Effects of sampling and preservation on apparent feeding by chaetognaths

Chaetoqnaths 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 um and 64 mu m 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 mu m mesh net undersampled small chaetognaths, resulting in different chaetognath species and length distributions and different prey compositions than those obtained from the 64 mu m 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. God-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.