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Effects on hatching in Littorina littorea after an oil spill
Volume 10/Number 9/September 1979
Island are thought to spend the winter in the waters off S.W. Greenland, while the remainder are found in the ice-free areas of the Barents Sea (Norderhaug et al., 1977). One can thus assume that nearly all the auks seen off the Varanger coast and those which were killed by the oil were part of the Russian population of Brunnich's Guillemots. Despite a possible mortality of 20 000 birds, the breeding population of Brunnich's Guillemots in the Barents Sea was thus probably not severely affected by what was first considered to be a serious disaster. This episode did, however, illustrate how very vulnerable certain seabirds, in this case auks, can be to very small oil spills. It also acted as a significant stimulant for those involved in the current, controversial
discussions concerning the planned exploration for oil in Norwegian waters north of 620N. I would like to thank Leon Johansen for allowing me to use his previously unpublished results of duck counts in Vadsl~, the Norwegian Meteorological Office for providing the weather data and the Norwegian Sales Organization for Herring for the Capelincatch figure. Financial and technical support was gratefully received from the World Wildlife Fund, Norway and the Norwegian Directorate for Wildlife and Freshwater Fish. Grastveit, J. ( 1971 ). SteLlers and ved V adso. Sterna, 10, 31 -33. Haftorn, S. (1971). NorgesFugler. Universitetsforlaget, Oslo. Norderhang, M., Brun, E. and M~llen, G. U. (1977).Barentshavets sj~fnglressurser. Forhold til tilknyting til status, milj¢problemer ng forskningsoppgaver., N o r s k Polar Inst. meddlr.. 104, 1-119.
0025-326X/79/0901--0235$02.00/0
MarinePollutionBulletin, Vol. 10, pp. 255-258 PergamonPressLtd. 1979.Printedin GreatBritain.
Effects on hatching in Littorina littorea after an oil spill JOHN TERJE STAVELAND Institute o f Marine Research, 5011 Bergen, Nordnes, Norway One year after an accidental spin of approx. 2000 t of Iranian crude oil on the west coast of Norway, specimens of the gastropod Littorina littorea were collected from the oil polluted shore and allowed to spawn in the laboratory. Snails were also collected from an unpolluted reference site. The oil contamination seemed to have no detectable effects on fertilization. However, the hatching success of the veHger larvae was significally less in the 'oil polluted' population. Some highly abnormal eggs were also observed in this egg population.
In February 1976, approx. 2000 t of Iranian crude oil were spilled off the west coast of Norway. Two days later, some of this oil contaminated the shoreline on Karmey Island. The incident was followed up by an extensive chemicalbiological investigation in the area. (Grahl-Nielsen et al., 1978). In March 1977, 13 months after the spill, significant amounts of oil hydrocarbons were still left in periwinkles from the oil polluted shore. Most of this was probably accumulated by grazing of the oil contaminated substratum and some by uptake from the water passing the gills. Laboratory investigations on the effects of oil pollution on marine animals indicate that the early life stages are the most sensitive in some organisms, e.g. crustaceans. (Rice et al., 1977) Most of these experiments have been carried out by exposing the eggs, sperm or larvae directly to oil polluted seawater in the laboratory. With few exceptions, no account has been taken of effects of oil on the maturing of eggs and sperm in the gonads. Rossi & Anderson (1977) detected high concentrations of diaromatic hydrocarbons in the gonads of the polychaete Neanthes arenaceodentata especially in the females, when exposed to fuel oil. High concentrations were also detected in the progeny. Linden (1976) found sublethal effects of oil on the reproduction in the amphipod Gammarus oceanicus.
Both the brood size and the frequency with which the male and female entered the precopulation stage were found to decrease in the presence of low concentrations of oil in the water. The purpose of the present work was to investigate if a long exposure to oil had any effects on fertilization and hatching success in Littorina littorea. No comparable work has been done on these gastropod before. However, Hargreave & Newcombe (1973) detected some sublethal effects of oil on crawling and respiration in the adult snail. L. littorea is a common, littoral gastropod found in great numbers along the Norwegian coast. At spawning, occurring mainly in the spring, one to six eggs are shed in each of approx. 500 disc-like egg capsules. After hatching, the free swimming veliger larvae feed in the plankton before sinking to the bottom where they metamorphose. Extensive bibliographies on the ecology and reproduction of L. littorea are given by Fretter & Graham (1962) and Fish
(1972).
