Effects of sampling and preservation on apparent feeding by chaetognaths

Chaetognaths are abundant predators of marine zooplankton. Their feeding typically has been quantified from gut contents of net-collected specimens. We evaluated the effects of mesh size and sampling duration on the gut contents of chaetognaths. Samples were compared from 333 μm and 64 μm mesh nets towed for 2 min and preserved immediately (controls), or towed for 5 min and preserved after 0, 5, 15, or 35 min. The 333 μm mesh net undersampled small chaetognaths, resulting in different chaetognath species and length distributions and different prey compositions than those obtained from the 64 μm mesh net. Prey loss from gut contents was substantial, with as much as 50 % of prey lost in tows of greater than 2 min duration. Cod-end feeding, as indicated by prey in the foregut, undigested prey, and non-prey items, was much less than prey loss. Actual chaetognath predation effects may be more than double estimates made using net tow durations greater than 2 min.