Mass sedimentation of gelatinous colonies of the prymensiophyte Phaeocystis pouchetii were observed in the upper 100 m of Atlantic water in the central Barents Sea. Sedimentation rates of particulate organic carbon and nitrogen as well as pigments were the highest recorded so far from oceanic environments of the North Atlantic or coastal areas of Norway. High relative concentrat~ons of phytoplankton pigments found in the traps are interpreted as a combination of sinlung of intact phytoplankton cells and undegraded pigments present in macrozooplankton faecal pellets. Evldence presented in this study implies that the zooplankton community of the Barents Sea was not able to control this phytoplankton spnng bloom. The suspended and sedimenting organic matter was rlch in carbon and pigments, but poor in nitrogen. This is explained by the presence of large amounts of carbon-rich mucilage which P. pouchetii colonies develop during their development. In addition to diatoms, sedimentation of a gelatinous phytoplankton species like P. pouchetii may contribute significantly to the formation of marine snow and vertical flux from the euphotic zone. However, degradation of P. pouchetii derived detritus at depths less than 100 m greatly diminishes the likely significance of P. pouchetii blooms in processes such as the carbon flux to the deep ocean and sequestering of CO2.

New techniques used during a recent study in the oligotrophic North Pacific Ocean demonstrated that coccoid cyanobacteria were the most abundant photoautotrophs. Despite their small size, they accounted for 64 % of the total photosynthesis, with specific growth rates of 1.6 d-'. Grazing experiments indicated that a diverse assemblage of micrograzers is able to consume and effectively metabolize chroococcoid cyanobacteria. In the open ocean, a significant trophic interaction occurs between cyanobacteria and micrograzers, components not included in the classical paradigm of the oceanic food web.In oligotrophic ocean systems, picoplankton (Sieburth et al. 1978) account for approximately 60 % of the inorganic carbon fixation (Li et al. 1983 and apparently have high specific growth rates , Douglas 1984, Landry et al. 1984. Chroococcoid cyanobacteria have been observed in the marine environment (Johnson & Sieburth 1979, Waterbury et al. 1979), but only recently have they been implicated as a substantial component of the autotrophic picoplankton. Information about cyanobacteria in situ growth rates, photosynthetic characteristics and contribution to higher trophic levels is still limited. Studies conducted with cultures of Synechococcus sp. demonstrated net specific growth rates of u p to 1.5 d-', saturating at low irradiance (Morris & Glover 1981). Preliminary field data indicate that picoplankton photosynthesis saturates at low irradiance, with maximal contributions to primary production at the base of the euphotic zone (Morris & Glover 1981, Li et al. 1983). However, the relative contribution of cyanobacteria to total photosynthesis has not been quantified. Few studies have investigated the cya- demonstrated their suitability as food for micrograzers, while ingestion, but not digestion, by calanoid copepods has been observed (Johnson et al. 1982).In the North Pacific gyre (35"N, 128"W), we studied the distribution and photosynthesis of cyanobacteria and their consumption by micrograzers. This region is typical of the oligotrophic subtropical open ocean in spring, with a mixed layer of 60 to 80 m, and a deep chlorophyll maximum between 90 and 105 m as shown by in situ profiles of density, fluorescence, and beam attenuation (Fig. 1). Integrated euphotic zone chlorophyll a was approximately 25 mg m-2. Fig. 2 illustrates the vertical distribution of cyanobacteria and acetone extracted chlorophyll a concentrations for discrete samples at the study site. Daily specific growth and grazing rates were calculated from the general exponential relation:where N, = concentration at time t; No = concentration at time zero; r = specific rate coefficient; t = time. References to rates in this paper are specific natural log rates as defined above. If the cyanobacteria population is in steady state, the specific rate constants for growth, U , grazing, g, and residual losses, 1, satisfy the equation: r = U -g -1 = 0. For our experiments, the loss term, 1, includes respiration and exudation by cyanobacteria, respiration and e...

Concentrations of extracted phycobiliproteins were measured a t a station off the Southern California coast, USA, from November 1985 to March 1986. The main pigment found was phycoerythrin-543 (PE) from Synechococcus spp. as described by Alberte et al. (1984). Concentrations of PE in water column, between 3 and 40 m, varied between 0.01 and 1 60 pg 1-' Maximum values were found between 3 and 22 m. In situ concentrations of PE were posit~vely correlated with cell numbers of Synechococcusspp., which ranged from 1.4 to 116 X 106 cells I-', and showed maximal values between 3 and 13 m. Because no other types of PE were detected, all PE measured was considered to come from Synechococcus-type cells. Cellular concentrations of PE varied between 2.1 and 40.3 X 10-' pg PE cell-', with an average value of 10 5?4.1 X IO-' vg PE cell-' above the 1 % isolume for PAR (Photosynthetically Available Radiation). Pigment per cell increased consistently with depth dunng autumn and spring and had low and relatively constant values in the winter. High PE:cell (>20 X lO-' pg PE cell-') was observed only below the 1 % isolume for PAR. For all samples, cellular concentration of PE was inversely correlated with incident PAR and was positively correlated to dissolved inorganic nitrogen (nitrate) concentration. Cyanobactena were not a dominant component of phytoplankton standing stock during this study, contributing an estimated 4 to 15 O/O of total chlorophyll in the water column, but had high specific growth rates, with maximal values of >0.75 d-' close to the surface. Absorption of light at 540 nm, as measured by in vivo absorption spectra of phytoplankton, was not correlated with PE concentration in the water column.