Biogeochemistry of aromatic hydrocarbons in the benthos of microcosms†

Investigations into the fate of petroleum compounds in the marine environment were carried out using experimental microcosms of two sizes and designs. Aromatic hydrocarbons or No. 2 fuel oil were spiked to the water of a 13 m³ continuous flow system and to a 2281 recycled flow system. The transport and alteration of this oil was traced in the sediment and benthic organisms (Glycera americana, Crepidula sp., and Nephtys incisa) of these microcosms. Measurable contamination was found in both sample types. The aromatic hydrocarbon distribution, including relative isomeric distribution (e.g., C₂‐phenanthrenes) was found to be different in sediment and in organisms from that which was originally introduced to the experimental microcosm. Differences in isomer distribution between Glycera and Crepidula were also detected. Based on the experimental data: molecular weight and specific isomeric form, biochemical processes, solubility, and particle adsorption/desorption influence the fate of petroleum compounds in benthic ecosystems.     

Uptake and depuration of organic contaminants by blue mussels (Mytilus edulis) exposed to environmentally contaminated sediment

Experiments were designed to expose blue mussels (Mytilus edulis) to contaminated sediment collected from Narragansett Bay, Rhode Island, USA in 1982. Measurements were taken to allow comparisons of the uptake and depuration of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). In addition, concentration factors in the mussels were calculated separately against the dissolved and particulate phase concentrations and the results from the exposure and control systems were compared. Both PAHs and PCBs were rapidly accumulated by the mussels exposed to the contaminated sediment. After the mussels were transferred to control seawater, individual PAHs were depurated with half-lives ranging from 12 to 30 d. Individual PCBs showed depuration half-lives which ranged from 16 to 46 d. Concentration factors in the mussels calculated against the particulate phase concentrations were very different in the exposure and control systems. Concentration factors calculated using only the dissolved phase concentrations (bioconcentration factors) showed excellent agreement in the two systems, possibly an indication that the dissolved phase was the direct source of the contaminants accumulated by the mussels. The bioconcentration factors for PCBs were higher than those of PAHs when compounds with similar n-octanol/water partition coefficients were compared.     

Short-term effect of microencapsulated hydrocarbons on shell growth of Mytilus edulis

Two North Sea crude oils, weathered crude oil, n-alkanes, medical liquid paraffin and a fish oil were microencapsulated and added to seawater. This gave a medium containing both water soluble fractions (WSF) and oil particles, and thus simulated the conditions in natural seawater contaminated with oil. The microencapsulated oils were fed to Mytilus edulis L. in different concentrations, and the growth in terms of shell length of the mussels was measured in intervals of 24 to 48 h for 4 to 12d. With the crude oilss A and B, weathered crude oil and n-alkanes at concentrations1 mg l^-1, shell growth rate decreased rapidly compared to controls. With liquid paraffin at levels of 1 to 12 mg l^-1, a small but significant negative effect on shell growth occurred after 5 d of exposure. Exposure to fish oil at 1 and 4 mg l^-1 gave no significant reduction in growth rate. The toxicity of the different hydrocarbons was not related to their content of aromatic fractions. Crude oil B was tested at concentrations ranging from 0.12 to 12 mg l^-1. At 0.12 mg l^-1 shell growth was not significantly different from the control, while at 0.25 and 0.50 mg l^-1 a temporary and significant stimulation of growth was observed. The product concentration (C)xresponse (R) shows a linear regression on exposure time (t). The regression model CxR=75-0.18t is used to estimate EC-values (effect of a given concentration) for given response levels. The model gives a very good fit to observed data.     

