Intercomparison of zooplankton (net) sampling systems: results from the ICES/GLOBEC sea-going workshop Journal Article

Authors: Skjoldal, Hein Rune; Wiebe, Peter H.; Postel, Lutz; Knutsen, Tor; Kaartvedt, Stein; Sameoto, Doug
Article Title: Intercomparison of zooplankton (net) sampling systems: results from the ICES/GLOBEC sea-going workshop
Abstract: An inter-comparison and evaluation of methods for sampling and determination of zooplankton distribution and biomass was conducted in a fjord environment (Storfjorden at Møre, Norway) from 2 to 13 June 1993. The inter-comparison was carried out with the German R/V “A. v. Humboldt” and the Norwegian R/V “Johan Hjort” and involved a total number of 38 scientific personnel from 8 countries.The inter-comparisons included the MOCNESS, BIONESS, MultiNet, LHPR, OPC, CPR, Gulf-V, CalCOFI 1-m Ring Net, and WP-2 net. In addition, acoustics data were collected with a Simrad EK500 echosounder operating on 4 frequencies (18, 38, 120, 200 kHz) and hydrographic, nutrient, phytoplankton, and meteorological data were collected to characterize the environment in which the comparisons were made; environmental changes were minor during the study. Mesh size of the net had a major influence on the biomass and species composition of the zooplankton community. There is a consistent relationship between retention (or escapement through the mesh) and the width of the organisms; about 50% of the organisms escape through the mesh at a width equal to the mesh size. The effect of towing speed on the extrusion of smaller organisms through the net can be substantial and adds to the loss due to escapement. Active avoidance of the sampler is only important for the larger macrozooplankton and not a significant problem for the mesozooplankton. Different vertical, oblique, and multiple opening/closing net systems produced similar estimates of zooplankton when operated with comparable mesh-sized nets and a sufficiently high mesh open area to mouth opening ratio. The choice of mesh size is important and 150 ?m mesh is possibly an optimal mesh size for use in coastal waters with neritic zooplankton communities. The results of this study corroborate the results of earlier studies and emphasize the necessity to pay particular attention to the size of mesh and speed of tow as it relates to extrusion of smaller zooplankton through the net mesh and avoidance of the mouth of the samplers by the larger ones. Replicate tow variability was also consistent with earlier studies and reflects the need to understand the interplay between the underlying patchiness of the zooplankton distributions and the method of sampling. No single net is suitable to sample across the wide size range of zooplankton from small mesozooplankton to macrozooplankton. Recent large interdisciplinary programs to assess marine ecosystem structure and dynamics have recognized this through the use of nets designed to sample particular size fractions in combination with video and acoustic remote sensing techniques.
Keywords: zooplankton; NORWAY; plankton nets; net avoidance; net extrusion; net intercomparison; plankton sampling error; mesh size; towing speed; dry mass biomass; Storfjorden
Journal Title: Progress in Oceanography
Volume: 108
ISSN: 0079-6611
Publisher: Elsevier  
Date Published: 2013
Start Page: 1
End Page: 42