134 B
.J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
determined at six P levels 24, 55, 86, 118, 149 and 180 Torr and the dissolved
O
2
oxygen levels were kept within 8 Torr of those designated levels. Therefore, a reading at 118 Torr represents the average oxygen consumption over the 110–126 Torr range.
The dissolved oxygen tension where M becomes dependent is termed the critical
O
2
oxygen tension P . P was determined by calculating regression lines for the two
c c
distinctly different parts of the relationship between oxygen consumption and P , the
O
2
horizontal high P segment and the sharply sloped low P
segment. P was designated
O O
c
2 2
as the intersection point of the two lines Cochran and Burnett, 1996. 2.10. Statistical analyses
Linear regressions were obtained by the least squares method and were tested for significance by analysis of variance of the regression. Covariance analysis was used to
test for differences of oxygen consumption with sex and activity, using lobster weight as the covariate. Student’s t-tests paired where necessary were used to evaluate
differences in the standard and active oxygen consumption rates at each experimental temperature. Paired Student’s t-tests were used to evaluate when postprandial and
post-handling oxygen consumption had returned to standard levels. Where appropriate a Student’s t-test for samples with unequal variances was used. Paired t-tests were also
used to evaluate if there was a daily rhythm to oxygen consumption by comparing the average night-time rate to the standard rate. Student’s t-tests were used to determine
which data points were included in each regression when evaluating P . Values which
c
were significantly lower than that recorded at 149 Torr were included in the lower line. All analyses were performed on the SPSS statistical package with the a set at 0.05. All
means are expressed as mean6S.E.
3. Results
3.1. Effect of temperature on oxygen consumption Active oxygen consumption was significantly higher P ,0.01 than standard oxygen
consumption at each temperature Fig. 1. Standard oxygen consumption M
O
2
increased exponentially with temperature T and is described by the equation:
2
LogM 5 0.047T 2 2.25 r 50.94, DF
, MS50.012, F 5674, P ,0.0001.
O 1,53
2
Active oxygen consumption increased greatly between 5 and 138C. At 17 and 218C active oxygen consumption rates increased, but they were not significantly higher
DF , MS50.0003, F 53.07, P 50.06 than at 138C. The response is described by the
2,29 24
2 2
equation: M 5 2 3.3 3 10
T 1 0.013T 2 0.044 r 50.89, DF , MS50.02, F 5
O 2,52
2
201, P ,0.0001. The quadratic model suggests a decline in oxygen consumption beyond 218C, but
more data points are required to confirm the presumption. The aerobic scope for activity increased as temperature increased from 58C, with a
maximum SFA recorded at 138C Fig. 1. The increase in the scope for activity over that
B .J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
135
Fig. 1. The effect of temperature on oxygen consumption mean6S.E.mg O g h of the southern rock
2
lobster, Jasus edwardsii N 512. Standard D and active O oxygen consumption rates both increased with temperature. The aerobic scope for activity mg O g h at each temperature is also shown h.
2
range was largely due to the increase in active oxygen consumption. At higher temperatures 17 and 218C the scope for activity decreased due to the declining rate of
increase of active M , associated with the exponential increase in standard M .
O O
2 2
Aerobic expansibility Table 1 was highest at 9 and 138C 2.79 and 3.00, respectively and was lowest at the extremes of the temperature range being 1.52 at 58C and 1.68 at
218C. The Q
of the standard oxygen consumption decreased as the temperature increased
10
Table 1 ranging from 4.3 Q to 2.3 Q
. The Q for the active lobsters
10 5 – 9 10 17 – 21
10
showed a very different pattern. Between 5 and 98C active oxygen consumption
Table 1 The aerobic expansibility of the southern rock lobster, Jasus edwardsii, at each experimental temperature
N 512
a
Temperature 8C
Aerobic Temperature
Q
10 b
expansibility range 8C
Standard M Active M
O O
2 2
5 1.52
5–9 4.3
19.4 9
2.79 9–13
3.0 3.6
13 3.00
13–17 2.6
1.1 17
2.13 17–21
2.3 1.3
21 1.68
Average –
5–21 3.0
6.4
a
The Q values of standard and active oxygen consumptions for each temperature range are shown along
10
with the average Q values over the whole temperature range.
10 b
Aerobic expansibility5active M standard M .
O O
2 2
136 B
.J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
increased markedly which resulted in a Q of 19.4. Q
values above 138C are
10 5 – 9 10
close to unity. 3.2. Effect of body size on oxygen consumption
The sex of the lobsters did not have a significant effect on either the standard SS50.003, F 51.00, P 50.32 or active SS50.004, F 50.58, P 50.45 oxygen
consumptions Fig. 2. Therefore, the data for both sexes have been pooled. A log–log plot of weight specific oxygen consumption mg O g h over wet body weight is
2
shown in Fig. 2. The standard and active rates of oxygen consumption M , mg
O
2
O g h decreased with increasing lobster wet weight W, g. The regression equations
2
describing the relationships are:
2
• Standard oxygen consumption: Log M
5 2 0.405 log W 2 0.396 r 50.69,
10 O
10
2
DF , MS50.37, F 599.9, P ,0.0001.
1,45 2
• Active oxygen consumption: Log M
5 2 0.312 log W 2 0.238 r 50.41, DF ,
10 O
10 1,45
2
MS50.22, F 530.5, P ,0.0001. There was no significant difference between the slopes of the regressions for standard
and active oxygen consumption SS50.01, F 51.77, P 50.186, although there was a significant increase in oxygen consumption with activity SS50.56, F 599, P ,0.0001.
