Symbiont Loss ("Bleaching') in the Reef-Dwelling Benthic Foraminifer Amphistegina Gibbosa in the Florida Keys in 1991-92

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Amphistegina spp are dependent upon diatom endosymbionts for growth and calcification. Symbiont loss was discovered in A. gibbosa in September 1991 in the Florida Keys when > 80% of post-juvenile ( > 0.6 mm in diameter) individuals were mottled or bleached in samples collected from depths of 10-30 m. Populations at Conch Reef were sampled between September 1991 and December 1992. Normal specimens dominated during winter months; symbiont loss resumed in March, peaked in June, with normal juveniles common by autumn. Population density in September 1992 was c5% of the density found in September 1991. Suppressed asexual reproduction, congenital deformities, and abnormal shell damage were observed in affected populations. Symbiont loss was also observed in Amphistegina spp. from Australia, Jamaica, Hawaii, and Palau in 1992. In the laboratory, symbiont loss can be induced in post-juvenile individuals in weeks by exposure to above-optimum intensities of fluorescent lights and within days by exposure to low doses of ultraviolet radiation. The injection of large quantities of volcanic aerosols into the atmosphere at low latitudes by Mt. Pinatubo in June 1991 may have altered the spectral quality of solar radiation reaching the sea surface in 1991 and 1992. Amphistegina individuals, which actively seek optimal visible light intensities, may be particularly vulnerable to an increase in ultraviolet radiation relative to available visible light.

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Oceanographic Literature Review, v. 42, issue 8