Copepod grazing and its potential impact on the phytoplankton development in the Barents Sea

Abstract

Compiled data from published and unpublished sources on copepod grazing of the large-sized copepods in the Barents Sea give wide ranges in grazing rates. Approximate average values indicate daily rations of 7-18% for copepodite stages V and VI and considerably higher values for the earliest copepodite stages. It is demonstrated that individual variability in gut fullness of copepods from a given locality is typically very high and not closely related to variable food abundance or depth of occurrence. There is no die1 feeding rhythm during the summer. and even when relating copepod grazing to a number of biotic and abiotic factors through stepwise linear regression analysis, much of the variability remains unexplained. It is suggested that feeding behaviour, food quality and feeding history of the copepods all play important roles as factors which regulate copepod grazing. Model simulations on the phytoplankton succession, using literature data on laboratory-determined growth characteristics for solitary cells and colonies of the prymnesiophyte Phaeocystis pouchetii and large diatoms, indicate that the extent of the mixed layer and selective grazing by zooplankton are important factors that may explain the occurrence of dense blooms of P. pouchetii colonies, frequently observed during the spring.

Different Observational Methods and the Detection of Seasonal and Atlantic Influence Upon Phytoplankton Communities in the Western Barents Sea

“…RDA results, derived from cell counts and absorption spectra, demonstrate that cosq values for silicic acid and nitrate concentrations correlate strongly with diatom dominance. Diatom blooms routinely occur as r-strategists in eutrophic spring conditions in the Barents Sea (Båmstedt et al, 1991) and may be found in close association with the marginal ice zone into summer (Strass and Nöthig, 1996), an observation consistent with the geographic and seasonal distribution of diatom biomass across our samples (Figure 3). However, the absence of this pattern in RDA derived from pigments (Figure 4B) requires explanation.…”

Biomass and productivity distributions and their variability in the Barents Sea

“…From Sakshaug et al (1994). Based on studies by Båmstedt et al (1991). Dalpadado and Skjoldal (1991), Hassel et al (1991), Haug et al (1991Haug et al ( , 1993, Hopkins and Nilssen (1991), Markussen and Øritsland (1991), Markussen et al (1992), Mehlum and Gabrielsen (1993), Nilssen et al (1992), Ryg and Øritsland (1991), Sakshaug and Slagstad (1992), Schweder et al (1992), Skjoldal (1990, 1992), and Wassmann (1990).…”

“…maxima. To maximise grazing and minimise sedimentation (''match''), phytoplankton blooms should not begin too early and they should be of long duration so that the probability of zooplankton stocks encountering phytoplankton blooms is maximised (Sakshaug and Skjoldal, 1989;Båmstedt et al, 1991;Hassel et al, 1991). The late and protracted phytoplankton blooms in the permanently ice-free Atlantic waters may represent good examples of ''match'' whereas the early blooms that arise where sea ice overlies Atlantic water may be textbook examples of mismatch, as are the early spring blooms in Norwegian fjords (Wassmann, 1990).…”