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The effect of oil pollution on survival of the tidal pool copepod, Tigriopus californicus
THE EFFECT OF OIL POLLUTION ON SURVIVAL OF THE TIDAL POOL COPEPOD, TIGRIOPUS CALIFORNICUS JOHN E. KONTOGIANNIS & CRAIG J. BARNETT
Biology Department, California State University, Northridge, California, USA
ABSTRACT
A study of the effect of simulated oil pollution on Tigriopus californicus indicated that a 1.5 mm thick layer of crude oil on the water surface caused the death o f all animals within three days, while a similar layer of mineral oil resulted in complete mortality in five days. When oxygen was added to the water containing crude oil, total mortality was delayed by two days. Approximately 100 ~ mortality was extended to seven days when crude oil was enclosed in a dialysis membrane bag immersed in the water and oxygen was supplied. When mineral oil was used and air provided, the animals survived as well as the controls. It was concluded that death resulted because the oil acts as a barrier to oxygen transfer between air and water, and because it contains substances toxic to Tigriopus.
INTRODUCTION
The problem of oil pollution in marine habitats has assumed international importance as increasingly large amounts of crude and refined oil continue to leak from offshore drilling platforms and ships at sea. It is of even greater concern when one realises that the most important links in marine food chains, the producers (phytoplankton) and first order consumers (microcrustaceans) run the greatest risk of being harmed by an oil spill, since they lack the motile power to leave an area which has been contaminated. Information dealing with the effects of oil on marine organisms is very general and sometimes contradictory. Rutzler & Sterrer (1970) found that after an oil spill splash zone pools covered by up to 2 cm of diesel oil were devoid of life; however, it was not known whether this condition was caused by chemicals in the oil or by the blocking out of light necessary to photosynthesis. North et al. (1965) found that 69
Era,iron. Pollut. (4) (1973) pp. 69-79-- 0 Applied Science Publishers Ltd, England, 1973--Printed in Great Britain
70
JOHN E. KONTOGIANNIS, CRAIG J. BARNETT
a concentration of 0.01-0.1 ~ of diesel oil in an emulsion of sea water impaired photosynthetic ability in kelp, and crude oil in concentrations ranging from 0.5 to 5 . 0 ~ was toxic to oysters, sand shrimp, and prawns (Chipman & Galtsoff, 1949). Quantities as small as 0-001 ml/litre were lethal to certain Black sea copepods (Mironov, 1969). On the other hand, Bellamy et al. (1967) and O'Sullivan and Richardson (1967), dealing with the 'Torrey Canyon' oil spill, reported that when an intertidal location is polluted with oil, and detergents are not used, mortality of indigenous animals is quite low. The Santa Barbara oil spill in 1969-70 was found to have only a temporary effect on the marine biota (Nicholson & Cimberg, 1971). Some crustacea, including barnacles and isopods, have actually been found either living on, or associated with, lumps of crude oil residue (Horn, 1970). Tigriopus californicus is a harpacticoid copepod commonly found in tidal pools above the high tide water mark along the west coast of North America from Vancouver, B.C. to the southern tip of Baja, California, Mexico (Belser, 1959). Although some research dealing with the ecology and physiology of the genus Tigriopus has been undertaken (Fraser, 1936; Shaw, 1938; Ranade, 1957; Matutani, 1961 ; Comita & Comita, 1966; K ontogiannis, in press), virtually no work has been done on the effects of oil pollution on these animals. This investigation was undertaken to determine if the survival of 7". californicus is affected by crude oil contamination, and, if so, to determine whether death is caused mainly by oil acting as a physical barrier to oxygen transfer between air and water or because of the presence of toxic chemicals in the oil itself.
