Early reproduction and development of dominant calanoid copepods in the sea ice zone of the Barents Sea—need for a change of paradigms?

Reproduction and growth of the dominant copepods Calanus finmarchicus, C. glacialis, C. hyperboreus and Pseudocalanus minutus were studied on transects across the sea ice zone of the northern Barents Sea in May and June 1997. C. glacialis and C. finmarchicus were numerically dominant and also the largest component of the biomass. C. hyperboreus was rather rare. Moderate levels of phytoplankton and eventually high concentrations of ice algae supported maximum egg production rates of 53.6 and 48.5 eggs female^–1 day^–1 of C. glacialis in May and June, respectively. Results of incubation experiments were supported by a tremendous abundance of C. glacialis eggs in the water column ranging from 7×10³ to 4.4×10⁴ m^–2 in May and from 9.8×10³ to a maximum of 9.7×10⁴ m^–2 in June. In contrast, C. finmarchicus spawned only in the vicinity of the ice edge, at a maximum rate of 30 eggs female^–1 day^–1. Egg sacs of P. minutus were often observed in the preserved samples, but contained only few eggs, which may be due to loss during sampling. The presence of considerable concentrations of young stages in May and June indicated successful recruitment of C. glacialis and P. minutus. Back calculation using published stage duration estimates indicates March/April as the begin of the reproductive and growth period for these species under the first-year ice of the Barents Sea. Hence, secondary production in the study area starts at the same time as in open water regions and polynyas in the northern North Atlantic. Although the role of ice algae in the nutrition of copepods was not clarified here, the significant relationship between phytoplankton chlorophyll and egg production of C. glacialis suggests that high reproductive activity has already been achieved at moderate food concentrations.Communicated by O. Kinne, Oldendorf/Luhe     

Life under Arctic sea ice – reproduction strategies of two sympagic (ice-associated) amphipod species, Gammarus wilkitzkii and Apherusa glacialis

The reproductive strategies of two gammaridean amphipod species, Gammarus wilkitzkii and Apherusa glacialis, that permanently inhabit the Arctic sea ice were investigated. G. wilkitzkii reaches sexual maturity at an age of 2 years and produces 128 ± 54 eggs fem.⁻¹ yr⁻¹. Mating takes place during fall and winter, and the development of the large eggs (0.60 to 0.80 mm diam.) lasts 6 to 7 months. The sex ratio of G. wilkitzkii was dominated by males in a proportion of 1.5:1. In vivo studies showed that juveniles are released in batches from the brood pouches of the females during April and May. A. glacialis reaches sexual maturity at the age of 1 year and produces 555 ± 151 eggs fem.⁻¹ yr⁻¹. The eggs are between 0.18 and 0.23 mm in diameter, and are the smallest known for gammaridean amphipods. Eggs are kept in packages of two to eight in the brood pouches of females. The sex ratio of A. glacialis was dominated by females in a proportion of 3:1. The high fecundity of both amphipod species, the release of juveniles in batches over a period of time, a high proportion of females (A. glacialis), and an elongated life-span with multiple spawnings (G. wilkitzkii) are discussed as possible adaptations to the specific and highly variable conditions under Arctic sea ice. Received: 29 December 1999 / Accepted: 8 March 2000     

Growth,under laboratory conditions,of turbot,Scophthalmus maximus,from the Ría de Vigo (north-west Spain)

Egg production rates of Calanus glacialis (Jaschnov) were measured in the laboratory (in 1985) and in the field (in 1983–1984). In the laboratory, daily egg production was studied over one month at alternating feeding and fasting conditions. Spawning ceased after 3 d of starvation and started as soon as females were reintroduced to food. Egg production increased stepwise at 3-d intervals. Females survived more than nine months in captivity. In the field, egg production was measured during PREMIZEX 1983 and MIZEX 1984 at 5 and 16 stations, respectively. High egg production was found in polynyas on the East Greenland Shelf, where melt water induced stratification which supported a spring bloom. Highest egg production was converted into 6.1% body carbon female^-1 d^-1. Under thick pack-ice no eggs were spawned. Spawning was induced in females from a station with low food abundance by feeding them on board ship. These results from both experiments and field studies show that egg production in C. glacialis is closely related to food availability. Thus, C. glacialis exhibits a reproductive behavior similar to that of C. finmarchicus, but not C. hyperboreus, the other two dominant species in this region.     

