Benthic Dynamic Modeling

Exploring how natural and human-caused factors determine winners and losers among the seafloor community­

Ecological modeling provides the mathematical toolkit with which to explore relationships between benthic dynamics (how organisms living on the seafloor change through space and time) and biophysical forcings (environmental factors, such as currents and water temperature, that impact biological organisms). Complementing the empirical work of RTI scientists at Palmyra Atoll, we are developing a suite of models to describe the details of benthic dynamics. Importantly, our modeling approach focuses on understanding the factors that alter vital rates of benthic organisms; for example, we are investigating how temperature, nutrients, consumers (and combinations thereof) alter patterns of recruitment, growth, and survivorship of key benthic taxa such as corals and algae.

The goal of our effort is not simply to describe the relationships among multiple forcings and benthic vital rates, but instead to discern the relationships most likely to affect emergent ecological dynamics on coral reefs – for example, how herbivores’ (fish, urchins etc.) grazing habits impact coral growth and death rates. In particular, our interest is in detailed study of those relationships that are strongest and thus most likely to affect the resilience of coral reefs across natural and human-made gradients in forcings. To achieve this goal, we must quantitatively assess the biological significance of each functional relationship.

Since beginning this work, we have explored how resilience is impacted by the spatial behavior of grazers, such as herbivorous parrotfishes. Using a numerical modeling approach, our results showed that more spatially constrained herbivores (i.e., those that forage over smaller areas) make a reef more resilient by providing a favorable environment on which coral juveniles can settle and grow. Our results also showed that the diet of the herbivore community is primarily determined by their space use, which provides insight into herbivore diet evolution.

We have also been using a stereotypical representation of the major disturbances on coral reefs (e.g., storms, coral bleaching, disease outbreak, crown-of-thorns starfish outbreak) and two structurally different models of the coral reef community, to demonstrate that coral communities respond in different ways to variations in the nature, frequency, and magnitude of disturbance events. For example, our results suggest that when considering hydrodynamic disturbances (i.e. storms, hurricanes), the frequency of the disturbance determines if reef community diversity will be impacted whereas the intensity of the disturbance determines how the reef community diversity will be impacted.

The Benthic Dynamic Model team plays a central role in RTI by synthesizing the knowledge gathered by other groups, advancing theoretical ecology, and , eventually, developing scenario-based forecasts of the reef composition for conservation professionals and managers.

This research is being co-led by Dr.Dylan McNamara from the University of North Carolina, Wilmington, and Dr. Stuart Sandin from the Scripps Institution of Oceanography, whose team includes Dr. Yoan Eynaud from the Scripps Institution of Oceanography.