Aspects of the study of the life cycles of Antarctic copepods

Abstract

Different approaches to the study of life cycle strategies of Antarctic copepods are described in an attempt to shed new light on our present knowledge. To date, most studies were carried out on abundance, horizontal and vertical distribution and stage composition during different seasons and in various regions. Hence, the seasonal pictures had to be compiled from different years and sampling regions. The physiological method includes measurements on e.g. egg production, feeding, respiration and excretion rates, C:N and O:N ratios, lipid and protein contents. However, both physiological and biochemical data are still rare. Results of field observations are given in this paper for investigations conducted within the last 15 years in the eastern Weddell Sea, while data of physiological parameters are based on a broader geographical region. In the eastern Weddell Sea, eight copepod species account for about 95% of copepod abundance and for more than 80% of copepod biomass. Within the calanoids, the small species Microcalanus pygmaeus dominates by numbers with 66%, while the large species Calanoides acutus and Calanus propinquus comprise together 52% of the biomass. Species abundance is lowest in winter and highest in summer/autumn, however, seasonal changes in the abundance of M. pygmaeus are small and this species occurs in similar quantities throughout the year. All copepod species show a distinct seasonal vertical distribution pattern and they occur in upper water layers in summer, in contrast to the other seasons. However, the depth layers of maximum concentration differ between species. The ontogenetic vertical migration is most pronounced in C. acutus and relatively weak in C. propinquus. The age structure also shows seasonal differences with the youngest population observed in summer for C. acutus, C. propinquus, Ctenocalanus citer or autumn for Metridia gerlachei, whereas the M. pygmaeus population is oldest during summer. The youngest copepodite stage and the males are not always present in C. acutus and C. propinquus. In contrast, all developmental stages and both sexes occur throughout the year in M. gerlachei, M. pygmaeus and C. citer. Gonad maturation in the dominant calanoid species proceeds well before the onset of phytoplankton production in the eastern Weddell Sea. However, the highest portion of females with ripe gonads and hence highest egg production rates coincide with the productive period in spring and summer. In autumn, ovaries of the three larger species C. acutus, C. propinquus and M. gerlachei are all spent. In contrast, the percentage of ripe females of the two smaller species, C. citer and M. pygmaeus, stays high in autumn. Egg production rates are highly variable within one region and species. Many copepods accumulate large depots of lipid, mainly wax esters. In contrast, five species (C. propinquus, C. simillimus, Euchirella rostromagna, Stephos longipes and Paralabidocera antarctica) almost exclusively synthesise triacylglycerols and not wax esters. The lipid content exhibits ...

Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea, Antarctica

“…Among the Southern Ocean zooplankton, a lot is known about the seasonal vertical migration behaviour of copepods. Most of them migrate seasonally, however, and show distinct species-and stage-specific and regional differences in migration amplitude and timing (Atkinson et al, 1992;Ward et al, 1997;Schnack-Schiel, 2001). Since there were no net hauls of plankton near the moorings during their deployment period, we can only speculate about the species composition of zooplankton whose migration is documented by our measurements.…”

Phenology and fitness of Calanus glacialis, C. finmarchicus (Copepoda), and their hybrids in the St. Lawrence Estuary

“…Conover 1988, Conover & Huntley 1991, Atkinson 1998, Schnack-Schiel 2001. Within the same environment, it is widely held that congener species of copepods have unique assortments of life-history traits, limiting interactions among them.…”

Ecophysiology of overwintering in the copepod Neocalanus plumchrus: changes in lipid and protein contents over a seasonal cycle

“…It has been proposed that copepods use protein as a metabolic substrate during overwintering in order to preserve lipid stores for reproduction (Kirkesaeter 1977, Jónasdóttir 1999, Schnack-Schiel 2001. It has also been suggested that protein may be used to fuel egg release in Neocalanus plumchrus (Evanson et al 2000).…”

“…Evidence for protein use during overwintering includes observed declines in total protein content (Kirkesaeter 1977); declines in nitrogen content (Tande 1982, Ohman et al 1989; low but measurable rates of ammonium excretion (Conover & Corner 1968, Cowen 1982; and low O:N ratios (Conover & Corner 1968, Kosobokova 1990, Schnack-Schiel 2001. Calanoid copepods are primarily ammonotelic, whereby the catabolism of proteins and nucleic acids produces ammonium (Corner & Cowey 1968).…”