Under-ice feeding and diel migration by the planktonic copepodsCalanus glacialis andPseudocalanus minutus in relation to the ice algal production cycle in southeastern Hudson Bay,Canada

The marine planktonic copepodsCalanus glacialis Jaschnov andPseudocalanus minutus (Kroyer) typically dominate the copepod biomass in spring under the ice in southeastern Hudson Bay, Canada. Females of both species exhibited significant diel feeding cycles, as measured by gut pigment content, throughout a bloom of ice algae at the ice-water interface in 1986. Periods of grazing correlated well with a nighttime vertical migration by females to within 0.2 m of the ice-water interface, suggesting that feeding took place at or just below the thermohaline boundary between seawater and the interfacial layer containing the ice algae. Seasonal melting of the ice bottom in mid-May resulted in freshening of the surface layer and release of the ice algae into the water column. FemaleC. glacialis andP. minutus responded by ceasing migration to the interface. Gut pigment content, and by reasonable assumption, feeding activity in the water column, increased substantially immediately after this event. In mid-May, the water column phytoplankton consisted of flagellates, sedimenting ice algal cells, and diatoms (Navicula pelagica andChaetoceros sp.) previously found at the interface and then growing in the water column. We conclude that algae growing at the ice-water interface, and sedimenting or actively growing algae derived from this interfacial layer, are a regular and principal source of nutrition for these pelagic copepods during and immediately after the ice algal bloom.     

Egg production of Calanus finmarchicus : effect of temperature, food and season

The use of the egg production rate of herbivorous copepods as an important parameter for understanding population dynamics and as an index of secondary production requires knowledge of the regulatory mechanisms involved and of the response to changes in food concentrations and temperature. Furthermore, the effects of season and generation on egg production have to be studied. In this context data are presented for Calanus finmarchicus from the northern North Atlantic. Prefed and prestarved females were exposed to different concentrations of the diatom Thalassiosira antarctica over 1 to 2 wk at 0 or 5 °C, and egg deposition was controlled daily. Egg production increased with higher food concentrations, but much less when prestarved. The effect of temperatures between −1.5 and 8 °C on egg production was studied in females maintained at optimum feeding conditions. Egg production rate increased exponentially over the whole temperature range by a factor of 5.2, from 14.2 to 73.4 eggs female⁻¹ d⁻¹, and carbon-specific egg production by 4, from 2.1 to 8.5% body C d⁻¹. The response to starvation was also temperature dependent. In both the temperature and feeding experiments egg production rate was regulated mainly by changes of the spawning interval, while changes of clutch size were independent of experimental conditions. Different responses to optimum feeding conditions were observed in females collected in monthly intervals on three occasions between March and May. The March females deposited more clutches than the April and May females. In May, >50% of the females did not spawn at all. Maximum egg production rates were never >25% of the rate expected at 5 °C, indicating endogenous control of egg production in addition to food and temperature effects. Received: 4 August 1996 / Accepted: 11 September 1996     

Egg production of the Arctic copepod Calanus glacialis: laboratory experiments

Egg production of single female Calanus glacialis Jaschnov fed with Thalassiosira antarctica at super-abundant concentrations (>300 g C l^-1) was determined over several weeks. Experiments were performed directly after collection from the East Greeland Current in June 1987 and 1988, and during resumed feeding after long-term starvation over 4 (October 1988), 4.5 (October 1987) and 6.5 (January 1988) mo. In addition, in June 1987, short-term starvation experiments of 5 and 15 d were conducted. Egg production was closely related to feeding in all experiments. While directly after collection eggs were produced within a few days, it took 2 wk (October 1987 and 1988) and 10 d (January 1988), respectively, to resume egg production after long-term starvation. During long-term starvation periods eggs were not laid. The decrease in total egg production with duration of starvation was due to decreasing clutch size and increasing spawning interval. In contrast, short-term starvation experiments only affected spawning interval. Interannual variability in egg production was high, with much higher clutch sizes in 1988. Average production rates in June 1988 correponded to 5% body C female^-1 d^-1, the maximum was 7.4% (1 274 eggs in 23 d). Carbon content of eggs was 0.40 g egg^-1. C. glacialis is well adapted to pulsed food events in the Arctic by its longevity; its ability to preserve its reproductive potential over several months; its rapid mobilization of ovaries; and by its high egg production rates. The implication of prolonged spawning capacity on life cycle studies is discussed.     

