Benthic community distribution in the Enewetak Atoll lagoon, Marshall Islands
Abstract:Benthic lagoon communities at Enewetak Atoll below 30 m depth are poorly known. Using a lowered camera system, submersible dives, and SCUBA, one hard and four soft substratum biological communities were identified. The soft substratum communities, termed 1) "open sand," 2) "algal film," 3) "algal flat," and 4) "button corals," tend to intergrade. Sharply delineated patches of dense Halimeda algae were encountered on level sandy bottoms, Based on 183 evenly spaced photographic stations, the lagoon bottom below 30 m was 85% soft and 15% hard substratum. Considerable bioturbation, principally by callianassid shrimps, was evident in benthic photographs and from in situ observations. Water at northern lagoon stations seemed more turbid, and the bottom few m of the water column often had an apparently increased particulate load throughout the lagoon. Halimeda-dominated algal flats may be limited in depth to about 50–55 m due to light penetration and may account for the reduced contribution of Halimeda plates to sediments in the central lagoon at 55–65 m depths. All previous studies at Enewetak and Bikini Atolls have ignored 1) the heterogeneous nature of lagoon benthic communities, 2) bioturbation, and 3) vertical fractionation of sediment by grain size when considering vertical distribution of radionuclides in the sediment column. The published estimates of radionuclide inventory in the Enewetak lagoon sediments could be in considerable error, and a reevaluation of all radiological data for lagoon sediments relative to the ongoing processes in the lagoon is needed.
Document Type: Research Article
Publication date: January 1, 1986
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