The rise of long-sediment-laden algal turfs: an additional negative feedback process limiting reef resilience

In an era of increasing disturbances, understanding the capacity for coral reefs to recover and the drivers that underpin resilience is critical for predicting the health of future coral reefs. Traditional resilience paradigms for Western Atlantic reefs suggest that high herbivore biomass and low macroalgal cover are tenets of resilient systems. Yet, it is clear that some locations, such as Florida’s reefs, and potentially other locations, are not well explained by this paradigm. Here, we suggest that the proliferation and increased dominance of long-sediment-laden algal turfs (LSATs) create an additional negative feedback process that helps explain the compromised resilience of Florida’s reefs and further extends the existing Western Atlantic model. Collectively, coral mortality, reef flattening, and intense grazing appear to have created a series of negative feedback processes that reinforce a flat, sediment-laden benthos that impedes the recovery of already diminished coral populations. Importantly, feedbacks associated with LSATs could be strengthened in the presence of high herbivore biomass, thereby undermining foundational expectations of resilience based on grazing pressure alone. Here, we outline this destructive cycle and provide support for the mechanisms that drive these feedbacks. Although we focus on the ecological context of Florida’s reefs, our expansion of the conceptual framework will likely apply to other reef systems in the Caribbean with similar ecological attributes. Mounting evidence suggests that LSAT dominance represents a novel ecosystem state for Western Atlantic reefs.