Egg production and lipid content of Calanus glacialis in spring: indication of a food-dependent and food-independent reproductive mode

Female Calanus glacialis were collected in early May 1989 in the pack ice region of the western Barents Sea and were fed or starved over 11 wk. Both groups laid eggs continuously during this period, however, fed females laid up to six times more eggs. During the first 10 d after collection, both groups spawned at low rates. There-after, fed females strongly increased spawning rates and maintained high egg production levels over 11 wk, while the rates of starved females decreased. During starvation they lost 70% body carbon, 50% body nitrogen and 70% lipids. The wax ester portion decreased from 86 to ca. 60% of total lipids. Three phases of gonad development and lipid metabolism were distinguished: early gonad development; gonad maturation with a rapid decrease in lipids, especially wax esters; and spawning under fed and starved conditions, where in fed females food provided most of the energy, whereas in starved females the lipid content strongly decreased.     

Optimizing the design of giant scallop (Placopecten magellanicus) spat collectors: field experiments

Field experiments were carried out in 1991 and 1992 in the Gulf of St. Lawrence (Québec, Canada) to examine the influence of various structural components of spat collectors on recruitment of the giant scallop (Placopecten magellanicus) and associated species. Components considered were monofilament diameter, heterogeneity (presence of knots), mesh size of external bags combined with monofilament density, and spatial arrangement of monofilament inside collectors. P. magellanicus spat were more abundant in collectors made with bags of intermediate mesh size (0.4x0.5 cm) containing low densities (2030 cm²) of monofilament than in other types of collectors. significant variations in spat numbers were, however, observed with other taxa such as Mytilidae, Hiatella arctica, Cerastoderma pinnulatum, Mya arenaria, Anomia simplex, Tellina sp., Veneridae, Dacrydium vitreum, Mactridae, Buccinidae, Littorina sp., Ostracoda and Foraminifera. Abundance of scallop spat did not vary significantly with spatial arrangement, diameter and heterogeneity of monofilament.Contribution to the program of GIROQ (Groupe Interuniversitaire de Recherches Océanographiques du Québec) and REPERE (Recherche sur le Pétoncle à des fins d'Élevage et de Repeuplement).     

Laboratory studies of the marine copepod Centropages typicus: egg production and development rates

Egg production and development rates of Centropages typicus (Krøyer) were studied in the laboratory under carying food and temperature conditions. Egg production rates in the laboratory ranged from 0 to 124 eggs female^-1 d^-1 and increased with food concentration up to a critical food concentration (P_c) above which egg production was constant. Egg production rates were influenced by temperature, with more eggs being produced at 15°C than at 10°C. Thalassiosira weisflogii and Prorocentrum micans were determined to be equally capable of supporting egg production at concentrations above P_c at 15°C. Rate of egg production was independent of adult female size when food and temperature were constant. Egg production rates of freshly captured females ranged from 0 to 188 eggs female^-1 d^-1 and were higher in April and May than in June or July. Hatching rates of eggs increased with increased temperature; 95% of the eggs at 15°C hatched within 48 h, while only 8% of the eggs at 10°C hatched within 48 h. Development rates, determined at 10°C in excess concentrations of T. weisflogii, were 23.0 d from egg release to copepodid state I, 27.0 d to stage II, 29.5 d to stage III, 32.2 d to stage IV, 38.5 d to stage V and 49 d to adulthood based on the average time required for 50% of the organisms in an experiment to attain a given stage. Adult males were usually observed 2 to 4 d before adult females, and therefore have a slightly faster rate of development. The effects of temperature, food type and food concentration on egg production and the seasonal appearances of diatoms in the New York Bight may account for the observed seasonal cycles in abundance of C. typicus in these coastal waters.     

The distribution of primary production relative to a cyclonic gyre in Baie des Chaleurs

Primary production within the Baie des Chaleurs, Canada, is dominated by a cyclonic gyre system. The pattern of production fits the theoretical expectation of increased productivity associated with colder, nutrient-rich water being brought closer to the surface within the gyre. Upper reaches of the bay, west of the gyre, follow a normal esturine form of circulation with lower rates of production. East of the gyre, in the Gulf of St. Lawrence, primary production is less.Travaux sur les Pêcheries du Québec, no. 30, Direction des Pêcheries, Ministère de l'Industrie et du Commerce du Québec.     

