I suspect that my publications on coral-reef fishes are highly cited because they address two fundamental questions that span the broad fields of marine ecology, fisheries, and conservation biology. First, what are the mechanisms that drive and regulate population dynamics? Second, what are the mechanisms that maintain local species diversity? These questions are related because population regulation is essential for species to persist. I was drawn to coral reefs as model systems for exploring these questions because the warm, clear, shallow water allows one to conduct detailed, long-term observations and manipulative experiments.

When I began my coral-reef research 25 years ago, the raging debate was whether competition or chance was the dominant ecological process regulating populations and allowing species to coexist. Combined with the work of many colleagues, our research has revealed that it is predation that has a central role in affecting both outcomes on coral reefs. Predatory fishes often cause regulating density-dependent mortality of juvenile fishes, and can keep the population densities of their prey below levels where competition leads to local species extinctions. Importantly, we have found that high species diversity of predators is important for regulating prey populations and maintaining high species diversity of prey because of complementary, synergistic effects among predatory species. The ramifications of these findings beyond understanding coral reef ecosystems are immense. Marine fisheries typically target and greatly reduce the abundance of predatory fish, which may be the most important regulators of many marine ecosystems.

Currently, we are expanding the spatial and temporal scales of our studies from local populations over years to regional metapopulations over generations. This expanded perspective will clarify the relevance of small-scale experimental studies typical of marine ecology to the large-scale observations and management challenges of fisheries biology. My advice to the next generation of researchers is to hold the paradox of integrating a variety of novel theoretical and empirical approaches while staying well-grounded in basic natural history. Nothing can replace direct, first-hand knowledge of a study system. For those studying marine fishes, it is imperative to get wet.

Mark A. Hixon, Ph.D.
Department of Zoology
University of Oregon
Corvallis, OR, USA