Seasonal and spatial controls on the delivery of excess nutrients to nearshore and offshore coral reefs of Brazil

We examined the influence of seasonality and anthropogenic activity on the delivery of land-based nutrients to coral reefs in eastern Brazil. Seawater and porewater were sampled during dry and rainy seasons in three nearshore and offshore reefs with distinct nutrient inputs along the south coast of Bahia State, and analysed for total oxidised nitrogen (TON), soluble reactive phosphorus (SRP), reactive silica (DSi), and chlorophyll (Chl a). Rainfall promotes significant increase in the load of nutrients to nearshore and offshore reefs. Concentrations in urbanized reefs are on average 25% higher than non-urban reefs. Differences in nutrient concentration between nearshore and offshore reefs are more pronounced during dry season, when the bulk of land-based nutrient contribution is confined to nearshore reefs. SRP values at the study sites are significantly higher than other coral reef areas, suggesting the occurrence of a permanent source of phosphorus along this highly terrigenous (siliciclastic) coast.