Water quality conditions on coral reefs at the Marino Ballena National Park, Pacific Costa Rica

Abstract

Marino Ballena National Park is located in an area thought to be chronically affected by high terrigenous sediment and nutrient loads, and high temperatures. Five coral reefs at MBNP were monitored monthly between August 2003 and April 2005. Suspended sediments, sedimentation, temperature, salinity, chlorophyll a, phosphate, silicate, nitrite, nitrate, and ammonia were measured monthly to identify which of those may have a preponderant role on the development and deterioration of the coral reefs inside the park. Live coral coverage was estimated yearly in permanent transects between 2003 and 2006. We observed a strong seasonality in the measured environmental parameters between the dry (december–April) and rainy seasons (May–November). Three principal components (PC) explained 73.6% of the variability among the environmental parameters. Reefs at MBNP are mesotrophic with respect to nutrients (PO4–3 0.241 μM, NO3– 0.299 μM, NO2– 0.058 μM, SiO4 16.064 μM) and chlorophyll a (1.01 μg L–1) concentrations. The impact of sedimentation ranges from moderate (44 mg cm–2 d–1) to heavy (117 mg cm–2 d–1). Both nutrient and sediment loading are linked to ongoing land erosion. Heavy rains carry nutrient and sediment flows into the Térraba River, and transports the nutrients and sediments into the protected area, contributing to the creation of environmental conditions in MBNP that are not typically favorable for reef development. However, the percent live coral coverage did not change significantly over the years, suggesting that corals may be increasing their tolerance to stressors.