Bioenergetics and survival of the marine snail Thais lima during long-term oil exposure

The carnivorous snail Thais lima was fed Mytilus edulis during a 28-d exposure to the water soluble fraction (WSF) of Cook Inlet crude oil. The LC-50 of T. lima declined from >3000 ppb aromatic hydrocarbons on Day 7 to 818±118 ppb on Day 28. The LC-50 of M. edulis declined from >3 000 ppb aromatic hydrocarbons on Day 7 to 1 686±42 ppb on Day 28. Predation rate declined linearly with increasing aromatic hydrocarbon concentration up to 302 ppb; little predation occurred at 538 ppb and none at 1 160 or 1 761 ppb. Snail absorption efficiency averaged 93.5% and did not vary as a function of WSF dose. Total energy expenditure (R+U) increased at 44 ppb aromatics and declined at lethal WSF exposures. At sublethal WSF exposures, percentages of total energy expenditure were: respiration (87%), ammonia excretion (9%) and primary amine loss (4%). These percentages did not vary as a function of WSF dose or time. Oxygen:nitrogen ratios were not affected by WSF concentration or time and indicated that T. lima derived most of its energy from protein catabolism. The uptake of aromatic hydrocarbons into the soft tissues of snails and mussels was directly related to the WSF concentration. Naphthalenes accounted for 67 to 78% of the aromatic hydrocarbons in T. lima and 56 to 71% in M. edulis. The scope for growth was negative above 150 ppb WSF aromatic hydrocarbons and above 1 204 ppb soft-body aromatic hydrocarbons. These snails were physiologically stressed at an aromatic hydrocarbon concentration which was 19% of the 28-d WSF LC-50 (818±118 ppb) and/or 48% of the 28-d LC-50 of soft tissue aromatics (2 502 ppb).     

Oil-induced disruption of foraging behaviour of the asteroid keystone predator, Coscinasterias muricata (Echinodermata)

A prey-localization test allowed the observation of the foraging behaviour of Coscinasterias muricata in the presence of Mytilus edulis and the disruption of this behaviour following oil exposure. Asteroids were exposed to dilutions of water-accommodated fractions (WAF) of Bass Strait stabilised crude oil (control, 2%, 10%). Effects of exposure (4 d) and depuration (20 d) were quantified using circular statistical analyses. Observations suggested that disruption of behaviour might be concentration-dependent. Control asteroids successfully located mussels during tests. A small proportion (3 of 16) of asteroids exposed to 2% WAF also located the mussels, while asteroids exposed to 10% WAF did not. Following depuration, exposed asteroids recovered their chemoreception capacities. It is concluded that (1) Coscinasterias muricata is able to locate prey mussels through chemoreception, (2) exposure to oil disrupts its foraging behaviour, and (3) the effect is reversible. Received: 4 March 1998 / Accepted: 25 November 1998     

Relationships between carbon and cadmium uptake in Mytilus edulis

The influence of six different food rations on carbon assimilation and net incorporation, and on shell and soft body growth in Mytilus edulis was determined over a 75-d period, starting in 1981. Using a triple tracer technique, interrelationships between carbon net incorporation (C-14) and cadmium accumulation from food (Cd-109) and seawater (Cd-115m) were investigated. With decreasing food rations there was an exponential increase of the carbon assimilation efficiency from 35 to 76% while the net incorporation efficiency increased approximately linearly, ranging from 15 to 32% at the highest and lowest food supply levels respectively. The carbon assimilation efficiency adapted to new conditions within 1 to 2 d while the adaptation of the net incorporation efficiency took about one month. Shells kept growing, even when the soft body lost weight. Within a 42-d elimination period, when the soft body lost 58% of the incorporated carbon, nothing was released from the shells. Cadmium accumulation from food was closely interrelated with carbon net incorporation and exhibited the same uptake kinetics. No homogeneity was found between carbon net incorporation and cadmium accumulation from seawater, and between the elimination of carbon and cadmium.     

