Understanding the distribution of plankton and inorganic aggregates in seawater lends vital insight into the dynamics of aquatic systems. Since the mid-60s, holographic imaging has held unique advantages for this application. In the July 8 issue of the Journal of Optics A: Pure and Applied Optics, UK researchers from Brunel University in Uxbridge and Aberdeen University in Aberdeen review the history of such imaging as well as their latest method using the HoloCam -- a camera that can capture in-line and off-axis holographic images of up to 100 liters of ocean water using a 532-nm, pulsed Nd:YAG laser and holographic plates. They report that the in-line holography is best suited for imaging 10- to 100-µm objects, while off-axis holography is superior for objects 500 µm and larger; however, both are suited for objects between 100 and 500 µm in size.