Trapping migrating zooplankton

James J Pierson, Bruce W. Frost, David Thoreson, Andrew W. Leising, James R. Postel, Mikelle Nuwer

Limnol. Oceanogr. Methods 7:334-346 (2009) | DOI: 10.4319/lom.2009.7.334

ABSTRACT: We have developed a method to determine if individual zooplankton make short-duration migrations, on the order of meters to tens of meters in vertical extent, between food-rich surface water and deeper, food-poor water. To do this, we developed a zooplankton trapping system, consisting of paired traps to catch zooplankton migrating downward and an inverted ring net to catch zooplankton migrating upward. These two trap systems were deployed simultaneously with the openings at the same depth, to catch zooplankton crossing a particular depth horizon, and samples were immediately sorted to make morphological and physiological measurements of individuals. Initial tests showed that there were differences in the ability to capture upward- and downwardmigrating marine zooplankton. In addition, physiological (gut contents) and morphological (prosome length) characteristics of individual copepods differed between those moving in opposite directions. These data support the hypothesis that copepods make repeated nighttime forays between deeper, food-poor water and the near-surface, food-rich waters. This is part of an ongoing study on the variability of this behavior in different conditions and over seasonal cycles, but the method may be applicable to other pelagic environments, to explore various ecological questions.