Microprofiles of oxygen in epiphyte communities on submerged macrophytes

Mussels (Mytilus edulis) transferred in net bags from clean to chronically mercury polluted water readily accumulated mercury during an exposure period of three months. Growth of the transplanted mussels had a diluting effect on the mercury concentration, but the absolute weight of mercury uptake increased throughout the entire period, though there was a tendency for decreased efficiency of the removal of mercury per liter of water filtered by the mussels. Mussels were also translocated from polluted to clean (laboratory) water to depurate mercury. The biological half-lives of mercury was 293 d for M. edulis from the chronically polluted area in contrast to only 53 d for mussels from a temporary massive mercury polluted area near a chemical deposit. In both cases about 75% of the total mercury in the mussels was inorganic, and it is suggested that both inorganic and organic mercury species were immobilized in mussels from the long-term mercury polluted area, whereas the immobilization capacity was exceeded in the short-term mercury exposed mussels near the chemical deposit. Very slow elimination of mercury was observed in the deposit-feeding bivalve Macoma balthica from the chronically polluted area, and about 6% of the total mercury was methyl-+phenyl-mercury. This is more than three times lower than found in M. edulis from the same collecting site. A pronounced difference in the mercury speciation (i.e., total mercury, total organic mercury, methyl-mercury and phenyl-mercury) in M. edulis from the two mercury polluted areas is thought to reflect the different character of the mercury pollution in the two areas.     

Water-soluble components of four fuel oils: Chemical characterization and effects on growth of microalgae

Approximately 50% of the compounds in the water solubles from 4 fuel oils have been identified via gas chromatography and mass spectrometry. In addition to the well-described types of compounds (naphthalenes, benzenes) expected in water-soluble extracts we have found phenols, anilines, and indoles. Of these classes of compounds methyl, dimethyl, and trimethyl derivatives are present in relatively high concentrations. The water solubles from the 4 fuel oils showed considerably different inhibitory effects to growth of 6 microalgae, 2 blue-greens, 2 greens, and 2 diatoms. Two of the fuel-oil extracts, Baytown and Montana, were lethal to blue-green algae. This was in part traceable to their content of p-toluidine which was found to be toxic to Agmenellum quadruplicatum, Strain PR-6, 1 g in the algal lawn-pad assay and 100 g/l in liquid culture. The water-soluble fraction from New Jersey fuel oil was lethal to the 2 green algae, with lesser effects on the 2 blue-greens. The 2 estuarine diatoms used as test organisms were not greatly inhibited by Baytown, Montana, or New Jersey fuel-oil water-soluble extracts. However, earlier work with an American Petroleum Institute fuel oil and the diatom Thallassiosira pseudonana (3H) showed that 3H was a very sensitive organism. Water solubles from the Baton Rouge fuel oil were almost without effect on the growth of all 6 microalgae. On the basis of the work herein and earlier work, a very cautious viewpoint is advisable in generalizing on the toxicity or lack thereof of a given fuel oil on the growth of different kinds of microalgae. On the other hand, with water solubles from toxic fuel oils such as Baytown or New Jersey the data clearly suggest that their potential for environmental damage is high, either through selective or enrichment effects on natural populations or through a lowering of total primary production.     

Depression of feeding and growth rates of the seastar Evasterias troschelii during long-term exposure to the water-soluble fraction of crude oil

To test the effect of petroleum hydrocarbons on predation by the seastar Evasterias troschelii (Stimpson, 1862) on the mussel Mytilus edulis (L.), we exposed the predator with the prey to six concentrations of the water-soluble fraction (WSF) of Cook Inlet crude oil. Seastars and mussels were collected at Auke Bay, Alaska, in November 1980. During a 28 d exposure in a flow-through system, seastars were more sensitive to the WSF than mussels: the LC₅₀ for the seastars was 0.82 ppm at Day 19 and, although no mussels were exposed to WSF for more than 12 d, none died. Daily feeding rates (whether in terms of number of mussels seastar^-1 d^-1 or dry weight of mussels seastar^-1 d^-1) were significantly reduced at all concentrations above 0.12 ppm. At 0.20, 0.28 and 0.72 ppm WSF, daily feeding rates (in terms of dry weight of mussels) were, respectively, 53, 37, and 5% of the control rate; at the two highest concentrations (0.97 and 1.31 ppm WSF), the seastars did not feed. Seastars at concentrations greater than 0.12 ppm WSF grew slower than individuals from the control group and the 0.12 ppm-treatment group combined. These laboratory results show that E. troschelii is more sensitive to chronic low levels of the WSF of crude oil. The possibility that such oil pollution could reduce predation and permit M. edulis to monopolize the low intertidal zone of southern Alaska remains to be studied.     

