From fringe to basin: unravelling the survival strategies of Calanus hyperboreus and C. glacialis in the Arctic Ocean

The large calanoids Calanus hyperboreus and C. glacialis dominate the zooplankton biomass in the central Arctic Ocean (CAO), but the absence of early life stages has raised speculation whether they complete their life cycle there, or whether they represent expatriates advected from adjacent regions. Our study, conducted across 2 transects of the CAO during fall 2011, focused on the distribution, stage composition, dry weight, individual lipid content, and egg production of these species. Although reproductive activity and early developmental stages were observed only on the fringes of the deep basins, late-stage copepodite and adult female abundances remained steady across the study area for C. glacialis and increased away from the shelves for C. hyperboreus. We found no decline in lipid content or dry weight in adult C. glacialis away from productive regions and only a minor reduction in adult C. hyperboreus. However, the lipid content and dry weight in C5 copepodites significantly decreased away from the shelf break, particularly in C. hyperboreus. This suggests that although early life stages struggle to survive in the resource-limited conditions of the deep CAO and even subadults remain vulnerable to starvation, adults have the resilience to survive long enough to be eventually transported by ocean currents to more favourable regions for reproduction. As such, we suggest that both species of Calanus are neither ‘residents’ nor ‘expatriates’ in the Arctic basins, but rather ontogenetic migrants that take advantage of different habitats within the Arctic Ocean to maximise their survival and reproductive success.publishedVersio

CAFF CBMP Report No. 19 - Circumpolar Biodiversity Marine Monitoring Plan - background paper

CAFF CBMP Report No. 19 - Circumpolar Biodiversity Marine Monitoring Plan - background pape

CAFF Monitoring Series Report No.3 - Arctic Marine Biodiversity Monitoring Plan (CBMP-MARINE PLAN)

CAFF Monitoring Series Report No.3 - Arctic Council's CAFF Working Group Arctic Marine Biodiversity Monitoring Plan (CBMP-MARINE PLA

Estimating juvenile copepod growth rates: corrections, inter-comparisons and recommendations

The 2 most common experimental methods used to estimate rates of juvenile growth in marine copepods are the molt rate (MR) method, and the artificial cohort (AC) method. Recently, we showed the equations used in the MR method to be incorrect, and proposed a modified molt rate (MMR) method. Here, using statistical and model approaches, we compare the AC and MMR methods under various scenarios to quantify their errors. Although the AC and MMR methods both use a combination of field sampling and simulated in situ incubations to estimate somatic growth, they differ in several important characteristics. The AC method determines growth by the change in mean weight during incubation. Mean weight of copepods in the samples can be determined directly, or inferred from mean weight by life stage or from length–weight regressions. We show that substantial error is avoided only if weights are measured directly (ACdirect). The ACdirect method is insensitive to variable age within stage due to mortality or variable recruitment in the sampled population, an important advantage over the MMR method. However, the ACdirect method is sensitive to variation in growth rate during incubation, which does not affect the MMR method. We therefore recommend that most experimental estimates of growth rate should apply the ACdirect method, with the MMR as a suitable alternative provided its biases are considered. An indirect method based on life stage is biased and we no longer recommend it, and an indirect method based on length–weight regression provides an intermediate level of bias