60
3 The Use of Scleractinian Corals for Heavy Metal Studies
Furthermore, studies have also examined the effects of various metals on the
fertilisation success of gametes and include Reichelt-Brushett and Harrison (2005);
Reichelt-Brushett and Hudspith (2016); and Gissi et al. (2017). Metal toxicological
studies have also been carried out on scleractinian coral larvae (Goh 1991; ReicheltBrushett and Harrison 2004). These studies show that metals affect all stages of the
life cycle of corals.
Synchronous spawning of corals provides a large number of individuals for
ecotoxicological testing and as such many studies such as Reichelt-Brushett and
Harrison (1999, 2005); Negri and Hoogenboom (2011); Gissi et al. (2017); LeighSmith et al. (2018) carried out substantial coral toxicology work on the early coral
life stages such as fertilisation success, larvae survival and development. Hudspith
et al. (2017) mentioned that fertilisation success is an important endpoint in ecotoxicological assays as it is sensitive and displays a quantifiable dose–response relationship at metal concentrations similar to those polluted environmental levels.
However, Summer et al. (2019) reported that trace metal toxicity to early life stages
of scleractinian corals varied between both the coral species and metal of interest.
Various reasons have been suggested for the analysis of different components of
corals. Coral skeletons are analyzed as they reveal past environmental data of the
marine environment. Coral tissues and the associated symbiotic algae tend to record
higher metal concentration than the skeleton (Jafarabadi et al. 2018), suggesting that
not all metals taken up by the tissue are transferred to the skeleton. Symbiotic zooxanthellae present in tissues of hermatypic corals (Reichelt-Brushett and McOrist 2003)
have been described as directly influencing the skeletal concentration of the metals
through the enhancement of calcification rates (Livingston and Thompson 1971).
Zooxanthellae may be involved in the direct uptake of metals in cases where potentially toxic metals are metabolically substituted for vitally essential elements such
as phosphorus (Howard and Brown 1984). Coral gametes and larvae are principally
sensitive to changes in water quality because they are released into the environment
to fertilise and undergo development where they are potentially in direct contact with
anthropogenic contaminants (Reichelt-Brushett and Hudspith 2016).
Stress in corals often gives rise to the expulsion of symbiotic zooxanthellae (Smith
et al. 2003), causing pale or white coloration, referred to as bleaching (discussed
in Chap 2). Yang et al. (2019) mentioned that coral bleaching is a key reason of
decreasing coral reef biodiversity. At higher concentrations, metals can be toxic to
corals (Reichelt-Brushett and McOrist 2003; Mohammed and Dar 2010; El-Sorogy
et al. 2012). Hence, if corals are exposed to high concentrations of toxic metals,
then zooxanthellae can be expelled (Harland and Brown 1989; Harland and Nganro
1990; Meehan and Ostrander 1997; Peters et al. 1997; Reichelt-Brushett and McOrist
2003; Bastidas and Garcia 2004), as they play an important role in the uptake of trace
metals.
However, due to different methods and techniques of analysis used, variation of
species as well as sample collection from polluted and unpolluted areas, makes it
difficult to compare directly the data that have been generated for heavy metals.
3 The Use of Scleractinian Corals for Heavy Metal Studies
Furthermore, studies have also examined the effects of various metals on the
fertilisation success of gametes and include Reichelt-Brushett and Harrison (2005);
Reichelt-Brushett and Hudspith (2016); and Gissi et al. (2017). Metal toxicological
studies have also been carried out on scleractinian coral larvae (Goh 1991; ReicheltBrushett and Harrison 2004). These studies show that metals affect all stages of the
life cycle of corals.
Synchronous spawning of corals provides a large number of individuals for
ecotoxicological testing and as such many studies such as Reichelt-Brushett and
Harrison (1999, 2005); Negri and Hoogenboom (2011); Gissi et al. (2017); LeighSmith et al. (2018) carried out substantial coral toxicology work on the early coral
life stages such as fertilisation success, larvae survival and development. Hudspith
et al. (2017) mentioned that fertilisation success is an important endpoint in ecotoxicological assays as it is sensitive and displays a quantifiable dose–response relationship at metal concentrations similar to those polluted environmental levels.
However, Summer et al. (2019) reported that trace metal toxicity to early life stages
of scleractinian corals varied between both the coral species and metal of interest.
Various reasons have been suggested for the analysis of different components of
corals. Coral skeletons are analyzed as they reveal past environmental data of the
marine environment. Coral tissues and the associated symbiotic algae tend to record
higher metal concentration than the skeleton (Jafarabadi et al. 2018), suggesting that
not all metals taken up by the tissue are transferred to the skeleton. Symbiotic zooxanthellae present in tissues of hermatypic corals (Reichelt-Brushett and McOrist 2003)
have been described as directly influencing the skeletal concentration of the metals
through the enhancement of calcification rates (Livingston and Thompson 1971).
Zooxanthellae may be involved in the direct uptake of metals in cases where potentially toxic metals are metabolically substituted for vitally essential elements such
as phosphorus (Howard and Brown 1984). Coral gametes and larvae are principally
sensitive to changes in water quality because they are released into the environment
to fertilise and undergo development where they are potentially in direct contact with
anthropogenic contaminants (Reichelt-Brushett and Hudspith 2016).
Stress in corals often gives rise to the expulsion of symbiotic zooxanthellae (Smith
et al. 2003), causing pale or white coloration, referred to as bleaching (discussed
in Chap 2). Yang et al. (2019) mentioned that coral bleaching is a key reason of
decreasing coral reef biodiversity. At higher concentrations, metals can be toxic to
corals (Reichelt-Brushett and McOrist 2003; Mohammed and Dar 2010; El-Sorogy
et al. 2012). Hence, if corals are exposed to high concentrations of toxic metals,
then zooxanthellae can be expelled (Harland and Brown 1989; Harland and Nganro
1990; Meehan and Ostrander 1997; Peters et al. 1997; Reichelt-Brushett and McOrist
2003; Bastidas and Garcia 2004), as they play an important role in the uptake of trace
metals.
However, due to different methods and techniques of analysis used, variation of
species as well as sample collection from polluted and unpolluted areas, makes it
difficult to compare directly the data that have been generated for heavy metals.