Human Impacts on Ecosystems

Oil spilled from a tanker does not stay put or stay toxic in one form. It spreads into a thin slick across the surface, then weathers: the lightest, most toxic compounds evaporate first, waves mix oil and water into a thick emulsion called mousse, and eventually some fractions become dense enough to sink or clump into tar balls that settle on the seafloor or wash onto shorelines. This spreading means contact is never the only path to harm. Fish absorb oil compounds through their gills and skin, and the birds, otters, and marine mammals that eat those fish take the toxins in too. A bird that preens oiled feathers swallows oil directly while trying to clean itself, and oiled feathers also lose their insulating structure, so birds can die of hypothermia or drown before any poison even takes effect.

Cleanup methods target different stages of that spread. Booms are floating barriers that corral oil before it drifts further, keeping it concentrated for removal. Skimmers then physically scoop or vacuum that concentrated oil off the surface. Dispersants work differently: they are chemicals that break the slick into tiny droplets, which spreads oil through the water column rather than removing it, trading a visible surface problem for wider but more dilute underwater exposure.

Warming water causes a different kind of damage with its own recovery window. Coral depends on symbiotic algae living in its tissue for food and color. Heat stress causes the coral to expel those algae, exposing the white skeleton beneath clear tissue — bleaching. A bleached reef is stressed and starving, not dead; if temperatures drop back to normal soon enough, the coral can reabsorb algae and recover. Only prolonged heat stress starves the coral long enough to kill it, linking this topic to the dose-response idea that duration and intensity of stress, not just exposure, determine lasting damage.