Geodesy

Transect

Ecology

Biology

Dormancy

Ocean gyre

Water mass

Seed dormancy

Salinity

Botany

Diel vertical migration

Geology

Oceanography

Latitude

Stratification (seeds)

Mesopelagic zone

Geography

Water column

Pelagic zone

Abundance (ecology)

Seasonality

Subtropics

Halocline

Germination

Progress In Oceanography

The vertical ranges and abundances of halocyprid ostracods in the surface 2000m of the water column are compared for two localities in the North Atlantic in the vicinity of 30°N, 23°W and 32°N, 63° 40′W (Ocean Acre). The samples collected at these two localities, positioned near the centre of the North Atlantic gyre, contained very similar assemblages of species. The vertical stratification of the species was similar between the two localities, although centres of abundance tended to be 100–200m deeper at Ocean Acre. Vertical migrations tended to be more extensive at Ocean Acre. The order of species abundances were very different at the two localities. A transect of 0–1000m oblique tows along 32°N linking the two positions showed no clear evidence of a faunal boundary between them despite the sudden occurrence of the 18°C water and the waning of the influence of Mediterranean Water to the west. The changes were clinal. Analysis of size spectra showed the trend towards more larger organisms with increasing depth was reversed below 800m. The results are discussed in relation to visual predation as a potentially important causal factor in effecting vertical distribution and diel migrations. In examining other theories of diel migration an examination of clutch sizes showed that the results were not consistent with diel migration conferring demographic advantage to the migrating species. Instead it seemed that the most favourable reproductive regime varied with depth and the degree of seasonality in the productivity cycle. The zoogeographic connotations of the results are discussed.

Studies on Atlantic halocyprid ostracods: their vertical distributions and community structure in the central gyre region along latitude 30°N from off Africa to Bermuda