MATERIAL AND METHODS
The Tigriopus californicus used in this study were collected from tidal pools at Flat Rock Point, Palos Verdes Estates, California. Water containing the animals was poured through silk-bolting cloth to strain out the organisms. The retained animals were then washed into a container filled with tidal pool water and transported to the laboratory, where they were placed into large beakers set in a constant temperature cabinet at 10°C. To prevent evaporation a glass plate was placed over each beaker. The only food available was unicellular algae and bacteria contained in their water. The animals were left under these conditions for at least one week before being used for experimental purposes. To investigate the effects of crude oil on the survival of T. californicus, and specifically to identify the major causes of mortality, five experiments were carried out. In each experiment seventy, 20 × 150 ram, test tubes, each containing fifty adult Tigriopus and sufficient sea water to produce a 20 ml volume, were used. Crude oil or mineral oil, with or without bubbling air, was added to the test tubes as indicated below. Corresponding controls without crude or mineral oil were also set up, and all test tubes were kept at 17.5°C in the dark from one to seven days.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
~71
To determine whether crude oil, placed directly on the water surface, affected the survival of Tigriopus by preventing the diffusion of oxygen, 0.5 ml of crude oil was added to each of seventy test tubes. This quantity of oil formed a layer 1.5 mm thick on the water surface. A second experiment was prepared with crude oil as above, but in addition filtered air was bubbled through the water of each test tube by means of Pasteur pipettes at a rate of 1-3 bubbles/second. These experiments were repeated using mineral oil to determine if death was due, in part, to impurities in the crude oil. Basically, mineral oil is crude oil without impurities (Stecher, 1968). To determine whether the mortality was due to diffusible substances in the oil or to mechanical effects of contact with the oil, another set of test tubes was aerated and 0-5 ml of crude oil, the same amount as was added to the surface of the previously-mentioned tubes, was encased in dialysis membrane bags and immersed in each test tube. Daily, for the duration of each experiment, the live animals in ten experimental and ten control test tubes were counted and discarded. Those animals which did not exhibit movement when stimulated by agitation were considered to be dead. In addition to the above experiments, a test was made to determine to what extent a layer of oil acts as a barrier to the diffusion of oxygen across the air-water interface. A layer of crude oil or mineral oil, each 1-5 nun in thickness, was placed on the surface of partially deoxygenated sea water contained in two one-litre graduated cylinders, and a third cylinder with only deoxygenated sea water was left exposed to the air. The concentration of dissolved oxygen in the water of each cylinder was determined, in duplicate samples, by the Winkler method (Welch, 1948) every day for a period of five days. The crude oil used in this study was obtained from Mobil Oil Corporation's field at San Ardo, California. It was a heavy, tar-like oil (sp. gr. 0.9799), which consisted of 7 5 ~ naphthenes, 17.3 ~ paraffins, 6.5 ~ aromatics and 2 . 2 ~ sulphur (Mobil Oil Corporation Sample No. 63-18453).
RESULTS
From Fig. 1 it can be seen that crude oil on the water surface was definitely detrimental to T. californicus. Approximately 92 ~ of the animals in the test tubes with oil died between the first and the second days, and by the end of the third day all were dead. In the controls, however, mortality was very low over a five-day period. When air was supplied, the mortality was somewhat reduced; 80 9/ooof the animals died between the first and third day but 100 K mortality did not occur until the end of the fifth day (Fig. 2). Direct contact with the crude oil was apparently not necessary to cause death, for even when the oil was encased in a dialysis membrane bag nearly all animals were dead by the seventh day (Fig. 3).
72
JOHN E. KONTOGIANNIS~ CRAIG J. BARNETT
I O0
_..i
80
m
AControls
60
C) Experimentals
In
Z
I,M U
40
a. 20
0 1
2
TIMEFig. 1.
3
4
5
DAYS
~ survival of T. californicus with crude oil on water surface. Vertical bars represent :~1 S.D. Each point represents mean ~ of survival for 10 replicates.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
73
100
._J
80
m
AControls
60
i,,-
X
ILl
C)
Experimentals
3
4
40
U n~ LU n_ 20
1
2
TIMEFig. 2.
5
DAYS
~ survival of T. californicus with crude oil on water surface and bubbling air. Data presented as in Fig. 1.
74
JOHN E, KONTOGIANNIS, CRAIG J. BARNETT
i00
,,..i
80
~e 60
Z 40 le ,u a. 20
J
I
I
I
I
,
1
2
3
4
5
6
TIME
Fig. 3.
-
7
DAYS
~ survival of T. californicus with crude oil in dialysis membrane bag and bubbling air, Data presented as in Fig. 1.