Decrease of net carbon flux in two species of mussels caused by extracts of crude oil

Effects of crude oil and salinity stress on the metabolism of two common filter-feeding animals (Mytilus edulis and Modiolus demissus) have been investigated. Carbon budgets have been calculated for each species under a variety of combinations of oil content and salinity. Both reduced salinity and the presence of crude oil tend to decrease the net carbon flux for each species; stresses from each source interacted in their effects on experimental animals. Although similar responses to oil were shown by each species, Mytilus edulis appeared to be slightly more resistant to oil than Modiolus demissus.     

Degradation of bacteria by Mytilus edulis

The uptake of several species of bacteria by the common mussel Mytilus edulis (L.) and the subsequent fate of some polymers of the bacteria have been investigated in a study carried out during 1981. Bacteria (Escherichia coli, Micrococcus luteus, M. roseus, Bacillus cereus, Staphylococcus aureus and a marine pseudomonad, 1-1-1) were radiolabelled by growth in medium containing ³H-thymidine and the uptake of bacteria by Mytilus edulis was monitored. Labelled and unlabelled bacteria, at initial concentrations of 0.5 to 1x10⁷ bacteria ml^-1, were cleared at similar, exponential rates with no significant difference in the rates for different bacteria: 90% of bacteria were cleared in a mean time of 1.93±0.12 h (SEM, n=63). Those bacteria with cell walls which were sensitive to M. edulis lysozyme were rapidly degraded by the mussel and ³H-labelled DNA was released in a form not precipitable by 10% trichloroacetic acid. Lysozyme-resistant bacteria (Micrococcus roseus and S. aureus) were cleared from suspension by Mytilus edulis but most were rejected intact. By measuring the rate of release of ³H-thymidine-labelled material from the mussel the rate of degradation of lysozyme-sensitive bacteria by M. edulis was found. For different bacteria the degradation rate varied from approx 2x10⁸ to 27x10⁸ bacteria h^-1 with an overall mean of 10x10⁸ bacteria h^-1. A thymidine- and diaminopimelicacid-requiring auxotroph of E. coli was radiolabelled with ³H-thymidine, ³H-diaminopimelic acid or ¹⁴C-glucose and fed to M. edulis. Bacteria were cleared and degraded by the mussel; ³H-diaminopimelic acid-labelled or ¹⁴C-glucose-labelled polymers were retained, whereas ³H-thymidine-labelled polymers were released into the surrounding water. Extracts of the digestive gland of M. edulis degraded lysozyme-sensitive bacteria to release ³H-thymidine-labelled material, but did not release ³H-thymidine-labelled material from lysozyme-resistant bacteria. It is concluded that M. edulis can select lysozymesensitive bacteria for subsequent processing and discriminate between bacterial polymers to reject DNA. Also, bacteria could provide a substantial fraction of the carbon requirement of the mussel.     

