Reaction of the movement of hydroplasma in the colony to a prolonged thermal shock and subsequent recovery at the optimal temperature in <i>Dynamena pumila</i> (L., 1758)

It was previously established that the movement of hydroplasma in many species of hydroids is not unidirectional, but pulsates in opposite directions in the common tube-like body (coenosarc) of the colonial organism. However, this pulsating reversible distribution system is effective in moving food particles. We studied the impact of a sharp increase in environmental temperature and a five-day thermal shock on the performance indicators of the distribution system of the colonial hydroid Dynamena pumila: the period and regularity of hydroplasma pulsations, range of movement, growth, coenosarc pulsations, etc. After an abrupt increase of 10 °C in the temperature of the water in which the colonies of the hydroid were kept in the laboratory within several hours, the activity of the distribution system increased (the frequency and amplitude of hydroplasma pulsations and the extent of flows), but already on the second day the growth of colonies stopped, and the coenosarc pulsations of hydroplasma flows became irregular with significant pauses. On the fifth day of thermal shock, the movement of hydroplasma stopped. Within a day after the cessation of the thermal shock, pulsatory movements of hydroplasma in the stolons resumed, and two days later they almost returned to normal, except for the insufficient extent to move food throughout the colony. During this time, the growth of the colonies has not yet recovered. The reaction of hydroplasmic movements in the stolons of D. pumila turned out to be advanced compared to morphological indicators and growth. Thanks to this, it becomes possible to more accurately and quickly determine the body’s response to an increase in ambient temperature.