In the wake of the epidemic, filamentous algae, which the sea urchins ate, exploded across the reefs. St. Croix saw a 27 percent increase in algal biomass within five days of the sea urchin die-off. In the course of two years, Jamaica’s reefs increased in algal cover from 1 percent up to 95 percent. More algae left less room for new coral colonies to recruit; 23 years later, the reefs of the region still echo with the effects, appearing so radically redesigned that many no longer exist as coral-dominated systems at all but as seaweed-dominant systems akin to farms of undersea lettuce. Even more significant, these changes appear to be permanent, since the primary surviving predators of the filamentous algae—herbivorous fishes—have been, and continue to be, extensively overfished by humans in the region. Diadema antillarum has not recovered either, a victim apparently of too few animals scattered over too wide an area to effectively spawn.
Across the world ocean, marine diseases are on the rise, fueled by, among other things, the desertification of Africa, which raises huge volumes of dust that off-loads bacterial and fungal spores into the weakened seas. Many coral diseases have appeared more frequently in the past 10 years, including white-band disease, black-band disease, dark-spots disease, red-band disease, white plague, white pox, yellow blotch disease, and so on. Photographs of reefs from the 1930s show little or none of these infestations.
With or without pestilences, coral reefs are under assault, and the exhaustive 2004 Status of Coral Reefs of the World warns that global warming is the single greatest threat to corals, with 20 percent of the world’s reefs so badly damaged they are unlikely to recover and another 50 percent teetering on the edge. Within the next 50 years, massive coral bleaching events on the order of the 1998 El Niño, which damaged or destroyed 16 percent of the world’s reefs, will become regular, possibly annual, occurrences. Sadly, most of the so-called nurseries of the sea face similar prognoses. Fifteen percent of the world’s seagrass beds have disappeared in the past 10 years alone, depriving marine species—from juvenile fish and invertebrates to dugongs, manatees, and sea turtles—of critical habitats. Likewise, kelp beds are dying at alarming rates; 75 percent are gone from Southern California alone—victims of, among other things, the demise of sea otters that regulate populations of kelp-eating sea urchins.
Among the most frightening news for coral reefs is the increasing acidity of the ocean as a result of rising levels of carbon dioxide. Scientists at the National Oceanic and Atmospheric Administration recently estimated the ocean has absorbed 118 billion metric tons of CO2 since the onset of the Industrial Revolution—about half of the total we’ve released into the atmosphere—with 20 to 25 million more tons being added daily. This mitigation of CO2 is good for our atmosphere but bad for our ocean, since it changes the pH. Studies indicate that the shells and skeletons possessed by everything from reef-building corals to mollusks to plankton begin to dissolve within 48 hours of exposure to the acidity expected in the ocean by 2050.
Coral reefs, buffeted by so many stressors, will almost certainly disappear. But the loss of plankton is even more worrisome. Collectively, marine phytoplankton have influenced life on earth more than any other organism, since they are significant alleviators of greenhouse gases, major manufacturers of oxygen, and the primary producers of the marine food web. Yet because many phytoplankton produce minute aragonite shells, these pastures of the sea may not survive changing pH levels. Zooplankton, meanwhile, are largely composed of the larval forms of all the ocean’s other life-forms—from fish to squid to shellfish—whose calcium carbonate constructions are also unlikely to survive changed pH levels*. By facilitating radical changes in these, the immense populations of the very small, we might as well erase the world as we know it, one bone, one seashell at a time.
YEARS AGO, WHILE I WAS FILMING aboard a small sailboat in the Turks and Caicos Islands, someone on the crew found a message in a bottle floating miles from any land. Since we did not readily have the means to open the barnacle-encrusted cap, the skipper took it to the stern of the boat, steadied his aim against the rocking of the waves, and with one blow from a hammer knocked the glass neck off. Four of us crowded close, yet none could catch the paper as it accidentally slipped overboard. Four of us dove in, but none could find the note in the currents swirling underwater.