Paytan's team monitored the pH and other conditions at ten ojos and conducted ecological surveys around each site. The researchers found that the number of coral species and the size of coral colonies declined with increasing proximity to the center of an ojo. Only a few species of hard corals were found in waters with the lowest carbonate saturation levels, closest to the ojos. These species are rarely major contributors to the framework of Caribbean reefs, but their ability to form carbonate skeletons in low-pH conditions warrants further study, Paytan said.
"We need to understand the mechanisms that allow these corals to calcify at these low-pH conditions. We should also make sure that the places where these species occur are protected," she said.
The low pH and low carbonate saturation near the ojos are comparable to the conditions scientists expect to see worldwide due to ocean acidification by the year 2100. Other conditions at the ojos are different, however, including somewhat lower salinity and high nutrient concentrations in the discharge water. Evidence from previous studies suggests that the low salinity is not responsible for the patterns seen around the ojos, since coral species that tolerate similarly low salinity occur in the region but were not found near the ojos. The high nutrient concentrations may benefit the corals, helping them compensate for the increased energy needed for calcification under low-pH conditions.
Elizabeth Crook, a graduate student in Earth and planetary sciences at UC Santa Cruz, is first author of the Coral Reefs paper. In addition to Crook and Paytan, the coauthors include Donald Potts, professor of ecology and evolutionary biology at UCSC, and Mario Rebolledo-Vieyra and Laura Hernndez at the Centro
|Contact: Tim Stephens|
University of California - Santa Cruz