Metallothionein induction inMytilus edulis exposed to cadmium

The exposure of mussels,Mytilus edulis, collected from Whitsand Bay, southwest England, in August 1988, to sublethal concentrations of cadmium (400µg l^–1) for 65 d resulted in the induction of metallothionein (MT) synthesis in the soft tissues. In cadmium-exposed mussels, metallothionein concentrations, measured by differential pulse polarography, increased by a factor of three, from 2 to 3 mg g^–1 to a maximum of 9 mg g^–1 after 30 d. No significant changes could be detected in controls. Cadmium accumulated in the soft tissues of mussels correlated significantly with metallothionein concentrations and can be described by the relationship: MT (mg g^–1)=0.045 Cd (µg g^–1)+3.03 (r=0.803,P<0.001). Gel chromatography of heat-treated cytosolic extracts showed that the accumulated cadmium is bound principally to the newly formed metallothioneins. Copper and zinc were also analysed in the whole soft-tissues and in subcellular fractions of cadmium-exposed mussels. Although copper concentrations were not affected by cadmium-exposure, zinc levels were significantly reduced. The results demonstrate that the induction of metallothioneins inM. edulis is a quantifiable biological response to sublethal levels of cadmium exposure.     

Cadmium kinetics in oysters — a comparative study of Crassostrea gigas and Ostrea edulis

The accumulation of cadmium was investigated in two species of oysters [Crassostrea gigas (L.) and Ostrea edulis (L.)] from the same environment and in oysters of the same species (O. edulis) from two different environments (contaminated and uncontaminated), under controlled laboratory conditions (33‰ salinity, 10°C, 100 μg Cd l^-1) for up to 111 d in 1982. C. gigas accumulated cadmium twice as fast as O. edulis (1.07 vs 0.52 μg Cd g^-1 wet wt d^-1). Furthermore, O. edulis from an uncontaminated environment accumulated cadmium faster than O. edulis from a metal-contaminated environment (0.52 vs 0.34 μg Cd g^-1 wet wt d^-1). There was no effect of cadmium exposure on total soft-tissue copper and zinc concentrations. Investigation of cytosolic metal-binding using Sephadex G-75 gel-permeation chromatography indicated that binding to very low molecular weight ligands (MW<1000) accounted for>70% of the cytosolic zinc in all oysters and>40% of the cytosolic cadmium in all oysters except O. edulis from Conwy at 83 d. In copper-contaminated oysters, excess copper was also associated with very low molecular weight ligands. Intermediate molecular weight cadmium/copper-binding proteins (similar to metallothionein in molecular weight) were observed in the cytosol and were shown to differ between species in terms of their behavior on Sephadex G-75. Finally, the distribution of accumulated cytosolic cadmium in O. edulis from the contaminated environment was shown to have a unique distribution, i.e., there was no cadmium associated with high molecular weight cytosolic macromolecules. The data indicate that both genetic and environmental factors influence cadmium accumulation in oysters.     

Uptake and incorporation of mercury into mercury-binding proteins of gills of Mytilus edulis as a function of time

Individuals of Mytilus edulis (collected from Sequim Bay, Washington, in April and August, 1980) were exposed to 5 g l^-1 mercury as HgCl₂ for 28 d. Gill mercury accumulation, mercury incorporation into the soluble fraction and low molecular weight, mercury-binding proteins of gills, and induction of these mercury-binding proteins were determined as a function of time. Short-term mercury uptake rates of excised gills were also determined for mussels sampled at intervals during exposure. Gill mercury accumulation occurred in three phases, represented by net uptake phases initially (up to Day 4) and toward the end of the exposure (Days 15 to 28), and an intermediate stable phase (Days 4 to 15). The stable phase was associated with induction of the predominant mercury-binding proteins and mercury incorporation into the proteins. After Day 15, the mercury-binding proteins were saturated and spillover of mercury into high molecular weight proteins had occurred. This was associated with saturation of the soluble fraction, increases of mercury on particulate fractions, and a loss of the ability of gills to maintain stable mercury concentrations. Mercury uptake rates of gills were not affected by the 28 d exposure of the whole organism.     