Methods Snails were collected from a rocky, moderately exposed oil polluted area and from a non polluted reference site. Several snails were observed in copulation position. Ten females from the oil polluted area and seven from the reference-site were sampled immediately after copulation had ended. The sex was verified from sex determination of the corresponding males after removal of their shells. In addition, 30 animals from each of the two sites were collected for an experiment in the laboratory. The water temperature was approx. 2°C, and the salinity 30%0. The four groups of snails were transferred to separate plasticcontainers each with 25 I. untreated seawater for transport to the Institute of Marine Research in Bergen. The animals 255
Marine Pollution Bulletin
appeared to be in good condition when transferred to the aquaria at the Institute. All the statistical methods used are taken from Sverdrup
(]964). Experiment 1 The two groups of females which had copulated were placed for spawning in separate Perspex aquaria (20 x 15 x 5 cm) having 90/an plankton gauze at the ends. The aquaria were immersed in a container with 120 I. seawater taken at 120 m depth outside the Institute. The water was continuously aerated. The next day, approx. 24 h after copulation, all the snails were removed from the aquaria. Experiment2 The randomly sampled snails were transferred to two aquaria with 120 l. seawater each. One day after sampling, three pairs were observed in copulation, one from the polluted area and two from the control site. These females were transferred to two aquaria for spawning as described previously. Six days after sampling, the water temperature had increased from 7.5°C to 11.0°C, with a constant salinity of 34°/00.The four spawning-aquaria were now immersed in an aquarium with running, UV-sterilized seawater with constant temperature (7.6 ° C) and salinity(,34%o). The sampling procedure was similar in the two experiments. Water samples containing egg capsules were taken regularly with a Pasteur-pipette from each egg population and transferred to a small Petri dish for binocular examination of living eggs and larvae. These were then transferred to vials and preserved in 4% formalin/ distilled water. Sampling started 2 and 4 h after the adult females were removed in experiment 1 and 2, respectively. The number of egg capsules in each sample ranged from 7 to 1044, with the highest number in the final samples taken 26 days after sampling of the adult. The preserved samples of eggs and larvae from both experiments were examined with respect to number of fertilized eggs and eggs markedly different from normal ones, number of unhatched larvae and total number of capsules. The criterion of fertilization in exp. 1 was visible egg cleavage in the second sample after spawning had occurred (approx. 24 h). The first sample in this experiment was taken too early after spawning. In experiment 2, the criterion of fertiliTation was visible egg cleavage in the first sample after spawning (approx. 4 h). Because of avoidance, the active swimming veliger larvae were under-represented in most of the samples. For this reason, the number of hatched veliger larvae in each sample was estimated by subtracting the total number of eggs and larvae remaining in the capsules from the total number of eggs/larvae in the sample. This total number of eggs/larvae were estimated by multiplying the number of capsules in the sample with the average number of eggs per capsule in all the prehatched samples from the same egg population. The hatching success in percent is illustrated in Figs 3 and 4.
TABLE 1 Experiment 1. Total number o f eggs and percentage fertilization in the second sample after spawning. The first sample was taken too early after spawning. Experiment 2. Total number of eggs and the mean percentage fertilization in the first two samples after spawning. Experiment
1
Locations
2
PoUuted
Non-polluted
Polluted
Non-polluted
32 97
135 96
271 100
422 I(30
No. of eggs °70fertilisation
spite of this, there seem to be no detectable effects on fertilization of the L. littorea eggs. Percentage fertilization in the four egg populations are given in Table 1. Although no significant differenceexists between the 'oil exposed' and the reference populations, there was a slightly smaller percentage fertiliTation among eggs spawned by animals which had copulated in their natural habitat relative to eggs from animals which had copulated in the laboratory. The number of eggs per capsule (e/c) varied much within the four egg populations (Figs l(a), l(b), 2(a) and 2Co)). During the hatching period a significant decrease in the e/c ratio occurred in exp. 2 (p=0.01 in the oil exposed and p = 0.0000in the reference population). However, in exp. 1, the significance levels were p=0.06 and p=0.47, respectively. The progressive decrease in the e/c ratio indicates a more successful hatching among larvae living several together than among single ones. The cumulative hatching success in exp. 1 is illustrated in Fig. 3. The eggs from the polluted site had a longer developmental time to hatching than those from the reference site. This difference seemed to increase as hatching proceeded. This delay, which presumably also increases the
T
2.0
:
Tv
,L
~
T '
T I
1.5 t/)
I
*
J-
.L
f15 o
I
I
I
I
I
I
I
b ¢o > t_ t~ _J
2.0
1.5
T ', T
1.0
4
8
12
16
20
24
Days
Results and Discussion The adult animals from the oil polluted area have been exposed to oil and oil components for more than a year. In 256
Fig. 1 Change in number o f eggs per capsule (e/c) with time after spawning in oil exposed (a) and control (b) populations in exp. 1. Each point represents one sample. Hatched vertical lines indicate + 2 standard deviations of the means.
