Settlement Effects on Favia fragum (Scleractinia, Faviidae) Exposed to Different Sediment Sources from Puerto Rico

Abstract:

Agricultural production and urban development in Puerto Rico have increased the rate of sedimentation to the coastal, marine environment, which has the potential to adversely affect coral-reef ecosystems. The processes of settlement and metamorphosis of coral larvae are integral to the maintenance and recovery of coral reefs, yet the effects of sedimentation in Puerto Rico on these processes are not well understood. Planulae from laboratory cultured colonies of Favia fragum were exposed to sediment from shallow, marine habitats of Guánica (Brown Inlet) and Peñuelas (Tallaboa Bay), Puerto Rico to determine how sediment source, concentration, and grain-size affect larval settlement. Planulae were exposed to six concentrations of Guánica and Peñuelas sediment ranging from 20 to 640 mg cm^-2 and to a single concentration (20 mg cm^-2) of Peñuelas sediment fractioned into five grain-size classes (<32 µm, 33-63 µm, 64-125 µm, 126-250 µm, and 251-500 µm). Larval settlement decreased as the concentration of sediment increased, resulting in a median effective concentration (EC50) of 31.2 mg cm^-2 for Guánica sediment and 1.7 mg cm^-2 for Peñuelas sediment. There was no apparent effect of sediment grain size on the settlement of planulae exposed to 20 mg cm^-2 of Peñuelas sediment. These results suggest that the source of sediment can be an important factor determining the success of coral settlement, and that coral settlement can be inhibited at concentrations of sediment that are below thresholds considered to be protective of reef-building corals.