RADIOLARIAN ASSEMBLAGES IN THE EASTERN TROPICAL ATLANTIC - PATTERNS IN THE PLANKTON AND IN SEDIMENT TRAP SAMPLES

Polycystine Radiolaria were studied in 40 Multinet (63 mu m) plankton samples collected in February-March 1988 in the eastern tropical Atlan tic (10 degrees N to 17 degrees S), from depths ranging between 0 and 300 m. A total of 148 taxa were recorded, most of them accounting for very low proportions of the individuals identified. The geographic dis tribution of polycystine assemblages throughout the area was relativel y homogeneous and quite unpatterned; no clear associations with latitu de, surface temperature, salinity or chlorophyll a were found. On the other hand, several radiolarians showed fairly distinct vertical profi les, allowing identification of forms preferring the uppermost 25-50 m , forms peaking at 50 to 150 m, and forms with highest percentage cont ributions below 150 m. Comparison of this planktonic collection with a similar survey carried out in 1983 in the same area indicates good ov erall agreement. In contrast, radiolarian compositions in sediment tra p samples deployed at 853 and 2195 m in close vicinity with some of th e plankton stations surveyed are totally different. Subsurface advecti on of shells produced at higher latitudes and integration of low radio larian abundances over large depth-intervals are the most likely cause of the inconsistencies.