Quantification of diel vertical migration by micronektonic taxa in the northeast Atlantic

Analyses of day/night changes in the bathymetric distribution of micronekto nic biomass at 16 stations in the northeastern Atlantic, sampled between 19 78 and 1994, provided quantitative estimates of the organic carbon fluxes a ssociated with diel vertical migration of individual taxa of micronekton. G elatinous taxa contributed 50-80% of the integrated standing crop by volume but. apart from tunicates. contributed relatively little to the active mig ratory fluxes when expressed in ter ms of carbon. Total micronektonic migra tory fluxes into the upper 200 tn ranged from 12.5 to 58 mgC per m(2). At 1 5 stations. fish and pteropods provided 50-80% of the fluxes into the upper 100, 200 and 400 m. At one station, tunicates (pyrosomes) contributed subs tantially. Wherever tunicates or the medusa Pelagia were swarming, migratio ns by other taxa appear to be suppressed. The mean proportions of the stock tin terms of biomass) of each of the dominant migratory taxa entering and leaving the upper 100 m were 23% for tunicates, 18% for fish, 22% for ptero pods. 8% for decapod crustaceans and 23% for euphausiids. The maximum propo rtions for these five taxa were 90%. 60%. 75%. 25% and 75%, respectively. S imilar estimates of the mean fluxes into and out of the upper 400 m were ge nerally higher. 19% for tunicate. 39% fur fish, 28% for pteropods, 49% for decapods and 55% for euphausiids: the respective maxima were 99%. 74%. 99%. 72% and 91%. It is estimated for fish that if these migrations occur throu ghout the year, they will result in an active carbon export (both POC and D OG) from the wind-mixed layer and immediate rub-thermocline depths of about 500% of the mean annual standing stock. If this estimate can be extended t o other taxa. then the material fluxes resulting from these active migratio ns will be quantitatively similar to those resulting from the deposition of phytodetritus at temperate latitudes.