A quantitative method for sampling littoral zooplankton in lakes: The Active Tube

The Active Tube was designed to sample zooplankton quantitatively in discrete habitats within the littoral zone of lakes. Its performance was compared with a commonly used method the Horizontal Timed Net Sweep at Enagh Lough East, Northern Ireland, in August 2006. The results revealed that the Timed Net Sweep under-samples zooplankton assemblages when compared with the Active Tube. The Active Tube collected 50% more cladoceran species over three plant habitats than the Timed Net Sweep method. The Active Tube results identified differences in zooplankton diversity between Alisma lanceolatum and Elodea canadensis habitats that were undetectable using the Timed Net Sweep. The Active Tube samples had cladoceran abundances per unit volume that were 2000 times greater than those collected using the Timed Net Sweep. Rank abundance plots showed that these differences in diversity and abundance gave rise to different descriptions of the community structure. The Active Tube plots revealed evenness in the Alisma lanceolatum and Phalaris arundinacea communities that was undetected in the Timed Net Sweep plots. Finally, the Active Tube samples contained three cladoceran species not previously recorded in Ireland: Ceriodaphnia reticulata, Ilyocryptus acutifrons, and Ophryoxus gracilis. The Active Tube method produces a more detailed description of littoral zooplankton assemblages, and it allows discrete habitats to be described.