Growth, Coenosarc Pulsations, and Hydroplasm Movement in the Colonial Hydroid Dynamena pumila (L., 1758) Placed in Flow-Through and Nonflow Cuvettes

Abstract

The coenosarc pulsations of the stolon and hydroplasmic flows (HFs) in the colonial hydroid Dynamena pumila (L., 1758) have been recorded in flow-through and nonflow, shallow cuvettes via time-lapse video microscopy. The water in the flow-through cuvette was refreshed during every 24 s. Each episode was video recorded for 2 h. Eleven indicators were used to compare hydroid reactions to maintenance in flowing and nonflowing water: the period and amplitude of pulsations of the stolon growing tip; the hourly stolon growth; the period and amplitude of transverse coenosarc pulsations; the period of unidirectional HF rate pulsations; the maximum velocity of HFs to and from the stolon tip; the distance of particle transfer per act of unidirectional HF; the volume of displaced hydroplasm per HF; and the percentage of the rest ratio in coenosarc pulsations and hydroplasm movement. On the whole, no significant changes in the coenosarc pulsations or in the growth and displacement of the hydroplasm were detected when they were compared sequentially in the same colonies in nonflowing and flowing water. At the same time, there were no changes in the growth, the frequency and amplitude of the transverse pulsations of the coenosarc, or the activity and extent of the hydroplasm currents. However, it was found that the period of growth pulsations increases by 20% in the regime with water exchange in comparison with the previous regime without flowing water. The period of HFs in the stolon increases by 42%, and the maximum current velocity decreases by 20% in flowing water. As a result, the calculated volume of moved hydroplasm in the stolon for one HF decreased by 30% in flow conditions.