75
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
100
.-J
80 m
60 I,-.
Z
luul U
40
i,M a_
20
0
I
2
3
TIMEFig. 4.
4
5
DAYS
% survival o f T. californicus with mineral oil o n water surface. D a t a presented as in Fig. 1.
76
JOHN E. KONTOGIANNIS, CRAIG J. BARNETT 100
80
> 60
X 40
m AConlrols
IIL C) E x p e r i m e n l a l s
I
I
I
I
I
I
I
1
2
3
4
5
6
7
TIME
-
DAYS
survival o f T. californicus with mineral oil and bubbling air. D a t a presented as in Fig. 1,
Fig. 5.
•
0
,u J
CONTROL
(~
MINERAL OIL
O
CRUDE OIL
:E
1
2
TIME
Fig. 6.
3
4
5
- DAYS
The influence o f crude oil and mineral oil on the rate o f oxygen diffusion across the airwater interface.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
77
Mineral oil, when placed on the water surface, proved to be almost as detrimental as crude oil when there was no aeration (Fig. 4). Between the second and third days approximately 75 ~ of the animals died, and by the fifth day all were dead. On the other hand, when air was provided the mineral oil appeared to have no detrimental effects (Fig. 5). There was no obvious difference between the control and experimental populations. Figure 6 shows that the crude oil used is an effective barrier to oxygen diffusion across the air-water interface, while the mineral oil allowed for negligible oxygen diffusion. DISCUSSION
The experimental results illustrate that crude oil is lethal for T. californicus. Such oil on the water surface not only acts as a physical barrier for the diffusion of oxygen across the air-water interface (Fig. 6), but apparently also contains toxic substances such as naphthalene, benzene and toluene (Boylan & Tripp, 1971). The lethal effect is much greater when both factors operate simultaneously (Fig. 1). In view of the chemical inertness of mineral oil on Tigriopus (Fig. 5), the high mortality rate is, in part, due to oxygen deprivation by an oil layer (Fig. 4). Figure 6 clearly indicates that mineral oil on the water surface allowed only very slow oxygen diffusion across the air-water interface. However, since the mortality rate of aerated Tigriopus, treated with crude oil, remains high and that of the controls very low (Fig. 2) one may conclude that the deaths were also due to toxic chemicals in the oil itself. This was shown by encasing crude oil in dialysis membrane bags and placing them in the aerated test tubes. Under these conditions nearly 100K mortality did not occur until the seventh day (Fig. 3). Furthermore, the near linearity of the curve suggests that toxic substances slowly diffused out of the dialysis bag into the water. In contrast to T. californicus (all of which were dead in three days when subjected to a crude oil concentration of 25 ml/litre) the pelagic copepods Acartia clausi and Oithona nana survived not more than a day when only 0.1 ml/litre of crude oil was added (Mironov, 1969). This may suggest that resistance to crude oil pollution among copepods differs from species to species and may be dependent upon habitat, as concluded by Nelson-Smith (1968); however, since Mironov (1969) does not give the composition of oil used, it is possible that the difference in survival times is the result of the use of oil with different compositions. Since T. californieus in its habitat experiences sudden and extreme environmental changes which would kill its more delicate oceanic relatives (Belser, 1959) and since it possesses a great degree of physiological lability which enables it to adapt readily to extreme environmental changes (Kontogiannis, in press), it would not be surprising if these animals also were able to survive longer in higher concentrations of oil pollution than their oceanic relatives which live in a comparatively static environment.
78
JOHN E. KONTOGIANNIS,CRAIGJ. BARNETT
In view of the present evidence, we conclude that the large amounts of crude oil which escape into the marine environment could cause a serious ecological imbalance, at least on a local level. Since microcrustaceans play a vital role in the transfer of energy from phytoplankton to fish, any factor which directly interferes with their survival would, at the same time, affect members of higher trophic levels which depend upon them for nutrition.
