The Johansen lab is stationed on the beautiful Coconut Island (http://www.himb.hawaii.edu) and our research in Hawai'i is dedicated to understanding how endemic and invasive coral reef fishes react and adapt to natural and anthropogenic environmental stressors. A primary focus of research is the consequences of catchment run-off (sedimentation, turbidity, industrial effluent) and rising ocean temperatures on near-shore reef fishes, utilizing the state of the art facilities at HIMB as well as the amazing coral reefs at our doorstep and throughout the Hawai'ian Archipelago.
Sediment tolerance thresholds:
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 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. We are planning several multidisciplinary projects to provide a greater understanding of sediment impacts on coral reef ecosystems, by combining our in-house specialized expertise in field ecology, behavioral ecology, and stress physiology of reef fishes. Our ultimate goal is to assist management and communities is restoring and retaining the health and productivity of these important socio-ecological systems.
Marine Heat Waves:
Herbivorous reef fishes perform ecological services that 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, 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.
The coral reefs of the southern Arabian Gulf are exposed to the most extreme temperatures of any coral reef ecosystem on Earth, with summer temperatures regularly exceeding 36C (97F). One of the big mysteries of these 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. 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, after successfully securing a highly competitive UAE Research and Innovation Grant. 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.
The Johansen Lab is also presently working closely with Professors John Burt and Holly Shiels via New York University Abu Dhabi, UAE, to spearhead coral reef research in the Arabian Gulf. The primary research focus in UAE is to investigate ecological and physiological trade-offs (costs and consequences) associated with survival under the extreme conditions of the Arabian Gulf (the warmest coral reef on Earth).