The effect of environmental factors on swimming activity insarsia tubulosaM. Sars (hydrozoa)

Two types of experiments were conducted to determine the effect of six environmental factors on the amount of time Sarsia medusae spend swimming (swimming activity). Sarsia housed in containers in groups of four, swam significantly more than either Sarsia housed in pairs or individually. This effect disappeared when the water volume per individual was held constant. Physical contact with other Sarsia or with the walls of the container is thought to be responsible for the increased activity of Sarsia in groups or in small volumes of water. A 2 × 4 factorial design was used to determine the effect of temperature, time since mechanical disturbance, starvation, and chemical food stimuli on swimming activity in Sarsia. No significant main effects or interactions were observed, due to the large standard deviation of the mean (25.05 ±13.65%) swimming activity. Mechanical disturbance at the beginning of the observation period tended to cause a trend toward lengthening interonset intervals. Sarsia's crumple response occurs most often at the end of swim bouts. It is suggested that it serves as an object‐avoidance response, as well as in defense.