Comparison of phytoplankton concentrations and cell volume measurements from the continental shelf off Cape Cod, Massachusetts, U.S.A.

Abstract

Phytoplankton composition and concentrations varied at stations across the shelf with maximum phytoplankton volumes not necessarily related to maximum concentration values. The shelf phytoplankton off Cape Cod, Massachusetts was composed of two major size classes: the ultraplankton (cells less than 10 microns in size), and net phytoplankton. Cell concentrations decreased along transects seaward, to increase near the shelf margin. Higher cell volume values coincided with increased cell counts east of Cape Cod, but were lower southward, increasing in the mid-shelf region, to decrease along the shelf margin. The shelf ultraplankton component typically represented over 90% of the standing crop, but less than 1% of its phytovolume. Associations are made between cell volumes and concentration combinations and different phytoplankton assemblages.