Behaviors evolve rapidly to environmental stressors and behavioral flexibility may allow fish to be resilient to the loss of coral reefs following mass bleaching events.
Coral reefs are structurally complex habitats with the highest diversity of fish anywhere on the planet (Sale, 2015). In recent decades, coral reefs have experienced extreme and rapid degradation due to global warming-induced bleaching events, algal overgrowth, and destruction by fisheries and tourism practices (Hodgson & Liebler, 2002; Lough, 2008; Madin, 2015). When coral reefs are degraded, up to 75% of reef fish species experience a significant decline in population size; for over 50% of species, the decline is greater than half of the original population size (Jones et al., 2004). Dead reefs can range from corals that have died but are still structurally intact to those which have become rubble. Rubble reefs do not have the structural complexity that provides habitat for many reef-associated species and, as such, host a less diverse assemblage of reef fish (Komyakova et al., 2013).
Fish with high behavioral flexibility or well adapted suites of behavior may be most resilient to the loss of healthy coral reefs.
With environmental change we expect natural selection to occur, such that organisms become well suited to their new habitats. However, coral loss due to mass bleaching events occurs rapidly. It may take many hundreds of generations for organisms to become morphologically adapted to a new environment, but behaviors are known to respond quickly to changing conditions. Behaviors are known to act as mechanisms for reducing mortality in changing environmental conditions. For example, fish can behaviorally respond to changes in predation risk by adopting more caution or risk aversion. We know that when coral reefs die some species become locally extinct faster than others. Specifically, fish which only feed on live corals are the first to go. Fish that rely on the structure of live coral for places to rest or reproduce are also quick to be lost. In theory, fish that can modify their behaviors to the use of collapsed reefs, or to be able to find alternative food sources may be better able to survive. My aim with this area of my research is to test the hypothesis that Fish with high behavioral flexibility or well adapted suites of behavior may be most resilient to the loss of healthy coral reefs.
Bali: The ideal location to measure behavioral response to coral loss
From April – May 2011, the Bali Marine Rapid Assessment Program (BMRAP) surveyed 27 locations in Bali to calculate a mortality index for coral and describe the benthic composition at each location (Lazuardi et al., 2013 Table 4.1). The benthic structure was categorized as hard coral, soft coral, dead coral, coral rubble, algae, other fauna, or abiotic at each site. Among the 27 sites, the percent cover of live coral ranged from 22-74% (Lazuardi et al., 2013 Table 4.3). The coral mortality index (Lazuardi et al., 2013 Table 4.4) ranged from 0.02 (low mortality) to 0.56 (high mortality). Some of the locations in the northwest region of Bali surveyed in 2011 were revisited in 2016, and a further coral decline of on average 40% was observed (Suparno et al., 2019). In recent years the Allen Coral Atlas project has used daily satellite imagery to generate a benthic map of the entire perimeter of Bali, where the substrate is categorized as coral, sand, rubble, rock, seagrass, or microalgae. There are large regions of coastline in Bali where each substrate type can be found. I will visit each of the 27 locations surveyed in the BMRAP and collect videos of reef fish swimming and behaving naturally on reefs using the stereo video camera system I will have built.