Accumulation,fractionation and release of oil by the intertidal clam Macoma balthica

The bivalve mollusc Macoma balthica accumulated hydrocarbons during 180 days of continuous exposure to Prudhoe Bay crude oil in seawater dispersions with nominal concentrations of 0.03, 0.3 and 3.0 mg l^-1. The mollusc's ability to concentrate oil from seawater increased with decreasing oil-in-water concentration. Decreases in oil burden began after 30 to 120 days (depending on the oil concentration) and continued for at least 60 days after exposure to oil ceased. Aliphatic and aromatic hydrocarbons were fractionated in markedly different ways by the bivalve. Branched and cyclic aliphatics in the molecular weight-range dodecane through hexadecane were preferentially retained over straightchain and their higher homologs. Larger and more substituted aromatic compounds were selectively concentrated. There appeared to be no selective concentration of aromatic sulphur compounds.Please address requests for reprints to Dr. D. G. Shaw at the Institute of Marine Science     

Very long-chain aliphatic hydrocarbons in lipids of mussels (Mytilus edulis) suspended in the water column near petroleum operations off Sable Island,Nova Scotia,Canada

Mussels (Mytilus edulis) suspended in the water column in 1994 and 1995 for the monitoring of oil drilling operations off Sable Island, Nova Scotia were examined for hydrocarbon profiles, particularly aliphatic hydrocarbons. A spring bloom of phytoplankton occurred during the 90-d suspension period in 1995. Hydrocarbons isolated from the 1995 suspended mussels showed very high concentrations of both biogenic hydrocarbons and very long-chain n-alkanes from C₂₀ to C₃₂, initially thought to be petrogenic. Both types of hydrocarbons were either not detected or were only present in trace amounts in the mussels suspended in 1994 at similar sites. The biogenic hydrocarbons in the 1995 mussels were apparently of planktonic origin, from the spring bloom, and were dominated by heneicosahexaene (21:6), followed by pristance, heptadecane, and varions monounsaturated and polyunsaturated phytenes, heptadecenes, nonadecenes and heneicosenes. They could be readily hydrogenated to yield the basic alkanes. The 1995 mussels suspended within 1 km from the oil well platform were probably slightly tainted by petrogenic hydrocarbons, as evidenced by the detection of phytane and high concentrations of total aliphatic hydrocarbons, whereas the mussels suspended 10 km from the platform showed only high concentrations of biogenic hydrocarbons and the novel long-chain n-alkanes. The occurrence of an unusual phytoplankton bloom during the suspension period severely interfered with the petroleum monitoring role of mussels by altering the mussel hydrocrbon profiles through the accumulation into and probably selective depuration of xenobiotic hydrocarbons from the mussel, tissues.J. Parsons (deceased)     

Hydrocarbon uptake and loss by the mussel Mytilus edulis

The dynamics of accumulation and elimination of hydrocarbons by the blue mussel Mytilus edulis were studied in a continuous-flow system. Mussels were exposed for as long as 41 days to 200 – 400 g/l of diesel fuel adsorbed on kaolin particles. Hydrocarbons were accumulated in the tissues in excess of 1000 times the exposure levels. Upon termination of dosing, the mussels exhibited a rather rapid loss of hydrocarbons for the first 15 to 20 days (biological half-life=2.7 to 3.5 days). Subsequently, however, elimination was reduced to a minimum and a considerable fraction of the hydrocarbons could be recovered from the tissues after as long as 32 days of depuration. The mussels exhibited definite signs of physiological stress due to chronic exposure to diesel fuel, although recovery was rapid upon termination of dosing. It is concluded that mussels could be utilized as a test organism for monitoring long-term hydrocarbon pollution in marine waters. The implications for the mussel culture industry are discussed.     

