Remove the algae-eating fish under these conditions, and you might as well have poisoned the coral directly. This urchin appears to have been the last line of defense against the algae after the progressive elimination of other algae-eating creatures. The first to go may have been the green sea turtle. Now endangered, the turtle once apparently roamed the Caribbean in immense herds, like bison on the Great Plains. The removal of its competitors must have given the urchin a great deal of room, and for most of this century it was one of the reefs' most common denizens.
Contemporary history offers no precedent for a die-off of that magnitude in a marine animal.
The urchin is reportedly back in evidence, at least in some areas of its former range, but until its relationship with the pathogen is better understood, it won't be possible to define its long term appetite for algae. With the algae, the pollution, and the warming waters, the Caribbean is becoming an increasingly hostile environment for the organism that has shaped so much of its biological character. The first such epidemic, called black-band disease, was detected in 1973 in Belizean waters. The bottom layer secretes highly toxic sulfides which kill the coral. The complex creeps very slowly over a head of coral in a narrow band, leaving behind only the bare white skeleton.