where fish biomass is <100 g/m2 but may exceed the combined biomass of all lower trophic levels of fishes when fish biomass exceeds ≈300 g/m2. Thus, when fish biomass is high, the fish trophic pyramid is upside down (Jackson, 2006; Sandin et al., 2008).
Reefs in Florida surveyed in 2005 (Newman et al., 2006) were also surveyed in 1880 (McClenachan et al., 2007). Only 30% of the 20 species that were common in 1880 were still common in 2005, and 40% of the formerly common species were absent in 2005. Most remarkably, 4 of the 20 formerly common species in 1880 are now listed as endangered or critically endangered, including the Nassau grouper (Epinephalus striatus), which was the mainstay of fish sandwiches in the Florida Keys for too many decades to the point that this once fantastically abundant species is entirely fished out.
Fishes and corals are not the only animals to have declined precipitously. Harvests of Florida commercial sponges peaked in 1924 at >3 million tons, and then crashed to nearly zero in the 1940s when stricken by disease (McClenachan, 2008). Today, the sponges have recovered to ≈11% of their abundance in the 1880s. The formerly abundant sea urchin Diadema antillarum also declined by 90–95% because of an outbreak of an unidentified disease in 1983 (Lessios et al., 1984), and much of the mortality of elkhorn and staghorn corals in the 1970s and 1980s was also due to outbreaks of disease (Aronson and Precht, 2001; Knowlton, 2001). Green turtles have declined by well over 99% from approximately 90 million in the 18th century to perhaps 300,000 today, and hawksbill turtles declined as precipitously from approximately 11 million to 30,000 (McClenachan et al., 2006). The total population of the extinct Caribbean monk seal in the 18th century was ≈230,000–340,000, abundance so great that all of the remaining fish on Caribbean coral reefs would be inadequate to sustain them (McClenachan and Cooper, 2008).
The restriction of abundant fish biomass to protected reefs shows that MPAs do work, oceanographic factors notwithstanding, so long as they are large, well protected, and enforced (Mora et al., 2006; Newman et al., 2006; Knowlton and Jackson, 2008). The more difficult question concerns the potential of protection from fishing to help to restore coral populations in the face of epidemic disease and global climate change (Friedlander and DeMartini, 2002; Hughes et al., 2003, 2007; Knowlton and Jackson, 2008). As for oysters in estuaries, overfishing, increased macroalgal abundance, and degraded water quality act synergistically to decrease coral growth, recruitment, and survival. Increased abundance of fleshy macroalgae and algal turfs may kill corals directly by overgrowth or indirectly by leaking