Technical abstract:
Humans have fundamentally changed key environmental drivers that structure ecological communities, creating an urgent need to better understand and predict the resilience of communities to these impacts. Nowhere is this need greater than for tropical reefs, where globally, and for at least five decades, communities have rapidly, and in many cases unexpectedly, shifted away from coral to other, often less desirable community states. On healthy tropical reefs, loss of coral often results in dominance by closely-cropped algal turf that can ultimately recover to coral. However, fishing of herbivorous fishes and increased nutrient and sediment supplies from developing watersheds can produce ‘ecological surprises’—the emergence of novel algal states that resist a return to short turf, even after human impacts cease. Understanding resilience, here defined as both resistance to and recovery from disturbance, of short turf communities is intrinsically linked to understanding the resilience of the novel emergent communities, which are often dominated by long turf or macroalgae. However, transitions among states, both forward and backward, are currently unpredictable, a limitation we hypothesize may be due not only to current environmental conditions, but also by the order of human impacts that have altered key ecological processes, a theory that has never been evaluated. We propose to interrogate the importance of the sequence of human impacts to community transitions and their resilience on tropical reefs. This proposal has four elements that advance fundamental understanding of community resilience to human impacts. First, a manipulative field experiment tests the effect of the order of human impacts on the resistance of short turf communities. This design sequentially increases fishing pressure, enhances nutrient supplies, and increases sedimentation, in all possible combinations of order, with no-change and simultaneous change treatments as controls. Second, recovery is measured following termination of experimental manipulations. This, in combination with Part 1, assesses both components of resilience and elucidates how order of impacts affects these key community properties. Third, to understand the mechanistic underpinnings of resilience, the resilience of both the original short turf and the emergent macroalgal states are assessed by measuring stabilizing feedbacks in all experimental plots. Fourth, for states that transition to macroalgae, algal traits are measured and related to stabilizing feedbacks to generalize results to other tropical reefs.
Principal Investigator: Peggy Fong
University of California-Los Angeles (UCLA)
Co-Principal Investigator: Caitlin Ryan Fong
University of California-Santa Barbara (UCSB-NCEAS)
Co-Principal Investigator: Halley Froehlich
University of California-Santa Barbara (UCSB)
DMP_OCE2413969_Fong_Fong_Froehlich (82.46 KB)
07/22/2024