Marine Biology

Nutrient loading and contaminant inputs

The symbiotic relationship between reef-building corals and zooxanthellae allows them to thrive in the nutrient-poor “marine deserts” of the tropical oceans. Addition of nutrients to the water may harm corals directly (if concentrations are sufficiently high) or make the environment less favourable for reefs by promoting growth of phytoplankton (which reduces water clarity and light availability) and of seaweeds (macroalgae) that compete with corals for space on the reef. Additional organic production resulting from nutrient loading can also increase populations of bioeroders that break down coral skeletons and reef structures.

Unlike nutrients, contaminants are generally human-produced toxic materials, which include heavy metals, pesticides and herbicides, solvents, fuels, and other compounds. These materials may be part of complex waste streams discharged to the ocean or adsorbed in sediment. Adverse effects of individual contaminants on the coral reef biota are difficult to document, trace, or separate from combined effects.