A long-term study of the effects of water-soluble fractions of No. 2 fuel oil on the survival,development rate,and growth of the mud crab Rhithropanopeus harrisii

Mud crabs, Rhithropanopeus harrisii (Gould), were exposed continuously for 6 months after hatching to water-soluble fractions (WSF) of No. 2 fuel oil. Survival, growth and development rate were monitored during this time. The zoeal stages were the most sensitive to fuel oil. A 20% WSF (0.36 ppm total naphthalenes, 1.26 ppm total hydrocarbons) was acutely toxic to these stages. Of the zoeal stages, the first stage appeared to be the most sensitive. The combined duration of the 4 zoeal stages was significantly increased by increasing WSF exposure concentrations. The megalopa and crab stages were not particularly sensitive to continued petroleum hydrocarbon exposure, particularly when compared to zoeal stages. However, mean duration of the megalopa and first crab stages was significantly affected by oil exposure. Individuals which survived the highest exposure concentrations as larvae appeared to grow larger during the crab stages, so that at the end of 6 months comparably staged crabs were equal to or larger than both control crabs and those exposed to low WSF concentrations. Stage distributions at the end of 6 months showed no differences due to WSF exposure. Sex ratios, which could be determined at the end of 6 months, were approximately 1, indicating no sex-related differential sensitivity to WSF exposure, at least as larvae or juveniles. The data indicate that these crabs possess considerable ability to recover from the effects of chronic sublethal exposure to petroleum hydrocarbons. The most deleterious effects of oil pollution on this species may be due to its impact on larval recruitment into the adult population.     

Effects of petroleum products on bull kelp (Nereocystis luetkeana)

Although research has been conducted on the effects of oil on the giant kelp Macrocystis pyrifera, no similar studies have been completed on bull kelp, Nereocystis leutkeana, the dominant kelp in Washington State, British Columbia, and Alaska. The effects of three petroleum products [diesel fuel, intermediate fuel oil (IFO), and crude oil] were tested before and after weathering on N. luetkeana. Whole plants were exposed to petroleum product for 4 or 24 h and then transferred to the field; observations on the condition of the plants were made daily for 7 d. In addition, controlled bioassays were performed to measure the effects of petroleum exposure on net photosynthetic rate (NP) and respiration rate (R), using light-and dark-bottle techniques. These experiments verified the susceptibility of N. luetkeana tissue to the damaging effects of direct exposure to several oil types. The 4 h exposures to weathered diesel and unweathered IFO, and 24 h exposures to unweathered and weathered diesel and IFO resulted in moderate to severe damage to kelp tissue (i.e., clearly delineated bleached line accompanied by tissue necrosis). Weathered diesel was more toxic than unweathered diesel. The most severe damage to bull kelp was concentrated at the meristematic zone (junction of stipe and bulb) where new tissue growth occurs. Petroleum type significantly affected stipe and blade NP, R, and NP:R ratios. Diesel treatments had a greater negative effect on NP than did the IFO treatments. Based on these experiments, the relative ranking of the damaging effects of petroleum treatment on bull kelp are weathered diesel>unweathered IFO>unweathered diesel>weathered IFO>unweathered crude>weathered crude.     

Les caryotypes de quelques espèces de bivalves et de gastéropodes marins

The karyotypes of the bivalves Ostrea edulis (2 n=20), Crassostrea gigas (2 n=20), Mytilus galloprovincialis (2 n=28) and M. edulis (2 n=28) were obtained from mitotic metaphases of branchial tissue by means of a cellular suspension technique. The occurrence of metacentric, submetacentric and telocentric chromosomes in O. edulis as well as differences in size between Pair 1 and Pair 10 emphasize the cytological interest of this species compared to C. gigas which possesses only metacentric and submetacentric chromosomes. The variation in Pair 2, which is telocentric in M. galloprovincialis and metacencentric in M. edulis, has been observed for the first time and may support taxological separation of these two species. The karyotypes of the mesogastropods Rissoa ventricosa (2 n=32) and Littorina neritoides (2 n=34) were obtained from mitotic metaphases of gonadal tissue by the same technique. Sexual chromosomes were identified in the karyotypes of R. ventricosa. At the beginning of spermatogenesis, the gonad of L. neritoides shows both haploïd and polyploïd meïotic metaphases which correspond to typical (germinal cells) and atypical (nurse cells) forms, respectively.