EFFECTS OF SAMPLING AND PRESERVATION ON APPARENT FEEDING BY CHAETOGNATHS

Chaetoqnaths are abundant predators of marine zooplankton. Their feedi ng typically has been quantified from gut contents of net-collected sp ecimens. We evaluated the effects of mesh size and sampling duration o n the gut contents of chaetognaths. Samples were compared from 333 um and 64 mu m mesh nets towed for 2 min and preserved immediately (contr ols), 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 differ ent chaetognath species and length distributions and different prey co mpositions than those obtained from the 64 mu m mesh net. Prey loss fr om gut contents was substantial, with as much as 50% of prey lost in t ows of greater than 2 min duration. God-end feeding, as indicated by p rey 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.