MEPS 140:41-58 (1996)  -  doi:10.3354/meps140041

Mesoscale spatial heterogeneity in chaetognath populations during upwelling abatement in the northern Benguela region

Duró A, Gili JM

In April 1986 abatement of upwelling in the northern Benguela coincided with strong penetration by Angolan waters. The combination of these 2 phenomena generated considerable spatial heterogeneity in the physical structure of the region. In addition, the vertical location and width of the pycnocline varied over the study area. This affected the spatial distribution of the chaetognaths, shifting the axis of spatial variation from one running inshore-offshore to one running latitudinally, north-south. A total of 19 species were present, with Sagitta setosa accounting for more than 70% of all individuals collected. Chaetognath species exhibited 4 distinct distribution patterns: some species were widely distributed throughout the entire region, though they tended to be concentrated preferentially in a certain area, while the remaining species were distributed exclusively in the southern, central, or northern parts of the region. On the whole, however, specific distribution patterns were closely related to the spatial extensions of one of 3 water masses identifiable in the region. The species in the southern part of the region had the deepest and most oceanic distribution, while the species in the northern part of the region had a more inshore distribution in the upper layers of the water column. The adaptability of chaetognaths to conditions of high turbulence like those in the pycnocline layer makes the location and strength of the pycnocline in each region one of the main factors responsible for the spatial heterogeneity observed.

Upwelling system · Pycnocline · Chaetognaths · Horizontal and vertical distribution · Northern Benguela · South Atlantic

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