Nortek Aquadopps Two Acoustic Doppler Current Profilers (ADCPs) are deployed in the reef to measure the currents sponges are exposed to. ADCPs emit sound waves and listen for the echoes that bounce back from particles moving through the water. The particles’ motion creates a Doppler shift in those echoes and allows the instruments to measure the speed and direction of currents above them. These ADCPs are set to measure current speeds from 50 cm to 5 meters above the seafloor, which is what the reef sponges would experience.
Nortek Vector with Optical Backscatter Sensor (OBS) The Vector is an Acoustic Doppler Velocimeter (ADV) and is used to calibrate the thermistor probes in situ. It emits pulses of sound from the yoke of the metal part of the instrument, then listens for the echoes bounced back off of particles in the water with its three prongs. The particles’ motion results in Doppler shifts that the instrument uses to calculate speed and direction of the water where it is measuring. The Optical Backscatter Sensor (OBS) detects particles in the water, which gives us a measure of sediments suspended in the water that can potentially clog a sponge or cause it to arrest its pumping.
Thermistors We use thermistors to compare water flow rates in ambient water to the excurrent flow coming out of a sponge osculum. The thermistors are custom instruments that use a Wheatstone bridge to detect temperature changes – an increase in the speed of water flow results in a drop in temperature (just like how one becomes chilled when standing in the wind).
“Thermoxy” paired thermistor/oxygen sensors Three thermistors are coupled with oxygen sensors to measure the oxygen consumption (and therefore metabolism) of the sponges that goes along with the pumping rates measured by the thermistors. The oxygen sensors are Pyroscience Firesting probes that use RedFlash technology as an optode-based oxygen detection. The oxygen sensors are custom-built instruments – each has a watertight housing with the fiber-optic cables in penetrator connectors to the Firesting.
Optical Backscatter Instruments Three optical backscatter instruments were deployed as standalone instruments. These OBS’s are the same types as those attached to the Vector and the Aquadopp. They detect changes in darkness in the water and the ‘murkiness’ reflects how much sediments are in the water.