Validation of a closed-housing filter skid for in-line sampling of aquatic organisms

A prototype shipboard filter skid (p1SFS) was designed and built to facilitate shipboard collection and concentration of ≥50 µm planktonic organisms from large volumes of water. The p1SFS consisted of two stainless steel filter housings, each containing a filter bag, arranged in parallel. Validation of the device examined the particle retention efficiency of filter bags (using inert polystyrene microbeads), the potential toxicity of filter skid materials and the capture efficiency of plankton collected with a filter skid versus a plankton net at two sample volumes (5 and 10 m3). Microbead recovery in filter bags was >89 and 100% for microbeads of 50 and 150 µm diameters, respectively. Exposure to the sealant used to close the filter bags' seams or stainless steel did not lead to mortality of two model zooplankton species. Overall, the concentration of ≥50 µm plankton in the p1SFS relative to concentrations in the plankton net (i.e. the capture efficiency, CE) was 108 ± 66% (mean ± 1 SD, n = 6). The p1SFS CE was higher in experiments with 5 m3 sample volume (147 ± 74%; n = 3) relative to experiments with a 10 m3 sample volume (69 ± 28%, n = 3), although the difference in CE between the sample volumes was not significant. Consequently, these experiments suggest this or similarly validated filter skids are appropriate for in-line sampling of plankton from relatively large volumes of water.