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We have investigated the relationships between covariations in environmental variables and variations in distributions of marine copepod diversity over an extensive latitudinal range from 86.5 degrees N to 46.5 degrees S. For this purpose, 7 data sets (representing 13,713 samples) of copepod species composition data and 11 environmental data sets were assembled. Principal components analysis was applied to investigate the relationships among the mean and seasonal variations in environmental descriptors (ocean temperature, chlorophyll a [ Chl a], net primary production, and other physical and chemical properties of the ocean) and their relationships with spatial variations in copepod diversity. High copepod diversity corresponded to a combination of high ocean temperature and salinity and low Chl a and nutrient concentrations (nitrate, silicate, phosphate). To a lesser extent, high-diversity regions were also correlated to low seasonal variability in oxygen, ocean temperature, and mixed-layer depth. Regression on principal components provided a robust prediction of global copepod diversity (R-2 = 0.45, p < 0.001) as our subset of environmental data was representative of the full range of environmental variability that occurs globally.

Dual-labeling assays were performed on the phytoplankton community of Lake Biwa (Japan) to estimate the ratio of inorganic carbon to nitrate-N uptake as a function of cell size and irradiance. The assays were conducted during a period of change in underwater light and phytoplankton species composition associated with typhoon-induced mixing events. There were consistent qualitative differences in the C:N uptake characteristics of large (>2 µm) versus small ( 2-µm fraction and negative for the small cells. This striking difference between the two fractions also corresponded to patterns in the C:N stoichiometry of the plankton. Surface samples of the >2-µm fraction had a higher C:N ratio than deep populations; this pattern was not seen in the 2-µm fraction. These observations imply that in aquatic ecosystems where nitrate plays an important role in the nitrogen economy of the phytoplankton, high-irradiance conditions favor maximum biomass production per unit of nitrogen uptake by large phytoplankton, and low-irradiance conditions favor a high biomass increment per unit of nitrogen uptake by small cells. These observations are consistent with the ecological distribution of large- versus small-cell phytoplankton in several types of freshwater and marine environments.

Several equations to estimate the vertical export of particulate organic carbon from the ocean's euphotic zone (POC F ) use variables that are determined at sea or are derived from remote sensing. One of the approaches requires reliable estimates off-ratios (NO 3 - uptake/total N uptake) that can be either determined directly from N uptake by phytoplankton or derived from total phytoplankton Chl a biomass or production (P T ) or from NO 3 - concentrations. By using a combination of theoretical considerations and field measurements, we show that f-ratios are linear functions of size-fractionated (>5 μm/ total) phytoplankton production (P L /P T ) and biomass. Comparison of our model with the more usual ∫-ratio = ∫(P T ) shows that the large residuals are spread over the range of P L /P T in the former, whereas they are concentrated at low P T in the latter. Because P T is low in most of the world oceans most of the time, use of our model may significantly improve the estimates off-ratio and thus of POC E .

The distribution of free bacteria in the St. Lawrence estuary was interpreted by means of bacterial fluxes and hydrodynamic residence times, derived from a circulation model, and growth and grazing rates, obtained from cultures. Bacterial abundances decreased exponentially along the salinity gradient, from 3.9 x 10 9 liter-' in freshwater to 0.5 x 10 9 liter -1 at salinity >20. The rates of growth (0.02-0.08 h -1 ) and grazing (0.01-0.09 h -1 ) were strongly correlated (r = 0.82), which suggests that bacteria tended toward a state of trophodynamic equilibrium (growth grazing). However, negative bacterial fluxes obtained from the model imply that the estuary is a sink for bacteria. Results from the circulation model and the cultures show that physical processes are important controlling factors of the distribution of bacteria and point to predation as the process causing bacterial losses in the estuary. Calculations show that small imbalances between growth and grazing can account for the observed distribution. Rates of dispersion and growth and grazing are of the same order of magnitude, which shows that biological processes are nevertheless significant relative to physical processes. Although the distribution of free bacteria appears largely under hydrodynamic control, the bacterial community is characterized by significant biological rates and can experience large transformations during estuarine transit.

Intensive monitoring of the maximum quantum yield of carbon fixation (&,,,) and of the minimum quantum yield of chlorophyll a in vivo fluorescence ($& was followed along the path of drifting buoys in the estuary and the Gulf of St. Lawrence, Canada. Samples were collected every third hour during two 24-h periods. Over the 170 measurements, &,,X varied by a factor of 20 [from 0.004 to 0.08 mol C (mol quanta))‘]. As predicted by a model of primary processes in photosystem 2, a significant and positive linear relationship was observed between $,,, and q5I;,. In the estuary, the covariability of &,,,, and $t;, seems to be driven by light, because it was observed only during daytime and was characterized by a parallel increase of &,,, and $r;, with depth. Examination of the spectral values of $FO suggests a contribution of photoprotectant carotenoids. In the gulf, because a parallel, although weaker, increase of &,, and rbr;, with depth also persisted during nighttime, nutrient deficiency is probably an additional cause of covariation between (6,,, and cbr;,. In both regions, an overall diel cycle was observed for $,,X with a maximum at around noon; $I;, did not show a clear diel periodicity. Despite the vertical covariability of &,,X and 4F0, the diel cycle of &,,X was uncoupled to $FO and thus to photosystem 2 activity. These results suggest a significant diel variation in the photosynthetic quotient of natural phytoplankton.

