AME 37:75-83 (2004)  -  doi:10.3354/ame037075

ABSTRACT: The temperature response of the oligotrich freshwater ciliate Meseres corlissi, a widely distributed but rare species, was investigated in laboratory cultures with the small cryptophyte Cryptomonas sp. as food. Experiments were conducted at saturating food levels and temperatures ranging from 12.5 to 30°C. The following ecophysiological parameters were measured: ingestion, growth and production rate, cell volume and gross growth efficiency. All these parameters peaked at temperatures ranging from 20 to 30°C. Encystment was also recorded in the temperature response experiments. Cyst formation was low (<1% of all ciliates) at temperatures above 20°C, increased to 18% at 20°C and reached a maximum (~80%) at 15 to 17.5°C. Food limitation had little impact on encystment at 25°C. Additional experiments at variable food levels yielded the numerical and functional response of the species at the temperature optimum (25°C). The experimental results suggest that M. corlissi is an opportunistic warm water species, able to cope with changes in food and temperature. When adequate environmental conditions are met, this ciliate should be highly competitive in freshwater habitats. The sparse findings of this species from natural habitats suggest, however, that although M. corlissi is globally distributed, it is not ubiquitous. The factors that restrict the occurrence of M. corlissi in freshwater remain unknown.

KEY WORDS: Adaptation · Ciliates · Oligotrichs · Cysts · Temperature response