CONTINUOUS MONITORING OF DISSOLVED OXYGEN ACROSS THE WATER COLUMN AT THE BIOLUMINESCENT BAY, LA PARGUERA, LAJAS, PUERTO RICO

Dissolved oxygen (DO) levels in the ocean are decreasing worldwide. According to a several studies, events of anoxic water have been reported across the world, including the Caribbean and the Gulf of Mexico. These incidents are related to the increase in primary productivity because of the high input of nutrients arriving to oceans. In the 1960’s, studies at Bahia Fosforescente (BF), located southwestern Puerto Rico, reported brine pollution affecting the biogeochemical processes in the bay. As a consequence, strong stratification events caused the deepest part of the bay to become anoxic for an extended period of time. No additional studies were realized to further monitor the trends and prevalence of these anoxic conditions. To address the lack of information in the bay, the vertical distribution of DO was determined collected. In addition, other environmental parameters, such as bioluminescence, temperature, salinity and the tidal regime were also measured. Overall, average DO levels of 6.5 mg/L were found near the surface. Periods of ca. 5 hours of hypoxia or anoxia were observed during the wet season (October) at 4m of depth. Observations of bioluminescence suggest that the higher values of bioluminescence correspond to bottom DO values <2.0 mg/. Halocline and thermocline were not observed during the period of low DO concentration. Various bottom anoxic events (shorter than 4 hours) were observed throughout the year from November to March; and an increase of DO levels coincide with the transition of high to low tide. The results suggest that high bioluminescence peaks are related to near bottom hypoxic events. The data do not suggest that thermohaline stratification is not necessary for the development of low DO concentration at the BF.