In estuarine, coastal, and shelf areas, blue crab, Dungeness crab, and lobster larvae also concentrate in the surface film during mid-day, drawn there by the abundance of sunlight. Because of its importance as a nursery for fish eggs and larvae, the microlayer has great economic value. So do contaminants deposited on the land, many of which eventually wash into rivers and then the oceans. Toxins in the microlayer typically occur at concentrations 100 to 10,000 times higher than in the water below. Concentrations of these contaminants hundreds or even thousands of times greater than EPA water quality standards have been measured in the sea-surface microlayer of Puget Sound, Chesapeake Bay and elsewhere.
Fish eggs are sensitive to environmental toxicants.
So are embryos and larvae, which are deformed or killed by hydrocarbons, metals, and pesticides. BaP is a strong carcinogen created by the combustion of coal, gasoline, and many wastes, including municipal trash. But sea-surface microlayer concentrations of PCB in Puget Sound are up to 130 times higher than EPA's water quality criterion. In controlled tests, more than half the samples from the Puget Sound microlayer caused a significant reduction in the normal hatching success of fertilized sole eggs. Unfortunately, these near-shore regions are the most important from the viewpoint of productivity.