Shortened duration of the annual Neocalanus plumchrus biomass peak in the Northeast Pacific

Abstract

The calanoid copepod Neocalanus plumchrus (Marukawa) is a dominant member of the spring mesozooplankton in the subarctic North Pacific and Bering Sea. Previous studies have shown interdecadal and latitudinal variation in seasonal developmental timing, with peak biomass occurring earlier in years and places with warmer upper ocean temperatures. Because N. plumchrus normally has a single dominant annual cohort, its seasonal timing can be indexed from measurements of total population biomass or by following progressive changes in stage composition. Early studies empirically found that peak upper ocean biomass occurred when about half of the pre-dormant population had reached copepodite stage 5 (C5). However, more recent comparisons derived from recent Continuous Plankton Recorder (CPR) data now show peak biomass when a larger fraction (> 80%) of the population is at C5. CPR samples the surface 10 to 15 m, but comparisons to depth-resolved BIONESS data show that this discrepancy is not an artefact of sampling depth. Other causes are either a prolongation of duration of pre-dormant C5 or a narrowing of the age range making up the annual cohort. We assessed changes in cohort width using a modification of Greve's cumulative percentile method, and found that average cohort widths in the Alaska Gyre were significantly narrower in

Phenology of pelagic seabird abundance relative to marine climate change in the Alaska Gyre

“…Such effects have been particularly well-documented in the North Atlantic. Fewer studies have been conducted in the North Pacific, but similar findings have been obtained, showing, for example, earlier seasonal peaks in abundance of large, energy-rich Neocalanus copepods in the Gulf of Alaska (Mackas et al 1998, Bertram et al 2001, Batten & Mackas 2009). The phenology of plankton abundance is critical to trophic interactions; if plankton are not available at the right time and place, the foraging ecology of predatory nekton may be compromised, possibly leading to reduced recruitment and population declines in upper trophic-level species (Cushing 1990, Mackas et al 2007, Sydeman et al 2009, Dorman et al 2011.…”

Marine plankton phenology and life history in a changing climate: current research and future directions

“…Used for indexing zooplankton.Based on cumulative biomass; easy to estimate; sensitive to small change; problematic in multi-modal cases.Greve et al . (2005), Batten and Mackas (2009)End of seasonYear day when an upper threshold percentile (e.g. 75th percentile) of annual or seasonal cumulative amount is reached; used for indexing zooplankton.(as for “start of seasonal increase”)Greve et al .…”

“…(2005)Duration of seasonNumber of days between “start” and “end” of season percentile thresholds.(as for “start of seasonal increase”)Greve et al . (2005), Batten and Mackas (2009)“Cardinal Dates”Produces date estimates for start, middle and end of season, based on parameters of a Weibull function fitted to annual or seasonal time series. Applied (so far) only to phytoplankton data.Provides flexible fit to a variety of peak shapes; can deal with multiple modes; but requires a prior within-year fitting step to estimate number of peaks and their separation dates.Rolinski et al .…”

Large-scale forcing of environmental conditions on subarctic copepods in the northern California Current system

“…Of the population structures of N. plumchrus at the three stations over the 11 years, all copepodite stages observed occurred in cold years, whereas only late stages were found in warm years, which is due likely to accelerated temperature-dependent growth during the warm years (Mackas et al, 1998;Batten and Mackas, 2009).…”