Robert Paine showed the importance of predators in maintaining an ecosystem. The same effects are occurring at scale across the entire California coast right now. Massive numbers of Sea stars (starfish) have died[1] due to "Sea star wasting disease"[2] which is caused by Sea Star Associated Densovirus (SSaDV)[3].
No sea stars causes huge numbers of sea urchins which causes the disappearance of kelp forests. My favorite kelp forest to scuba dive in the Monterey Bay is now an urchin barren[4]. No fish, no sea otters, just sea urchins. I was there a month ago and it is gone.
[1]: http://news.nationalgeographic.com/2015/03/150401-urchins-se...
[2]: https://en.wikipedia.org/wiki/Sea_star_wasting_disease
[3]: http://phys.org/news/2014-11-densovirus-devastating-sea-star...