Grazing and Zooplankton Production as Key Controls of Phytoplankton Production in the Open Ocean

Abstract

THANKS TO NASA's Coastal Zone Color Scanner (CZCS, 1978(CZCS, -1986, nearly ocean-wide coverage of the distribution of phytoplankton pigment in the upper part of the euphotic zone and, in effect, in the mixed layer of the open ocean, is now available. This coverage includes seasonality and interannual variability. The CZCS observations confirm that the physics of the ocean provide the backbone of the geographic and temporal patterns of pigment distribution and, by inference, of primary production rate. For example, phytoplankton concentrations and production are enhanced where upwelling or seasonal overturn of the water column replenishes nutrient concentrations in the mixed layer, whereas the timing of this enhancement may be controlled by upwelling, seasonal overturn, or the mixed layer becoming shallower than the critical depth.I propose that the next task is to understand the cause of the phytoplankton concentrations and to be able to predict them and the temporal rate of change of concentrations on the scale of several days to seasons. I will show that this major challenge for biological oceanography cannot be addressed without a vastly improved understanding of the zooplankton. Understanding the animals is of intrinsic interest, which is also true for phytoplankton. However, the task of predicting phytoplankton concentrations and their rates of change also may be considered as a subset of the challenge of anticipating the effect of climate change on, e.g., the geographic and temporal (seasonal) distribution of the sign of the CO2 gradient between atmosphere and sea via the connection between phytoplankton concentration and photosynthesis, or on plankton community composition and its feedback to the atmosphere from changes in the distributions of DMS producers.

Reflections About Chance in My Career, and on the Top-Down Regulated World

“…In conclusion, as previously noted in Banse (1994) and illustrated in Figure 2, the bottom-up controlled cell division rates (measured, estimated from remotely sensed chlorophyll, or calculated from environmental data) greatly overestimate the rate of population change during a bloom. Moreover, they cannot even predict the correct sign of the change because of the neglect of mortality.…”

Estimating the carbon flux through main phytoplankton groups in the northwestern Mediterranean

“…A discussion of the impact of grazing on 14 C experiments has been recently taking place (Banse 2002;Marra 2003). In an answer to Banse, Marra questioned the importance of grazing in all situations.…”

“…Sedimentation, viral infection, and autolysis are loss processes that might become significant at certain periods (Agustí and Duarte 2000;Becquevort and Smith 2001;Brussaard 2004). However, grazing is arguably the main mechanism that consumes the organic mater produced by phytoplankton (Banse 1994). Therefore, production and grazing condition most of the C flux through phytoplankton.…”

Maximal sustainable sinking velocity of phytoplankton

“…(14) using the parameter values of Table 1 limitation, dynamic changes in grazing pressure, virus attacks and all kinds of other factors well known to affect phytoplankton dynamics (e.g. Martin et al 1990, Suttle et al 1990, Banse 1994. Indeed, even if light conditions are favorable for sinking phytoplankton, the phytoplankton may still be suppressed by factors not considered here, like nutrient limitation or increased grazing pressures.…”