J. Zool., Lond. (1966) 149, 163-173

The oxygen consumption of some intertidal gastropods in relation to zonation

EYVOR E. SANDISON*

Department of Zoology, Westfield College, University of London

(Accepted 8 February 1966)

(With 4 figures in the text)

The series of gastropods Thais lapillus, Littorina littorea, L. littoralis and L. saxatilis inhabit successively higher intertidal zones, and it was thought that they might show respiratory adaptation in relation to their various periods of exposure and submergence. To investigate this the respiratory rates of each species in air, and in water, have been measured at regular intervals over a period of 12 hours, and also subsequent to three and 16 hours drying.

When placed in water the respiratory rate of L. saxatilis is shown to be influenced by a diurnal rhythm, and that of L. littorea by the tidal cycle; L. littorea also shows a diurnal rhythm in air. Similar rhythms may occur in other species but are masked by snail activity.

Respiratory rate is found to be higher in air than in water in all species; this can be reversed by preliminary drying, L. saxatilis being affected least and T. lapillus most severely.

In the four gastropods studied there appears to be a gradation in respiratory rate in which species inhabiting successively higher intertidal levels have higher rates of respiration; however, when the respiratory rate is considered as a function of body weight the apparent gradation in oxygen consumption is found to be illusory.

Contents

Introduction . . . . . . . . . . . . Material and methods . . . . . . . . Rhythmical influences on respiration . . . . The effect of drying on oxygen consumption . . Respiratory rate, body weight and intertidal zonation Conclusion . . . . . . . . . . . . References . . . . . . . . . . . .

Oxygen consumption in air and in water ..

Page . . . . . . . . . . 163 . . . . . . . . . . 164 . . . . . . . . . . . 165 . . . . . . . . . . 166 . . . . . . . . . . 169 . . . . . . . . . . 169 . . . . . . . . . . 172 . . . . . . . . . . 172

Introduction

The ability of intertidal marine gastropods to utilize both atmospheric and dissolved oxygen has been demonstrated by a number of workers (Raffy, 1933; Fischer, Duval & Raffy, 1933; Newcombe, Miller & Chappell, 1936; Gompel, 1938; Hazelhoff, 1938; von

Previously at the Department of Zoology, University of Edinburgh, Scotland. 12 163

164 EYVOR E. S A N D I S O N

Brand, Nolan & Mann, 1948; Sandeen, Stephens & Brown, 1954), but as yet no attempt has been made to relate the degree of utilization of either free or dissolved oxygen to the intertidal level a t which the animals live. Different levels are exposed to air for different periods so that the respiratory reaction of snails could be a factor in determining their position on the shore.

In order to investigate these points, the gastropods Thais (Nucella) lapillus (L.), Littorina littorea (L.), L . littoralis (L.), L. saxatillis (Olivi) and L. neritoides (L.) were chosen as representative of snails inhabiting successively higher intertidal zones. The respiratory reaction of these gastropods to varying periods of exposure to air has been investigated.

Material and methods

Snails were collected weekly from their level of maximum abundance at Port Seton, Firth of Forth; T. lapillus from rocks at mean low water neap tide (M.L.W.N.T.); L. littorea from just below mid tide level (M.T.L.); L. littoralis from Fucus at M.T.L. and L. saxatilis from stones at mean high water neap tides (M.H.W.N.T.). L. neritoides does not occur at Port Seton and was occasionally obtained from exposed rocks above mean high water spring tides (M.H.W.S.T.) at Cullercoats, Northumberland. On collection the snails were placed in a tidal tank synchronized to the tidal cycle at Port Seton.

Oxygen uptake in air was measured in a Scholander & Edwards (1942) type volumetric respiro- meter with two respiratory chambers each of 30 ml capacity. Exhalent CO, was absorbed on Whatman no. 40 filter paper saturated with 5 % KOH which was renewed at 3 to 5 h intervals. Allowing an equilibration period of 30 min at 18"C, readings accurate to k0.3 pllh were obtained.

A constant flow method was adopted for the measurement of respiration by snails in water. Dissolved oxygen was determined by a modified micro-Winkler technique using a spectrophoto- meter to estimate iodine. At 18"C, and with two respiratory chambers each of 15 ml capacity, the standard error of the mean of 10 consecutive readings was 0.016 pllml.

