Nutrification impacts on coral reefs from northern Bahia, Brazil

Abstract

Coral reefs extend for 20 km along the north coast of the state of Bahia, Brazii. 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 infiltration of nutrients and pathogens is facilitated by both the soil permeability and an accented hydraulic head, which eventually leads to the percolation of nutrient-rich groundwater seaward to the reefs. The groundwater nutrient concentrations (nitrate, nitrite, ammonia, phosphate and silicate) from Guarajuba beach (a highly urbanised area) are over 10 times higher than groundwater from Papa Gen te beach, an area of low human occupation. The pH values of the groundwater samples also indicate the predominance of reducing conditions in Guarajuba, due to the high availability of organic matter and consequent bacterial activity. Additionally, faecal coliform data indicate domestic wastewater as the source of groundwater contamination. High densities of macroalgae and heterotrophic organisms on the impacted reefs, as well as higher concentrations of nutrients, evoke the effects of eutrophication on this coral reef ecosystem. These data suggest that the high availability of nutrients is affecting the trophic structure in the study area, especially in Guarajuba, with the increased turf and macroalgae growth reducing light penetration to the coral colonies, competing with them for space and inhibiting the settlement of new corallarvae.

Pathologies and mortality rates caused by organic carbon and nutrient stressors in three Caribbean coral species

“…In the second 30 d experiment, M. annularis and P. furcata were separately exposed to 25 mg l -1 of starch, lactose, arabinose and mannose. All treatment concentrations reflect levels previously reported for impacted reefs (March 1977, Webber & Roff 1995, Costa et al 2000, Van Duyl & Gast 2001.…”

The relative importance of nutrient enrichment and herbivory on macroalgal communities near Norman's Pond Cay, Exumas Cays, Bahamas: a “natural” enrichment experiment

“…Our findings of the importance of nitrogen enrichment to increased herbivory are consistent with results of recent monitoring in the Negril Marine Park, Jamaica, where sewage and agricultural runoff have resulted in DIN enrichment of shallow reefs that support higher biomass of fleshy macroalgae, higher tissue %N of macroalgae, higher densities of sea urchins, and lower cover of hard corals compared to the deep reefs where lower DIN concentrations occur (Lapointe and Thacker, 2002). Similar trophic alteration from sewage pollution was reported for coral reefs off northern Bahia, Brazil, where the high availability of wastewater nutrients resulted in increased abundance of macroalgae, sea urchins, and heterotrophic organisms, ultimately resulting in decreased coral cover (Costa et al, 2000).…”

Nutrient-induced perturbations to δ13C and δ15N in symbiotic dinoflagellates and their coral hosts

“…In spite of their seeming robustness, coral reef ecosystems appear to be particularly vulnerable to changes in water quality (Smith et al 1981, Lapointe 1997. Recent assessments rate changes to coastal discharge as one of the most serious threats facing coral reef ecosystems worldwide (Tomascik & Sander 1985, 1987a, 1987b, Lapointe 1997, Vitousek et al 1997a, Edinger et al 1998, Costa et al 2000, Heikoop et al 2000b, McCulloch et al 2003. The rapid growth of human populations and associated land use transformations in tropical coastal areas has led to an increase in the discharge of sewage, storm water and agricultural run-off onto coral reefs (Gerlach 1981, Vitousek et al 1997b.…”