The vertical structure of a pelagic community in the tropical ocean

Abstract

The vertical structure of the ecosystem in the euphoti0 zone of the western Equatorial Pacific has been studied. The studies were based on a continuous sounding of the bioluminescence field, with simultaneous, vertically aimed s~mpling made with the aid of a 51 water bottle and plankton nets. The biolumineseence field has a two-maxima structure with a more pronounced and permanent lower maximum found in the oligotrophic regions as deep as 60 to t00 m. In the narrow (10 m) layer of maximum bioluminescence, the concentration of zooplankton, as well as the concentration, activity and production of bacteria and phytoplankton, are several times higher than those in immediately adjacent waters at greater or lesser depth. At the same time, the concentration of nutrient salts in that layer diminishes sharply and approaches zero in the overlying water. Analysis of the data obtained shows that the production processes above the lower maximum layer are dependent not only on the turbulent influx of nutrient salts from the underlying layers, but also on the horizontal supply from the zone of upwelling. A pelagic community, in its different time aspects from the moment of water ascending until its sinking in the convergence zone, is suggested as a common system for modelling.

Southwestward extent of chlorophyll-enriched waters from the Peruvian and equatorial upwellings between Tahiti and Panama

“…Southwest of the observed SSCC increase, the possibility that surface waters with a low chlorophyll content cap a n active chlorophyll maximum cannot b e excluded. The chlorophyll maximum at or near the surface in divergent zones is expected to sink and progressively weaken at convergences (Vinogradov et al 1970); our UW-OW transition detected at the sea surface might then underestimate rather than overestimate the width of the enriched zone.…”

Role of planktonic bacteria in productivity and cycling of organic matter in the Eastern Pacific Ocean

“…Samples were taken at 32 stations in 140 1 plastic bottles at 12-15 different depths between the surface and 200 m. At some stations samples were collected down to 2 000 m. Sampling depths in the euphotic zone were selected after recording protiles of temperature, chlorophyll, and bioluminescence in order not to miss the microplankton maxima (Sorokin, 197 1;Vinogradov et al, 1970;Gitelson et al, 197 1). Total bacterial number was estimated by direct microscopic counts on membrane filters (SYN-POR-7, Czechoslovakia, pore size 0.2 pm) (Sorokin & Kadota, 1972;Sorokin, 1971).…”

Zooplankton Abundance and Diversity in the Tropical and Subtropical Ocean

“…Overall, the deep-sea zooplankton community is characterized by strong latitudinal and bathymetric gradients and its diversity mainly regulated by complex interactions among environment and the species-specific performances. However, the major driving mechanisms generating the structure of the pelagic deep sea still poorly understood [4,5]. In this vast environment, zooplankton supports life and represents a key component in the functioning of the ocean food web.…”

“…However, available data show that zooplankton abundance in the deep-sea decreases with depth [27], the rate of this decrease varies in different geographical areas [5,[28][29][30], and changes in diversity and community structure still are poorly resolved. The feeding mode of zooplankton also varies with depth, with herbivorous and omnivorous species occurring in the epipelagic, and carnivores and detritivores copepods increasing toward the bathypelagic zone [31].…”