After the mass mortality of Diadema antillarum, researchers began searching intensely for data on this unprecedented disturbance, as the coral reef ecosystems began to change almost more quickly than scientists could monitor them. For all the controlled studies that had been performed on reef organisms in the past few decades, this sudden and accidental change could provide vastly more data on reef interactions. The reefs became a living laboratory, demonstrating one tremendous urchin removal experiment.

Data began accumulating almost immediately. By the end of 1984, researchers had already proposed what is currently held as the only supported hypothesis about the origin of this mortality: that the mortality was caused by a species-specific biological pathogen that spread by urchin contact and by water currents in the Caribbean Sea, Atlantic Ocean, and Gulf of Mexico (Lessios et al. 1984a). Lessios et al. (1984a) also predicted correctly that the absence of Diadema antillarum would be reflected in significant changes in algal, coral, and echinoid communities, and by altered patterns of bioerosion.

Actually, the latter prediction is actually more of an extrapolation, because the type of changes that Lessios et al. predicted were already happening in 1984. In fact, at some research sites, the direct impact of urchin mortality on algal abundance and community structure was alarmingly visible within a few weeks or months of the mass mortality event. Levitan (1988a) noted a 30-fold increase in algal biomass at St. John, U.S. Virgin Islands, just 6 months after the urchin mortality.

Elsewhere the response of algae was similar. Figure 10 illustrates the transition in Jamaican coral reef surfaces from primarily coralline cover to primarily algal cover. Note that the transition has not shown any significant reversal during the decade following the mass mortality. The subsequent response of a limited increase in fish herbivory was also widely documented. Researchers in Panamá reported threefold increases in the population density and grazing intensity of several herbivorous reef fishes in response to the sudden increase in available algal food resources (Robertson 1991). This increase in fish density, however, was from a very small stock, and it leveled off before the herbivory of fishes could ever make up for the lack of urchin herbivory.