BUT WAIT, THERE'S MORE -
Ballast etc from cargo ships, oil spills, ...
http://en.wikipedia.org/wiki/Marine_pollution
Kelp Forests
Over the last century, they have been the focus of extensive research, particularly in trophic ecology, and continue to provoke important ideas that are relevant beyond this unique ecosystem. For example, kelp forests can influence coastal oceanographic patterns and provide many ecosystem services to humankind.
http://en.wikipedia.org/wiki/Kelp_forest