Monday, 2 November 2009

Zooplankton distribution (some results)

Preliminary results suggest that mesozooplankton biomass was highly variable throughout the survey and ranged from 11 to 94 mg /m^3. Total zooplankton wetmass was highest south-east of the Comoros and lowest south west of the islands (see below). Spatially this pattern coincided closely with the position of a cyclonic and anti-cyclonic eddie in the vicinity of the Comoros.
As in previous cruises in the region, the horizontal (geographical) distribution of zooplankton suggests that warm-core eddies contain overall very little zooplankton when compared to cold-core eddies and frontal boundary regions. While this result needs to be reinvestigated once updated altimetry data is available, current data suggest that zooplankton biomass increases drastically outside of the warm-core eddies.
The predominant taxa in the smaller size fractions from most stations were:

280μm – 500μm: copepods (also some gastropods, ostracods and amphipods)
500μm – 1mm: copepods (also some amphipods, ostracods and euphausiid nauplii)
1mm – 2mm: small euphausiids and chaetognaths (also some large copepods, amphipods, decapods)

The larger size fractions were more variable in composition, with euphausids, decapods, fish larvae and gelatinous zooplankton making up the bulk of the biomass. These larger size fractions of the zooplankton tended to make up a large proportion of the total biomass only during night-time stations.
Further and more detailed analysis of the multinet samples and the 180um Bongo samples is still outstanding and cannot yet be commented on.

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