Being able to figure out what marine protected areas are for, and even where they are, requires imagination. It’s not like on land, where we can see the parks and pass through their entrances and read the helpful explanatory signs.

In the ocean, the boundaries are more ephemeral. Someone draws them on a map, but they’re impossible to see when you’re down in the water, swimming among the corals and marveling at the sea slugs.

It’s harder still to know precisely what’s goes on in a marine equivalent of a park or see what creatures live there and how they’re faring. And measuring the effects of marine parks is more complicated than, say, doing a wolf survey, or assessing the tree canopy. Many marine parks around the world are in immensely complex, ferociously deep bits of the ocean. They’re fiendishly tough to study and only a few researchers do it well.

Personally, I hadn’t given marine parks any thought until I was in Townsville, Queensland a few years ago doing research on the Great Barrier Reef. About 99 per cent of the reef is a world heritage site, all of it contained within a tightly monitored Australian park. Current rules ban fishing of any kind in about a third of its vast area and fishing in the rest of it is tightly controlled through licenses, permits, quotas, restrictions on gear and size of fish caught, and some closures within the fishable areas. The Australians take their reef very seriously indeed.

Once I dived on it, I could see why. Visible from space, the largest living structure on the planet, the Great Barrier Reef is a magical place, considered one of the wonders of the world and I spent hours exploring some of its northerly reaches, enthralled at the dense coral cover, the brilliant schools of fishes, the turtles floating nonchalantly through the water. It all looked so healthy.

Not so. The lower two-thirds of the reef, especially, is in trouble and getting worse. A 2014 status report explains that despite all the protection, the outlook for the Great Barrier Reef as a whole is “poor.” It has deteriorated since the last assessment in 2009 and “is expected to further deteriorate in the future.”

The biggest threat to the Great Barrier Reef? The report says it’s something park managers have little control over: carbon dioxide. The build-up of greenhouse gases in the atmosphere is slamming the reef. The water is warmer, bleaching the corals, often killing them. That warmth makes creatures flee to cooler waters, shredding the complex food chain.

Carbon makes the water more acidic, devastating vulnerable young marine creatures and stressing many that make body parts out of calcium carbonate – shells, reefs, bones, teeth. Already the ocean is more acidic than it’s been in 55 million years. And the extra carbon in the atmosphere makes the climate more volatile, prone to more cyclones and other extreme weather, all of it damaging to the reef.

So I’ve asked myself: why the heroics to enforce it as a protected area? Why the global push to create even more marine parks, including in Canada? Why not work on reducing the use of fossil fuels as the ultimate answer?

I’ve asked people whose work I respect, including Sabine Jessen at the Canadian Parks and Wilderness Society, Josh Laughren of Oceana Canada, the Canadian academics Isabelle Côté, Natalie Ban and Paul Snelgrove, Paul Marshall of the Great Barrier Reef Marine Park Authority, Steve Fletcher, head of the marine program at the United Nations Environment Programme, and many others.

It comes down to the concept of triage. Setting aside some of the most spectacular and most endangered bits of the ocean from harmful human activity is what we can do right now. We may not be able to cure the cancer, but we can treat the lump. At its most enlightened, making parks may even be, Fletcher said, a way to protect parts of the ocean we know will be severely affected soon. But all the scientists know marine parks are not going to be enough in the long run.

Over time, the only way to preserve life as we know it in the ocean – including all those fish we rely on for protein – is to curb carbon emissions.

The scientists I’ve been speaking with are crossing their fingers that we’ll do that soon enough that some small pieces of vibrant ocean will still be around to resurrect the whole system. 

Click here to explore the marine areas that are protected by Parks Canada or the Department of Fisheries and Oceans Canada. While Canada contains more marine areas that are protected in some capacity than those shown here, they are overseen by some combination of the provinces, territories or First Nations.