The Johansen Fish Resilience Lab is stationed on the beautiful Moku-o-loe (Coconut) Island (http://www.himb.hawaii.edu), utilizing the state of the art facilities at Hawaii Institute of Marine Biology (HIMB) as well as the amazing coral reefs at our doorstep and throughout the Hawaiian Archipelago. Our research focuses on how tropical coral reef organisms react and adapt to natural and human-induced environmental stressors and include work to understand species habitat selection, range-shift, habitat invasions, and the environmental requirements of species to function and thrive. All of our work is designed to help preserve, restore and sustain coral reef ecosystems despite growing environmental disturbance. Our dedicated education and research-student training also encompass coral reef ecology, environmental stress responses of reef organisms, physiological tolerance, movement patterns and behavioral ecology of fishes.
WHY ARE WE LOSING FISH ?
Herbivorous reef fishes are critical for the resilience of coral reefs by promoting and facilitating the settlement, growth and survival of corals and coral recruits. The protection of herbivorous fishes is seen as an essential management tool for the conservation and protection of coral reefs, as reductions in herbivore abundance can lead to uncontrolled algal growth and degradation of coral habitat. However, long-term ocean warming and episodic marine heatwaves (i.e. discrete periods of extremely high ocean temperatures that can persist for days to months) pose a major threat to herbivores. Recent observations during heatwaves have documented sharp declines of >50% in the abundance of coral reef fishes across all trophic levels and a loss of herbivores on reefs exposed to extreme heating. We are presently working to assess the effects of ocean warming on herbivorous fishes (i.e. determine resilient and sensitive species), and to evaluate the degree to which heating may compromise the delivery of herbivore services – that is, to help maintain reefs in a coral-dominated state via the removal of algae, particularly during periods of coral bleaching.
Sediment tolerance thresholds:
Nearshore tropical coral reef are a source of vital ecosystem services to over 600 million people worldwide, providing fisheries, tourism and shoreline protection. Yet, along with global climate change, coral reef organisms are exposed to multiple local stressors related to human activities, including coastal developments and land-use practices that result in nutrient and sediment discharge to near-shore reefs. High sediment and nutrient run-off cause a loss of fish species (inclusive of many herbivorous fishes that eat algae), increased algal growth, and loss of coral. Consequently, sediment and nutrient run-off is now classified as one of the primary and most damaging threats to coral reefs worldwide, but this is also a threat that can be dealt with effectively at the local scale. To retain ecosystem health and minimize the risk of decline, there is a need for well-informed scientific information on which to base management relating to threshold limits of sediment discharge and establishment of water quality standards. We are conducting several multidisciplinary projects to clarify sediment impacts on coral reef fishes, by combining our in-house specialized expertise in field ecology, behavioral avoidance, and stress physiology of reef fishes. Our ultimate goal is to quantify the water quality condition required to maintain healthy fish populations on inshore reefs (incl. herbivores), and assist management and local communities in reaching those water quality conditions.
The coral reefs of the southern Persian / Arabian Gulf (PAG) are exposed to the most extreme temperatures of any coral reef ecosystem on Earth, with summer temperatures regularly exceeding 36C (97F). These reefs are exposed to conditions that are similar to those projected for most coral reefs under unabated climate changes in the years to come, and already seen during extreme heatwaves. One of the big mysteries of these PAG coral reefs is the fact that many reef fish species seem to disappear from visual censuses during seasonal extremes. Prevailing theory suggests that reef fishes may be migrating away from the reefs to deeper, cooler water to survive the summer months. Alternatively, they may become dormant within the reef matrix, only to emerge again once conditions improve. Over the next couple of years (2020-2022) we are putting this question to the test. Using the Arabian Gulf reefs as a natural laboratory for how many other coral reefs around the globe will fare under climate change and ocean warming, the outcome of this study will be informative to fisheries and environmental managers alike. For this project, the Johansen Fish Resilience Lab is working closely with Professors John Burt and Holly Shiels via New York University Abu Dhabi, UAE, to spearhead new coral reef research in the Arabian Gulf to investigate ecological and physiological trade-offs (costs and consequences) associated with survival under the extreme thermal conditions of the warmest coral reef on Earth.