Diel migrating zooplankton can contribute
significantly to dissolved carbon and nutrient
export by respiring and excreting surface-ingested
particulate organic matter below the mixed layer.
Active export of particulate organic carbon (POC)
and particulate organic nitrogen (PON) due to
defecation at depth has rarely been considered in
carbon export budgets. I measured the gut passage
time (GPT) of three common migrant species at the
Bermuda Atlantic Time-series (BATS) site, using
the gut fluorescence method, to determine whether
GPT is slow enough to allow active export of POC
and PON to depth. Mean GPT for the copepods
Pleuromamma xiphias and Euchirella messinensis was
191 min and 114 min, respectively, and for the
euphausiid Thysanopoda aequalis was 41 min,
exceeding previously reported GPT for
non-migrating animals by a factor of 6. Between 18
and 81% of the initial gut pigment was retained in
animal guts upon descent below a mixed layer of
150 m. By comparing pigment ingestion rates (gut
fluorescence technique) with total ingestion rates
(CHN analysis of fecal material) we estimated that
71-85% of the migrant diet originated from
non-plant material, which we included in our
estimates of active POC/PON export. We applied the
mean weight-specific active POC/PON export rate
for the three species to the total migratory
zooplankton biomass using data from the BATS
zooplankton time-series. Mean active POC (PON)
flux at BATS was 0.94 mg C m^-2 d^-1 (0.18 mg N
m^-2 d^-1) and the maximum was 5.27 mg C m^-2 d^-1
(1.02 mg N m^-2 d^-1), corresponding to a mean of
3% (4%) and a maximum of 18% (20%) of the mean
gravitational POC (PON) flux measured by sediment
traps at 150 m. Migrants also contributed
significantly to passive flux via production of
sinking fecal pellets during the night in surface
waters. This passive flux exceeded active POC flux
by ~10-fold. Freshly released feces by migrators
at depth could be a valuable food source for
mesopelagic organisms, in contrast to feces
produced in surface waters which decompose while
settling through the water column.