By Chris Adams

The world’s oceans are vast – and so are their problems.

Don Boesch, president of the University of Maryland Center for Environmental Science, said that human activities are hurting oceans in multiple ways, from depletion of the world’s fisheries to melting ice caps and the resulting sea level rise.

“I don’t know one ocean scientist who isn’t just blown away by how much documented change there is in the world’s oceans,” Boesch said. Despite the political debates that surround it, among scientists “it’s not a matter of controversy.”

Boesch is one of the nation’s top oceanographers and served on a federal commission studying the BP Deepwater Horizon oil spill, which damaged the Gulf of Mexico.

As for the impact of climate change: There have already been changes in polar regions, shifting species distributions, coral bleaching. Some of those impacts might not be reversible.

Boesch described how oceans play a large role in the world’s climate by storing carbon dioxide, methane and heat; how fish have been depleted by overfishing and bycatch unintentionally getting caught up in fishing nets; how ocean acidification is changing the pH composition of some waters and impacting sea life; and how plastics and other trash have created watery landfills around the globe.

“Plastics are now something of great concern,” he said, describing major rafts of tangled plastics floating in the world’s oceans.

And he talked about three major “dead zones” – in the Chesapeake Bay, the Baltic Sea and the Gulf of Mexico – where humans are trying to reverse the impacts that have killed life in vast areas of those bodies of water. In some, there have been changes for the better, although there is a long way to go before those dead zones are eliminated.