From the Hensen net toward four-dimensional biological oceanography

The development of quantitative zooplankton collecting systems began with Hensen (1887 Berichte der Kommssion wissenschaftlichen Untersuchung der deutschen Meere in Kiel 5, 1–107; 1895 Ergebnisse der Plankton-Expedition der Humbolt-Stiftung. Kiel and Leipzig: Lipsius and Tischer). Non-opening closing nets, opening closing nets (mostly messenger based), high-speed samplers, and planktobenthos net systems all had their start in his era — the late 1800s and early 1900s. This was also an era in which many of the fundamental questions about the structure and dynamics of the plankton in the worlds oceans were first posed. Fewer new systems were introduced between 1912 and 1950 apparently due in part to the two World Wars. The continuous plankton recorder stands out as a truly innovative device developed during this period (Hardy 1926b Nature, London 118, 630). Resurgence in development of mechanically-based instruments occurred during the 1950s and 1960s. A new lineage of high-speed samplers, the Gulf series, began in the 1950s and a number of variants were developed in the 1960s and 1970s. Net systems specifically designed to collect neuston first appeared in the late 1950s. During the 1960s, many focused field and experimental tank experiments were carried out to investigate the hydrodynamics of nets, and much of our knowledge concerning net design and construction criteria was developed. The advent of reliable electrical conducting cables and electrically-based control systems during this same period gave rise first to a variety of cod-end samplers and then to the precursors of the acoustically and electronically-controlled multi-net systems and environmental sensors, which appeared in the 1970s. The decade of the 1970s saw a succession of multi-net systems based both on the Bé multiple plankton sampler and on the Tucker trawl. The advent of the micro-computer stimulated and enabled the development of sophisticated control and data logging electronics for these systems in the 1980s. In the 1990s, acoustic and optical technologies gave rise to sensor systems that either complement multiple net systems or are deployed without nets. Multi-sensor systems with high data telemetry rates through electro-optical cable are now being deployed in towed bodies and on remotely operated vehicles. In the offing are new molecular technologies to identify species in situ, and realtime data analysis, image processing, and 3D/4D display. In the near future, it is likely that the use of multi-sensor systems deployed on autonomous vehicles will yield world wide coverage of the distribution and abundance of zooplankton.