During back-to-back summers of 2015-16, a global ocean warming event reached the Hawaiian Islands and caused significant mortality of a broad spectrum of corals. The elevated ocean temperatures had a devastating effect on some coral species (e.g., Cauliflower coral; Pocillopora meandrina) yet had lesser effect on some of the more resilient coral species (e.g., mushroom, plate and disc corals). Naturally, everyone who became aware of the mass bleaching event hoped that this represent a one-time event. Sadly, this appears not to be the case.
Figure 1 illustrates seasonal changes in water temperatures since 1985 with the 2015-16 warming event shown as the uppermost red line. Then, water temperature peaked at > 84 oF (29 oC). At temperatures above 82 oF, corals typically become stressed and begin expelling their zooxanthellae symbiont. Without the presence of the photosynthetic symbiotic algae in their tissues, corals essentially become starved for nutrients and soon die; a process referred to as bleaching.
The summer and Fall of 2019 is shaping up to be as devastating or worse that 2015-16 (see uppermost black line in Figure 1). By mid-August, ocean temperature along the Kona Coast had reached 83 oF. The rate of increase in temperature (i.e., slope of this year’s change in temperature) exceeds that observed in 2015-16 and naturally this has everyone very concerned.
To further understand and to help mitigate this warming trend, several individuals and government agencies have swung into action and are making efforts to work together. The purpose of this blog is to highlight one individual’s effort; that of Dr. Greg Asner (Arizona State University).
Dr. Asner is currently mobilizing all resources within Hawaii to monitor the process of bleaching across the Hawaiian Islands in real time. He has requested that individuals and organizations post observations relating to bleaching on a Website: hawaiicoral.org. He has requested that individuals post details on degree of bleaching at varying dive sites within Hawaii using the following scoring system:
Level 1: Some corals look pale but are not bleached white.
Level 2: Small portions of corals are bleached white.
Level 3: Large areas of coral are bleached white.
Corals suffer from many stressors in addition to warming oceans. To minimize as many stressors as possible and to thereby reduce the likelihood for bleaching, Dr. Asner requests that we adhere to the following code-of-behavior:
- Avoid touching the reef while diving, snorkeling or swimming
- Do not stand or rest on corals
- Use sunscreens with no oxybenzone or octinoxate
- Boaters should use mooring buoys, or anchor only in sandy areas and keep anchor chains off the reef
- Fishers should reduce or stop their take of herbivores, such as parrotfish, surgeonfish, and sea urchins. Herbivores clear reefs of algae, which over-grow and kill corals during bleaching events
- Take extra precaution to prevent contaminants from getting to the ocean like dirt from neighboring earth work, chemical pollution from fertilizers, and soaps and detergents getting to storm drains
To support this program, Aquatic Life Divers will be completing two Eco-Dives each week (Tuesdays and Sundays) and uploading their observations to hawaiicoral.org during the coming weeks. We encourage individuals and groups to join our dives and participate in monitoring. The dives will include both in-water monitoring activities and on-boat educational activities.