UC San Diego

Coral reef benthic communities form a critical part of coral reef systems linked to human societies. Using a complex systems approach that highlights inter-dependencies between substrate-bound organisms competing for space and ecological patterns that constrain demographic and competitive processes, the coral reef benthic system is dynamically characterized from the coral colony scale to the island scale with numerical models and data analysis techniques. In Chapter 2, I quantify and analyze reef-building coral colony change with colony areal coverage and longevity. Using over 4,300 Caribbean colonies measured over 4.5 years, proportional change in area of smaller colonies was found to be greater than for larger ones, following expectations of allometrically constrained growth. In terms of longevity, larger colonies lived longer than smaller ones, an effect that was lessened by colony fission and fusion, indicating these processes could confer a survival advantage. Overall, the results support a critical dependence of coral colony demography on size and morphology. In Chapter 3, I analyze the effect of spatial patterning on reefscape change over decadal time spans. Using a cellular model that simulates the interactions between four benthic functional groups, I find that reefscape (dm-km) dynamics can be categorized robustly with four distinct stages, including a transient stage dominated by nonlinear competitive dynamics. Increasing levels of colony spatial aggregation (clumpiness) results in a longer duration transient stage, prolonging arrival to the steady state. Results have potential implications for reef monitoring and restoration; for example, high initial aggregation slows loss in degraded reefs and low initial aggregation accelerates growth in healthy reefs. In Chapter 4, I describe derivation of a novel island-scale continuum coral reef model based on the cellular model used in Chapter 3. Numerical solutions of the resulting twelve coupled nonlinear partial differential equations (describing change of functional group fractional covers, nondimensional boundary lengths between functional groups, mean colony size and fish biomass density) match key aspects of the cellular model, as well as producing emergent patterns that go beyond what is observed in the cellular model. In Chapter 5, I describe a novel framework for using these results to build models of coupled societal-reef systems.