CONCLUSIONS 1. Tigriopus californicus, collected from the tidal pools on the California Coast, were tested for susceptibility to oil pollution. 2. Results indicated that 1.5 mm thick layer of crude oil on the water surface caused the deaths of all animals within three days, while a similar layer of mineral oil resulted in complete mortality in five days. When oxygen was added to the water containing crude oil total mortality was delayed by two days. Approximately 100 ~o mortality was delayed seven days when the animals were not coming in direct contact with the crude oil. When mineral oil was used and air provided the animals survived equally as well as the controls. 3. It was concluded that death resulted because the oil acts as a barrier to oxygen transfer between air and water, and because it contains substances toxic to Tigriopus.
ACKNOWLEDGMENTS The authors wish to thank Professors Jim W. Dole and Marvin Cantor who critically read and made helpful suggestions during the preparation of the manuscript. Thanks are also due to Mr Chuck Spivak for his help regarding petroleum chemistry. REFERENCES BELLAMY,D. J., CLARKE,P. H., JOHN, D. M., JONES,D., WHITTICK,A. & DARKE,T. (1967). Effects of pollution from the Torrey Canyon on littoral and sublittoral ecosystems. Nature, Lond., 216, 1170-3. BELSER,B. L. (1959). The research frontier. Where is science taking us? Saturday Rev., 42, 58. BOYLAN,D. B. • TRIPP, B. W. (1971). Determinations of hydrocarbons in seawater extracts of crude oil and crude oil fractions. Nature, Lond., 230, 44-7. CHIPMAN,W. A. & GALTSOFF, P. S. (1949). The effects ofoil mixed with carbonized sand on aquatic animals. US Fish and Wildlife Special Report (1), 1-52. COMrrg, G. W. & COMITA,J. J. (1966). Egg production in Tigriopus brevicornis. In Some contemporary studies in marine science, ed. by H. Barnes, 171-85. New York, Hafner. FRASER,J. H. (1936). The occurrence,ecology, and life history of Tigriopusfulvus(Fischer). J. mar. bioL Ass. U.K., 20, 532-6. HORN, M. H. (1970). Petroleum lumps on the surface of the sea. Science, N.Y., 168, 245-6. KONTOGIANNIS,J. E. (1973). Acquisition and loss of heat resistance in adult tide pool copepod, Tigriopus californicus. Physiol. Zo~il., in press.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
79
MATUTANI,K. (1961). Studies on the heat resistance of Tigriopusjaponicus. Pubis Seto mar. biol. Lab., 9, 133-65. MIRONOV, O. G. (1969). The effect of oil pollution upon some representatives of Black Sea zooplankton [in Russian]. Zool. Zh. Ukr., 48, 980-4. NELSOS-SMITH, A. (1968). The effect of oil pollution and emulsifier cleansing on shore life in southwest Britain. J. Appl. Ecol., 5, 97-107. NICnOLSON, N. L. & CIMaERG, R. L. (1971). The Santa Barbara oil spills of 1969: a post spill survey of the rocky intertidal. In Biological and oceanographical survey of the Santa Barbara Channel oil spill, 1969-1970, ed. by D. Straughan, 343-50. Allan Hancock Foundation, Sea Grant Publ. No. 2. NORTH, W. J., NEUSHUL, M. & CLENDENNING,K. A. (1965). Successive biological changes observed in a marine cove exposed to a large spillage of mineral oil. Syrup. Poll. mar. Micro-org. Prod. pdtrol., Monaco, 1964, 335-54. O'SOLLlVAN, A. J. & RICHARDSON, A. J. (1967). The Torrey Canyon disaster and intertidal marine life. Nature, Lond., 214, 448 and 541. RANADE, M. R. (1957). Observations on the resistance of Tigriopus fulvus (Fischer) to changes in temperature and salinity. J. mar. biol. Ass. U.K., 36, 115-9. RUTZL~R, K. & STERRER, W. (1970). Oil pollution damage observed in tropical communities along the Atlantic seaboard of Panama. BioScience, 20, 222--4. SHAW, T. H. (1938). Some observations on the life history of a tidepool copepod Tigriopusfulvus (Fischer). Bull. Fan meml Inst. Biol., 8, 9-16. STECHER, P. (1968). The Merck Index: an encyclopedia of chemicals and drugs. New Jersey, Merck & Co. WELCH, P. S. (1948). Limnological methods. New York, McGraw-Hill.
