Vertical distribution of zooplankton in Canary Island waters: implicationsfor export flux

Zooplankton biomass, gut fluorescence and electron transfer system (ETS) ac tivity were measured in vertical profiles (0-900 m) in two different size c lasses ( < 1 and > 1 mm) in Canary Island waters. Both size fractions displ ayed a typical pattern of distribution with higher biomass, gut fluorescenc e and ETS in the shallower layers at night. By day, however, the vertical d istribution varied between the size fractions, with higher biomass of the s mall fraction in the 0-200 m and a layer of large organisms at depth ( simi lar to 500 m). For both size fractions. average ETS activity was higher by day than at night at depths between 200 and 600 m. Similarly, gut fluoresce nce was slightly higher by day below 200 m, The downward export of respirat ory carbon was 1.92 and 4.29 mg C m(-2) d(-1) for samples obtained southwes t of Gran Canaria Island and west of Tenerife Island respectively, being 2. 68 mg C m(-2) d(-1) for the whole area. These values represented 16-45% (22 -28% for the area) of the calculated passive particulate export production resulting from primary production. The estimated "gut flux" accounted For 0 .35 (western zone) and 2.37 mg C m(-2) d(-1) (southwest of Gran Canaria), b eing 1.28 mg C m(-2) d(-1) for the whole area and represented between 3 and 25% (11-14% for the whole area) of the estimated passive particle export f lux. These results agree with previous estimates and suggest that diel-migr ant zooplankton can play an important role in the downward flux of carbon. (C) 2001 Elsevier Science Ltd. All rights reserved.