Vertical distribution and abundance of natant harpacticoid copepods on a vegetated tidal flat

The vertical distribution in the water column of an assemblage of species of harpacticoid copepods was studied on a vegetated tidal flat in the Fraser River estuary, British Columbia. Natant harpacticoids were collected at discrete levels with a sled-sampler made of 5 cylindrical filtering baskets centered respectively at 56, 156, 256, 356 and 456 mm above the sediment surface. Samples were collected bi-weekly from February 11 to May 27 in 1986. The vertical distribution of Zaus aurelli in the water column was roughly pyramidal with a maximum abundance at intermediate sampling levels (156-256 mm). The vertical distribution of Harpacticus uniremis was variable: maximum abundance was observed at the lowest or intermediate (156-256 mm) sampling levels. The vertical distribution of Tisbe spp. had exponential characteristics with maximum abundance at the lowest sampling level. The abundance of natant harpacticoids in the water column was computed by integrating their vertical distribution curves. The maximum abundance of Tisbe spp., Zaus aurelii, and Harpacticus uniremis was respectively 10.6, 1.96 and 0.46 individuals per cm ² of bottom area. Recognition of specific localized patterns in the vertical distribution of natant harpacticoids and knowledge of their total abundance could ease investigations of their recognized role in the diet of the juveniles of several fish species.