Integrating a thermistor flowmeter and time lapse imagery to monitor sponge (Porifera) behaviour

A digital, four-channel thermistor flowmeter was developed as an experimental tool for measuring pumping rates in marine sponges, particularly those with small excurrent pores (oscula). The flowmeter is integrated with time lapse cameras and has an accuracy of ±5 mm s -1 over the range of 5–200 mm s -1 , a spatial resolution of 1.4 mm, and an adjustable temporal resolution of 5 seconds. Combining flowmeters with time lapse imagery yielded valuable insights into the contractile behaviour of oscula in Cliona orientalis, revealing four distinct oscula states: (1) osculum open with extended papilla, (2) osculum closed with extended papilla, (3) osculum closed with papilla retracted, and (4) osculum closed with papilla retracted and contraction of region surrounding osculum. Osculum area was positively correlated to measured excurrent velocities, indicating that sponge pumping and osculum contraction are coordinated behaviours. Diel trends in pumping activity and osculum contraction were also observed, with sponges increasing their pumping activity to peak at midday and decreasing pumping and contracting oscula at night. Short-term elevation of the suspended sediment concentration within the seawater initially decreased pumping rates by up to 90%, ultimately resulting in closure of the oscula and cessation of pumping. The thermistor flowmeter developed here will be a valuable tool to monitor behaviour, physiology and ecophysiology of sponges.

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