Composition of wax esters is linked to diapause behavior of Calanus finmarchicus in a sea loch environment

Abstract

We studied the seasonal lipid dynamics of Calanus finmarchicus from Loch Etive, a semi-enclosed fjordic environment on the west coast of Scotland, in relation to the diapause behavior of this species. Levels of total lipid and triacylglycerol in individual copepodid stage V (CVs) exhibited clear seasonal trends, with highest levels in June and progressively decreasing through late summer to winter. Wax esters in CVs were more variable, but followed a similar pattern. An index of the level of unsaturation of wax esters, effectively an indicator of the levels of polyunsaturated fatty acids in the wax ester reserves, were highest in midsummer and declined progressively through autumn and winter. Fatty acid analysis of total lipid in the CVs confirmed that the amounts of polyunsaturated fatty acids in the wax esters decreased, while amounts of saturated and monounsaturated fatty acids remained comparatively stable. Polyunsaturated wax esters are selectively catabolized by C. finmarchicus during diapause. Previous studies have linked unsaturation of wax esters in calanoid copepods to the initiation of diapause and buoyancy control, and we hypothesize that selective catabolism of polyunsaturated wax esters is linked to the processes of diapause termination and ascent to surface waters.

Unexpected Levels of Biological Activity during the Polar Night Offer New Perspectives on a Warming Arctic

“…Those Calanus specimens inhabiting deep oceanic waters (>500 m) may exhibit a more profound form of dormancy during winter [18][19][20] than in shallow waters (<500 m water depth), perhaps since shallow-water populations may need to be more active to counteract buoyancy forces [21]. However, Calanus can successfully overwinter in shelf and coastal waters (<500 m), and they are usually found at greater depth during autumn and winter [22][23][24], with their ascent related to ice breakup and the onset of the spring bloom [22,23]. Our results reveal not only that Calanus commence their ascent long before light and food become abundant but also that zooplankton respiration rates per unit biomass in the uppermost 100 m of water column in Kongsfjorden were higher in January than in May or September ( Figure 2C) and within the range of measurements made in July north of Svalbard [25].…”

Calanus finmarchicus seasonal cycle and diapause in relation to gene expression, physiology, and endogenous clocks

“…In the open ocean, C. finmarchicus diapauses at depths between 400 m and 1000 m (Hirche ; Heath et al ) where seasonal changes of environmental parameters are minimal or absent. The potential lack of seasonal cues for triggering emergence has led to the proposal of an hourglass model based on the gradual depletion of wax esters (Miller et al ; Campbell et al ; Saumweber and Durbin ; Clark et al ) mediated by lipid‐derived hormones (Irigoien ; Pond et al ) or based on continuous slow development (Hind et al ). However, our results from Loch Etive contradict this view.…”

On the surprising lack of differences between two congeneric calanoid copepod species, Calanus finmarchicus and C. helgolandicus

“…Location Maximum WE (lg C) Kattner and Krause (1987) North Sea 30 Kattner and Krause (1989) North Sea 49.808 Ohman and Runge (1994) St. Lawrence 11.356 Heath and Jónasdóttír (1999) Faroe-Shetland Channel 100 Clark et al (2012) Loch Ewe 100 Marker et al (2003) Bergen 77 Marker et al (2003) Tromso 82 Hygum et al (2000a) Mesocosms 60 Hygum et al (2000b) Mesocosms 72 Rey-Rassat et al (2002b) Mesocosms 142 Jónasdóttír (1999) Faroe-Shetland Channel 200 (Rey-Rassat et al, 2002b). However, individuals were raised at different temperatures in this study: C. finmarchicus at 8°C and C. helgolandicus at 15°C.…”

“…The temperature at which lipids can undergo liquid-solid phase transitions is dependent on the level of unsaturation (Pond and Tarling, 2011), and selective catabolism of saturated and unsaturated wax esters may play a key role in aiding neutral buoyancy during overwintering (Clark et al, 2012). The physical properties of C. finmarchicus lipids in general needs further study, and so the relative importance of lipids to buoyancy regulation remains unclear.…”