EVALUATION OF A REMOTELY OPERATED VEHICLE (ROV) AS A TOOL FOR STUDYING THE DISTRIBUTION AND ABUNDANCE OF ZOOPLANKTON

Conventional methods for measuring 2ooplankton distributions are too l aborious and time consuming to permit sufficient temporal and spatial resolution in many instances. An ability to make more efficient and pr ecise measurements would be useful. We evaluated the potential for usi ng the video system of a commercially available remotely operated vehi cle (ROV) to measure the distribution and abundance of zooplankton by calibrating ROV counts with counts based on a conventional sampling pr ocedure (a Schindler trap), and by using an ROV to measure the density of zooplankton in a small lake. As configured here, this particular R OV was suitable for measuring the density of the cladocerans Daphnia a nd Holopedium. It was also suitable for assessing the distribution, bu t not absolute densities, of Chaoborus and Leptodora. Image quality wa s inadequate for quantitative estimates of copepod (Diaptomus minutus) abundance, and prevented us from studying behavioral responses of cop epods to the vehicle. We conclude that the ROV has at least three usef ul features: it can be used to locate patches of those species that ar e imaged effectively; a large number of samples (videotapes) can be co llected almost synoptically with high spatial resolution; the ROV enab les in situ observation of zooplankton. The ROV also has three importa nt limitations: the small image volume makes it difficult to study rar e organisms; inadequate image resolution precludes studies of relative ly small organisms (e.g. the calanoid copepod D. minutus); zooplankton respond to the presence of the ROV.