Mathematical relationships are developed to derive potential export (i.e. sedimentation, grazing, or advection) from the proportions of production and biomass in two size fractions of phytoplankton. Size-fractionated data (540 points) from 40 published studies are plotted on a productionbiomass diagram, from which potential export is predicted. The predictions are supported by published information. Six ecological domains are defined from the positions of data points on the production-biomass diagram: equatorial/tropical oceanic, tropical neritic, and subtropical oceanic waters, ocean North Atlantic, Southern Ocean, and upwelling areas together with coastal northwest Atlantic blooms. The resulting picture is coherent, especially when the heterogeneity of data sources is considered

A scattering layer of Calanusjnmarchicus was sampled every 90 min during 48 h in the lower St. Lawrence estuary. Grazing activity (phytoplankton pigments in the gut) and the percentage of recently and nonrecently fed copepods (from observation of food in the gut) were monitored in two strata (O-30 m and 30-100 m). Phytoplankton was restricted to the upper stratum. A bimodal twilight grazing rhythm was observed: the first feeding period, in the upper stratum, begins after sunset; it is followed by the “midnight sinking” in the deeper stratum (2-3 h), during which the gut content is evacuated; after this, the animals return to the upper stratum for a second meal, before the dawn descent. In both migrations, there was a dynamic interchange of individuals between the two strata, which masked the fact that all the copepods migrated to the upper stratum and that a dawn rise actually happened. The feeding time in the warmer surface water was very short. Feeding ceased rapidly even if phytoplankton concentration was low. A large increase in the number of migrants did not change the feeding patterns. Results support the hypothesis that the behavior of C. jinmarchicus during the central phase of vertical migrations in late summer is closely linked to an in situ grazing rhythm.

Subtracting dark 14C fixation from light 14C fixation can lead to serious underestimates of phytoplankton production in aquatic environments. Light, temperature, and nutrient time-course experiments show that there is an active and an inactive incorporation component of 14C in the dark. The active incorporation can be prevented by adding DCMU (dissolved in water) to either a light or a dark bottle, thus estimating the inactive component. It is therefore recommended that a DCMU treatment be subtracted from the standard light carbon dioxide fixation for accurate estimation of phytoplankton production.

In April 1983, differential-enrichment bioassays were conducted on natural sea-ice microalgae from Hudson Bay, Canadian Arctic. Incubations were done both in the laboratory (at about 4“5°C) and in situ at the ice-water interface (- 1.5”C). Actual growth of the cultures was nutrient limited. On the basis of our observations and using recalculated data from the literature, we tentatively set the mean generation time of Arctic-ice microalgae between 8 and 17 days. Nitrogen was demonstrated to govern the algal yield when illumination and grazing allowed the algae to grow. The low (NO,- + NO,- + NH,+):P0,3- mean ratio (5.9) in the water at the ice interface leads to the same conclusion. In situ dissolved inorganic nitrogen and phosphorus progressively decreased during the course of sampling, but were never exhausted. We hypothesize that the K, of epontic as well as of other benthic microalgae is higher than that of phytoplankton, so that they cannot deplete the natural nutrient reservoir. We conclude that the bottom-ice dynamics is controlled not only from above, by the seasonal (climatic) changes in light intensity as generally assumed, but also from below, by the shorter term (hydrodynamic) events of vertical mixing that replenish the ice-water interface with nutrients.

The photosynthetic 14C assimilation of phytoplankton from the St. Lawrence estuary was measured under various artificial light regimes, combining different intensities, colors, and high frequency fluctuations. The light fluctuations consisted of rapid alternation of high and low light intensities of equal duration. In the first set of experiments, the photosynthetic response was measured under red, green, blue, and white light, steady or fluctuating (2.5 Hz). Under fluctuating light, the color: white 14C assimilation ratios were significantly higher than those under steady light. In the second set of experiments, light saturation curves were made under fluctuating (10 Hz) and steady lights. No differences were recorded for PBmax but the photosynthetic efficiencies α were 30% higher under fluctuating light. Vertical distribution of rapid light fluctuations, together with light intensities and color, is therefore of ecological significance. These experiments also raise the problem of deck incubations, where not only the color is modified but also the frequency of light fluctuations, leading to a median error as high as 30%.