The ocean is being bombarded from several directions and the effects can be not only predicted with computer models but can be seen right now first-hand. Some time ago I ran a post on the impact of domoic acid on wild life (and potentialy humans, too). Domoic acid is a toxin produced by phytoplankton algae and the issue presented in the post was that man's "treated" sewage waste products, pumped far off shore were, in essence, over-fertilizing the algae and thereby increasing the level of algae-based toxins.
We know about avoiding consuming shellfish during certain months due to annual concentrations of these and other shellfish toxins. And we avoid swimming in the ocean during periods of "red tides" when the phytoplankton population explodes. Unfortunately, sealife does not know or cannot avoid exposure and so there has been an increase in poisoned animals, in particular seals and sea lions which are susceptible to domoic acid's neurological effect..
Just this past weekend, a diver friend of mine opted for a hike at Palos Verdes peninsula in Southern California when dive conditions were not good. In just one hike around the point, he came across eight dead mature sea lions. All dead due to shellfish neuro-poisoning? Perhaps. in fact, based on reports from local marine mammal centers, very likely.
But treated sewage is not the only source of the problem. Algae can also be fed by the increasing levels of CO2. On the positive side, there are blueprints for algae-based alternative fuel plants to channel the greenhouse gases they produce during processing back into their algae crop. But outside of those controlled environments, in the open sky and open ocean, CO2 produces ocean acidification, which is gaining a lot of attention lately, and feeds the phytoplankton algae, adding to a vicious cycle.
Another example of the cascade effect of our actions, greenhouse gas emissions not only disrupt global temperatures and raise the ocean's ph level above acceptable limits, but also over-feed phytoplankton which impacts sealife and our commercial use of shellfish.