(b) Design of the VERTEX trap and attachment to the mooring cable.
(After Knauer et al. 1979.)
The main flaws are:(^1) Lots of zooplankton are attracted to traps and swim in. If the collecting
tube contains preservative, then they die and become part of the sample,
estimated to be up to four times the actual sinking particulate flux. One
solution is to ignore the problem. Another is to have a zooplankton expert
pick out animals that have the appearance of having been preserved fresh.
Michael Peterson and colleagues invented an indented rotating sphere (IRS)
valve to place in the throat of the trap. The plug keeps zooplankton from
entering the main trap body so they can depart again; meanwhile, particles
collect in dents and shallow grooves on the top of the sphere. The dents are
turned down and back up intermittently, dropping collected particles into
the preservative below. Recent modifications (Peterson et al. 2005) include
coupling these collectors to net cones with 1 m diameter mouths suspended
with wave absorbers from surface floats. Data from these traps are now