Volume 10/Number 9/September 1979
75
zo
i ,," ._= -=
50
t~ .c:
#
1.5
25
"i I
I
I
I
t
I
4
b
._1
2.C
8
12 16 Days
20
24
Fig. 3 Cumulative percentage hatching as function of time since spawning in exp. 1. Each point represents one sample. • - - - • oil exposed: • - • control: 4 k - - • both oil exposed and control.
T ~
1.5 75
1.0
;
8
1'2 1=6 Days
20
2'4
Fig. 2 Change in number of eggs per capsule (e/c) with time after spawning in oil exposed (a) and control Co) populations in exp. 2. Each point represents one sample. Hatched vertical lines indicate :t: 2 standard deviations of the means.
.c
50
t~
25
vC
predation pressure put on the embryos, may have been due to a retarded metabolic rate. If not, however, a prolonged time to hatching would imply a greater embryonic demand on the yolk reserves, giving the newly hatched veliger larva a nutritional disadvantage at the onset of a critical period of pelagic life. The final percent hatching was also significantly less in the' oil polluted' ones (19 < 0.0000). In the second experiment, i.e., with eggs fertilized in the laboratory, there was no obvious difference in time of hatching between the oil exposed and the control population. However, total hatching success was significantly less (p < 0.0000) among larvae from the oil polluted area relative to the reference population (Fig. 4). Thus oil exposure of the adults seems to have a retarding effect on embryonic development in this species. The difference in hatching success between the control populations in exp. 1 and 2, i.e. 74.0°70 and 81.8070, respectively, may have been a consequence of different laboratory stress and the great difference in the number of eggs per capsule. The even greater difference between the oil exposed populations, 55.4070 and 70.9070 in exp. 1 and 2, respectively, is possibly a result of greater sensitivity towards the different environmental stress in the laboratory among oil polluted larvae than among control ones. Several eggs from the oil polluted area stopped developing after two or three cleavages, but most of the eggs reached later stages. Some abnormal eggs were observed, mainly in exp. 1. They consisted of three to eight irregular blastomeres lying in the same plane. At hatching, veliger larvae from the oil polluted area seemed to have shorter periods of ciliary movement, followed by greater resting periods than the reference larvae. This indicates a sublethal
~v
4
8
12 16 Days
20
24
Fig. 4 Cumulative percentage hatching as function of time since spawning in exp. 2. Each point represents one sample. O - - - 0 oil exposed: [ ] - - - [ ] control: ~ - - - ~ both oil exposed and control.
effect from the oil pollution which may have adverse effects on feeding success. The effects of oil pollution on the embryonic development in L. littorea found in this investigation, supports the assumptions made by Monk et ai. (1978), concerning the effect of oil pollution on Littorina saxatilis. They observed a sudden decrease in the L. saxatilis population 2 years after a spill of 15-25 t of diesel fuel or light gas oil at Mongstad, Norway. A reduced reproductive capability was assumed to be the main reason rather than a delayed mortality of the individuals present during the spill. As L. littorea eggs are easy to obtain and keep in the laboratory, this species will be suitable for future research regarding the effects of crude oil or oil products on the reproduction of marine animals. The vivipary of L. saxatilis makes it possible to study reproduction effects in this species in situ.
