Seasonal patterns of seston characteristics in Bedford Basin, Nova Scotia, relative to zooplankton feeding: A multivariate approach1

Abstract

Seasonal changes of the characteristics of the particulate organic matter from Bedford Basin were studied at four different depths during 15 months. The data (particle counts in Coulter Counter channels, counts of taxonomic categories, and chemical measurements) are best analyzed as multivariate parameters. Principal component analyses show for each depth the groups of channels responsible for the maximum variability; taxonomic categories and chemical measurements projected onto the graphs as “supplementary” items reveal their potential associations with some channels. Correspondence analysis allows a dual analysis of the size spectra and the sampling dates. In the surface waters, size spectra are influenced by biological productivity, whereas at depth the analyses mostly specify the type of sedimenting material. Regardless of depth, the size spectral diversity is associated with particles ranging from 8 to 25.4 µm. They are responsible for most spring production and some summer and fall. production. Several multivariate associations are found (e.g. between flagellates and particles in the 8.0–12.7‐µm size range, diatoms and particles in the 16.0–25.4‐µm size range, dinoflagellates and particles in the 40.3–50.8‐µm size range). Size heterogeneity at depth is related to pulses of sedimenting small and medium size particles, although the particulate standing stock at 30 m consists of large detrital material. The association between microzooplankton and nanoplankton observed at 2.5 and 5 m illustrates a trophic relationship. The grazing pressure by the large population of ciliates limits the growth of small cells, and their distribution, to the surface layer. A summer maximum of ATP without associated chlorophyll is probably related to such feeding activity and to the high growth rate and short division time of protozoans.