Biology Department, California State University, Northridge, California, USA
ABSTRACT
A study of the effect of simulated oil pollution on Tigriopus californicus indicated that a 1.5 mm thick layer of crude oil on the water surface caused the death o f all animals within three days, while a similar layer of mineral oil resulted in complete mortality in five days. When oxygen was added to the water containing crude oil, total mortality was delayed by two days. Approximately 100 ~ mortality was extended to seven days when crude oil was enclosed in a dialysis membrane bag immersed in the water and oxygen was supplied. When mineral oil was used and air provided, the animals survived as well as the controls. It was concluded that death resulted because the oil acts as a barrier to oxygen transfer between air and water, and because it contains substances toxic to Tigriopus.
INTRODUCTION
The problem of oil pollution in marine habitats has assumed international importance as increasingly large amounts of crude and refined oil continue to leak from offshore drilling platforms and ships at sea. It is of even greater concern when one realises that the most important links in marine food chains, the producers (phytoplankton) and first order consumers (microcrustaceans) run the greatest risk of being harmed by an oil spill, since they lack the motile power to leave an area which has been contaminated. Information dealing with the effects of oil on marine organisms is very general and sometimes contradictory. Rutzler & Sterrer (1970) found that after an oil spill splash zone pools covered by up to 2 cm of diesel oil were devoid of life; however, it was not known whether this condition was caused by chemicals in the oil or by the blocking out of light necessary to photosynthesis. North et al. (1965) found that 69
Era,iron. Pollut. (4) (1973) pp. 69-79-- 0 Applied Science Publishers Ltd, England, 1973--Printed in Great Britain
70
JOHN E. KONTOGIANNIS, CRAIG J. BARNETT
a concentration of 0.01-0.1 ~ of diesel oil in an emulsion of sea water impaired photosynthetic ability in kelp, and crude oil in concentrations ranging from 0.5 to 5 . 0 ~ was toxic to oysters, sand shrimp, and prawns (Chipman & Galtsoff, 1949). Quantities as small as 0-001 ml/litre were lethal to certain Black sea copepods (Mironov, 1969). On the other hand, Bellamy et al. (1967) and O'Sullivan and Richardson (1967), dealing with the 'Torrey Canyon' oil spill, reported that when an intertidal location is polluted with oil, and detergents are not used, mortality of indigenous animals is quite low. The Santa Barbara oil spill in 1969-70 was found to have only a temporary effect on the marine biota (Nicholson & Cimberg, 1971). Some crustacea, including barnacles and isopods, have actually been found either living on, or associated with, lumps of crude oil residue (Horn, 1970). Tigriopus californicus is a harpacticoid copepod commonly found in tidal pools above the high tide water mark along the west coast of North America from Vancouver, B.C. to the southern tip of Baja, California, Mexico (Belser, 1959). Although some research dealing with the ecology and physiology of the genus Tigriopus has been undertaken (Fraser, 1936; Shaw, 1938; Ranade, 1957; Matutani, 1961 ; Comita & Comita, 1966; K ontogiannis, in press), virtually no work has been done on the effects of oil pollution on these animals. This investigation was undertaken to determine if the survival of 7". californicus is affected by crude oil contamination, and, if so, to determine whether death is caused mainly by oil acting as a physical barrier to oxygen transfer between air and water or because of the presence of toxic chemicals in the oil itself.