Winter studies on zooplankton in Arctic seas: the Storfjord (Svalbard) and adjacent ice-covered Barents Sea

Zooplankton was sampled in the Storfjord and ice-covered Barents Sea during March 2003. Environmental conditions represented a typical winter situation with low air temperatures, close pack ice, and extremely low chlorophyll concentrations. Polar water dominated the hydrographic regime in the upper layers. Zooplankton distribution reflected spatial variability of hydrography. The copepods Pseudocalanus spp., Oithona similis, Microsetella norvegica together with gastropod larvae were most numerous. Biomass averaged for the entire water column varied from 3.3 to 14.3 mg dry mass m⁻³, Calanus glacialis and Parasagitta elegans contributed most, followed by C. finmarchicus, Oithona similis, and Pseudocalanus spp. Various holoplankters showed reproductive activity, especially cyclopoid copepods and chaetognaths. A few C. glacialis females laid eggs in situ, but when fed diatom cultures rapidly increased their egg production. Meroplankton including larvae of nudibranchia, bivalvia, ophiuroida, polychaeta, and bryozoa were also present. Our data demonstrate that the pelagic community of the seasonally ice-covered Barents Sea was not in a “sleeping” state at the end of the winter, but in addition to dormant stages, a portion of mainly omnivorous and several carnivorous species was reproducing.     

Oil exposure in a warmer Arctic: potential impacts on key zooplankton species

Oil exploration activities are rapidly increasing in Arctic marine areas with potentially higher risks of oil spills to the environment. Water temperatures in Arctic marine areas are simultaneously increasing as a result of global warming. Potential effects of a combination of increased water temperature and exposure to the PAH pyrene were investigated on fecal pellet and, egg production and hatching success of two copepod species, Calanus finmarchicus and Calanus glacialis, sampled in Disko Bay, Greenland on 23–25 April 2008. The two species were exposed daily to nominal pyrene concentrations of 0-0.01-0.1-1-10-100 nM at water temperatures of 0.5, 5 and 8°C for 9 and 7 days, respectively. Daily measurements of faecal pellet production, egg production and hatching showed different responses of the two species to the applied stressors. When temperature increased, low concentrations of pyrene caused a decrease in faecal pellet production by C. finmarchicus, whereas C. glacialis faecal pellet production showed no negative response to pyrene exposure when temperatures increased. Pyrene exposure decreased egg production of C. finmarchicus at all temperatures, but the species was more sensitive at 0.5 and 8°C. A lag period of 1 day before egg production began was prolonged with several days when warmer water was combined with pyrene exposure. Egg production by C. glacialis was only negatively affected by pyrene in a dose-dependent manner at 0.5°C. Hatching success in both species was not affected by pyrene, where increased water temperatures led to a higher hatching success. In conclusion, C. glacialis seemed to be the less sensitive of the two species to the stress combination of increased water temperature and pyrene exposure. As a consequence of the differential responses of the two species, their competition can be impaired with a consequent impact on energy transfer between trophic levels.     

Life history of the golden ring cowry Cypraea annulus (Mollusca: gastropoda) on Okinawa Island,Japan

Two mark-recapture studies, regular population censuses, field observations, and laboratory culture were used to study the life history of the tropical marine gastropod Cypraea annulus Linnaeus, 1758 from Cape Maeda, Okinawa Island, from April 1984 to March 1986. In the field, the average rate of increase in shell length of marked juvenile snails was 1.0±0.3 mm wk^-1 (N=13), with a maximum of 1.5 mm wk^-1 (initial shell length 10.6 to 17.2 mm). In the laboratory, the maximum growth rate of juveniles was 3.0 mm wk^-1 with food ad libitum. Snails with primordial teeth on the shells grew at a rate of 0.1 to 0.5 mm wk^-1 for about 2 wk. The adults continued to grow at a similar rate for an additional 3 to 6 wk, and ceased detectable growth when some females started spawning egg masses. In the littoral zone on Okinawa Island, snails reproduced throughout the year. Egg masses brooded by three females (shell length 17.4 to 21.3 mm) in the field contained 90 000 to 133 000 ova. In the laboratory, brooding periods of three females lasted 6,8, and 9 d. The estimated average frequency of spawning was 5 egg masses female^-1 yr^-1. The mean shell length of adult females (20.3 mm) was significantly larger than that of adult males (19.6 mm). The life-history strategy of C. annulus is characterized by rapid growth, high fecundity, and repeated spawning throughout the year.     

