Annual hydrological variation and hypoxic zone in a tropical coral reef system

The “Parque Nacional Sistema Arrecifal Veracruzano” (PNSAV), a coastal reef system located in the corridor of the southwestern Gulf of Mexico, is an ecosystem with different environmental characteristics when compared to most tropical coral reefs. The current study aims to describe the hydrological variation of temperature, salinity, density, oxygen, nitrogen and chlorophyll-a from March, 2011 to March, 2012. A total of 13 sampling stations distributed along the PNSAV were used to describe the temporal variation of the physicochemical characteristic of the area. There was a good correlation between the physicochemical and biological variables according to a multivariate statistical analysis (cluster and PCA) performed using all variables. The correlation value among the physicochemical and biological variables was about the same for all stations despite the differences in coral coverage. It was found that the PNSAV had different seasons (dry, rainy, northern and transition seasons or southern and northern wind seasons) depending on the variables used to perform the analysis. Finally, some stations depicted a hypoxic area in front of the Jamapa River owing to bacterial activity, which maybe one of the explanation of the absence of coral reef structures in this area.