LAUSR

Eutrophication is one of the causes of the degradation of reefs worldwide. The aim of this research is to determine if sewage discharge reaches the fore reefs at northwest of Cuba using δ 15 N in tissues of the octocorals Eunicea flexuosa and Plexaura kuekenthali and the concentration of microbiological and physical-chemical variables. Thirteen reefs at 10-m depth were selected near river basins and far from the urban and industrial development of Havana City. Branch tips of both species were collected, the concentrations of nutrient and microorganisms in water samples were quantified, and horizontal visibility in the water (Vis) was determined. Overall, δ 15 N of E . flexuosa ranged from 1.5 to 6.3‰ and P . kuekenthali from 1.7 to 6.7‰. The tissue of both species was significantly enriched in 15 N in reefs near polluted watersheds compared with reefs far from pollution by anthropogenic activities. The δ 15 N of both species showed a positive and significant correlation with the concentration of fecal and total coliform bacteria, heterotrophic bacteria, and NH 4 + and a negative and significant correlation with the Vis. The δ 15 N of the two species and microbiological and physical-chemical variables evidenced water quality decline by sewage discharge that reached reefs near polluted watersheds.