(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1996-06)
Gin, Karina Y. H.
Characteristics of microbial size spectra (bacteria and phytoplankton) were examined in
relation to changes in ecosystem productivity and environmental perturbations. Samples
were obtained from productive coastal waters in Massachusetts and Cape Cod Bays,
oligotrophic waters in the Sargasso Sea and high nutrient, low chlorophyll waters in the
equatorial Pacific. In general, a relative predominance of larger bacteria and
phytoplankton cells was observed in early spring, where low temperatures resulted in wellmixed
waters and high nutrient concentrations. Seasonal succession was accompanied by
a shift in the size spectrum to smaller cells, coinciding with rising temperatures,
stratification of the water column and diminishing nutrient concentrations. In stratified
waters, larger mean bacteria and phytoplankton sizes were observed in surface and deep
waters, whereas smaller sizes were observed around the chlorophyll maximum. Bacteria
and phytoplankton growth were well correlated with mean bacteria sizes varying
positively with mean phytoplankton sizes. Data pooled from all locations showed that the
size spectral characteristics most sensitive to environmental change were the mean cell
size, bacteria intercept and phytoplankton slope of the normalized concentration size
spectrum. Increases in ecosystem productivity, chlorophyll, particulates and nutrients
were generally accompanied by shifts in the size spectra to larger bacteria and
phytoplankton.