Fish, J. D. (1972). The breeding cycle and growth of open coast and estuarine populations of Littorina littorea. J. mar. biol. Ass. U.K., 52, 1011-1019. Fretter V. & Graham, A. (1962). British Prosobranch Molluscs. London: Ray Society. Grahl-Nielsen, O., Staveland, J. T. & Wilheimsen, S. (1978). Aromatic hydrocarbons in benthic organisms from coastal areas polluted by Iranian crude oil. J. Fish Res. B d Can., 35,615-623.
257
Marine Pollution Bulletin
Hargrave, B. T. & Newcome, C. P. (1973). Crawling and respiration as indices of sublethal effects of oil and a dispersant on an intertidal snail, Littorina iittorea. J. Fish. Res. Bd Can., 30. 1789-1792. Heller, J. (1975). The taxonomy of some British Littorinaspedes with notes on their reproduction. Zooi. J. Linn. Soc. Lond., 56, 131-151. Linden, O. (1976). Effects of oil on the reproduction of the amphipod Gammarus oceanicus, A mbio 5, 36-37. Monk, D. C., Cowell, E. B. & Syratt, W. J. (1978). The littoral ecology of the area around Mongstad refinery, Fensfjorden, during the three years after refinery commissioning, 1975-1977. Report to Rafinor a/s and Company, Mongstad. London: British Petroleum Company.
Rice, S. D., Short, J. W. & Karinen, J. F. (1977). Comparative oil toxicity and comparable animal sensitivity. In Fate and Effects of Petroleum Hydrocarbons in Marine Organisms and Ecosystems, D. A. Wolfe (ed.). Pergamon Press, Oxford, pp. 78-94. Rossi, S. S. & Anderson, J. W. (1977). Accumulation and release of fueloil-derived diaromatic hydrocarbons by the polychaete Neanthes a~naceodentata. Mar. Biol., 39, 51-55. Sverdrup, E. (1964). Lov og tilfeldighet, II, 8.2. Universitetsforlaget, Bergen.
0025-326X/79/0901-0258$02.00/0
Marine Pollution Bulletin, Vol. 10, pp. 258-259
PergamonPressLtd. 1979.Printed in GreatBritain.
Observations of Mercury Levels in Branchiostoma caribaeum A. JERNELOV,
O . L I N D i ~ N a n d L. L I N D E S T R O M
Swedish Water and A i r Pollution Research Institute (IVL), B o x 21060, S-lO0 31 Stockholm, Sweden
CITY OF
/ G
E
N
~
CARIBBEAN SEA
v
km
Fig. 1 The Cartegena Bay with the sampling stations for lancelets, Branchiostoma caribaum. The concentrations of mercury found in the lancelets from the different stations are given in ppb. 258
Island are thought to spend the winter in the waters off S.W. Greenland, while the remainder are found in the ice-free areas of the Barents Sea (Norderhaug et al., 1977). One can thus assume that nearly all the auks seen off the Varanger coast and those which were killed by the oil were part of the Russian population of Brunnich's Guillemots. Despite a possible mortality of 20 000 birds, the breeding population of Brunnich's Guillemots in the Barents Sea was thus probably not severely affected by what was first considered to be a serious disaster. This episode did, however, illustrate how very vulnerable certain seabirds, in this case auks, can be to very small oil spills. It also acted as a significant stimulant for those involved in the current, controversial
discussions concerning the planned exploration for oil in Norwegian waters north of 620N. I would like to thank Leon Johansen for allowing me to use his previously unpublished results of duck counts in Vadsl~, the Norwegian Meteorological Office for providing the weather data and the Norwegian Sales Organization for Herring for the Capelincatch figure. Financial and technical support was gratefully received from the World Wildlife Fund, Norway and the Norwegian Directorate for Wildlife and Freshwater Fish. Grastveit, J. ( 1971 ). SteLlers and ved V adso. Sterna, 10, 31 -33. Haftorn, S. (1971). NorgesFugler. Universitetsforlaget, Oslo. Norderhang, M., Brun, E. and M~llen, G. U. (1977).Barentshavets sj~fnglressurser. Forhold til tilknyting til status, milj¢problemer ng forskningsoppgaver., N o r s k Polar Inst. meddlr.. 104, 1-119.
0025-326X/79/0901--0235$02.00/0
MarinePollutionBulletin, Vol. 10, pp. 255-258 PergamonPressLtd. 1979.Printedin GreatBritain.
