Large-scale patterns in the distribution of planktonic and micronektonic biomass in the north-east Atlantic

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Abstract
The distribution of pelagic (macroplankton and micronekton) biomass as measured by displacement volumes integrated over the top 1000 m has been compiled from data collected both by day and by night from 23 stations, mostly in the north-east Atlantic. The total ranges were smaller than had been expected based on published ranges of annual primary production (macroplankton, 7.6–110.8 ml m−2; micronekton, 2.7– 39.4 ml m2). Highest values were observed either in the regions associated with the equatorial upwelling or to the north of 40° N where there is marked seasonality in the production cycle. Night-time estimates tended to be higher than daytime catches, although not significantly so, probably because of avoidance. Macroplankton estimates with one exception were larger than for micronekton (ratio range 0.8 to 6.1); the ratio tended to be higher in oligotrophic regions. Night-time increases in the top 100 m as a result of diel vertical migration were highly variable, with no clear geographical trend, although the highest increases (>20 mlm−2 macroplankton and micronekton combined) occurred at the two stations at which the highest standing crops were observed. The very limited seasonal coverage in the data indicated biomass varied seasonally by a maximum factor of two.

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