Is Untreated Sewage Impacting Coral Reefs of Caye Caulker, Belize?

Abstract

Pollution from untreated human sewage is one of several environmental concerns in the coastal waters of Belize. This study utilized distributions of fecal sterols and foraminiferal assemblages to determine if human sewage is affecting the coral reef system off the coast of Caye Caulker, Belize. A total of 125 sediment samples were collected from which fecal sterol concentrations (coprostanol, cholestanol and cholesterol) and diagnostic stanol ratios, sediment texture (% mud), and foraminiferal ecological indices, including species richness, density, and diversity, and the FORAM Index (FI), were assessed. Elevated concentrations of coprostanol were primarily found inshore, with 20 samples exceeding 100 ng/g. The two stanol ratios, evaluated together, confirmed presence of human sewage at 17 sites. Foraminiferal assemblages were dominated by Quinqueloculina, Trochulina , Archaias and Asterigerina . Predominance of sand-sized sediments and the prevalence of Trochulina rosea and Asterigerina carinata reflected the active hydrodynamic regime, particularly on the eastern side of the caye. While the FI values overall indicated that water quality is conducive to reef growth and recovery, data from 37 samples indicated that the area is experiencing environmental change, especially on the southwestern side. Significant positive correlations were found between coprostanol and both foraminiferal density and diversity, while coprostanol and FI were negatively correlated. These results indicate that human sewage is inducing nutrification, which may be promoting reported increases in macroalgal abundances throughout Belize, though the active wave and current regimes are limiting the impacts on the eastern, Caribbean-facing side of Caye Caulker.