H .I. Daly, L.S. Peck J. Exp. Mar. Biol. Ecol. 245 2000 197 –214
199
that metabolic reactions are slowed by approximately half when ambient temperature falls by 108C. A Q
of less than 2 denotes insensitivity or acclimation to temperature
10
change and a Q of more than 2 denotes increased sensitivity, with an expected range of
10
1–3 Calow, 1981. Q calculations for E
. cirrhosa acclimated to two temperatures and
10
a combined Q including both E
. cirrhosa and P. charcoti has allowed the assessment
10
and comparison of the effects of temperature.
2. Materials and methods
During the austral summers of 1993 and 1994, inshore trawls at depths of 50–150 m at Signy Island in the South Orkney Islands 608 439 S, 458 389 W caught a number of
specimens of P . charcoti. The specimens were maintained in the aquarium at the BAS
station on Signy Island prior to being transferred by ship to the UK. The annual temperature range at this site varies from around 21.88C in winter to 10.38C in
summer Clarke et al., 1988; Clarke and Leakey, 1996. In May 1993, a single male octopus specimen 1 initially weighing 64 g live weight,
was returned to the UK. It began feeding shortly after arrival and appeared healthy throughout the 18 months that it was maintained in the aquarium. The specimen fed
irregularly on frozen thawed krill Euphausia superba, live amphipods Bovallia gigantea and live mussels Mytilus edulis, and increased in weight to 74 g before dying in
November 1994 after releasing a single spermatophore. In May 1994, a further 13 P
. charcoti were returned, from which two males specimens 2 and 3 initially weighing 47
and 27 g wet weight, successfully established in the aquarium. They fed regularly on live isopods, Antarcturus sp., and mussels M
. edulis, and increased in body weight until they both died in November 1994 weighing 51 and 30 g, respectively. The three healthy
specimens showed apparently normal behaviour. They were all held in the cold aquarium system in Cambridge which is cooled to 060.58C Ward and Peck, 1997, and
were maintained in a light regime of 12-h dimmed light and 12-h darkness.
For the duration of the trial all the P . charcoti specimens were fed on M. edulis. All
food was weighed before addition to each holding tank, and remains removed and weighed after feeding. Frequently, mussels had to be opened using a scalpel before the
octopuses would feed. On their arrival in the aquarium live Antarctic isopods, Antarcturus sp., were successfully used to feed the octopuses. Unfortunately, only a
small stock of live isopods were available for use as food. The frozen thawed krill, E
. superba, were used as food for specimen 1 on its arrival, and this was only initially
successful when individual defrosted krill were placed under the web on a length of wire and moved gently until the octopus closed its arms and web around it. After feeding
successfully for a few weeks during the trial all the specimens rejected any further food offered. Samples of the type of food consumed were dried to constant weight to obtain a
conversion factor for wet to dry weights.
All three specimens were weighed at intervals of 7–14 days throughout the trial to monitor total growth. Specimens were removed from the tanks with nets and weighed in
a plastic beaker. The mass of any water released from the mantle cavity of the octopus was obtained after returning the individual to the aquarium and subtracted from total
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.I. Daly, L.S. Peck J. Exp. Mar. Biol. Ecol. 245 2000 197 –214
mass. The specimens were not anaesthetised, and the period of handling during weighing was kept brief to minimise stress to the animal.
A 1015-ml glass respirometer chamber was used for trials with the 73 g specimen and a cylindrical 237 ml plastic respirometer was used for the two smaller specimens Fig.
1. Both chambers were supplied with seawater from a raised header tank and had controllable flow-rates and ports filled with silicon sealant for taking samples Fig. 1.
To determine the oxygen consumption rates V O , each specimen was placed in the
2
respirometer and it was sealed, making sure that there were no air bubbles trapped in the system. A gentle flow of oxygenated water was passed through the respirometer, at a
21
rate of approximately 600 ml min , for 1 h, while observing the behaviour of the
specimen and recording the activity and time required for the animal to settle. After this period, the flow was stopped at taps A and B Fig. 1, to seal the system. The oxygen
concentration was determined from 25 ml samples, taken using a gas-tight syringe through a port filled with silicon sealant at the top of the chamber Fig. 1. The sample
taken was sufficiently small to make replacement of the volume removed unnecessary.
