Areas of Research
Our group studies coral reef ecosystems to answer fundamental questions of population biology, trophic dynamics, and spatial ecology.
Marine ecosystems offer unique opportunities to study basic principles of ecology, complementing insights gained from terrestrial systems. Coral reefs, in particular, facilitate detailed study of population dynamics and species interactions. We focus our efforts to understand the role that reef fish play in controlling ecosystem dynamics, with specific interests in predator-prey and competitive interactions.
Given the conservation significance of coral reef ecosystems, we make efforts to link our research with tangible problems that are of interest to the management community. We are currently applying ecological studies to answer two core questions:
- What type of management maximizes the long-term yield of tropical reef fisheries?
- Which members of the reef community are most valuable for buffering coral reef ecosystems from the growing effects of global climate change?
Our research is focused in two regions. In the islands and atolls of the remote central Pacific, we explore ecological dynamics across gradients of anthropogenic and oceanographic conditions. This area includes a number of uninhabited islands, offering unique opportunities to study the ecology of so-called ‘baseline’ reef ecosystems, namely reefs in the absence of local human activities like fishing and pollution. On the coral reefs of the more densely populated Caribbean (largely on Curacao in southern Caribbean), we study how human activities can affect coral growth or be managed to improve coral growth and recovery.
We believe that ecologists are essential members of the resource management community, offering advice regarding the likely consequences of current or proposed management strategies. Through collaboration with social scientists and through active outreach efforts, we strive to communicate our results to a broad cross-section of our community.
Growth and productivity of coral reef fish
A long history of targeted fishing has reduced the prominence of apex predators in the sea. However, historical studies and surveys of remote island areas reveal that marine predators can dominate marine ecosystems. On coral reefs, the biomass of predatory fishes (including sharks, snappers, and groupers) can exceed that of prey fishes creating an inverted trophic pyramid. Thermodynamic constraints assure that such a ‘top-heavy’ trophic structure can only be supported through a ‘bottom-heavy’ pattern of productivity, with lower trophic level organisms growing more quickly than the apex predators. The outstanding questions remain, what are the detailed patterns of productivity that support predator-heavy reef communities, and what are the functional consequences associated with removing apex predators?
We have been studying fish assemblage structure from coral reefs across the central Pacific using underwater visual survey techniques. We use these data to describe systematic patterns of change associated with predator removal, including changes in longevity and species composition. We also collect detailed life history information, including size-at-age and length-weight relationships, for many little-studied Pacific fish species. Combining these data with tailored statistical estimators, we have the capacity to test basic hypotheses relating assemblage structure to the potential fisheries productivity of these tropical multi-species fisheries.
Fish, benthos, and microbes – the trifecta of coral reefs
There are thousands of species that share coral reefs, and these species interact in countless ways. Because of the many relationships among these species, the overall ‘health’ of a coral reef cannot be assessed by focusing only on one group of organisms. Fish depend on the many species living on the bottom (including corals, seaweed, and the many mobile invertebrates) for shelter and food. The species living on the bottom (composing the so-called ‘benthos’) survive because marine bacteria maintain stable water chemistry. But the individual health of species on the benthos and of fish can be compromised by dramatic changes of the microbial community.
We study the linkages among the fish, benthos, and microbes on a number of coral reef ecosystems from across the Pacific. The United States Pacific Remote Insular Areas offer a rare opportunity to study truly intact coral reefs. Due to their federal protection from fishing and other human impacts, the atolls support among the healthiest reefs documented. For example, Kingman and Palmyra in the northern Line Islands support a massive fish assemblage dominated by top predators, a benthic assemblage composed largely of reef-building coralline algae and corals, and clear water with only limited microbial abundance and activity. The structure of these reefs stands in stark contrast to nearby Kiritimati and Tabuaeran, Kiribati Line Islands that support reefs with much less fish mass (with a particularly notable absence of large predators), an abundance of fleshy algae, and a highly active microbial community. We use this natural laboratory to study the ecological feedbacks between fish, the benthos, and microbes that are critical for determining the fate of coral growth in the face of global climate change.
Coral reefs of the tropical US Pacific – a natural laboratory
Coral reefs provide important services to people living near the coasts across the tropics, but in turn, human activities change the structure and the functioning of the reefs upon which coastal populations depend. In order to best use and maintain the natural resources of coral reefs, it is essential that we understand the structure and functioning of reefs from across a spectrum of human use and activity. The Coral Reef Ecosystem Division of NOAA (PIFSC) has been monitoring the coral reefs of the US Pacific for the past decade, quantifying key aspects of the biology, chemistry, and physics of over 40 islands and atolls of the tropical Pacific. The Pacific Islands region is NOAA’s largest geographical management area, and includes much of the nation’s most biologically diverse and pristine coral reef ecosystems. In three archipelagos, these nearly pristine reefs are neighbored by islands with human populations that have altered the structure of the reef community. As such, the US Pacific provides a replicated ‘natural experiment’ of the effects of human activity on coral reef structure and functioning.
With the support of the joint NSF and NOAA funding program, CAMEO our group has begun a collaboration with colleagues at the Coral Reef Ecosystem Division. Our aim is to synthesize these monitoring data to gain fundamental insights into the ecology of Pacific coral reefs, with specific reference to the roles played by human stressors at the local (e.g., fishing, pollution) and global (e.g., climate change) scale. This project will use the comprehensive set of ecosystem data to test and validate reliable indicators of coral reef health, thereby establishing clear metrics for the improved management of coral reefs worldwide.