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You are here: /main/research expeditions/CReefs 2006/journals/Day 9

Day 9
October 16, 2006
By Andy Collins, NOAA, NOS, NWHIMNM -
Education and Outreach Specialist

Zoanthids, corraline algae, and red algae. Photo: Gustav Paulay.
Zoanthids, corraline algae, and red algae.
Photo: Gustav Paulay.

Yesterday was the most productive day yet for the collections by scuba and snorkel. The survey site was one of the back reef areas on the North side of the atoll. The edge of an atoll is composed of three distinct areas – the fore reef, the reef crest and the back reef. The fore reef area faces the open ocean and slopes upward to the reef crest at or near the surface. This area typically takes the full force of open ocean swells and breaking waves and it is inhabited by organisms that can tolerate high energy, and a lot of water movement. On the interior of the atoll, beyond the reef crest, is the back reef. This area is more protected, and in the atolls of the Northwestern Hawaiian Islands it is usually quite shallow and inhabited by encrusting corals and corraline algae that form a maze of coral mounds and ridges interspersed with channels of sand and rubble. It is a complex, shallow habitat that is permeated with holes, and many places for smaller reef fish and other organisms to hide. Back reef areas on the north side of the atolls are exposed to intense wave energy from large northwest winter swells that wash over the reef crest, and may not exhibit this growth pattern. The survey team observed this in the back reef area surveyed yesterday, where instead of corals and corraline algae occupying most of the space, it was occupied by zoanthids (colonial anemones). Zoanthids feed by capturing planktonic organisms from the water with their stinging tentacles, and they may benefit from a high energy environment with high water flow. As an interesting aside, the chapter on zoanthids in John Hoover’s book on Hawaii’s invertebrates mentions that some zoanthids possess a potent toxin and “Hawaiian warriors in the Hana district of Maui often smeared the tips of their spears with zoanthid mucus before battle. Wounds from such spears were usually fatal.”

A well-camouflaged crab hidden among the algae. Photo: Gustav Paulay.
A well-camouflaged crab hidden among the algae. Photo: Gustav Paulay.
The invertebrate teams collected at least 25 species of crabs from the site surveyed yesterday, and the algae team collected species of branching corraline algae not seen before. The coral rubble in this area was more eroded, and several species of polychaetes (worms) were found, many more than were found in the denser and less eroded rubble from previous days sampling. This made Leslie Harris, our worm expert, very happy. The area was also productive for ascidians (sea squirts) and Tito found five or six species. Jim Maragos, our coral expert, found three new corals he had not seen at French Frigate Shoals before, and this is surprising since Jim has been working in the NWHI for several years, but this is really the first time he has had the opportunity to do intensive surveys on a large diversity of habitats at the atoll. Jim has been on several of the annual monitoring cruises to the NWHI, but these cruises usually try to cover a large area to assess health of the ecosystems and monitor changes at specific sites. The assessment cruises have not really given him the opportunity to do broader exploration. The flavor of this whole expedition is quite different from what has come before, and with the experts aboard not only collecting organisms but identifying them, it is giving us a whole new understanding of the biodiversity of French Frigate Shoals.


*All images and information from French Frigate Shoals are provided courtesy of the Northwestern Hawaiian Islands Marine National Monument, Hawaiian Islands National Wildlife Refuge, the Northwestern Hawaiian Islands State Marine Refuge, and NOAA's Pacific Islands Fisheries Science Center in accordance with permit numbers NWHIMNM-2006-015, 2006-01, 2006-017, and DLNR.NWHI06R021 and associated amendments.

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