Eutrophication can also increase the severity of diseases (Bruno

Eutrophication can also increase the severity of diseases (Bruno et al., 2003) and lead to competitive advantage for macroalgae that respond by rapid growth, smothering corals or blocking light (Lapointe, 1997 and Walker and Ormond, 1982), although evidence for different trajectories also exists (McCook, 1999a and McCook, 1999b). Sediments that are influenced by outflow from industrial areas can

contain relatively high levels of lead, cadmium, copper, tin, nickel and iron (Amin et al., 2009 and Todd et al., 2010). In particular, copper is known to inhibit coral recruitment, fertilisation and development (Reichelt-Brushett and Harrison, 2005 and Negri and Hoogenboom, 2011). Light-enhanced calcification is responsible for most of the skeletal growth of reef-building corals (Goreau, 1959). Low light decreases calcification in zooxanthellate scleractinian corals, being approximately three times lower in darkness than in light (Kawaguti and Sakumoto, 1948 and Gattuso et al., 1999). Titlyanov (1991), however, noted that enhanced utilisation of light by zooxanthellae in three stony corals can result in stable levels of primary production in a wide light range (20–90% PAR). Low light GPCR & G Protein inhibitor levels may also inhibit the development

of coral larvae (Rogers, 1990). Similar patterns of photo-acclimation (through photophysiological adaptations) across gradients of increased turbidity have been demonstrated by Hennige et al., 2008 and Hennige et al., 2010. Although certainly also related to a variety of other environmental factors, species diversity of corals generally tends to decrease sharply with increasing (chronic) turbidity (Rogers, 1990, Becking et al., 2006 and Cleary et al.,

2008). Long-term turbidity stress can shift the species composition of reefs through the death of more light demanding corals and the subsequent replacement by usually deeper-living, more shade-tolerant ones at certain depths (Pastorok and Bilyard, 1985). Dikou and van Woesik (2006b) noted in Singapore the occurrence of deeper-water genera such as Merulina, Pachyseris and Mycedium found in relatively Immune system shallow (3–4 m) depths was most likely due to high turbidity levels. Also in Singapore, Goh et al. (1994) considered the sediment-impacted light environment to be the main factor controlling coral colony form. Foliose forms tended to dominate the shallow reef with more massive and encrusting forms found deeper. Corals can react either actively or passively to sediments, which in many ways defines their capability to withstand prolonged sedimentation. Passive shedding refers to corals taking advantage primarily of their shape to allow increased runoff of sediment, to maintain parts of the corallum above sediment, or to use water currents to remove accumulated sediment (Stafford-Smith and Ormond, 1992, Stafford-Smith, 1993, Riegl, 1995, Riegl et al., 1995 and Sanders and Baron-Szabo, 2005).

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