Biology Trumps Management: Feedbacks and Constraints of Life-History Traits

Abstract

The geologic record suggests a diverse array of reef-building corals will survive increasing CO₂, but the relative prevalence of different types will shift and the reefs will become degraded and eroded. Although many corals may not go extinct, if pH decreases effectively, reef ecosystem services will deteriorate because bioerosion will accelerate and, for some coral species, net skeletal construction will require more energy when the aragonite saturation state decreases. A similar pattern of many genera of reef-building scleractinian corals surviving, but with relatively little reef accretion, was seen through the roughly 140 million years from the Late Jurassic to the late Paleogene when the calcite seas (Mg/Ca mole ratio <2) and pH <7.8 were unfavorable for aragonitic reef accretion. The geologic record suggests that the corals most vulnerable to extinction were the fast-growing branching species because the traits that provide fast growth have tradeoffs with traits that provide tolerance of stressful environments. Iteroparous animals such as corals are adapted for survival under stressful conditions at the expense of fecundity. Surveys have recorded widespread decreases in living coral cover, but the less visible decrease in fecundity from stress may be more insidious to population recovery. Reduced fecundity and less dense population distribution can act synergistically to produce Allee effects in sessile animals such as corals. Natural coral-reef ecosystems give the appearance of inverted trophic pyramids, but when fished down by about 80 %, recovery has usually not happened, possibly because the larger individuals in the populations were a major source of fecundity. Although biomass of eukaryotes appear to be in inverted trophic pyramids, the turnover and energy is in the form of standard pyramids and although large individuals in the upper trophic levels are especially sensitive to exploitation, subsistence economies can be maintained by harvesting the medium-sized individuals. Large individuals matter more than population biomass because of the distinct roles of large individuals in ecological processes maintaining coral-reef ecosystems and the relatively large reproductive potential of big fishes. The functional traits of both the coral-reef ecosystem and its component animals provide a greater potential for exploitation by globalization in a service-based economy than with an extractive economy, as exemplified by Palau.