Oceans form two-thirds of the surface area of our planet. Our understanding of this environment even after several decades of research is best described as rudimentary. The watery abyss is home to the world's largest and most diverse biological ecosystems. Monitoring of these ecosystems and the study of the physical and biological evolution of the oceans is of paramount importance to our increased comprehension and understanding of the oceans. Efficient monitoring relies on the collection of data over long periods of time and in diverse sea conditions. Stationary or moving sonar systems have already proven invaluable for this task. However, most of these systems are fixed in their mode of operation, possessing little or no flexibility. Thus, when the environment changes data retrieval often becomes difficult or impossible. Changing the characteristics of the monitoring device to match the local sea conditions is a possible solution to this problem. In this paper the hardware and software implementation of a system that realises this function is presented together with some preliminary transmission tests in the Mediterranean Sea. The system, VERTLINK is designed to collect, store and transmit physical and bio-acoustical data to an end-user. The system, a half-duplex underwater communication link, com- prises two units-a sea-bed unit and a surface unit. The sea-bed unit, under the control of the surface unit, records oceanographic data and then transmits it to the sea-surface unit. The latter is linked to a computer station on-board a survey vessel via a physical cable or to shore station by means of a radio link. Using this system the end-user is able to change the way the sea-floor unit acquires and transmits data. The modulation rate/technique can be changed from 2-DPSK to 8-DPSK, allowing data retrieval to be changed according to sea noise conditions. The power level can be varied from 20% to 100%, to achieve more efficient use of power resources and the sea-floor unit can be told to release.