Patterns of resistance and resilience of the stress-tolerant coral Siderastrea radians (Pallas) to sub-optimal salinity and sediment burial

The coastal lagoons of south Florida, U.S., experience fluctuating levels of sedimentation and salinity and contain only a subset of the coral species found at the adjacent reefs of the Florida Reef Tract. The dominant species within these habitats is Siderastrea radians, which can reach densities of up to 68 colonies m- 2 and is commonly exposed to salinity extremes (< 10 psu to > 37 psu) and chronic sediment burial. In this study, we document the patterns of resistance and resilience of S. radians to sub-optimal salinity levels and sediment burial in a series of short-term, long-term, acute, chronic, single-stressor, and sequential-stressor experiments.S. radians displayed remarkable patterns of resistance and resilience and mortality was documented only under prolonged (≥ 48 h) continuous exposure to salinity extremes (15 and 45 psu) and chronic sediment burial. A reduction in photosynthetic rates was documented for all salinity exposures and the decrease in photosynthesis was linearly related to exposure time. Negative impacts on photosynthetic rates were more severe under low salinity (15 psu) than under high salinity (45 psu). Corals exposed to intermediate, low-salinity levels (25 psu), exhibited initial declines in photosynthesis that were followed by temporary increases that may represent transient acclimatization patterns. The impacts of sediment burial were influenced by the duration of the burial period and ranged from a temporary reduction in photosynthesis to significant reductions in growth and tissue mortality. The maintenance of P/R ratios > 1 and the rapid (< 24 h) recovery of photosynthetic rates after burial periods of 2-24 h indicates that S. radians is able to resist short-term burial periods with minor physiological consequences. However, as burial periods increase and colonies become covered at multiple chronic intervals, sediment burial resulted in extended photosynthetic recovery periods, reduced growth, and mortality. Under normal conditions (i.e., no salinity stress), S. radians was very effective at clearing sediments, and > 50% of the colonies' surface area was cleared within 1 h. However, clearing rates were influenced by physiological status, and prior exposure to sub-optimal salinity significantly reduced the clearing rates of stressed colonies.The response of S. radians to disturbance documented in this study characterizes this species as highly stress-tolerant and provides an explanation for its present high abundance in both reef and marginal environments. Moreover, the key life-history attributes of S. radians, such as brooding reproductive strategy, small colony size, high stress-tolerance, and high recruitment rates, suggest the potential for this species to replace reef-building taxa under increased disturbance scenarios in Florida and elsewhere in the region.