The number of snails placed in each respiratory chamber varied with species from one individual of T. lapillus and L. littorea to two of L. littoralis and five of L. saxatilis. Snails were free to move within the respiratory chamber. When occasionally a snail fell on its shell and made vigorous efforts to right itself, the experiment was abandoned.

The oxygen consumption of snails in air, and in water, was measured following three different treatments.

(1) The normal respiratory rate was measured in air, and in water, during the 12 h of daylight (if daylight failed, artificial illumination was used). In these "daylight" experiments the snails were taken from the tidal tank and placed directly in the respiratory chamber, excess water being removed from the shells of those to be placed in air.

(2) The second treatment was designed to measure respiratory reaction after a normal period of exposure on the shore. In these experiments the snails were dried on filter paper for 3 h at 18°C before being placed in the respiratory chambers.

(3) In the third series of experiments respiratory activity was measured following an abnormally long dry period. A stream of air, dried over calcium chloride and silica gel, was passed over the snails for 16 h before taking respiratory measurements in air and in water.

All experiments were conducted at 18"C, and a 1 h equilibration period was allowed. Snails to be submerged were placed in undiluted sea water with an oxygen concentration of 4 to 6 rnlll. Weight is expressed as weight of soft tissues, i.e. excluding the operculum and shell.

OXYGEN C O N S U M P T I O N O F SOME I N T E R T I D A L G A S T R O P O D S 165

Oxygen consumption in air and in water “Daylight” respiratory rate

The respiratory rates of Thais and Littorina spp. were measured in air and in water throughout the 12 hours between 08.00 and 20.00 hours GMT. The experiments were so arranged that with each species three tests were done in air and three in water when high tide at Port Seton occurred in the morning. Similar experiments were done when high tide was in the afternoon. Graphs of the hourly oxygen consumption of each species in air and in water are deposited at the British Museum (Natural History). The results are summarized in Table I.

TABLE I

Average rate of oxygen consumption of Thais and Littorina spp. in air and in water between 8.00 and 20.00 h GMT and average weight

Species

200.1 (f 8.2) t 0.087 76.9 ( f 3.9) 0.096 L. saxatilis 217.0 (k6.5) 0.217 54.9 (f 3-7) 0,236 L. littoralis 117.4 ( f 3.7) 0.576 49.4 ( f 3.1) 0.728 L. littorea

T. lapillus 109.8 ( 2 7.1) 1.091 44.0 (k 2.3) 1.240

t Standard error of the mean is given in brackets.

It is evident from Table I that, even allowing for a 2.5% error estimated by Pattee (1 962) to be inherent in comparison of oxygen uptake using different techniques, all four species of snail (L. neritoides was not included) had higher rates of oxygen consumption in air than in water. Moreover, in species living at successively higher intertidal levels there was a tendency towards successively higher rates of oxygen consumption in both air and water. But it so happens that in the species of Thais and Littorina chosen, snail weight decreased in species living higher up the shore, and as respiratory rate (O,/g/hour) is known to be weight dependent, this would affect the interspecific comparison of respiratory rates.

Respiratory rate after three hours drying After three hours drying on filter paper and a one-hour equilibration period in the res-

piratory chamber, oxygen uptake in humid air and in water was measured over the two hours from 13.30 to 15.30 hours GMT. The results are given in Table 11.

This is the only series of experiments in which L. neritoides was included. When placed in water this snail displayed two different respiratory rates; in two experiments in which the snails were kept fully immersed prior to the three hours drying period, an oxygen consumption of 106.5 pl/g/hour was recorded, whereas in the other 12 experiments where snails were kept on moist Fucus, they respired at an average rate of 351.7 pl/g/hour. In interpreting these two distinct respiratory rates it is assumed that when the snails were

166 EYVOR E. S A N D I S O N

kept on moist weed rather than fully immersed before the experiment, they built up an oxygen debt which was repaid on submergence. A similar respiratory pattern was recorded by Fischer, Duval & Raffy (1933) who found the oxygen consumption of L. neritoides to increase sixfold when immersed in water after a few days in a moist atmosphere.

TABLE I1

Average rate of oxygen consumption of Thais and Littorina spp. in air and in water after 3 h drying

No. of Average O2 consumption

Species In air In water experiments Gllglhr)

106.5 t 2 - L. neritoides 12

L. saxatilis 15 L. littoralis 15 L. littorea 15

89.6 (k4.9) 351.7 (216.5) 145.0 (k5.2) 98.4 (27 .0 ) 82.5 (24.4) 98.1 (23 .8 ) 46.4 (rt 5.1) 96.0 (& 2.8) 57.2 (26.4) 59.2 (58.1) T. lapillus 15

t Snails kept in water before the experiments. $ Standard of the mean given in brackets. This Table also appears in Lewis, 1964.

