Equivalence of copepod and insect diapause

189

122

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.

Section: Discussionmentioning

confidence: 38%

Overwintering of Calanus finmarchicus and Calanus helgolandicus

Hirche¹

1983

189

122

“…Acartia, Tortanus, and several other heterarthrandnd genera produce diapause eggs. In the Calanidae and related families (all among the amphascandrids) there is a quiescent phase, or possibly a true diapause (Elgmork & Nilssen 1978), at one or more of the copepodite stages. There has been research on both types of rest-ing stage, and for resting eggs this has included some work on the events in the habitat that trigger diapause egg production (Johnson 1979, Marcus 1982, Sullivan & McManus 1986) and on conltions allowing hatching of such eggs (Uye & Fleminger 1976).…”

Section: Phenology In Calanoid Copepodsmentioning

confidence: 99%

Phenology in Calanus finmarchicus; hypotheses about control mechanisms

Miller¹,

Cowles²,

Wiebe³

et al. 1991

164

114

Calanus finmarchicus (Gunnerus) stratify nariowly near 500 m depth dunng their fifth copepodite resting phase in North Atlantic Slope Water off southern New England USA They probably a c h~e v e this by migration to a specific, daytime isolume Photoperiod information provided by light intensity at depth could serve as a cue for termination of the resting phase Population data on tooth formation and gonad growth show that the reshng stock prepares foi termination in late winter and matures in February-March Photopel~ods are lengthening throughout that seasonal interval, and might cue arousal An endogenous, long-range timer that cues arousal after an interval of rest is another possible mechamsm

“…Copepod dormancy may be described in similar terms to that of insects (Watson & Smallman 1971b, Elgmork & Nilssen 1978, Grice & Marcus 1981. 'Quiescence' refers to a state of retarded development as a direct response to adverse environmental conditions, whilst 'diapause' refers to a genetically controlled state of arrested development, triggered by a stimulus preceding the onset of environmental adversity (Grice & Marcus 1981).…”

Section: Introductionmentioning

confidence: 99%

Seasonal occurrence and hatching of calanoid eggs in sediments of the northern Baltic Sea

Katajisto¹,

Viitasalo²,

Koski³

1998

The seasonal occurrence and hatching of benthic eggs of calanoid copepods were studied for 1 yr in the surface sediments at 2 sites (a 33 m deep archipelago area and a 42 m deep site in an enclosed bay) off the SW coast of Finland, northern Baltic Sea. Eggs were abundant at both sites (up to 4 and 6 X 106 eggs m-2). At the archipelago site, most eggs belonged to Acartia bifilosa and A. tonsa; at the bay site, eggs of Eurytemora affinis and Acartia spp. occurred. At the archipelago site, the egg numbers in the surface sediment followed closely the seasonal abundance of the planktonic Acartia spp. females. The eggs collected from the sediment were Incubated at temperatures corresponding to the in situ bottom temperatures. Hatching of the A. bifilosa eggs occurred throughout the year, but it was most intensive in autumn when water stratification broke and the deep water warmed up to 13°C. It is suggested that a large number of the A. bifilosa eggs sink to the bottom prior to hatching m shallow coastal areas of the Baltic Sea. Hatching of the benthic eggs occurs throughout the year and the rate of naupliar emergence from the sediments depends on benthc condtions and processes (e.g. temperature, sediment resuspension and bioturbation). At the bay site, where the surface water layer was hydrographically separated from the deep water, the coupling between the benthic egg abundance and the planktonic populations was not so obvious. The dominant species E. affinis carries its eggs in an egg sac unhl hatching, and probably only the diapause eggs, which are produced in autumn, fall to the bottom. A. tonsa was abundant in the water column at both study sites in autumn, even outnumbering other Acartia spp. in some samples. The eggs of the species only hatched in autumn, when the incubations were conducted at 10 to 13°C. It is probable that A. tonsa spends most of the year as benthic resting eggs In the northern Baltic Sea. In contrast, A bifilosa and E. affinis occurred in the plankton in winter at both study sites, though in low concentrations. They thus have 2 possible sources of recruitment when conditions are again favourable for population growth in spring: hatching of benthc eggs and reproduction by the overwintering population.