SAIPAN, CNMI (20 Sep 2003) -- The volcanic eruption on Anatahan not only buried the island in ash and killed its vegetation but it also caused heavy sedimentation on the waters surrounding the island, resulting in massive coral deaths. Federal and local scientists fear that the impact of ash sedimentation on Anatahan's waters, its coral reefs and marine life would continue for many years. The scientists-who were among the group aboard the National Oceanic and Atmospheric Administration's Oscar Elton Sette ship-found this out during a scientific expedition in the Marianas. In certain areas, the scientists said they spotted not a single fish. Although the Emergency Management Office and the U.S. Geological Survey have reported that recent volcanic emissions had no ash content, the scientists said rainfall washes the thick layers of ash into the sea. "Rainfall continues to wash ash onto the reefs, and seas and ocean swells continue to remix this sediment in the water column and deposit it on the reefs. Coral reefs along the northern side were largely buried in ash with only the highest points protruding above," reads a portion of the progress report for the Marianas Archipelago Reef Assessment and Monitoring Program. The marine scientists had to bear with poor underwater visibility due to thick ash sediments in the waters. Poor visibility affected the quantification of fish communities at a depth of nine to 15 meters, the report said, although it described the fish groups as sparse. "No fish were seen along some transect lines," the report stated. "In contrast, a site along the western side of the island off a rocky cliff provided about 12-meter visibility and high hard-substrate relief, but was heavily coated with ash deposits with evidence of many corals recently killed and buried." | | On this side, the report noted sightings of many fish, including large ones. "Herbivorous parrotfishes and surgeonfishes were also present, in spite of reports of no living algae at the site. No other sites with workable visibility were found around the island, although the southern side was not surveyed because of even stronger seas and swell conditions." Scientists believe that before the massive coral deaths on Anatahan, its waters used to have well-developed reefs. The condition was evidenced by the "nice diversity of recently dead coral skeletons," they said. The scientists only found 10 to 15 species of corals on most sites, except for the southwestern side, where 44 coral species were documented. "The southwestern side had a high abundance of coral-dwelling commensals, such as the Christmas tree worm Spirobranchus giganteus," according to the report. "Sites on the northern side of the island were covered in deep ash, and visibility in the water column was reduced to less than a meter. Only two species of green algae were found growing on emergent rocks." Earlier, the Oscar Elton Sette's scientific mission also discovered that Maug, the second northernmost island in the Northern Marianas, has a submerged volcanic crater that is showing signs of activity. Marine monitoring conducted on the island showed that volcanic vents are releasing warm water. "Vents that released warm water (100oF +) and gas bubbles were prevalent at a site located inside the crater on the northern end of the east island. A layer of yellow silt, clinging to everything, also characterized the site." SOURCE - Saipan Tribune |