Table I1 also shows that following three hours exposure, the respiratory rates of Thais and the other three species of Littorina were lower in air than their corresponding “day- light” respiratory rates, whereas in water the respiratory rates were higher. The degree of lowering or raising of the respiratory rate varied with species, and only L. saxatilis retained its ability to respire more in air than in water.

Respiratory rate after I6 hours drying

Following 16 hours in a dry airstream and a one-hour equilibration period, therespiratory rates of the four gastropods were measured between 10.00 and 16.00 hours GMT (Fig. 1).

In all four species the oxygen consumption in water was at first higher than that in air. As the experiment proceeded this situation slowly changed ; in air the oxygen consumption tended to increase over the second and third hours, then remained steady, while in water a similar increase was followed by a fall in respiratory rate. By the sixth and seventh hours after the prolonged period of drying the snails in water had almost resumed their “day- light” rates of respiration, but the snails which were kept in air were still unable to respire at their normal “daylight” level.

Rhythmical influences on respiration

The variation in respiratory rate of Thais and Littorina spp. over 12 hours is indicated in Table I by stating both the mean and the standard error of the mean for each species. Activity, the best known modifier of respiration, may have accounted for some of the

O X Y G E N C O N S U M P T I O N O F SOME I N T E R T I D A L G A S T R O P O D S 167

variation, but snail activity was sporadic, and it became impossible to correlate active periods with variations in oxygen uptake. On the other hand, the experiments occupied the same 12 hours of the day, and the state of the tide was known, so that respiratory rhythms synchronous with the diurnal and tidal cycles, such as Sandeen et al. (1954) found in L. Zittorea breathing in air, could be detected.

Accordingly, the data obtained from the “daylight” respiratory rates were subjected to an analysis of variance for diurnal and tidal influences. For this analysis the day was divided into three periods each of four hours, and tides were considered as high or low & three hours at Port Seton.

, L. soxofi/is

I2O t r ‘M 100-

E L

E 80- L. ftttoro/is

k I I .- Y

L . /More0

x” 0 T: lopillus

2oi- 0 10.00 11*00 12.00 13.00 14.00 15.00 16*0010~0 11.00 12.00 1390 14.00 15-00 16.00

2nd 3rd 4th 5th 6th 7th 2nd 3rd 4th 5th 6th 7th Time (GMT)

hour of experiment

FIG. 1. The oxygen consumption of Thais and Lirforinu spp. after 16 h in a dry air stream. (a) Air and (b) water.

A summary of the analysis of variance is given in Table I11 in which the variance of the Residual is considered to be largely due to snail activity. When the estimated variances due to diurnal and tidal rhythms are tested against the Residual variance, it appears that amongst snails placed in air L. Zittorea only was affected by extrinsic rhythms. In this species time of day had a significant influence on respiration (P = 0-01), and the snail was found to use more oxygen between 8.00 and 12.00 hours than at any other time of the day. There was also a suggestion from the analysis that respiratory variation was synchronous with the tidal rhythm, but this was not conclusively demonstrated (P = 0-025).

The analysis of variance further showed that both L. saxatilis and L. Zittorea, when placed in water, were influenced by extrinsic rhythms. L. saxatilis displayed a highly significant correlation (P = 0.001) between the time of day and respiratory rate, in which

168 E Y V O R E. S A N D I S O N

the snail utilized more oxygen in the morning and evening than between 12.05 and 16.00 hoursin the afternoon. On the other hand, the time of day had a barely significant influence (P = 0.025) on the respiration of L. Zittorea, whereas tidal rhythms clearly affected the respiratory rate (P = 0-Ool), and the snail consumed more oxygen at high tide than at low.

