Cozumel Island, MexicoDescending into the clear blue water of the Colombia Reef, off Cozumel in Mexico, there are two ways to look at what greets you. One is as a fantastic, calming world of peace and harmony, so different from our hectic lives on shore. The soft corals sway in the current, colorful fish swim lazily by, and turtles float happily above.

But this is a mirage. The reality is more like a war zone. It’s every critter for itself: The angelfish eat the corals, some of which strike back with tiny harpoons; the barracudas eat the angelfish, which hide behind sponges. And the sponges, says Joseph Pawlik, are secretly plotting to take over the whole reef.

Pawlik, an ecologist and leading sponge