Effects of sampling and preservation on apparent feeding by chaetognaths

Chaetognaths are abundant predators of manne 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 pm and 64 pm 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 I.lm mesh net undersampled small chaetognaths, resulting in different chaetognath species and length distributions and different prey compositions than those obtained from the 64 pm 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 ~t e m s , 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.