30
2 Coral Reef Ecosystem
photosynthates can provide up to 100% energy to the coral host (Muscatine 1990;
Muscatine et al. 1981; Falkowski et al. 1984; Tremblay et al. 2012).
Heterotrophy plays an important role in the energy budget of scleractinian
corals since many nutrients cannot be supplied by photosynthesis and have to be
acquired through feeding (Houlbréque and Ferrier-Pagés 2009; Tagliafico et al.
2018). Heterotrophic nutrition is considered most important at night (Porter 1976;
Muscatine and Porter 1977) and this occurs when the sessile coral colonies fulfill a
role as natural filter and water cleaning systems by capturing plankton, sediments,
seston and organic particles from the water column (Seeman 2013). Corals can
ingest (meso/macro) sized zooplankton (Grottoli et al. 2006; Palardy et al. 2008;
Anthony et al. 2009; Grottoli et al. 2014; Levas et al. 2015) by nematocyst discharges
and tentacle grabbing (reviewed by Houlbréque and Ferrier-Pagés 2009); pico- and
nano-plankton (Tremblay et al. 2012); suspended particulate matter (SPM) (Anthony
1999a, b; Anthony and Fabricius 2000; Bessell-Browne et al. 2017). The SPM on
coral reefs consists of diverse food sources such as detrital matter, resuspended sediment, coral mucus and excretory products from other animals and these are used
through heterotrophic feeding.
Heterotrophy increases in high turbidity and low light circumstances (Anthony
2000; Anthony and Fabricius 2000); and following bleaching events (Grottoli et al.
2006; Bessell-Browne et al. 2014). Increase in habitat depth leads to a decrease in
photosynthetic production, due to light limitation and thus some coral species depend
on zooplankton grazing to sustain metabolism (Palardy et al. 2008; Tremblay et al.
2012). With increasing depth, the light availability reduces due to attenuation by the
water column (Williams et al. 2018) and the heterotrophic energetic subsidies such
as zooplankton and particulate organic matter increases (Hamner et al. 1988; Genin
et al. 2005; Palardy et al. 2008).
Furthermore, heterotrophic nutrition dominates during bleaching events owing to
a decrease in photosynthetic production (due to loss of symbionts or photosynthetic
pigments) (Hughes et al. 2010; Tremblay et al. 2012). Elevated sea surface temperatures (SSTs) enable corals to lose their endosymbiotic algae and/or endosymbiotic
algal pigments rendering them pale white (Hoegh-Guldberg and Smith 1989, Jokiel
and Coles 1990; Glynn 1996; Brown 1997a, b; Hoegh-Guldberg 1999; D’Croz et al.
2001; Rodrigues and Grottoli 2007). Therefore, there is a dramatic decrease in photosynthesis and hence a deficiency in coral carbon budget of up to 80% (Muscatine
et al. 1981; Falkowski et al. 1993; Grottoli et al. 2006; Palardy et al. 2008; Tremblay
et al. 2012; Grottoli et al. 2014; Levas et al. 2015).
2.4 Benefits of Coral Reefs
Coral reefs form a unique ecosystem with a high biodiversity, are exceptionally
valuable and thrive in nutrient poor waters. Coral reefs constitute only 0.2% of the
world’s marine ecosystem and estimated to harbour around one third of all described
2 Coral Reef Ecosystem
photosynthates can provide up to 100% energy to the coral host (Muscatine 1990;
Muscatine et al. 1981; Falkowski et al. 1984; Tremblay et al. 2012).
Heterotrophy plays an important role in the energy budget of scleractinian
corals since many nutrients cannot be supplied by photosynthesis and have to be
acquired through feeding (Houlbréque and Ferrier-Pagés 2009; Tagliafico et al.
2018). Heterotrophic nutrition is considered most important at night (Porter 1976;
Muscatine and Porter 1977) and this occurs when the sessile coral colonies fulfill a
role as natural filter and water cleaning systems by capturing plankton, sediments,
seston and organic particles from the water column (Seeman 2013). Corals can
ingest (meso/macro) sized zooplankton (Grottoli et al. 2006; Palardy et al. 2008;
Anthony et al. 2009; Grottoli et al. 2014; Levas et al. 2015) by nematocyst discharges
and tentacle grabbing (reviewed by Houlbréque and Ferrier-Pagés 2009); pico- and
nano-plankton (Tremblay et al. 2012); suspended particulate matter (SPM) (Anthony
1999a, b; Anthony and Fabricius 2000; Bessell-Browne et al. 2017). The SPM on
coral reefs consists of diverse food sources such as detrital matter, resuspended sediment, coral mucus and excretory products from other animals and these are used
through heterotrophic feeding.
Heterotrophy increases in high turbidity and low light circumstances (Anthony
2000; Anthony and Fabricius 2000); and following bleaching events (Grottoli et al.
2006; Bessell-Browne et al. 2014). Increase in habitat depth leads to a decrease in
photosynthetic production, due to light limitation and thus some coral species depend
on zooplankton grazing to sustain metabolism (Palardy et al. 2008; Tremblay et al.
2012). With increasing depth, the light availability reduces due to attenuation by the
water column (Williams et al. 2018) and the heterotrophic energetic subsidies such
as zooplankton and particulate organic matter increases (Hamner et al. 1988; Genin
et al. 2005; Palardy et al. 2008).
Furthermore, heterotrophic nutrition dominates during bleaching events owing to
a decrease in photosynthetic production (due to loss of symbionts or photosynthetic
pigments) (Hughes et al. 2010; Tremblay et al. 2012). Elevated sea surface temperatures (SSTs) enable corals to lose their endosymbiotic algae and/or endosymbiotic
algal pigments rendering them pale white (Hoegh-Guldberg and Smith 1989, Jokiel
and Coles 1990; Glynn 1996; Brown 1997a, b; Hoegh-Guldberg 1999; D’Croz et al.
2001; Rodrigues and Grottoli 2007). Therefore, there is a dramatic decrease in photosynthesis and hence a deficiency in coral carbon budget of up to 80% (Muscatine
et al. 1981; Falkowski et al. 1993; Grottoli et al. 2006; Palardy et al. 2008; Tremblay
et al. 2012; Grottoli et al. 2014; Levas et al. 2015).
2.4 Benefits of Coral Reefs
Coral reefs form a unique ecosystem with a high biodiversity, are exceptionally
valuable and thrive in nutrient poor waters. Coral reefs constitute only 0.2% of the
world’s marine ecosystem and estimated to harbour around one third of all described