Nutrification impacts on coral reefs from northern Bahia, Brazil

Coral reefs extend for 20 km along the north coast of the slate of Bahia, B razil. Over the last 15 years, this region has experienced an acceleration of generally unplanned urbanisation, with the irregular and indiscriminate use of septic tanks in urban centres contaminating the groundwater. This in filtration of nutrients and pathogens is facilitated by both the soil perme ability and an accented hydraulic head, which eventually leads to the perco lation of nutrient-rich groundwater seaward to the reefs. The groundwater n utrient concentrations (nitrate, nitrite, ammonia, phosphate and silicate) from Guarajuba beach (a highly urbanised area) are over 10 times higher tha n groundwater from Papa Genre beach, an area of low human occupation. The p H values of the groundwater samples also indicate the predominance of reduc ing conditions in Guarajuba, due to the high availability of organic matter and consequent bacterial activity. Additionally, faecal coliform data indi cate domestic wastewater as the source of groundwater contamination, High d ensities of macroalgae and heterotrophic organisms on the impacted reefs, a s well as higher concentrations of nutrients, evoke the effects of eutrophi cation on this coral reef ecosystem. These data suggest that the high avail ability of nutrients is affecting the trophic structure in the study areal especially in Guarajuba, with the increased turf and macroalgae growth redu cing light penetration to the coral colonies, competing with them for space and inhibiting the settlement of new coral larvae.