Tidal variations in the photosynthesis of estuarine phytoplankton isolated in a tank

In 1981 two large (1 200 1) seawater samples from the St. Lawrence Estuary were kept under constant temperature and light conditions for periods of 50 and 68 h, respectively. In both tank experiments, semidiurnal variations in NH₄ were observed that could be related to cyclical NH₄ uptake by the phytoplankton. Semidiurnal cycles in photosynthetic efficiency (^B) and intracellular chlorophyll a in the tank, phased on tides at sea, were also evidenced in both experiments. These results support the hypothesis that variations in phytoplankton photosynthetic activity, which are possibly endogenous, can be phased on semidiurnal variations in vertical tidal mixing (variations of the mean light conditions in the mixed layer). In addition, observed variations in intracellular chlorophyll a suggest the possibility of endogenous cycles of phytoplankton light and shade adaptation.Contribution to the program of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

Phytoplankton photosynthetic adaptation to high frequency light fluctuations simulating those induced by sea surface waves

In order to test the ability of phytoplankton to adapt to the high frequency light fluctuations induced by sea surface waves, the green alga Dunaliella tertiolecta was grown under both steady and fluctuating (0.1, 1.0 and 10 Hz) illuminations. The latter conditions reproduced those fluctuations experienced by phytoplankton in the upper photic layer. For each culture, photosynthesis versus irradiance were measured under four incubation frequencies (steady, 0.1, 1.0 and 10 Hz fluctuating illuminations). Results indicated that growth rates were similar for algae grown under steady light and 10 Hz fluctuating light (0.26–0.33 d^–1). Cells grown at 0.1 and 1.0 Hz showed lower growth rates (0.17–0.26 d^–1). Chlorophyll a and b were significantly higher under 0.1 and 10 Hz frequencies than under steady illumination; at 1.0 Hz, there were no significant differences with steady light. No changes in carotenoids were evidenced at any frequency tested. Photosynthetic measurements showed that algae grown under steady illumination had higher photosynthetic efficiency and capacity when incubated under steady and 0.1 Hz fluctuating light. Photosynthetic characteristics of algae grown under 0.1 Hz illumination did not show any clear responses to fluctuating light. Algae grown under 1.0 or 10 Hz had higher photosynthetic efficiency and capacity than those grown under steady illumination, when incubated under 1.0 and 10 Hz light. This suggests that microalgae grown under high frequency illumination (1.0 and 10 Hz) can adapt their photosynthetic characteristics to the rapidly fluctuating light regime experienced during growth, and that algae grown under steady conditions respond better to steady or slowly fluctuating (0.1 Hz) light. Such an adaptation provides a means of probing the photosynthetic responses of phytoplankton to vertical mixing.Contribution to the program of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

A new source of dimethylsulfide (DMS) for the arctic atmosphere: ice diatoms

We report the first evidence that pennate diatoms growing within the bottom layer of first-year ice in the Arctic produce significant amounts of particulate dimethylsulfoniopropionate (DMSP_p) and dissolved DMSP+DMS. In 1992 in Resolute Passage, a tributary of Barrow Strait, DMSP_p concentrations within the bottom layer of ice reached 1055 mg S m^-3 at the end of the vernal bloom, a value one order of magnitude higher than the maximum value reported in antarctic ice. Bottom-ice concentrations in DMSP_p and DMSP_d+DMS were significantly correlated with the abundance of the dominant pennate diatom Nitzschia frigida. Intracellular concentration in DMSP of ice algae was very low (0.001 pg cell^-1) at the end of April when algae were light-limited and reached 1.17 pg cell^-1 in mid-May following an increase in light and algal growth. We calculate that the rapid release of the dissolved DMSP+DMS from the ice into surface waters following the ice break-up will generate a sea-to-air DMS flux of 0.7 mg S m^-2 d^-1, a pulse ten times higher than the mean arctic summer flux. We estimate that this 1-d pulse represents up to 5% of the annual DMS emission in the Arctic.     