Effects on hatching in Littorina littorea after an oil spill JOHN TERJE STAVELAND Institute o f Marine Research, 5011 Bergen, Nordnes, Norway One year after an accidental spin of approx. 2000 t of Iranian crude oil on the west coast of Norway, specimens of the gastropod Littorina littorea were collected from the oil polluted shore and allowed to spawn in the laboratory. Snails were also collected from an unpolluted reference site. The oil contamination seemed to have no detectable effects on fertilization. However, the hatching success of the veHger larvae was significally less in the 'oil polluted' population. Some highly abnormal eggs were also observed in this egg population.
In February 1976, approx. 2000 t of Iranian crude oil were spilled off the west coast of Norway. Two days later, some of this oil contaminated the shoreline on Karmey Island. The incident was followed up by an extensive chemicalbiological investigation in the area. (Grahl-Nielsen et al., 1978). In March 1977, 13 months after the spill, significant amounts of oil hydrocarbons were still left in periwinkles from the oil polluted shore. Most of this was probably accumulated by grazing of the oil contaminated substratum and some by uptake from the water passing the gills. Laboratory investigations on the effects of oil pollution on marine animals indicate that the early life stages are the most sensitive in some organisms, e.g. crustaceans. (Rice et al., 1977) Most of these experiments have been carried out by exposing the eggs, sperm or larvae directly to oil polluted seawater in the laboratory. With few exceptions, no account has been taken of effects of oil on the maturing of eggs and sperm in the gonads. Rossi & Anderson (1977) detected high concentrations of diaromatic hydrocarbons in the gonads of the polychaete Neanthes arenaceodentata especially in the females, when exposed to fuel oil. High concentrations were also detected in the progeny. Linden (1976) found sublethal effects of oil on the reproduction in the amphipod Gammarus oceanicus.
Both the brood size and the frequency with which the male and female entered the precopulation stage were found to decrease in the presence of low concentrations of oil in the water. The purpose of the present work was to investigate if a long exposure to oil had any effects on fertilization and hatching success in Littorina littorea. No comparable work has been done on these gastropod before. However, Hargreave & Newcombe (1973) detected some sublethal effects of oil on crawling and respiration in the adult snail. L. littorea is a common, littoral gastropod found in great numbers along the Norwegian coast. At spawning, occurring mainly in the spring, one to six eggs are shed in each of approx. 500 disc-like egg capsules. After hatching, the free swimming veliger larvae feed in the plankton before sinking to the bottom where they metamorphose. Extensive bibliographies on the ecology and reproduction of L. littorea are given by Fretter & Graham (1962) and Fish
(1972).
Methods Snails were collected from a rocky, moderately exposed oil polluted area and from a non polluted reference site. Several snails were observed in copulation position. Ten females from the oil polluted area and seven from the reference-site were sampled immediately after copulation had ended. The sex was verified from sex determination of the corresponding males after removal of their shells. In addition, 30 animals from each of the two sites were collected for an experiment in the laboratory. The water temperature was approx. 2°C, and the salinity 30%0. The four groups of snails were transferred to separate plasticcontainers each with 25 I. untreated seawater for transport to the Institute of Marine Research in Bergen. The animals 255
Marine Pollution Bulletin
appeared to be in good condition when transferred to the aquaria at the Institute. All the statistical methods used are taken from Sverdrup
(]964). Experiment 1 The two groups of females which had copulated were placed for spawning in separate Perspex aquaria (20 x 15 x 5 cm) having 90/an plankton gauze at the ends. The aquaria were immersed in a container with 120 I. seawater taken at 120 m depth outside the Institute. The water was continuously aerated. The next day, approx. 24 h after copulation, all the snails were removed from the aquaria. Experiment2 The randomly sampled snails were transferred to two aquaria with 120 l. seawater each. One day after sampling, three pairs were observed in copulation, one from the polluted area and two from the control site. These females were transferred to two aquaria for spawning as described previously. Six days after sampling, the water temperature had increased from 7.5°C to 11.0°C, with a constant salinity of 34°/00.The four spawning-aquaria were now immersed in an aquarium with running, UV-sterilized seawater with constant temperature (7.6 ° C) and salinity(,34%o). The sampling procedure was similar in the two experiments. Water samples containing egg capsules were taken regularly with a Pasteur-pipette from each egg population and transferred to a small Petri dish for binocular examination of living eggs and larvae. These were then transferred to vials and preserved in 4% formalin/ distilled water. Sampling started 2 and 4 h after the adult females were removed in experiment 1 and 2, respectively. The number of egg capsules in each sample ranged from 7 to 1044, with the highest number in the final samples taken 26 days after sampling of the adult. The preserved samples of eggs and larvae from both experiments were examined with respect to number of fertilized eggs and eggs markedly different from normal ones, number of unhatched larvae and total number of capsules. The criterion of fertilization in exp. 1 was visible egg cleavage in the second sample after spawning had occurred (approx. 24 h). The first sample in this experiment was taken too early after spawning. In experiment 2, the criterion of fertiliTation was visible egg cleavage in the first sample after spawning (approx. 4 h). Because of avoidance, the active swimming veliger larvae were under-represented in most of the samples. For this reason, the number of hatched veliger larvae in each sample was estimated by subtracting the total number of eggs and larvae remaining in the capsules from the total number of eggs/larvae in the sample. This total number of eggs/larvae were estimated by multiplying the number of capsules in the sample with the average number of eggs per capsule in all the prehatched samples from the same egg population. The hatching success in percent is illustrated in Figs 3 and 4.
