Abstract

To investigate forcing factors on a coastal plankton food web, primary production was measured every 2 weeks for 28 years. On a decadal scale, the North Atlantic Oscillation (NAO) correlated positively to primary production (gamma = 0.44, P = 0.021) and winter surface nitrate (gamma = 0.60, P = 0.0014) and phosphate (gamma = 0.66, P = 0.0003; gamma = 0.60, P = 0.0014). This suggests that climate forcing through increased wind and vertical mixing leads to higher entrainment of nutrients which stimulate yearly primary production. The highest production occurred in summer (1105 +/- 16 mg C m(-2) day(-1)) and correlated positively with zooplankton biomass (gamma = 0.61, P = 0.037), but showed no relation to phytoplankton biomass. Estimated phytoplankton grazing by copepods was low, but ciliates had the potential to remove all the phytoplankton biomass daily. Copepods, in turn, could exert a strong predation on ciliates which indicates a top- down regulation of phytoplankton biomass. Advection of copepods into the fjord and predation of jellyfish are suggested as the main regulatory factors for the copepod populations. We conclude that climate affects the pelagic ecosystem in the fjord through the NAO, but that biological interactions through grazing and predation by copepods regulate the system on a seasonal scale, indicative of a trophic cascade.

Keywords

pelagic production; grazing; ciliates; copepods; top-down control; trophic interaction

Published in

Journal of Plankton Research
2016, Volume: 38, number: 4, pages: 1092-1102

SLU Authors

• Belgrano, Andrea

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    
  • Swedish Institute for the Marine Environment

Sustainable Development Goals

SDG14 Life below water


UKÄ Subject classification

Evolutionary Biology
Oceanography, Hydrology, Water Resources
Ecology


Publication Identifiers

DOI: https://doi.org/10.1093/plankt/fbv094

Permanent link to this page (URI)

https://res.slu.se/id/publ/68967