Understanding marine life is as important as understanding life of fish and habitat. Environment is divided into spatially into the pelagic division (http://en.wikipedia.org/wiki/Pelagic_zone) and benthic division (http://en.wikipedia.org/wiki/Benthic_zone).
But the currents in the ocean play an important role in all sea life, and interestingly enough, only one current, the West Wind Drift, goes around Earth completely uninterrupted by continents. The gulf stream influences eastern United States, south America’s east coast, Europe’s west coast and Africa’s west coast.
Otherwise the other ocean currents go in circles, so whatever happens in Japan, ultimately effects western United States. Then you have the water mass which also influences the water and travel. http://en.wikipedia.org/wiki/Ocean_gyre
Seawater movements are very complicated. Surface currents, subsurface currents, vertical currents (like upwelling), down-welling (where water is sinking, like near the poles), and tides all contribute to the mixing of the oceans of Earth. Although we know a lot about the general currents, each particular place on Earth has its own unique specific currents, many of these seasonal.
If you were a marine animal and knew all the currents in the oceans you could travel everywhere from top to bottom and to every continent and island.
Knowing about the sea is what makes enjoying sea-life whether in its environment or on a plate.