MATERIAL AND METHODS
The Tigriopus californicus used in this study were collected from tidal pools at Flat Rock Point, Palos Verdes Estates, California. Water containing the animals was poured through silk-bolting cloth to strain out the organisms. The retained animals were then washed into a container filled with tidal pool water and transported to the laboratory, where they were placed into large beakers set in a constant temperature cabinet at 10°C. To prevent evaporation a glass plate was placed over each beaker. The only food available was unicellular algae and bacteria contained in their water. The animals were left under these conditions for at least one week before being used for experimental purposes. To investigate the effects of crude oil on the survival of T. californicus, and specifically to identify the major causes of mortality, five experiments were carried out. In each experiment seventy, 20 × 150 ram, test tubes, each containing fifty adult Tigriopus and sufficient sea water to produce a 20 ml volume, were used. Crude oil or mineral oil, with or without bubbling air, was added to the test tubes as indicated below. Corresponding controls without crude or mineral oil were also set up, and all test tubes were kept at 17.5°C in the dark from one to seven days.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
~71
To determine whether crude oil, placed directly on the water surface, affected the survival of Tigriopus by preventing the diffusion of oxygen, 0.5 ml of crude oil was added to each of seventy test tubes. This quantity of oil formed a layer 1.5 mm thick on the water surface. A second experiment was prepared with crude oil as above, but in addition filtered air was bubbled through the water of each test tube by means of Pasteur pipettes at a rate of 1-3 bubbles/second. These experiments were repeated using mineral oil to determine if death was due, in part, to impurities in the crude oil. Basically, mineral oil is crude oil without impurities (Stecher, 1968). To determine whether the mortality was due to diffusible substances in the oil or to mechanical effects of contact with the oil, another set of test tubes was aerated and 0-5 ml of crude oil, the same amount as was added to the surface of the previously-mentioned tubes, was encased in dialysis membrane bags and immersed in each test tube. Daily, for the duration of each experiment, the live animals in ten experimental and ten control test tubes were counted and discarded. Those animals which did not exhibit movement when stimulated by agitation were considered to be dead. In addition to the above experiments, a test was made to determine to what extent a layer of oil acts as a barrier to the diffusion of oxygen across the air-water interface. A layer of crude oil or mineral oil, each 1-5 nun in thickness, was placed on the surface of partially deoxygenated sea water contained in two one-litre graduated cylinders, and a third cylinder with only deoxygenated sea water was left exposed to the air. The concentration of dissolved oxygen in the water of each cylinder was determined, in duplicate samples, by the Winkler method (Welch, 1948) every day for a period of five days. The crude oil used in this study was obtained from Mobil Oil Corporation's field at San Ardo, California. It was a heavy, tar-like oil (sp. gr. 0.9799), which consisted of 7 5 ~ naphthenes, 17.3 ~ paraffins, 6.5 ~ aromatics and 2 . 2 ~ sulphur (Mobil Oil Corporation Sample No. 63-18453).
RESULTS
From Fig. 1 it can be seen that crude oil on the water surface was definitely detrimental to T. californicus. Approximately 92 ~ of the animals in the test tubes with oil died between the first and the second days, and by the end of the third day all were dead. In the controls, however, mortality was very low over a five-day period. When air was supplied, the mortality was somewhat reduced; 80 9/ooof the animals died between the first and third day but 100 K mortality did not occur until the end of the fifth day (Fig. 2). Direct contact with the crude oil was apparently not necessary to cause death, for even when the oil was encased in a dialysis membrane bag nearly all animals were dead by the seventh day (Fig. 3).
72
JOHN E. KONTOGIANNIS~ CRAIG J. BARNETT
I O0
_..i
80
m
AControls
60
C) Experimentals
In
Z
I,M U
40
a. 20
0 1
2
TIMEFig. 1.
3
4
5
DAYS
~ survival of T. californicus with crude oil on water surface. Vertical bars represent :~1 S.D. Each point represents mean ~ of survival for 10 replicates.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
73
100
._J
80
m
AControls
60
i,,-
X
ILl
C)
Experimentals
3
4
40
U n~ LU n_ 20
1
2
TIMEFig. 2.
5
DAYS
~ survival of T. californicus with crude oil on water surface and bubbling air. Data presented as in Fig. 1.
74
JOHN E, KONTOGIANNIS, CRAIG J. BARNETT
i00
,,..i
80
~e 60
Z 40 le ,u a. 20
J
I
I
I
I
,
1
2
3
4
5
6
TIME
Fig. 3.
-
7
DAYS
~ survival of T. californicus with crude oil in dialysis membrane bag and bubbling air, Data presented as in Fig. 1.
75
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
100
.-J
80 m
60 I,-.
Z
luul U
40
i,M a_
20
0
I
2
3
TIMEFig. 4.
4
5
DAYS
% survival o f T. californicus with mineral oil o n water surface. D a t a presented as in Fig. 1.
76
JOHN E. KONTOGIANNIS, CRAIG J. BARNETT 100
80
> 60
X 40
m AConlrols
IIL C) E x p e r i m e n l a l s
I
I
I
I
I
I
I
1
2
3
4
5
6
7
TIME
-
DAYS
survival o f T. californicus with mineral oil and bubbling air. D a t a presented as in Fig. 1,
Fig. 5.
