Abstract
The Gulf of Papagayo at the northern Pacific coast of Costa Rica experiences pronounced seasonal changes in water parameters caused by wind-driven coastal upwelling. While remote sensing and open water sampling already described the physical nature of this upwelling, the spatial and temporal effects on key parameters and processes in the water column have not been investigated yet, although being highly relevant for coral reef functioning. The present study investigated a range of water parameters on two coral reefs with different exposure to upwelling (Matapalo and Bajo Rojo) in a weekly to monthly resolution over one year (May 2013 to April 2014). Based on air temperature, wind speed and water temperature, three time clusters were defined: a) May to November 2013 without upwelling, b) December 2013 to April 2014 with moderate upwelling, punctuated by c) extreme upwelling events in February, March and April 2014. During upwelling peaks, water temperatures decreased by 7°C (Matapalo) and 9°C (Bajo Rojo) to minima of 20.1 and 15.3°C respectively, while phosphate, ammonia and nitrate concentrations increased 3 to 15-fold to maxima of 1.3 μmol PO4 3- L-1, 3.0 μmol NH4 + L-1 and 9.7 μmol NO3 - L-1. This increased availability of nutrients triggered several successive phytoplankton blooms as indicated by 3- (Matapalo) and 6-fold (Bajo Rojo) increases in chlorophyll a concentrations. Particulate organic carbon and nitrogen (POC and PON) increased by 40 and 70% respectively from February to April 2014. Dissolved organic carbon (DOC) increased by 70% in December and stayed elevated for at least 4 months, indicating high organic matter release by primary producers. Such strong cascading effects of upwelling on organic matter dynamics on coral reefs have not been reported previously, although likely impacting many reefs in comparable upwelling systems.
Highlights
IntroductionSunlit, clear, oligotrophic and carbonate-supersaturated conditions for optimal growth [1]
Coral reefs require warm, sunlit, clear, oligotrophic and carbonate-supersaturated conditions for optimal growth [1]
The differences in single parameters were mostly detected between extUPW and noUPW, and between extUPW and UPW, and between noUPW and UPW (DOC)
Summary
Sunlit, clear, oligotrophic and carbonate-supersaturated conditions for optimal growth [1]. The Eastern Pacific Warm Pool with sea surface temperatures above 27°C is interrupted by seasonal coastal upwelling zones in the gulfs of Tehuantepec (Mexico), Papagayo (Costa Rica—Nicaragua), and Panama (Panamá) [8,9]. These upwelling systems are caused by narrow wind jets blowing from land to sea during the northern hemisphere winter, when high pressure systems in the Caribbean promote strong winds that are canalized through topographical gaps in the volcanic mountain range of Mesoamerica [10,11]. Nutrient concentrations up to 15 μmol L-1 nitrate and 1.3 μmol L-1 phosphate were measured during upwelling periods in the Gulfs of Papagayo and Panama [12,17]
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