2.5 Threats to Coral Reefs
35
Natural resuspension events, terrestrial runoff, dredging and dredging related
activities (such as dredge material disposal in offshore disposal grounds) can
temporarily increase suspended sediment concentrations in the water column (Jones
et al. 2015, Duckworth et al. 2017) and once suspended, fine terrestrial clays have
the potential to remain in suspension for long periods (Storlazzi et al. 2015). Prouty
et al. (2010) mentioned that terrestrial runoff contains sediment, nutrients as well as
pollutants that can affect the health and resilience of corals.
Erftemeijer et al. (2012) reported that dredging operations have contributed to
the loss of coral reef habitats, directly due to the removal or burial of reefs, and
indirectly as a consequence of lethal or sublethal stress to corals caused by elevated
turbidity and sedimentation. Collective effects linked with sediment inputs include
direct mortality, reduced growth, lower calcification rates and reduced productivity,
bleaching, increased susceptibility to diseases, physical damage to coral tissue and
reef structures (breaking, abrasion), and reduced regeneration from tissue damage
(Erftemeijer et al. 2012).
Enhanced sediment load is attributed to human activities, which is considered a
major threat to coral reefs (Bryant et al. 1998; Hughes et al. 2003; Wilkinson 2004).
High turbidity and sedimentation rates may depress coral growth and survival due to
attenuation of light available to symbiotic zooxanthallae and redirection of energy
expenditures for clearance of settling sediments (Erftemeijer et al. 2012). Sediments
also affect the fertilization of broadcast spawning coral species (Ricardo et al. 2018).
Furthermore, sedimentation can affect coral recruitment and have impacts on
other (non-coral) reef-dwelling organisms, reduced species diversity and increased
mortality, reduced calcification and growth rates, decreased net production and
increased respiration (Rogers 1990; Crabbe and smith 2005; Fabricius 2005; Jupiter
et al. 2008; Erftemeijer et al. 2012).
Chemical pollution, associated with run off, is one of the most wide-spread
anthropogenic disturbances to the marine environment and usually includes pernicious pollutants such as polychlorinated biphenyls (PCBs), pesticides and trace
elements (Burke et al. 2011; Fey et al. 2019). Agricultural, industrial and urban
activities contribute to chemical pollution. Coastal agricultural practices have led
to an increase in pesticides and fungicides in waterways. Run-off from agricultural
activities increases pollution especially in the form of nitrogen and phosphate (DeBashan and Bashan 2004) thus causing eutrophication. Eutrophication is simply the
gradual increase in the concentrations of nutrients in a water body; usually from
runoff from land and these lead to excessive growth of algae in the water body. Pesticides have been identified as important non-point source pollutants since residues
have been detected in several coral reef systems (Haynes et al. 2000; Lewis et al.
2009; Brodie et al. 2012).
Fonseca et al. (2019) highlighted that metals turn out to be one of the main pollutants in the marine environment and a major threat to the growth and reproduction
of stony corals and especially Cu contamination can eventually cause ecological
and economic disservice associated with the loss of integrity of coral reefs. Negri
et al. (2011) mentioned that pollution and increased SST together impact upon corals
during the vulnerable early stages of their development.
35
Natural resuspension events, terrestrial runoff, dredging and dredging related
activities (such as dredge material disposal in offshore disposal grounds) can
temporarily increase suspended sediment concentrations in the water column (Jones
et al. 2015, Duckworth et al. 2017) and once suspended, fine terrestrial clays have
the potential to remain in suspension for long periods (Storlazzi et al. 2015). Prouty
et al. (2010) mentioned that terrestrial runoff contains sediment, nutrients as well as
pollutants that can affect the health and resilience of corals.
Erftemeijer et al. (2012) reported that dredging operations have contributed to
the loss of coral reef habitats, directly due to the removal or burial of reefs, and
indirectly as a consequence of lethal or sublethal stress to corals caused by elevated
turbidity and sedimentation. Collective effects linked with sediment inputs include
direct mortality, reduced growth, lower calcification rates and reduced productivity,
bleaching, increased susceptibility to diseases, physical damage to coral tissue and
reef structures (breaking, abrasion), and reduced regeneration from tissue damage
(Erftemeijer et al. 2012).
Enhanced sediment load is attributed to human activities, which is considered a
major threat to coral reefs (Bryant et al. 1998; Hughes et al. 2003; Wilkinson 2004).
High turbidity and sedimentation rates may depress coral growth and survival due to
attenuation of light available to symbiotic zooxanthallae and redirection of energy
expenditures for clearance of settling sediments (Erftemeijer et al. 2012). Sediments
also affect the fertilization of broadcast spawning coral species (Ricardo et al. 2018).
Furthermore, sedimentation can affect coral recruitment and have impacts on
other (non-coral) reef-dwelling organisms, reduced species diversity and increased
mortality, reduced calcification and growth rates, decreased net production and
increased respiration (Rogers 1990; Crabbe and smith 2005; Fabricius 2005; Jupiter
et al. 2008; Erftemeijer et al. 2012).
Chemical pollution, associated with run off, is one of the most wide-spread
anthropogenic disturbances to the marine environment and usually includes pernicious pollutants such as polychlorinated biphenyls (PCBs), pesticides and trace
elements (Burke et al. 2011; Fey et al. 2019). Agricultural, industrial and urban
activities contribute to chemical pollution. Coastal agricultural practices have led
to an increase in pesticides and fungicides in waterways. Run-off from agricultural
activities increases pollution especially in the form of nitrogen and phosphate (DeBashan and Bashan 2004) thus causing eutrophication. Eutrophication is simply the
gradual increase in the concentrations of nutrients in a water body; usually from
runoff from land and these lead to excessive growth of algae in the water body. Pesticides have been identified as important non-point source pollutants since residues
have been detected in several coral reef systems (Haynes et al. 2000; Lewis et al.
2009; Brodie et al. 2012).
Fonseca et al. (2019) highlighted that metals turn out to be one of the main pollutants in the marine environment and a major threat to the growth and reproduction
of stony corals and especially Cu contamination can eventually cause ecological
and economic disservice associated with the loss of integrity of coral reefs. Negri
et al. (2011) mentioned that pollution and increased SST together impact upon corals
during the vulnerable early stages of their development.