Pyrosomas are the large group of pelagic tunicates whose trophic role in pelagic communities has not yet been sufficiently studied. We ran across a local area of high concentration of the most widespread and commonest species of pyrosomas, Pyrosoma atlanticum, 450 miles off the Congo river mouth. The following was estimated: gut pigment content, defecation rate, organic carbon and pigment content of fecal pellets, and sinking rate. Based on these data and the measured number of pyrosomas colonies the grazing impact on phytoplankton and the fecal pellet flux were calculated. During the night swarms of 50–65 mm P.atlanticum removed 53% of phytoplankton standing stock in the 0–10 m layer; sparsely distributed pyrosomas consumed only 4%. The grazing impact in the 0–50 m layer was only 12.5 and <1% respectively. The fecal pellet flux resulting from nocturnal feeding of P.atlanticum while swarming made up 1.4–1.6 × 10⁶ pellets m⁻² 10 h⁻¹ or 305–1035 mg C m⁻² 10 h⁻¹ and 1.4 × 10⁵ pellets m⁻² 10 h⁻¹ or 87.4 mg C m⁻² 10 h⁻¹ while non-swarming. Incubation experiments showed the rapid degradation of fecal pellets at 23°C: the loss of pigment and carbon content was ˜60–70% after 45 h. We believe that given the sinking rate of 70 m day⁻¹ the main part of fecal material does not leave the upper water column and is retained in the trophic web of the epipelagic layer.

Main features of the zooplankton distribution and the ecological characteristics of the dominant species in the northern Benguela during different phases of upwelling are discussed. The composition of the zooplankton between 17 and 27°S was similar each year. Among the 20°30 most abundant species, 3°4 copepods dominated, influencing the distribution of total zooplankton biomass. During quiescent upwelling, zooplankton abundance was low and there were no significant differences in the inshore-offshore distribution of zooplankton biomass, the maximum occurring over the slope. During active upwelling, zooplankton biomass increased significantly, the maximum over the shelf being constituted almost entirely of developmental stages of herbivorous copepods. Over the inner shelf, all stages of the copepod Calanoides carinatus were feeding actively, removing up to 5 per cent per day of the standing stock of phytoplankton. Comparison of daily ration, respiration rate and biochemical composition of C. carinatus reve...

Studies were conducted at the end of June 2011 in the coastal region of the northeastern part of the Black Sea. The bulk of the Noctiluca scintillanspopulation was observed in the thermocline and...