One of the factors responsible for this discrepancy may be the effect of the duration of exposure (Fig. 2). Tolerance limits of corals for total suspended matter (or suspended-sediment RG7422 cell line concentration) reported in the literature range from <10 mg L−1 in reef areas not subject to stresses from human activities to >100 mg L−1 in marginal reefs in turbid nearshore environments (Marshall and Orr, 1931, Roy and Smith, 1971, Mapstone et al., 1989, Hopley et al., 1993, Larcombe et al., 2001, Hoitink, 2003 and Sofonia and Anthony, 2008) (Table 4). This wide range demonstrates that different coral species and corals in different geographic regions may respond differently to turbidity increases. Thermal
tolerances in corals have also been reported to vary geographically (Weeks et al., 2008). Some corals have been shown to possess the ability to (temporarily) switch between
autotrophy and heterotrophy or to make adjustments to their respiratory demands in response to episodic turbidity stress events (Telesnicki and Goldberg, AZD9291 solubility dmso 1995 and Anthony and Fabricius, 2000) but these data are limited to a few coral species. Reduced photosynthetic capacity may lead to reduced energy reserves for maintenance and growth. Corals contain large lipid stores under normal (non-stressed conditions), but a recent study indicated that 30–50% depletion of those reserves may occur during stress events within a matter of weeks (Anthony et al., 2007). In certain locations, coral reefs persist in highly turbid areas (Perry, 2005 and Perry and Smithers, 2010). Larcombe et al. (1995) described the characteristics of
suspended sediment concentrations of marine waters near inner-shelf fringing coral reefs in northern Australia and related these to the prevailing oceanographic and meteorological conditions. High temporal and spatial variation in near-bed SSCs corresponded to wind-generated swells, which, within 1 km of the reefs, produced near-bed SSCs of well over 200 mg L−1. At the fringing coral reefs SSCs ranged from 5 mg L−1 to 40 mg L−1. Flushing of these bays by tidal currents was important to prevent the build-up of suspended sediment in the water around the coral reefs. Other extremely turbid reefs were described by Anthony and Larcombe (2000) from Halifax Bay, Australia, where “coastal turbid-zone Histamine H2 receptor reefs” occur in water less than 4 m deep, with turbidity sometimes over 100 NTU (∼220 mg L−1) as a result of wave-induced resuspension, and wind-driven longshore currents prevent accumulation of fine-grained sediment. In turbid situations, the key to sustained coral growth appears to be low sediment accumulation, frequently assured by strong tidal flushing, although recent studies from the GBR indicate that reefs in these settings can have quite high accretion rates. While reef growth was found to be possible under such conditions, these reefs hosted relatively moderate species numbers and sometimes had poorly consolidated frameworks (Hopley et al., 2007).