Concepts of Resilience
Two different concepts of resilience exist in coral reef science (Nÿstrom et al. 2008). The first concept, engineering resilience (Holling 1996; Gunderson 2000), refers to the capacity of a coral reef to return to its previous state after a disturbance, such as a major storm event or a disease outbreak (Nÿstrom et al. 2008). Although I will explore the concept of phase shifts in a later lab note, the term state refers to whether a coral reef is dominated by coral or a different benthic organism, such as algae. Coral reefs may experience fluctuations in the amount of coral over time (e.g., due to mortlaity caused by competition with other species such as algae) and experience different states. Engineering resilience measures the time it takes to return to that initial coral-dominated state (Nÿstrom et al. 2008). The other concept is ecological resilience (Holling 1973; Gunderson 2000), which describes the resistance of an ecosystem to change (Pimm 1984). More specifically, it is, "the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function" (Walker et al. 2004). If a coral reef experiences a disturbance (like a disease outbreak or storm event), then ecological resilience is the ability of individual corals or the coral community to resist change to a different state, such as an algal-dominated state (Nÿstrom et al. 2008). Ecological resilience expresses the difficulty (or ease) with which an ecosystem can switch between alternative stable states, with more resilient ecosystems having higher barriers to switching (Ives & Carpenter 2007; Nÿstrom et al. 2008). Engineering and ecological resilience and the capacities of the coral reefs of Easter Island and Salas y Gómez to resist and recover from natural and anthropogenic disturbances will be the main topics of my doctoral thesis.