31 Aug 2023

Effects of Sedimentation on Three Hawaiian Coral Species under Laboratory Conditions

Abstract: Sedimentation can occur near a dredge operation in pulses over days, and potentially impact coral reefs occurring in close proximity. To improve the ability to predict the effects of dredging on corals, the effects of sedimentation in two 18-day experiments were studied for three common coral species representing different morphologies. In a laboratory setting, coral fragments were exposed to four sedimentation concentrations dosed every four days ranging from 0 to 60 mg cm-2. Separate experiments were performed in series, once with fine grain sediment and repeated with a coarse grain sediment. A 30-day sediment free observation period followed each experiment. Coral responses were measured throughout the experiment and at the end of the 18-day exposure and 30-day sediment free observation period. Photosynthetic yield, lipid ratios, tissue color, tissue loss, growth, and sediment cover varied among the treatment groups. All coral species were minimally affected when sediment concentrations were at or below 6 mg cm-2. P. meandrina and P. lobata experienced the most sediment coverage and tissue loss when exposed to sediment concentrations >30 mg cm-2 for either sediment. M. capitata experienced no sediment coverage or tissue loss when exposed to either sediment, but a reduction in photosynthetic yield at 60 mg cm-2 fine grain sediment was observed. During the 30-day post-exposure sediment free observation period, P. meandrina tissue loss continued, P. lobata nearly completely regrew lost tissue, while M. capitata showed no lingering effects. This study improves the US Army Corps of Engineers (USACE) ability to estimate the impacts of dredging on coral reefs.