Mesozooplankton abundance, biomass and copepod secondary production at the Barents Sea polar front, June 2011

Study Extent

Mesozooplankton (0.25-4 mm) abundance (ind. m-3) and biomass (mg C m-3) and copepod secondary production (mg C m-3 d-1) at four stations (M1-M4) across the Barents Sea polar front, covering Atlantic to Arctic waters (75-78 °N) in June 2011.

Sampling

Mesozooplankton was sampled with a WP-2 net (Hydro-Bios) with 180 µm mesh, 0.57 m diameter net opening and filtering cod-end. Filtration volume was estimated from opening diameter and sampling depth. Three vertical net hauls were taken during day (around noon, WP2-day) and during night (around midnight, WP2-night) at all stations, at fixed depth intervals of 0-50 m, 50-100 m, and 100m-bottom by using a closing mechanism. The content of the cod-end was concentrated over a 90 µm mesh on deck and preserved with buffered formaldehyde at 4 % final concentration. To increase the resolution in the surface and to quantitatively sample the small copepod species and young developmental stages, one GoFlo profile was sampled at daytime at each station in the upper 50 m. Samples were taken from 1, 10, 20, 30, 40 and 50 m depth. The content of the water bottle (30 liters) from each individual depth was concentrated over a 20 µm mesh and preserved with buffered formaldehyde at 4 % final concentration. Mesozooplankton were counted and determined to species and developmental stage under a Leica dissecting microscope at 40x magnification. Mesozooplankton abundance was converted into biomass, based on species and stage-specific carbon weight relationships. Daily copepod secondary production (mg C m−3 d−1) in the upper 50 m water column was calculated as the sum of the product of biomass and weight-specific growth rate of each individual stage within the copepod population. Copepod growth rate was determined using four different growth rate models, namely Hirst & Bunker 2003 (HB_copepod_secondary_production, based on copepod body weight, chlorophyll a concentration, in-situ water temperature), Hirst & Lampitt 1998 (HL_copepod_secondary_productioncopepod, based on body weight, in-situ water temperature), Huntley & Lopez 1992 (HuLo_copepod_secondary_production, based on in-situ water temperature) and Zhou et al. 2010 (Zhou_copepod_secondary_productioncopepod, based on body weight, chlorophyll a concentration, in-situ water temperature, assimilated food input).

Method steps

1. Daily copepod secondary production (mg C m−3 d−1) in the upper 50 m water column was calculated as the sum of the product of biomass and weight-specific growth rate of each individual stage within the copepod population. Copepod growth rate was determined using four different growth rate models, namely Hirst & Bunker 2003: https://doi.org/10.4319/lo.2003.48.5.1988 Hirst & Lampitt 1998: https://doi.org/10.1007/s002270050390 Huntley & Lopez 1992: https://doi.org/10.1086/285410 Zhou et al. 2010: https://doi.org/10.1093/plankt/fbq054

Four stations (M1-M4) across the Barents Sea polar front, covering Atlantic to Arctic waters (75-78 °N). M1: Lat 78.097, Lon 28.125, bottom depth: 278 m M2: Lat 76.949, Lon 29.711, bottom depth: 235 m M3: Lat 76.491, Lon: 29.863, bottom depth: 282 m M4: Lat 74.910, Lon 30.003, bottom depth: 371 m M2 M3 M4