Marine Science Faculty Publications

Influence of Environment on the Test Shape of Amphistegina

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Test shape in Amphistegina spp. grown in culture is influenced by light availability and water motion. Saturation light level for A. gibbosu was between 6 and 14 μE/s m2; growth rates at 14 and 40 μE/s m2 were 5.9%/d and thickness-to-diameter (T/D) ratios were 0.36. At reduced light levels, growth rates and T/D ratios were reduced down to 3.9%/d and 0.31 at 3.9 μE/s mz. Saturation light level for A. Zessonii was between 14 and 40 μE/s m2; growth rate at the higher level was 7.8%/d and T/D ratios were 0.41. Likewise, growth rates and T/D ratios were reduced at reduced light levels, down to 1.3%/d and 0.36 at 1.6 μE/s m2. The thickest tests, with T/D ratios of up to 0.5, were found in both species when grown at saturation light levels with gentle water motion. Sectioned tests revealed that differences in T/D ratios are a direct result of differences in secondary lamellar thicknesses; secondary lamellae of Amphistegina subjected to water motion were as much as 50% thicker than those of individuals grown without water motion.

Symbionts isolated from A. gibbosa from Puerto Rico were small diatoms of the genus Nitzschia. Although specific identification of the symbiont could not be made because sieve plates were lost, the symbiont is distinct from three other Nitzschia spp. found in Indo-Pacific Amphistegina.

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Journal of Foraminiferal Research, v. 16, issue 3, p. 224-231