a complex cycling of inorganic and organic carbon between
the coral host, the skeleton it secretes, and its endosymbiotic algae (Reynaud et al.
2002; Hughes et al. 2010). Burmester et al. (2018) reported that when obtaining
energy via photosynthesis, the coral holobiont (host animal plus symbionts) is functioning as an autotroph, and when obtaining energy via predation, it is functioning
as a heterotroph.
Autotrophic (or photoautotrophic) nutrition is essentially through the mutualistic
symbiosis (mentioned in Sect. 2.2) between the coral polyp and the Symbiodinium
spp (zooxanthellae) and this nutritional interaction is one of the key reasons for
the success of corals in nutrient poor tropical waters (Tremblay et al. 2012). The
zooxanthellae play an important role in the energy budget of hermatypic corals
by capturing sunlight and converting into energy-rich compounds (photosynthates);
which are then transferred to the cells of the coral polyp and in exchange get shelter
and nourishment (with nutrients such as nitrogen and phosphates). The translocated
29
maximum can lead to a breakdown of the symbiosis (Mieog et al. 2009) and thus the
loss of symbiotic algae from the host (Muller-Parker et al. 2015).
The photosynthetic pigments of the symbiotic algae are responsible for the color
of the coral (Jones 1997; Falkowski and Dubinsky 1981; Dove et al. 2001; Fine and
Loya 2002) and this can vary from white, yellow, brown and olive to red, green, blue
and purple (Holden 1999).
Corals stress out when environmental conditions are altered and this leads to
the expulsion of the Symbiodinium spp (or a decrease in the photosynthetic pigment
concentration within the zooxanthellae) (Holden 1999). Environmental perturbations
(such as an increase in seawater temperature) lead to global climate change and induce
dysfunction and collapse of symbiosis leading to zooxanthellae loss or so-called
‘bleaching’; which causes visible paling of coral colonies, and this phenomenon has
led to severe worldwide decline of coral reefs (Brown and Howard 1985; Guzman
and Jimenez 1992; Gardener et al. 2003; Baker et al. 2008; Weis 2008; Bielmyer
et al. 2010; Ganot et al. 2011; Bielmyer-Fraser et al. 2018).
‘Bleaching’ refers to the change of coloration, revealing the white skeleton, and
is considered the initial response to a stress of the host and/or the photosynthetic
symbiont (Jones 1997; Perez et al. 2001; Baker et al. 2008; Muller-Parker et al.
2015). The extent of bleaching depends on the type of stress and the duration of
it. Corals may recover from bleaching, depending on the intensity and duration of
the stress, but if the algal symbiont communities are not restored relatively quickly
(typically 2–4 weeks); corals may die (Mieog et al. 2009; Bielmyer et al. 2010;
Bielmyer-Fraser et al. 2018).
2.3 Coral Nutrition
Reef building corals exhibit mixotrophy, relying on both the photoautotrophic products of their endosymbiotic algae and the nutrients acquired through heterotrophic
predation (Goreau et al. 1971; Muscatine and Porter 1977; Hughes and Grottoli 2013).
Mixotrophy results in a complex cycling of inorganic and organic carbon between
the coral host, the skeleton it secretes, and its endosymbiotic algae (Reynaud et al.
2002; Hughes et al. 2010). Burmester et al. (2018) reported that when obtaining
energy via photosynthesis, the coral holobiont (host animal plus symbionts) is functioning as an autotroph, and when obtaining energy via predation, it is functioning
as a heterotroph.
Autotrophic (or photoautotrophic) nutrition is essentially through the mutualistic
symbiosis (mentioned in Sect. 2.2) between the coral polyp and the Symbiodinium
spp (zooxanthellae) and this nutritional interaction is one of the key reasons for
the success of corals in nutrient poor tropical waters (Tremblay et al. 2012). The
zooxanthellae play an important role in the energy budget of hermatypic corals
by capturing sunlight and converting into energy-rich compounds (photosynthates);
which are then transferred to the cells of the coral polyp and in exchange get shelter
and nourishment (with nutrients such as nitrogen and phosphates). The translocated