What happens in the ocean as a hurricane passes over?

Large marine animals, such as dolphins and sharks, seem to sense these storms as they approach. They may sense changes in air or water pressure or changes in salinity due to heavy rainfall. Such free-swimming animals swim into deeper, calmer waters away from shore and return to shallower areas days or weeks after the storm has passed.

Not all marine animals survive hurricanes. Corals, crabs, and other animals that cannot swim large distances may be smothered by sediment stirred up by the waves. Fish that live near shore may get washed into ponds or lagoons. If the water they land in is too fresh or full of sediment, they can die.

But hurricanes can also boost marine life when mixing of surface and deeper waters triggers phytoplankton blooms. The colder waters from below are high in nutrients needed by phytoplankton for growth. As they mix with surface waters, they trigger a phytoplankton bloom at the surface. This, in turn, leads to an explosion of bacteria and zooplankton that feed on phytoplankton. For several weeks after a hurricane passes through, the ocean experiences an increase in marine life. This attracts a variety of larger animals, including seabirds that fly toward storms to take advantage of the feast that follows in their wake.

As phytoplankton consume the available nutrients, they eventually begin to die off, as do some of the bacteria and animals that consumed them. Falling bits of these organisms travel deep into the ocean, where they support deep-sea ecosystems.

Wind-driven waves also increase the amount of oxygen in surface waters by promoting mixing between water and air. Hurricane-force winds can help move oxygen deeper into the ocean. But the amount of oxygen available to marine life may be limited if a storm churns up sediment from the seafloor. This is most likely to happen when a storm travels over shallow waters, such as a continental shelf.