TABLE 1 Experiment 1. Total number o f eggs and percentage fertilization in the second sample after spawning. The first sample was taken too early after spawning. Experiment 2. Total number of eggs and the mean percentage fertilization in the first two samples after spawning. Experiment
1
Locations
2
PoUuted
Non-polluted
Polluted
Non-polluted
32 97
135 96
271 100
422 I(30
No. of eggs °70fertilisation
spite of this, there seem to be no detectable effects on fertilization of the L. littorea eggs. Percentage fertilization in the four egg populations are given in Table 1. Although no significant differenceexists between the 'oil exposed' and the reference populations, there was a slightly smaller percentage fertiliTation among eggs spawned by animals which had copulated in their natural habitat relative to eggs from animals which had copulated in the laboratory. The number of eggs per capsule (e/c) varied much within the four egg populations (Figs l(a), l(b), 2(a) and 2Co)). During the hatching period a significant decrease in the e/c ratio occurred in exp. 2 (p=0.01 in the oil exposed and p = 0.0000in the reference population). However, in exp. 1, the significance levels were p=0.06 and p=0.47, respectively. The progressive decrease in the e/c ratio indicates a more successful hatching among larvae living several together than among single ones. The cumulative hatching success in exp. 1 is illustrated in Fig. 3. The eggs from the polluted site had a longer developmental time to hatching than those from the reference site. This difference seemed to increase as hatching proceeded. This delay, which presumably also increases the
T
2.0
:
Tv
,L
~
T '
T I
1.5 t/)
I
*
J-
.L
f15 o
I
I
I
I
I
I
I
b ¢o > t_ t~ _J
2.0
1.5
T ', T
1.0
4
8
12
16
20
24
Days
Results and Discussion The adult animals from the oil polluted area have been exposed to oil and oil components for more than a year. In 256
Fig. 1 Change in number o f eggs per capsule (e/c) with time after spawning in oil exposed (a) and control (b) populations in exp. 1. Each point represents one sample. Hatched vertical lines indicate + 2 standard deviations of the means.
Volume 10/Number 9/September 1979
75
zo
i ,," ._= -=
50
t~ .c:
#
1.5
25
"i I
I
I
I
t
I
4
b
._1
2.C
8
12 16 Days
20
24
Fig. 3 Cumulative percentage hatching as function of time since spawning in exp. 1. Each point represents one sample. • - - - • oil exposed: • - • control: 4 k - - • both oil exposed and control.
T ~
1.5 75
1.0
;
8
1'2 1=6 Days
20
2'4
Fig. 2 Change in number of eggs per capsule (e/c) with time after spawning in oil exposed (a) and control Co) populations in exp. 2. Each point represents one sample. Hatched vertical lines indicate :t: 2 standard deviations of the means.
