58
3 The Use of Scleractinian Corals for Heavy Metal Studies
colonies into the water column such that external fertilization, larval development
and dispersal take place (Harrison et al. 1984). Harrison (2011) and Kerr et al. (2011)
reported that about 87–90% of corals release sperm and /or eggs to seawater and thus
fertilisation occurs within the water column.
Mass spawning involves the synchronous release of gametes and is dependent on
the geographical location, occurring in the summer, once a year over a few nights
following the full moon (Harrison et al. 1984). For instance, throughout annual mass
spawning events on the Great Barrier Reef, Australia, up to 150 coral species release
their gametes synchronously into the water column (Reichelt-Brushett and MichalekWagner 2005). Within the first 24 h, the planula larvae of broadcast spawning corals
develop and generally settle onto the substrate within 3–5 days of spawning (Babcock
and Heyward 1986). Synchronous spawning among hermatypic corals maximises
reproductive success and allows genetic exchange among otherwise asexual colonies
(Harrison et al. 1984).
In brooding corals, fertilization occurs within the polyp where the fertilized eggs
develop to form the planula larvae within the gastrovascular cavity of the polyp
and this usually occurs within the remaining 10–13% of the corals (Hidaka 2016).
Nonetheless, in both spawners and brooders, the planula larvae transform to polyps
after settlement (Hidaka 2016). Natural or anthropogenic stressors such as increase
in water temperature, coral bleaching, or pollution can influence the reproductive
cycles and sustainability of coral gametes (Ward et al. 2002; Harrison and Ward
2001; Hudspith et al. 2017).
3.3 Biogeochemistry of Scleractinian Corals
Environmental factors such as water chemistry, sedimentation, pollution and surface
temperature induce scleractinian corals to incorporate the heavy metals in their living
parts and skeletons. According to Al-Rousan et al. (2007), heavy metals occur in the
coral skeletons as a result of structural incorporation of metals into the aragonite
(Goreau 1977), inclusion of particulate materials in skeletal cavities (reviewed by
Howard and Brown 1984), surface adsorption onto exposed skeleton (St John 1974;
Brown et al. 1991), and chelation with the organic matrix of the skeleton (Mitterer
1978).
Heavy metals are incorporated into the crystal lattice coral skeleton through substitution of dissolved metal species via calcium substitution (Ferrier-Pages et al.2005).
Howard and Brown (1984) highlighted that through feeding, corals incorporate heavy
metals present in seawater into their tissue and skeleton either as dissolved ion or as
particulate forms. The dissolved ions are taken up by the zooxanthallae and tissue
and later transferred to the skeleton whilst the particulate forms are ingested by the
plankton and transferred to the tissue (Howard and Brown 1984). The uptake of
metals from the aquatic environment is usually through the living organism and then
translocated to the nonliving component (skeleton); with the incorporation of metals
3 The Use of Scleractinian Corals for Heavy Metal Studies
colonies into the water column such that external fertilization, larval development
and dispersal take place (Harrison et al. 1984). Harrison (2011) and Kerr et al. (2011)
reported that about 87–90% of corals release sperm and /or eggs to seawater and thus
fertilisation occurs within the water column.
Mass spawning involves the synchronous release of gametes and is dependent on
the geographical location, occurring in the summer, once a year over a few nights
following the full moon (Harrison et al. 1984). For instance, throughout annual mass
spawning events on the Great Barrier Reef, Australia, up to 150 coral species release
their gametes synchronously into the water column (Reichelt-Brushett and MichalekWagner 2005). Within the first 24 h, the planula larvae of broadcast spawning corals
develop and generally settle onto the substrate within 3–5 days of spawning (Babcock
and Heyward 1986). Synchronous spawning among hermatypic corals maximises
reproductive success and allows genetic exchange among otherwise asexual colonies
(Harrison et al. 1984).
In brooding corals, fertilization occurs within the polyp where the fertilized eggs
develop to form the planula larvae within the gastrovascular cavity of the polyp
and this usually occurs within the remaining 10–13% of the corals (Hidaka 2016).
Nonetheless, in both spawners and brooders, the planula larvae transform to polyps
after settlement (Hidaka 2016). Natural or anthropogenic stressors such as increase
in water temperature, coral bleaching, or pollution can influence the reproductive
cycles and sustainability of coral gametes (Ward et al. 2002; Harrison and Ward
2001; Hudspith et al. 2017).
3.3 Biogeochemistry of Scleractinian Corals
Environmental factors such as water chemistry, sedimentation, pollution and surface
temperature induce scleractinian corals to incorporate the heavy metals in their living
parts and skeletons. According to Al-Rousan et al. (2007), heavy metals occur in the
coral skeletons as a result of structural incorporation of metals into the aragonite
(Goreau 1977), inclusion of particulate materials in skeletal cavities (reviewed by
Howard and Brown 1984), surface adsorption onto exposed skeleton (St John 1974;
Brown et al. 1991), and chelation with the organic matrix of the skeleton (Mitterer
1978).
Heavy metals are incorporated into the crystal lattice coral skeleton through substitution of dissolved metal species via calcium substitution (Ferrier-Pages et al.2005).
Howard and Brown (1984) highlighted that through feeding, corals incorporate heavy
metals present in seawater into their tissue and skeleton either as dissolved ion or as
particulate forms. The dissolved ions are taken up by the zooxanthallae and tissue
and later transferred to the skeleton whilst the particulate forms are ingested by the
plankton and transferred to the tissue (Howard and Brown 1984). The uptake of
metals from the aquatic environment is usually through the living organism and then
translocated to the nonliving component (skeleton); with the incorporation of metals