On the Biology of <i>Calanus finmarchicus</i>. V. Seasonal Distribution, Size, Weight and Chemical Composition in Loch Striven in 1933, and their Relation to the Phytoplankton

" Wimpenny (1938) has shown that the percentage of copepods taken in the sea with food in the gut tends to be higher at night than by day. Most planktonic animals perform diurnal vertical migrations, of greater or less extent.' Wimpenny's observations may well be a consequence ,of such migrations. , On the other hand, during investigations. into grazing rate of planktonic copepods (Fuller, 1937;Gauld, 1951) some of the measurements have suggested that there is a diurnal variation in the rate at which the copepods ' collect their food, even under laboratory conditions when migration is impossible, and that they filter the water more quickly at night than by day. The variation in the percentage of copepods containing food may be caused simply by changes in the rate of feeding, this being controlled either by the amount of light in their environment or by some internal rhythm affecting their behaviour.An investigation of diurnal variations in the feeding behaviour of Calanus finmarchicus'(Gunn.) was undertaken to investigate (i) its behaviour in nature:, and (ii) the possible existence of alternations of feeding and resting periods under laboratory conditions. This species was chosen because it is the dominant copepod species in the Clyde sea area, is readily obtainable ill reasonable numbers at all times of the year, and has already been the subject of investigation of feeding rate. . FIELD OBSERVATIONS MethodsCalanus were obtained from la-min. hauls of 50-em. coarse tow-nets (26 meshes to the inch) taken at 4-hourly intervals through 24 hr. Three nets were fished at once, 25 fathoms apart on a trawl warp, to the end of which was attached a cable depressor (Barnes, 1951). Rigged in this way, the uppermost net fished 2-3 m., the second 35-40 m. and the lowest c. 75-80 m. from the surface. There was no means of closing the nets before hauling, but the percentage of the fishing time spent by the lower nets in. the upper strata' was small and unlikely to have interfered greatly with the results. The hauls were taken at a station just outside Tarbert, Loch Fyne. At this station deep water

Section: Resultsmentioning

confidence: 85%

Diurnal Variations in the Grazing of Planktonic Copepods

Gauld¹

1953

“…All the foregoing light experiments, with the possible exception of that on May 10th, were done on the first brood which is occasionally found near the surface (Marshall, Nicholls and Orr, 1934). Stage V Calanus from a summer brood were used for a similar respiration experiment in the sea in August at the surface, 0.5, 2,3, 5 and 10 metres ( Figure 7 and Table XI).…”

Section: L1;ghtmentioning

confidence: 99%

“…per 1000 per hour (1922) or roughly three times our value in the dark. From January to March the Stage V weigh about 15 mg. per 100 individuals (Marshall, Nicholls and Orr, 1934) and the oxygen consumption at 5°C. is about 0.17 ml.…”

Section: F~)qd Requirements Of Calanusmentioning

confidence: 99%

On the Biology ofCalanus finmarchicus. Part VI. Oxygen Consumption in Relation to Environmental Conditions

Marshall¹,

Nicholls²,

Orr³

1935

Self Cite

SUMMARY1. Experiments have been done to determine the oxygen utilisation by male, female and Stage V Calanus under different environmental conditions.2. An initial fall in the respiration of adult Calanus was observed during the first few hours after capture. Stage V do not show this clearly. It is found more often in winter than in summer.3. The lethal temperature varies from 24° C. in winter to 26° C. in summer. Stage V Calanus are more resistant to high temperatures than adults.4. Respiration rises with increase of temperature from 0° C. to 20° C. The increase does not follow van't Hoff's law. The oxygen consumption of males and females is about the same, while that of Stage V is lower. Above 20° C. there is a harmful effect.5. Within the limits studied (pH 7.4–pH 8.5) change in hydrogen-ion concentration has no effect on respiration.6. Calanus are unaffected by an increase in the oxygen content of the water, but are sensitive to low oxygen tensions. Below a concentration of about 3 ml. per litre the respiration decreases. At concentrations between 1 and 2 ml. per litre they are killed. They are more resistant at 5° C. than at 15° C. and Stage V are more resistant than adults at both these temperatures.7. Calanus can become acclimatised to salinities as low as 35–40% seawater (S=12‰–13.6‰), but their respiration is lowered at a salinity of 50%.8. Light has a striking effect on Calanus. It may increase the respiration by 100% or more. This effect can be detected also in the sea, but not below 5 metres. Continuous exposure to light is harmful.9. The bearing of these results on the distribution of Calanus is discussed.10. From the amount of oxygen used in respiration, calculations of the food required are made and these are compared with the results given by Putter for Calanus and other copepods.

“…A few observations have been made on the feedingof the young stagesof Calanusin the laboratory, but none are available on feeding under natural conditions. It has been suggested (Marshall, Nicholls & Orr, 1934) that the success or failure of a brood of Calanus in the sea might depend on the presence of a rich food supply during its development. Experiments were therefore undertaken to find what organisms could be ingested by the nauplii and early copepodite stages, how much of the different foods could be digested, and how much water they could filter in a day.…”

mentioning

confidence: 99%

On the biology ofCalanus finmarchicusIX. Feeding and digestion in the young stages

Marshall¹,

Orr²

1956

Self Cite

Little is known about the food of the nauplii and early copepodite stages of copepods, although it has usually been assumed that the food particles must be smaller and perhaps more concentratedthan for adults. A few observations have been made on the feedingof the young stagesof Calanusin the laboratory, but none are available on feeding under natural conditions. It has been suggested (Marshall, Nicholls & Orr, 1934) that the success or failure of a brood of Calanus in the sea might depend on the presence of a rich food supply during its development. Experiments were therefore undertaken to find what organisms could be ingested by the nauplii and early copepodite stages, how much of the different foods could be digested, and how much water they could filter in a day. METHODSThe use of food cultures labelled with radioactive phosphorus (32P)enables an accurate measure to be made of the amount taken in, and'the methods used in earlier experiments on feeding in adult and Stage V Calanus (Marshall & Orr, 1955b)were found to be useful for the younger stagesalso. When photosynthetic organisms are grown' in a medium containing inorganic 32p it is rapidly taken up and the culture can then be used in different concentrations to measure the amount filtered and the amount assimilated in a given time. A variety of food organisms of different sizes and belonging to different systematic groups was used. In each experiment the copepods were put in bottles filled with a culture of known concentration of the food to be tested and the bottles were then tied in dark cloth bag!i and attached to a wheel revolving slowlyso that the culture was kept in suspension. All experiments were carried out in a cool aquarium. At the end of the experiment, which lasted from 16to 24 h, the bodies, and sometimesthe faecal pellets also, were removed and washed. They were then dried and exposed on a disc or planchette under the end window of a Geiger counter to measure the radioactivity .The results are shownas countsper minute. Specimenswerealsokept in filtrate from the radioactive culture to measure the uptake, if any, of 32pin solution.