When the data were plotted as total oxygen consumption mg O h then both standard
2
and active rates were positively correlated to the wet weight, with slopes of 0.595 and 0.688, respectively. The weight-specific aerobic scope for activity decreased significantly
Fig. 2. A log–log plot of weight specific oxygen consumption M , measured in mg O g h against body
O 2
2
weight g range5186–2180 g of the southern rock lobster, Jasus edwardsii. Standard O and active h oxygen consumption rates of males clear symbols and females black symbols are shown.
B .J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
137
DF , MS50.002, F 513.7, P 50.0006 with weight, and for a 700 g lobster was
1,45
approximately 0.05 mg O g h. As indicated by the similarity between the b values,
2
there was no significant difference DF , MS50.055, F 50.20, P 50.65 in aerobic
1,45
expansibility with weight. The mean aerobic expansibility was 2.7260.08 6S.E. with a range between 2 and 4.
3.3. Effect of diurnal rhythm on oxygen consumption Lobster weight did not have a significant affect DF
, MS5193.1, F 50.77,
1,20
P 50.78 on the night-time increase in oxygen consumption. Lobsters consumed significantly DF , t 57.916, P ,0.001 more oxygen at night, with consumption up to
42
four times the daytime rates being recorded. Average night-time consumption was 48.366.1 higher than standard oxygen consumption. Using standard oxygen consump-
tion as a measure of oxygen consumption during the entire 12-h daylight period, and the recorded night-time rates, routine oxygen consumption was calculated to be 24.2
higher than the standard rate. Video recordings demonstrated that lobsters were very active at night, continuously moving walking around the respirometer, whilst during
daylight hours they were generally immobile. The oxygen consumption of a 728-g lobster over a 48-h period is shown in Fig. 3 to demonstrate the general diurnal
response.
3.4. Effect of emersion and handling on oxygen consumption Handling and emersion caused a significant t 56.75, P ,0.001 increase in oxygen
Fig. 3. Oxygen consumption mg O g h of an undisturbed 728 g southern rock lobster Jasus edwardsii
2
over a 48-h period. Each symbol represents oxygen consumption over a 20-min measuring period. The lobster was in complete darkness between 6 p.m. and 6 a.m. The line is drawn for ease of viewing.
138 B
.J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
Fig. 4. The effect of handling and emersion on oxygen consumption mean6S.E.mg O g h of the southern
2
rock lobster, Jasus edwardsii N 510. Pre-handling h and recovery d oxygen consumption rates are shown. The break represents the 0.5-h emersion and handling period. The asterisk indicates when oxygen
consumption of recovering lobsters is not significantly different to the pre-handling level. Each reading represents the oxygen consumption rate measured over a 20-min period after the time noted.
consumption upon re-immersion Fig. 4. From the initial high level after re-immersion, oxygen consumption declined slowly until it was not significantly different t 51.67,
P 50.13 from the pre-emersion level at 4.5–5.0 h.
3.5. Effect of feeding on oxygen consumption Oxygen consumption increased after feeding, reaching a maximum 10–13 h after
feeding Fig. 5. The maximum oxygen consumption was 1.72 times the preprandial level. From this maximum level, oxygen consumption slowly declined until it was not
significantly different P ,0.05 from the preprandial level after 42 h. The effect of the diurnal rhythm on oxygen consumption during the postprandial period did not appear to
be strong, although it seems to become an influence on the second night after feeding. The influence of normal night-time activity may have prevented oxygen consumption
from returning to standard M
earlier than recorded. However, oxygen consumption
O
2
during the daylight, 1 day after feeding was still 1.42 times the preprandial level. A large peak in oxygen consumption, lasting approximately 1 h, was recorded immediately after
feeding Fig. 5.
3.6. Effect of dissolved oxygen levels on oxygen consumption Settled lobsters were able to maintain a constant rate of M
as the dissolved oxygen
O
2
level of the water decreased Fig. 6. Standard M was maintained down to a critical
O
2
oxygen tension P of 58 Torr. Below the P , M decreased linearly with the dissolved
c c
O
2
B .J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
139
Fig. 5. Oxygen consumption mg O g h6S.E. of the southern rock lobster, Jasus edwardsii , over a 48-h
2
period N 511. The lobsters were fed squid, Nototodarus gouldii, 3 of the lobsters body weight at 9.00 a.m. on the first day. Preprandial h and postprandial d oxygen consumption rates are shown. Each symbol
represents the average oxygen consumption over 1 h ie. two measuring periods. For ease of viewing lines are drawn between succeeding data points. The asterisk indicates when postprandial oxygen consumption is not
significantly different to the preprandial level.
Fig. 6. The relationship between dissolved oxygen tension Torr and oxygen consumption mean6S.E.mg O g h of settled O N 515 and active m N 512 southern rock lobsters, Jasus edwardsii. The aerobic
2
scope for activity mg O g h d is also plotted as a function of the dissolved oxygen tension.
2
140 B
.J. Crear, G.N.R. Forteath J. Exp. Mar. Biol. Ecol. 252 2000 129 –147
oxygen level. M of active lobsters decreased with decreasing dissolved oxygen levels
O
2
but the rate did not become significantly different until the dissolved oxygen tension was 86.3 Torr. The P for active lobsters was calculated to be 93 Torr. The aerobic scope for
c
activity decreased with the dissolved oxygen tension and was controlled by the active M . The scope at 86.3 Torr is 73 of that of the maximum, however, at 55 Torr the
O
2
scope is only 25 of the maximum aerobic scope.
4. Discussion
