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A question of coral

With coral under siege worldwide, Lau Island reefs offer clues to their protection.

© CI/Mark Erdmann

By Douglas Fenner
June 5, 2017

Editor’s note: The living backbone of the world’s reefs, coral is suffering. Destructive fishing practices and warming waters are killing coral around the world, most notably Australia’s Great Barrier Reef, which has seen historic die-offs in the past year.

With experts scrambling to determine why some reefs are thriving while others struggle, the team of scientists on the expedition to the Lau Islands were anxious to get a glimpse at the health — and diversity — of the region’s coral species. As coral taxonomist Douglas Fenner writes, the expedition left the team with as many questions as answers.

Two of us recorded coral species diversity on the recent Conservation International cruise in the Lau Islands; Ron Vave photographed as many different corals as possible, and I recorded species names, took many photos, and collected a few samples. We do this because we love coral reefs, with their beauty, their fabulous diversity of organisms, and their importance to human communities: Coral reefs protect shorelines from wave and storm erosion, and are the chief source of protein and food security for coastal people.

But even a moderate amount of fishing can have major impacts on coral reefs, including a reduction in the number and size of fish that eat algae. Algae compete with corals, and when too many algae-eaters are removed, the algae can overgrow and kill corals; when corals die from other causes — such as bleaching caused by warmer waters — algae grow over the dead corals and make it hard for new corals to get a foothold.

As Mark Erdmann described, reef health was variable in the sites we visited. My interest, though, was in the coral species themselves.

We survey species on coral reefs because the more species are present, the more species can be protected by a marine protected area. As human pressures on coral reefs increase, we want to make sure that high-diversity, functioning coral reef ecosystems remain for future generations, and can continue to provide benefits to people.

What we found

This survey found 206 species of coral, a good number for this part of the Pacific.

Our surveys of coral species in the Lau Islands found six species that had not been found in Fiji before and another nine that may be species that haven’t been found in Fiji before, but need confirmation from coral skeleton samples. (Coral species are defined based on their skeletons, so secure identification may require skeleton samples.)

One exciting species is Euphyllia paradivisa. Until a few years ago, it was known to exist only in the Coral Triangle, an area bordered roughly by the Philippines, eastern Indonesia, northern Papua New Guinea and the Solomon Islands.

Then, I found a colony in American Samoa and photographed it, many thousands of miles from “home,” the only locations it was known from. It had a distinct, copper color. The colony we found here, on our last dive in the Lau Islands, has that same color. After the first colony was found in American Samoa, several more colonies were found there with a different color. The American Samoa discovery seemed to be a huge puzzle — how could it be so far from home?  Why was the species not known between American Samoa (to the east of the Lau Islands) and the Coral Triangle (far to the west)? The discovery here helps bridge that gap, and suggests that there just hasn’t been enough searching in the gap between American Samoa and the Coral Triangle to find it. It illustrates that while we now know much more about which corals live where then we did just a couple decades ago, we still have much to learn.

Another exciting find is what we think may be Pavona diffluens, a species originally known only from the Red Sea in the Middle East. Then a coral taxonomist based in Guam discovered what seemed to be this species in Guam and then found it in American Samoa; later I found colonies in American Samoa, and now a few colonies in the Lau Islands. More study will be necessary to determine whether this is really Pavona diffluens, or a new similar species.

Several corals — as many as 20 — could not be identified in the water. Examination of their skeletons in consultation with the scientific literature may reveal either that they were named long ago in some very obscure publication and are currently not recognized, or that they are new species. One such coral is a knobby little coral with a very distinctive surface. Another has finger-like branches that are quite rough and prickly.

There are actually several corals that look like this last species, but with small variations in shape. It is not yet clear how many species there are in this group, but most of the possible new species are at least somewhat similar to this one.

The fieldwork is just the beginning. Now begins the long process of studying the photos, samples and literature to determine the species of these corals. What we learn could help enable us to protect these reefs for a long time to come.

Douglas Fenner is a coral taxonomist who accompanied the expedition.

Top photo: Douglas Fenner surveys hard coral diversity on Navatu reef.