Resurveying Hawaii after a major coral bleaching event

Image: Getting ready to dive with the SVII



The XL Catlin Seaview Survey team has gathered again in Hawaii to revisit our study sites in four of Hawaii’s main islands: Big Island, Maui, Molokai, and Lanai.


This is our third visit to these reefs since mid-2015, and each time our reaction after the dive has been different. On our first trip, the excitement of diving in the Hawaiian reefs built up day-by-day as we explored diverse reef systems, dominated by colourful coral species amongst lava rocks. During this first trip, we noticed corals had just started to bleach at very incipient levels. But as temperatures built up during summer to above the normal maxima, which coincided with masses of warm water stationary around Hawaii, we had witnessed the onset of a major and global bleaching event.  



A major transformation


During our second trip, we observed a major transformation of the reef, where colourful and picturesque landscapes had turned bright white. Although we are now on our third visit to the reefs here, the team aboard wait anxiously for our divers to return with news of their experiences.


We have already completed the first few dives along the coast of the Big Island, Maui, Molokai and Lanai on this trip, and the aftermath of coral bleaching is highly variable. On one hand, there is no doubt the thermal anomalies during the past summer have left a profound scar on Hawaiian reefs, where mortality has been highly noticeable in some reefs (> 50%). An eerie feeling descends upon the team after these dives.


On the bright side however, other reefs in areas apparently more dynamic, in terms of oceanographic climatology, seem to have exhibited much less change. Species such as the cauliflower (Pocillopora spp) and the lobe corals  (Porites lobata) are amongst the most affected, while finger (Porites compressa) corals have shown little-to-no change. Species such as the rice corals (Montipora cf capitata) were highly bleached (close to 100%) during our second evaluation, but they have shown little change, with certain exceptions such as reef sites in Northern Maui.



Evaluating the impact


During this trip we will be evaluating about 35-40 reef sites, across about 60 km of reef surveyed on the main islands of Hawaii. This data will allow us to evaluate overall impact of such thermal anomaly on reef systems, as well as what the attributes of reef communities and surrounding coastal conditions could alter the response of these reefs to such thermal anomaly. Such information will be freely available from our online data tool, the XL Catlin Global Reef Record: