We describe the design and construction of an underwater sensor actuator network to detect extreme temperature gradients. We are motivated by the fact that regions of sharp temperature change (thermoclines) are a breeding ground for certain marine microorganisms. We present a distributed algorithm using local communication based on binary search to find a thermocline by using a mobile sensor network. Experiments using a mote testbed demonstrated the validation of this approach.We also discussed the improvement of energy efficiency using a submarine robot as a data mule. Comparison between experimental data with and without the data mule show that there are considerable cost savings in the sensor network due to the data mule.