Overwintering of Calanus finmarchicus and Calanus helgolandicus

Abstract

Overwintering of Calanus finmarchicus and C. helgolandicus was studied in the field and in laboratory experiments in a shallow (120 m) Swedish fjord and in a deep (650 m) Norwegian fjord. In the Norwegian fjord 2 populations were found in late summer and autumn: in the surface layer the copepods were smaller and more active with high respiratory and digestive enzyme activities. The deep population, consisting of Copepodid stage V (CV) and a few females, was torpid, had large oil sacs and empty guts. Their respiratory and digestive enzyme activities were very low. In the Swedish fjord CV in deep layers weighed much less than those in the Norwegian fjord. Weight-specific respiration was intermediate between deep and surface population in the Norwegian fjord. It is concluded that overwintering copepodids do not feed. Metabolic rates allowed successful overwintering only in the Norwegian fjord. Experiments performed on several occasions during overwintering witnessed -in contrast to the situation in field populations -increased rates of respiration and moulting. Mortality during moulting and time span between capture and onset of moulting decreased during autumn and winter. These observations suggest internal development during overwintering.

Heat shock protein expression during stress and diapause in the marine copepod Calanus finmarchicus

“…Like Hsp70A, Hsp22 was induced upon handling in shallow samples; however, Hsp22 expression was elevated in diapausing animals. These observations could be explained by differential induction of Hsp22 during the process of collecting active and diapausing samples (i.e., if Hsp22 is more inducible in diapausing copepods); however, we consider this unlikely since diapausing copepods are expected to be in a state of torpor with reduced responsiveness to external stimuli (Hirche, 1983).…”

“…Diapause is characterized by a persistent reduction of metabolism, increased stress resistance, and an arrest of development at a specific life stage (Kostál, 2006). Many aspects of true diapause are observed in the physiology of dormant C. finmarchicus, including a preparatory phase that precedes unfavorable environmental conditions (Dahms, 1995;Hirche, 1996), a dormancy phase characterized by an endogeneous arrest in development, reduction of metabolism and respiration (Hirche, 1983;Ingvarsdóttir et al, 1999), and gene expression patterns consistent with increased stress resistance (Tarrant et al, 2008), and a distinct post-dormancy phase when development resumes (Hirche, 1996). Therefore, we refer here to the C. finmarchicus dormancy as a facultative diapause; however, we recognize that not all individuals or populations of C. finmarchicus appear to enter a diapause state at the same time 4 or of similar intensity (Hirche, 1996), which is dissimilar from the true diapause observed in other well-characterized organisms (e.g.…”

“…Diapause in C. finmarchicus is identified by a combination of classic behavioral, morphological, and biochemical characteristics: diapausing C5 copepodids accumulate at depths below 200 to 300 m in oceanic waters (Heath et al, 2004;Miller et al, 1991;Sameoto and Herman, 1990), have empty guts with thin epithelia (Bonnet et al, 2007;Hirche, 1983), and have large oil sacs (Miller et al 2000). Indicative of arrested development, diapausing copepods have reduced transcriptional activity (i.e.…”

Seasonal movements and behaviour of basking sharks from archival tagging: no evidence of winter hibernation

“…The winter diving activity, as during summer, may serve to locate discrete layers of zooplankton prey. Energy-rich calanoid copepods such as Calanus finmarchicus and C. helgolandicus, the predominant prey of basking sharks, over-winter in shelf and shelf-edge deep water (100 to 2200 m) (Hirche 1983, Williams & Conway 1984, Heath et al 2000 and so may be the targets of the very deep dives we measured. Non-migrating, deep-water copepods such as Euchaeta spp.…”

Vertical distribution and population structure of Macrosetella gracilis (Copepoda: Harpacticoida) in the Red Sea in relation to the occurrence of Oscillatoria (Trichodesmium) spp. (Cyanobacteria)

“…The high number of oil droplets observed in the deep-living females indicate considerable lipid storage, typical for resting stages of calanoid copepods (Conover 1962, Hirche 1983, Alldredge et al 1984. A biochemical analysis of the Macrosetella gracilis specimens for physiological determinations such as protein, lipid or enzyme content is not practicable after fixation in formaldehyde.…”