•
0
,u J
CONTROL
(~
MINERAL OIL
O
CRUDE OIL
:E
1
2
TIME
Fig. 6.
3
4
5
- DAYS
The influence o f crude oil and mineral oil on the rate o f oxygen diffusion across the airwater interface.
EFFECT OF OIL POLLUTION ON A TIDAL POOL COPEPOD
77
Mineral oil, when placed on the water surface, proved to be almost as detrimental as crude oil when there was no aeration (Fig. 4). Between the second and third days approximately 75 ~ of the animals died, and by the fifth day all were dead. On the other hand, when air was provided the mineral oil appeared to have no detrimental effects (Fig. 5). There was no obvious difference between the control and experimental populations. Figure 6 shows that the crude oil used is an effective barrier to oxygen diffusion across the air-water interface, while the mineral oil allowed for negligible oxygen diffusion. DISCUSSION
The experimental results illustrate that crude oil is lethal for T. californicus. Such oil on the water surface not only acts as a physical barrier for the diffusion of oxygen across the air-water interface (Fig. 6), but apparently also contains toxic substances such as naphthalene, benzene and toluene (Boylan & Tripp, 1971). The lethal effect is much greater when both factors operate simultaneously (Fig. 1). In view of the chemical inertness of mineral oil on Tigriopus (Fig. 5), the high mortality rate is, in part, due to oxygen deprivation by an oil layer (Fig. 4). Figure 6 clearly indicates that mineral oil on the water surface allowed only very slow oxygen diffusion across the air-water interface. However, since the mortality rate of aerated Tigriopus, treated with crude oil, remains high and that of the controls very low (Fig. 2) one may conclude that the deaths were also due to toxic chemicals in the oil itself. This was shown by encasing crude oil in dialysis membrane bags and placing them in the aerated test tubes. Under these conditions nearly 100K mortality did not occur until the seventh day (Fig. 3). Furthermore, the near linearity of the curve suggests that toxic substances slowly diffused out of the dialysis bag into the water. In contrast to T. californicus (all of which were dead in three days when subjected to a crude oil concentration of 25 ml/litre) the pelagic copepods Acartia clausi and Oithona nana survived not more than a day when only 0.1 ml/litre of crude oil was added (Mironov, 1969). This may suggest that resistance to crude oil pollution among copepods differs from species to species and may be dependent upon habitat, as concluded by Nelson-Smith (1968); however, since Mironov (1969) does not give the composition of oil used, it is possible that the difference in survival times is the result of the use of oil with different compositions. Since T. californieus in its habitat experiences sudden and extreme environmental changes which would kill its more delicate oceanic relatives (Belser, 1959) and since it possesses a great degree of physiological lability which enables it to adapt readily to extreme environmental changes (Kontogiannis, in press), it would not be surprising if these animals also were able to survive longer in higher concentrations of oil pollution than their oceanic relatives which live in a comparatively static environment.
78
JOHN E. KONTOGIANNIS,CRAIGJ. BARNETT
In view of the present evidence, we conclude that the large amounts of crude oil which escape into the marine environment could cause a serious ecological imbalance, at least on a local level. Since microcrustaceans play a vital role in the transfer of energy from phytoplankton to fish, any factor which directly interferes with their survival would, at the same time, affect members of higher trophic levels which depend upon them for nutrition.
CONCLUSIONS 1. Tigriopus californicus, collected from the tidal pools on the California Coast, were tested for susceptibility to oil pollution. 2. Results indicated that 1.5 mm thick layer of crude oil on the water surface caused the deaths of all animals within three days, while a similar layer of mineral oil resulted in complete mortality in five days. When oxygen was added to the water containing crude oil total mortality was delayed by two days. Approximately 100 ~o mortality was delayed seven days when the animals were not coming in direct contact with the crude oil. When mineral oil was used and air provided the animals survived equally as well as the controls. 3. It was concluded that death resulted because the oil acts as a barrier to oxygen transfer between air and water, and because it contains substances toxic to Tigriopus.
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