TABLE I11

Synopsis of an analysis of variance of the effect of time of day and high and low tide on the oxygen consumption of Thais and Littoha spp. in air and water

Source of Estimated Variance Species variation variance d.f. ratio “P”

In air L. saxatilis

L. littoralis

L. littorea

T. lapillus

In water L. saxatilis

L . littoralis

L. littorea

T. lapillus

Time Tide Residual

Time Tide Residual

Time Tide Residual

Time Tide Residual

Time Tide Residual

Time Tide Residual

Time Tide Residual

Time Tide Residual

2082 2494 2192

850 1557 1703

3806 3392 722

35 2347 1181

7491 1568 875

1427 1884 598

1278 4073

343

323 449 372

2 0.94 1 1.10

48

2 0.51 1 0.93

54

2 5.20 1 4.70

48

2 0.29 1 1.98

48

2 8.56 1 1.79

48

2 2.38 1 3.15

48

2 3.72 1 11.80

48

2 0.86 1 1 -20

60

0.01 0.025

0.001 -

0.1 0.1

0.025 0.001

Respiration of L. Zittorea from Port Seton therefore confirmed the findings of Sandeen et aZ. (1954) in that when the snail is placed in humid air it displays a well-defined diurnal respiratory rhythm, with the suggestion of a superimposed tidal rhythm. However, this has not been found to extend to submerged L. Zittorea from Port Seton, for in this case a persistent tidal rhythm was clearly demonstrated and a diurnal rhythm was less clearly defined.

O X Y G E N C O N S U M P T I O N O F SOME I N T E R T I D A L GASTROPODS 169

200

r \

160- d F

r 0 .- z 120- 5 " 8 0 - & I

6

c 0

0 r

40

The effect of drying on oxygen consumption The oxygen consumption of Thais and Littorina spp. has been found to be higher in air

than in water when measured over 12 hours with no preliminary drying. After three hours drying the oxygen consumption in air of each species fell, whereas in water it rose (Fig. 2); but following 16 hours drying the oxygen consumption of each species was higher in water than in air. A complete reversal of their relative utilization of dissolved and free oxygen had therefore been accomplished by drying the snails for 16 hours prior to oxygen deter-

-

-

minations being made.

, "Ooylight" 3 h 1 6 h

( a )

240

I60

120

80

40 - "Daylight" 3 h 16h

(b)

FIG. 2. The average rates of oxygen consumption of L. saxatilis (a), L. Iittoralis (O), L. lirrorea (0) and T

Respiratory rates at 3 h and 16 h are the average rates of the 2nd and 3rd h after transfer to the respiratory lapillus ( X ) in (a) air and (b) water in the "daylight" experiments and after 3 h and 16 h drying.

chamber.

This effect of preliminary drying on respiratory rate may to some extent account for the discrepancy between the present results and those of Littorina species quoted by previous workers. Thamdrup (1935) working on L. Zittorea, and Fischer et al. (1933) and Raffy (1933) on L. rudis (saxatilis) and L. neritoides, recorded substantially higher respiratory rates for these snails in water than in air; but Thamdrup took measurements over a two- hour period and does not cite pre-experimental treatment. On the other hand, Fischer et al. (1933) and Raffy (1933) kept L. suxatilis in air for three days before submergence in water, which moreover, was supersaturated with oxygen. This pre-experimental treatment would tend to lower the oxygen consumption of snails in air and raise that in water. Furthermore, Fischer et al. (1933) showed that increasing the oxygen content of the water, also increased the oxygen consumption of the snails.

Respiratory rate, body weight and intertidal zonation It has already been observed that the respiratory rates of the four species of snail given

in Table I cannot be directly compared because of the different sizes of the species and the

1 70 EYVOR E. SANDISON

relationship which exists between body weight and respiratory rate per gram. This relation- ship has been expressed by Zeuthen (1953) and Hemmingsen (1960) in a wide range of animals to be n = 0.75 in the equation

metabolism = k x body weight n.

2oor

Average body weigh? (P)

FIG. 3. The relationship between the “daylight” respiratory rate in air and in water and average body weight of

Lines of n = 0.75 are drawn for air and water. L. saxatilis (n), L. littoralis (e), L. littorea (0) and T. lapillus ( x).

If one accepts this valuation, then the apparent increase of respiratory rate in species inhabiting successively higher intertidal levels can be re-examined. When the “daylight” respiratory rates in air and in water of the four species of snail are plotted on double logarithm paper against the average body weight of each species, and lines for n = 0.75 for respiration in air and water are drawn (Fig. 3), it is found that the respiratory rates of L. saxatilis, L. littorea and T. lapillus lie remarkably close to those lines. In other words, when the size difference between the species is taken into account, the graph shows that there is no difference in the respiratory rates of L. saxatilis, L. littorea and T. lapillus corresponding to differences in intertidal level.

