Macroalgal δ15N indicates land-derived elemental pollution on nearshore coral reefs of Curaçao, southern Caribbean

Coral reef ecosystems are increasingly exposed to a wide variety of anthropogenic pollutants. This study evaluated the spatial and seasonal distribution of land-derived substances on fringing reefs of the Caribbean island of Curaçao during two wet- and two dry seasons (2021-2023), to determine whether spatial differences in δ¹⁵N values can serve as a proxy for other forms of pollution, including nutrient availability and potentially toxic elements. The spatial distribution of δ¹⁵N signatures of macroalgal tissues along the island's coast was compared to tissue concentrations of 32 nutrients and non-essential elements. Tissue concentrations of many micronutrients (Cu, Fe, Mn, Se, Si, Zn) and non-essential elements (Al, Pb, Ti) correlated positively with δ¹⁵N. Elemental concentrations and δ¹⁵N values showed a strong positive correlation with the amount of coastal alteration. Higher rainfall was associated with elevated δ¹⁵N values, and this association intensified with increased coastal alterations, while δ¹⁵N values decreased with depth. Elemental pollution was measured during one wet season, but since it correlated positively with δ¹⁵N, it is likely to follow similar temporal and spatial patterns as δ¹⁵N values. Certain non-essential elements were found in high concentrations at only a few sites near industrial, heavily developed areas, and a landfill. Despite such local deviations for specific elements, our findings support the use of isotopic signatures in benthic organisms as a proxy for anthropogenic inputs on coral reefs and show that precipitation increases the effect of land-use changes on pollution run-off to nearby coral reefs.