Sensitivity of marine ciliates (Protozoa, ciliophora) to high thermal stress

Abstract

The range of sensitivity of marine ciliates to temperatures approaching lethal maxima was determined under a variety of biotic and abiotic conditions. Twelve species of ciliates representing different taxa, sizes and modes of locomotion were examined. A simple heating apparatus consisting of a heated microscope stage was employed to subject the organisms to acute heat stress.

Heat resistance in the ciliates was influenced by cultivation temperature, salinity and nutrition. Temperatures of LD₅₀ ranged from 31.5 °C for Uronema marinum Dujardin to 39 °C for Condylostoma arenarium Spiegel. When cultivated at low temperatures (10 °C), Euplotes crassus (Dujardin) was more resistant to heat shock at high salinities (35‰) than at low salinities (15‰). The effect of salinity on thermal resistance diminished as the ciliates were cultivated at higher temperatures (30 °C). Thermal sensitivity depended also on the temperature of acclimation. E. crassus was more sensitive to heat stress when it was cultivated on single strains of bacteria than when it was cultivated on a mixture of bacteria. Furthermore the type of bacteria offered as food also influenced its sensitivity to heat shock.