Two summers ago I participated on my first research cruise to the NWHI. As one of four benthic divers, I counted corals, identifying them to species, measuring their size, and estimating how much of each colony was alive and whether it was healthy or diseased. All surveys were done at historic monitoring sites that were marked with stainless steel transect markers and on this cruise we are re-surveying sites that we visited in 2008. Once again, I am measuring corals along the same permanently marked transects and I am looking forward to seeing how sites in the NWHI have changed over the last two years.
Out of all the reefs that we surveyed in 2008, the one that I was most excited to re-visit was FFS-12 located just south of Disappearing Island, a small sand spit in the southern region of French Frigate Shoals (FFS). In 2008, FFS-12 was characterized by massive tabulate coral, Acropora cytherea, which were so abundant that colonies often overlapped, creating a magnificent home for corals and other invertebrates. Acropora corals are extremely rare across the Hawaiian Archipelago but they are fairly common at FFS where in a few locations, such as FFS-12, these coral dominate the benthos.
As we approached the site from our small boat, I gathered my snorkel gear in preparation for our first task: to free-dive and locate the permanent transect markers. As soon as our boat driver gave the okay, I rolled into the water anxious to see the impressive table corals. Once the bubbles from the engine cleared, I dove down and immediately noticed a dramatic difference from my last dive at FFS-12. Instead of the magnificent field of pink table coral that we saw in 2008, the reef appeared gray and many of the large colonies were absent being replaced by dead coral and small fragments of live coral. Obviously, a major disturbance had occurred since 2008!
Indeed, the first major hurricane originating from the central Pacific since Hurricane Ioke in 2006, passed through the NWHI in late October, 2009. Hurricane Neki was downgraded to a tropical storm by the time it reached the NWHI on October 23, 2009, but the storm passed directly over FFS creating large southerly waves and strong winds. Little damage was reported at Tern Island, the only populated island at FFS; however the wind and waves generated by the storm caused Disappearing Island to… well… DISAPPEAR! These conditions likely caused the damage that we observed at the relatively shallow (30 feet) reef at FFS-12.
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While I was saddened by the large impact that Hurricane Neki had on one of my favorite reefs in the NWHI, it is important to view this event from its ecological as well as historical context. Hurricanes are natural phenomena and coral reefs have evolved ways to cope with these disturbances. Hurricane Neki was the first major storm in the Hawaiian Archipelago since Hurricane Iniki in 1992, and Neki’s storm swell created large, powerful southerly waves that are rare in the NWHI. Therefore, southerly reefs in the NWHI such as FFS-12 grew with relatively little disturbances for a LONG time which could explain the numerous large colonies that were common prior to October 2009!
In 2010, few colonies had diameters larger than 1 meter, with most colonies being fragments or broken pieces of former colonies. This is one mode of asexual reproduction called “coral fragmentation” where one colony is broken into smaller colonies which can reattach to the reef and begin to grow again. Fragmentation may be an important mode of reproduction for some coral species and may be especially important for corals in the NWHI because of the islands remote location that rarely receive coral larvae (babies) from other reefs in the Pacific (which is another mode of reproduction: sexual). Therefore, storms may be important for growth of the tabulate Acropora population at FFS, as they break up larger colonies and spread their fragments around the reef.
Only time will tell how the Acropora corals at FFS-12 will recover. The remote location and protected status of Papahānaumokuākea National Marine Monument ensures that recovery will not be complicated by anthropogenic activities such as coastal development and runoff, but this status does not safeguard these reefs from global climate change and related effects from ocean acidification. However, recovery may depend most on the frequency of large southerly waves events. Who knows, if the NWHI are spared from a major hurricane over the next decade or two, we may expect the reef at FFS-12 to once again be dominated by large tabulate corals and the extent of the reef may even grow in size!
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