The respiratory rate of L. littoralis in air is a little above the n = 0.75 line in Fig. 3. This could mean that the snail is relatively better adapted to obtaining oxygen from air than are the other species ; but, if the behaviour of the snail is observed, it is seen to keep the oper- culum open and even to crawl when exposed to air, while Thais and the other species of Littorina keep the operculum closed. It is therefore, probable that the relatively higher rate of oxygen consumption of this snail in air is related to its active behaviour rather than to any respiratory adaptation to zonation.

Interspecific comparision of the respiratory reaction of snails to three and 16 hours drying can also be made by plotting the appropriate respiratory rates against weight on double logarithm paper (Fig. 4).

O X Y G E N C O N S U M P T I O N O F SOME I N T E R T I D A L G A S T R O P O D S 171

Figure 4 (a) shows that the respiratory reactions of L. littoralis, L. littorea and T. lapillus were similar when the snails were placed in water after a three-hour drying period, whereas L. saxatilis respired at a relatively lower rate; but, when the snails were kept in air after the drying period, respiratory reaction varied with species, and only L. littoralis and T. Zapillus showed similar reactions.

Average body weight (g)

FIG. 4. The relationship between oxygen consumption in air and in water and average body weight of L. saxatilis

Lines of n = 0.75 in air and water are inserted. Broken lines represent n = 0.75 in the “daylight” experiments. O), L. littoralis (O), L. Zittoreu (O), and T. lapillus (x), (a) After 3 h and (b) after 16 h drying.

However, it should be remembered that after three hours drying respiratory measure- ments were always made in the afternoon when, according to the results of the analysis of variance (p. 168), a persistent diurnal rhythm would tend to lower the respiratory rate of L. saxatilis in water and of L. littorea in air. In these experiments the possibility of a tidal in- fluence on respiration was minimized by ensuring that respiratory recordings for each species were spread equally over high and low-tide periods.

172 EYVOR E. SANDISON

Diurnal respiratory rhythms could therefore account for the rather low respiratory rate of L. Zittorea in air and of L. saxatizis in water when compared with L. littoralis and T. ZapiZZm, but not for the relatively higher rate of oxygen uptake by L. saxatilis in air as shown in Fig. 4 (a).

This distinctive respiratory behaviour of L. saxatilis may be explained as follows. The snail was collected from M.H.W.N.T., and would, therefore, be regularly exposed to air for longer periods than would L. ZittoraZis and L. Zittorea collected from M.T.L. or T. ZapiZhs from M.L.W.N.T. When exposed to drying for three hours the respiratory pattern of the snails from the middle and lower shore was changed, and instead of obtaining more oxygen from air than from water as was normally the case, the reverse was found (Fig. 4 (a)). However, three hours exposure affected the ability of L. saxatiZis to respire in air to a lesser extent (the measurements in water may not be typical because of the diurnal respira- tory effect), and thus it is possible that this species was displaying respiratory adaptation to the longer periods of exposure found at the higher inter-tidal levels.

Following a period of 16 hours drying the respiratory rate of each species of snail was higher in water than in air (Fig. 4 (b)). Moreover, the respiratory reaction of each species to this unnaturally long period of drying followed a similar pattern when the oxygen consumption/weight relationship was taken into account. The one exception was the inability of T. Zapillus to regain a normal rate of oxygen consumption in air after prolonged exposure; this could be related to the low intertidal position of the snail.

Conclusion

The experiments on snails from different intertidal levels at Port Seton indicate that under “normal” conditions neither Thais nor Littorina spp. show respiratory adaptation in their relative uptake of atmospheric or dissolved oxygen which can be correlated with intertidal level. However, the greater respiratory stability of L. saxatiZis to a three-hour period of drying, and the relative inability of T. Zapillus to recover normal respiration in air after unnaturally prolonged drying may both be related to their intertidal positions on the shore.

A diurnal rhythm of respiration is shown by L. saxatilis in water, and possibly by L. Zittorea in air, and a respiratory rhythm synchronous with the local tidal cycle is displayed by L. Zittorea in water. Similar rhythms may be present in other species, but their recogni- tion is masked by snail activity.

I am grateful to Professor M. M. Swann and Mr G. Friend for helpful discussion during the early stages of the investigation, and also to Professor J. E. Webb for comments on the manu- script.

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