.c
50
t~
25
vC
predation pressure put on the embryos, may have been due to a retarded metabolic rate. If not, however, a prolonged time to hatching would imply a greater embryonic demand on the yolk reserves, giving the newly hatched veliger larva a nutritional disadvantage at the onset of a critical period of pelagic life. The final percent hatching was also significantly less in the' oil polluted' ones (19 < 0.0000). In the second experiment, i.e., with eggs fertilized in the laboratory, there was no obvious difference in time of hatching between the oil exposed and the control population. However, total hatching success was significantly less (p < 0.0000) among larvae from the oil polluted area relative to the reference population (Fig. 4). Thus oil exposure of the adults seems to have a retarding effect on embryonic development in this species. The difference in hatching success between the control populations in exp. 1 and 2, i.e. 74.0°70 and 81.8070, respectively, may have been a consequence of different laboratory stress and the great difference in the number of eggs per capsule. The even greater difference between the oil exposed populations, 55.4070 and 70.9070 in exp. 1 and 2, respectively, is possibly a result of greater sensitivity towards the different environmental stress in the laboratory among oil polluted larvae than among control ones. Several eggs from the oil polluted area stopped developing after two or three cleavages, but most of the eggs reached later stages. Some abnormal eggs were observed, mainly in exp. 1. They consisted of three to eight irregular blastomeres lying in the same plane. At hatching, veliger larvae from the oil polluted area seemed to have shorter periods of ciliary movement, followed by greater resting periods than the reference larvae. This indicates a sublethal
~v
4
8
12 16 Days
20
24
Fig. 4 Cumulative percentage hatching as function of time since spawning in exp. 2. Each point represents one sample. O - - - 0 oil exposed: [ ] - - - [ ] control: ~ - - - ~ both oil exposed and control.
effect from the oil pollution which may have adverse effects on feeding success. The effects of oil pollution on the embryonic development in L. littorea found in this investigation, supports the assumptions made by Monk et ai. (1978), concerning the effect of oil pollution on Littorina saxatilis. They observed a sudden decrease in the L. saxatilis population 2 years after a spill of 15-25 t of diesel fuel or light gas oil at Mongstad, Norway. A reduced reproductive capability was assumed to be the main reason rather than a delayed mortality of the individuals present during the spill. As L. littorea eggs are easy to obtain and keep in the laboratory, this species will be suitable for future research regarding the effects of crude oil or oil products on the reproduction of marine animals. The vivipary of L. saxatilis makes it possible to study reproduction effects in this species in situ.
Fish, J. D. (1972). The breeding cycle and growth of open coast and estuarine populations of Littorina littorea. J. mar. biol. Ass. U.K., 52, 1011-1019. Fretter V. & Graham, A. (1962). British Prosobranch Molluscs. London: Ray Society. Grahl-Nielsen, O., Staveland, J. T. & Wilheimsen, S. (1978). Aromatic hydrocarbons in benthic organisms from coastal areas polluted by Iranian crude oil. J. Fish Res. B d Can., 35,615-623.
257
Marine Pollution Bulletin
Hargrave, B. T. & Newcome, C. P. (1973). Crawling and respiration as indices of sublethal effects of oil and a dispersant on an intertidal snail, Littorina iittorea. J. Fish. Res. Bd Can., 30. 1789-1792. Heller, J. (1975). The taxonomy of some British Littorinaspedes with notes on their reproduction. Zooi. J. Linn. Soc. Lond., 56, 131-151. Linden, O. (1976). Effects of oil on the reproduction of the amphipod Gammarus oceanicus, A mbio 5, 36-37. Monk, D. C., Cowell, E. B. & Syratt, W. J. (1978). The littoral ecology of the area around Mongstad refinery, Fensfjorden, during the three years after refinery commissioning, 1975-1977. Report to Rafinor a/s and Company, Mongstad. London: British Petroleum Company.
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0025-326X/79/0901-0258$02.00/0
Marine Pollution Bulletin, Vol. 10, pp. 258-259
PergamonPressLtd. 1979.Printed in GreatBritain.
Observations of Mercury Levels in Branchiostoma caribaeum A. JERNELOV,
O . L I N D i ~ N a n d L. L I N D E S T R O M
Swedish Water and A i r Pollution Research Institute (IVL), B o x 21060, S-lO0 31 Stockholm, Sweden
CITY OF
/ G
E
N
~
CARIBBEAN SEA
v
km
Fig. 1 The Cartegena Bay with the sampling stations for lancelets, Branchiostoma caribaum. The concentrations of mercury found in the lancelets from the different stations are given in ppb. 258