Rising sea levels may decrease sunlight penetration—and thus reduce photosynthesis—in the deepening coral seas. And increased flooding is almost certain to bring more pollutants from land to sea.

On top of all that, oceans everywhere are now threatened by overfishing, pollution, and invasive species.

In the ocean at large, some 90% of predators in the top trophic levels have been eliminated by overexploitation (a.k.a., fishing pressure). Such heavy losses disrupt the interdependent relationships needed to sustain each community. For example, without grazer fish to keep it in check, algae overgrows on coral. Fishing pressure inflicts other wounds as well: Bottom trawling can decimate seabeds, crushing or burying organisms that live close to the beds and uncovering those that need to remain buried (see LaunchPad Chapter 31). Cyanide spray, used to stun fish for aquarium collection, kills most fish and coral that encounter it. And dynamite, also used in fishing, physically destroys reefs and other ecosystems around it.

Meanwhile, sediments and high levels of nutrient runoff from agricultural areas are boosting algae production and creating algal blooms, which in turn smother corals and block sunlight, reducing photosynthesis. Trash from both land and sea and petroleum from ships and boats are also polluting the marine environment at unprecedented rates.

Invasive species pose yet another threat; more than 80% of ocean harbors around the world now host at least one invasive species. Whether they arrive in the ballast water of ships, escape from aquaculture pens, or are moved in the aquarium trade, the outcome is the same: They wreak havoc on aquatic ecosystems. “We don’t even know how much damage they’re doing,” says Slattery, who has studied the impact of invasive lionfish on reefs near The Bahamas. “The fact is, we know much less about the oceans than we do about land. But if you think about it, that makes protection even more vital, because we need to err on the side of caution.” INFOGRAPHIC 29.7

29-18

29-19