Egg production and feeding by copepods prior to the spring bloom of phytoplankton in Fram Strait,Greenland Sea

Reproductively activeCalanus hyperboreus (Krøyer) andC. glacialis Jaschnov were captured in the upper 100 m of Fram Strait (77° to 79°N) in late winter 1987. There was no evidence of a phytoplankton bloom; chlorophylla concentrations were uniformly low (<0.1 mg m^–3), and nitrate concentrations were uniformly high (>11.3 mg-at m^–3). Gut-fullness measurements indicated that females were ingesting very little. The maturation state of gonads of bothC. hyperboreus andC. glacialis indicated that 75% of females were in a ripe condition consistent with observed egg laying. The lipid content of females laying eggs was reduced in both species compared to that of females not laying eggs. InC. hyperboreus the reduction was 39% and inC. glacialis it was 44%. All the evidence suggests that bothC. hyperboreus andC. glacialis were laying eggs in late winter by using lipids stored previously; they were not relying on ambient concentrations of phytoplankton. The daily rate of egg laying byC. glacialis using lipids in late winter exceeded the rate reported for summer when ambient food supplies have been shown to be necessary. It is suggested that individuals, spawned well in advance of the spring bloom of phytoplankton, may comprise a major portion of the annual recruitment to the entire population ofC. glacialis in this area, and that their life cycle can be completed within 1 yr. NeitherMetridia longa (Lubbock) norC. finmarchicus (Gunnerus) laid eggs during this study.     

Population structure of two Antarctic ice-associated copepods, Drescheriella glacialis and Paralabidocera antarctica, in winter sea ice

The spatial distribution and population structure of two dominant ice-associated copepods, Drescheriella glacialis and Paralabidocera antarctica, were studied during winter at nine locations in east Antarctic fast ice. These species accounted for at least 90% of the total metazoan abundance at each location. Abundances were high, reaching 175 individuals l^-1 (190,000 m^-2) for D. glacialis and 660 l^-1 (901,000 m^-2) for P. antarctica. These abundances were probably partly supported by the high biomass of ice-algae (Pearson correlation coefficient, r=0.75), as indicated by chlorophyll-a concentrations (1.7-10.1 µg l^-1). The population structures of each species suggested very different life-history strategies. All developmental stages of D. glacialis were isolated from the ice cores, including females with egg sacs, supporting the hypothesis that this species reproduces in the sea ice during winter. This strategy might assist D. glacialis in leading a continually colonising existence, whereby it responds opportunistically to the availability of favourable habitat patches. The populations of P. antarctica were composed primarily of nauplii (>99%), consistent with past observations of a synchronised life cycle for this species. The strong coupling of the developmental cycle of P. antarctica to the growth and decay of sea ice suggests that local extinctions might occur in areas where ice break-out is unpredictable.     

Circadian variations in photosynthetic assimilation and estimation of daily phytoplankton production

In August 1984, hourly measurements of photosynthetic characteristics were carried out during 96 h, at 5 and 10 m, on a natural population of phytoplankton in the St Lawrence Estuary. Synchronous circadian variations of similar amplitude (max./min.: 2 to 3) were observed at the two depths in both the photosynthetic capacity (P _m ^B ) and the photosynthetic efficiency (^B). Maximum values occurred at around noontime and minima during the night. Estimates of daily specific productivity were computed with and without the observed circadian variability. Large differences (15 to 70%) were evidenced between estimates.Contribution to the programs of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Maurice Lamontagne Institute (Department of Fisheries and Oceans)     

Acclimatization to intertidal conditions modifies the physiological response to prolonged air exposure inMytilus edulis

Both the tolerance of air exposure and the metabolic means by which mussles,Mytilus edulis, face air exposure can be modified by intertidal acclimatization. Short-term intertidal acclimatization enhanced the tolerance of air exposure most in early summer. Prevention of air breathing increased the mortality of wild and non-acclimatized cultured (i.e., control) mussels, but only slightly enhanced that of intertidally acclimatized mussels, suggesting their increased dependence upon anaerobic metabolism. In June, anaerobic end products accumulated in the adductor muscle of cultured but not of wild mussels. Intertidal acclimatization shifted the pattern and rates of metabolite accumulation. Control mussels accumulated succinate and alanine in the adductor muscle while intertidally acclimatized mussels accumulated strombine + alanopine, albeit at far lower levels. Pyruvate kinase (PK) from adductor muscle of intertidally acclimatized mussels was gradually activated during prolonged air exposure, while that of control and wild mussels was more inhibited. In July and August, during prolonged air exposure, the PK from the most viable mussles generally was the most inhibited. Prevention of air breathing did not markedly change the time course of PK inhibition during air exposure. Cultured mussels used in the present study were obtained from growers in Québec, and wild mussels were collected from the Baie des Chaleurs (Québec, PQ) in 1988.