In phytoplankton of the eastern tropical Pacific Ocean from 25 to 90 percent of the biomass (measured as chlorophyll a) and 20 to 80 percent of the inorganic carbon fixation were attributable to particles that could pass a screen with a 1-micrometer pore diameter. Evidence is presented that these are indeed autotrophic cells and not cell fragments.

Many issues in biological oceanography are regional or global in scope; however, there are not many data sets of extensive areal coverage for marine plankton. In microbial ecology, a fruitful approach to large-scale questions is comparative analysis wherein statistical data patterns are sought from different ecosystems, frequently assembled from unrelated studies. A more recent approach termed macroecology characterizes phenomena emerging from large numbers of biological units by emphasizing the shapes and boundaries of statistical distributions, because these reflect the constraints on variation. Here, I use a set of flow cytometric measurements to provide macroecological perspectives on North Atlantic phytoplankton communities. Distinct trends of abundance in picophytoplankton and both small and large nanophytoplankton underlaid two patterns. First, total abundance of the three groups was related to assemblage mean-cell size according to the 3/4 power law of allometric scaling in biology. Second, cytometric diversity (an ataxonomic measure of assemblage entropy) was maximal at intermediate levels of water column stratification. Here, intermediate disturbance shapes diversity through an equitable distribution of cells in size classes, from which arises a high overall biomass. By subsuming local fluctuations, macroecology reveals meaningful patterns of phytoplankton at large scales.

The seasonal variation in temperature characteristics of photosynthetic and heterotrophic activities in the microbial plankton of Bedford Basin, Nova Scotia, was investigated. Measurements were made of the photosynthetic uptake of [14C]bicarbonate and its incorporation into cellular protein as well as the heterotrophic uptake of 3H-labeled amino acids and their incorporation into cellular protein. Activity-temperature curves were analyzed objectively by nonlinear estimation of parameters from various mathematical models. Over the seasonal cycle, the cardinal temperatures and a parameter formally equivalent to the thermodynamic enthalpy of activation for most of the four processes measured were positively correlated with the water temperature. The temperature sensitivity of metabolic activity (i.e., change in activity per unit change in temperature) was indexed by the tangent to the activity-temperature curves. When this index was expressed in dimensionless form by normalization to the scaling factor of the activity-temperature curves, the resulting relative temperature sensitivity, evaluated at the prevailing temperature, proved to be statistically invariant throughout the year. During the height of the spring bloom, the water temperature (-0.3°C) was not so low as to inhibit metabolic activity of either the phytoplankton or the bacterioplankton. The evidence suggests that 2282