Professor University of California, Los Angeles, California, United States
Abstract: Coral reefs have experienced multiple disturbances leading to coral-algal phase shifts. In the South Pacific, this shift is often toward Turbinaria ornata, a relatively large, physiologically- complex macroalga with traits that facilitate the formation of dense patches that have expanded rapidly in abundance, range, and habitat usage since the 1980s. T. ornata’s patches are alternate stable states to corals that exhibit stabilizing internal feedbacks through provisioning of associational refuge from herbivory for juveniles. We tested the usefulness of a trait-based ecological approach to exploring this stabilizing feedback by examining traits of large ( >10 cm) and small (< 3cm) algal thalli from within and at the edge of 21 T. ornata patches. Height and wet weight, related to resource acquisition, confirmed the difference in thalli sizes. Toughness was measured to examine resistance to herbivory. To establish whether there was a tradeoff in ecological strategies that could be detected using functional traits, we measured tensile strength to examine resistance to physical disturbance as patches are known to flourish in high wave-energy environments. PERMANOVA detected differences across all traits between thallus size but not whether they were within or at the edge of a patch. T-tests comparing individual traits across size revealed that small individuals were about half as tough and half as strong as large individuals. Thus, small thalli are more susceptible to herbivory and disturbance compared to the larger thalli protecting them, demonstrating a stabilizing within-patch feedback. Overall, our results show that trait-based approaches are useful methods for detecting internal stabilizing feedbacks that exist within well-studied systems without the need for large-scale or long-term experiments. As coral reefs further shift to algal dominated environments, determining how T. ornata’s modification to environmental drivers changes traits of juvenile congers and associated species is an imperative step to examining what novel suite of ecosystem functions will emerge.