Fig. 1. The glass A and plastic B respirometers used in oxygen consumption and nitrogen excretion trials. Oxygenated water from a header tank flowed in tap a and out at tap b, and was collected to monitor
flow-rate.
H .I. Daly, L.S. Peck J. Exp. Mar. Biol. Ecol. 245 2000 197 –214
201
To ensure complete mixing of the water, the chamber was gently inverted three times before sampling. Very limited mantle ventilatory movements were observed, and the
inversion movement did not appear to unduly disturb the animals. Samples were taken every 10–30 min and oxygen content obtained via injection into a couloximeter Hersch,
1973; Peck and Uglow, 1990. During trials the respiration chambers were screened from the room to minimise visual disturbance. Oxygen levels in the respirometer were
not allowed to fall below 100 mmHg to minimise the possibility of stress caused by low oxygen tension. Trials where air bubbles were observed in the chamber, or when the
specimen became highly active were abandoned, so that only resting metabolism with minimum activity was recorded.
Nitrogen excretion trials were carried out alternating with the respiration trials over the same time period and using the same respiration chambers. Oxygenated water was
21
passed through the chamber with the specimen inside at approximately 600 ml min for
1 h before the chamber was sealed. Repeat samples of 20 ml were taken at the beginning and end of an hour-long trial, with the chamber being inverted three times before
sampling to ensure complete mixing. Ammonia concentration was measured using the phenolhypochlorite method described by Liddicoat et al. 1975, as modified by
Catalano 1987, and scaled to a sample volume of 10 ml Clarke et al., 1994. Calibration was achieved by spiking seawater samples with a range of concentrations of
ammonium sulphate solution.
V O and nitrogen excretion rates were obtained from comparisons with parallel
2
controls no animal in chamber. All visible faeces were removed from the holding tanks daily and wet weight
recorded. Although the faeces were delicate and were easily broken up on contact, care was taken during collection, and an estimated 80 was successfully recovered. As only
small amounts of faeces were produced the error introduced into the energy budget during collection was small. Faeces were oven dried on filter paper and the dry weight
recorded.
Healthy specimens of E . cirrhosa were obtained by the Department of Zoology,
University of Aberdeen from local commercial trawl fishermen. In October 1994 several E
. cirrhosa specimens were transferred by rail from Aberdeen to the cold marine aquarium at BAS, Cambridge. The smallest specimens available were used to allow a
more direct comparison of respiration rates, as they were closest in size to the P .
charcoti used earlier. Smaller specimens also experienced less stress when being placed in the respirometer chambers. Although there was mortality of some E
. cirrhosa during transportation, two male specimens, with wet weights of 300 and 323 g, were
successfully established in the aquarium, were active and appeared healthy. The specimens were held at 11.58C on arrival, which was the approximate sea temperature at
the time of capture, and not disturbed for 48 h to allow them to settle and acclimate. A large glass respiration chamber, similar in shape to A Fig. 1, but of 2701-ml volume,
with taps for controlling flow-rate and silicon sealant filled ports for sampling was used during trials. Chambers were sealed, trials run and samples processed using the same
method as for P
. charcoti. The specimens were held at 11.58C for 10 days with trials every 2–3 days before being transferred to a room at 4.58C. They were transferred in
their holding tank, which was allowed to cool to the ambient temperature overnight.
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.I. Daly, L.S. Peck J. Exp. Mar. Biol. Ecol. 245 2000 197 –214
After a further 48 h acclimation time, respiration trials were carried out every 3 days for 9 days. The specimens were then transferred to 08C, but both died within 24 h of
transfer. Body mass and volume were recorded at the beginning and end of the trials. Specimens usually remained inactive during trials but on occasion showed some
increased activity in arm movements, which was noted. Trials where considerable activity, such as jetting, was recorded were abandoned.
Throughout the experiment the E . cirrhosa were not fed. The exact time that the
specimens last fed before respiration trials began is unknown, but, assuming that they fed regularly in the wild, it would have been approximately 4 days prior to experimenta-
tion. Attempts were made to provide live food Carcinus maenas at the start of the trial to establish a known feeding time, but this proved unsuccessful due to high prey
mortality during transportation.
The joule has been used here as the energy unit, and the conversion factor to calories is 1 calorie54.184 J Schmidt-Nielsen, 1991.
3. Results
