Spatio-temporal Variability of Chlorophyll-A in the Coastal Zone of Northeastern Brazil

Coastal areas are important regions for global primary productivity. However, understanding the spatio-temporal dynamics of coastal phytoplankton dynamics is challenging due to the multiple environmental factors involved. Here, we use remote sensing and geostatistical techniques to demonstrate the influence of key environmental variables (i.e. sea surface temperature; current intensity; wind speed; photosynthetically active radiation and flow of larger rivers) on spatio-temporal variability of chlorophyll-a in the coastal region of Alagoas State, northeastern Brazil. Chlorophyll-a had high spatial variation (0.03–18.23 mg m−3), with highest mean values observed on the continental shelf up to 50 m depth and towards the southern part of the study area. Seasonally, the highest average values were found between April and June (0.721 mg m−3) and the lowest values between October and December (0.376 mg m−3). Multivariate analysis indicated that the spatio-temporal variability of chlorophyll-a in shallow zones is mainly influenced by seasonal variation in the hydrological regime of rivers and wind-induced coastal currents. This contrasts with deeper zones, where chlorophyll-a variability is strongly linked to water temperature and light availability. Moreover, areas with inshore coral reefs typically had reduced chlorophyll-a levels, possibly due to the blocking of nutrients at river mouths.