The Arctic pteropod<Emphasis Type="Italic"> Clione limacina</Emphasis>: seasonal lipid dynamics and life-strategy

During various seasons from May 2001 until July/August 2003, the lipid dynamics of the pteropod Clione limacina from Kongsfjorden, Svalbard, were investigated with respect to ontogenetic development and life-cycle. Polytrochous larvae, which were dominant in spring (April, May), composed the lipid-richest specimens of the population, with total lipid of about 50% of dry mass (%DM). Major lipid classes were triacylglycerols (TAG) and 1-O-alkyldiacylglycerol ethers (DAGE), accounting on average for 53.1 and 21.9% of total lipid, respectively. Until summer, larvae grew to adults by utilising their storage lipids. In July/August, lipids were depleted to about 10%DM due to maturation and reproduction. Almost all animals in autumn (September) were mature and able to replenish their lipid deposits by accumulating DAGE (26.7%) and TAG (39.6%). This is probably the prerequisite for successful overwintering.Principal component analysis (PCA), based on the fatty acid compositions, revealed ontogenetic differences between polytrochous larvae, and small and full-grown adults. Higher proportions of 18:4(n-3) and 14:0 were found in polytrochous larvae and smaller adults during spring. Both fatty acids were highly significantly correlated with the proportions of TAG, which were used for growth and development because they are presumably easier to metabolise. PCA also divided C. limacina specimens into DAGE-rich and DAGE-poor. We suggest that DAGE are a long-term energy store and hypothesise that they are necessary during periods of food scarcity, but may also serve as an energy source for reproduction. The fatty acids 17:1(n-8), 15:0, 16:1(n-7) and 18:1(n-7) were significantly correlated with the proportion of DAGE but not with TAG. These fatty acids, which do not originate from their only prey, Limacina helicina, are synthesised de novo. Their abundance reflects an efficient lipid production by C. limacina. Based on the results of lipid biosynthesis and accumulation in combination with the population structure, we suggest that C. limacina has at least a 2-year life-cycle in Svalbard waters.Communicated by M. Kühl, Helsingør     

Ontogenetic and seasonal changes in lipid and fatty acid/alcohol compositions of the dominant Antarctic copepods Calanus propinquus,Calanoides acutus and Rhincalanus gigas

Lipid compositions of the dominant Antarctic copepods Calanoides acutus, Rhincalanus gigas and Calanus propinquus from the Weddell Sea have been investigated in great detail. Copepods were collected during summer in 1985 and late spring/early winter in 1986. The analyses revealed specific adaptations in the lipid biochemistry of these species which result in very different lipid components. The various copepodite stages of C. acutus synthesize wax esters with long-chain monounsaturated moieties and especially the alcohols consisted mainly of 20:1(n-9) and 22:1(n-11). R. gigas also generates wax esters, but with moieties of shorter chain length. The fatty alcohols consisted mainly of 14:0 and 16:0 components, while the major fatty acids were 20:5, 18:4 and 22:6, of which 18:4 probably originated from dietary input. In contrast, C. propinquus accumulates triacylglycerols, a very unusual depot lipid in polar calanoid copepods. Major fatty acids in C. propinquus were the long-chain monounsaturates 22:1(n-9) and 22:1(n-11), which may comprise up to 50% of total fatty acids. In C. acutus and C. propinquus there was a clear increase of long-chain fatty acids with increasing developmental stage. In contrast, the fatty acid and alcohol composition of the R. gigas copepodite stages were characterized by the dominance of the polyunsaturated fatty acids as well as high amounts of the monounsaturates 18:1(n-9) and 16:1(n-7). There was a considerable decrease of the dietary fatty acid 18:4(n-3) towards the older stages during summer; in late winter/early spring 18:4 was only detected in very low amounts. This tendency was also found in the other two species, but was less pronounced. In all three species dry weight and lipid content increased exponentially from younger to older stages. The highest portion of wax esters, or of triacylglycerols in C. propinquus, was found in the adults. Dry weight and lipid content were generally higher during summer. In late winter/early spring the variability was more pronounced and lipid-rich specimens showed a selective retention of long-chain monounsaturated fatty acids, whereas in lipid-poor specimens these fatty acids were very much depleted.     

The fate of dietary lipids in the Arctic ctenophore Mertensia ovum (Fabricius 1780)

Lipids of the Arctic ctenophore Mertensia ovum, collected from Kongsfjorden (Svalbard) in 2001, were analysed to investigate seasonal variability and fate of dietary lipids. Total lipids, lipid classes and fatty acid and alcohol compositions were determined in animals, which were selected according to age-group and season. Changes in lipids of age-group 0 animals were followed during growth from spring to autumn. Total lipids increased from May to September. Lipids as percentage of dry mass were lowest in August indicating their use for reproduction. Higher values occurred in September, which may be due to lipid storage for overwintering. Wax esters were the major lipid class accounting for about 50% of total lipids in age-group 0 animals from July and August. Phospholipids were the second largest lipid fraction with up to 46% in this age-group. The principal fatty acids of M. ovum from all age-groups were 22:6(n-3), 20:5(n-3) and 16:0. Wax ester fatty alcohols were dominated by 22:1(n-11) and 20:1(n-9) followed by moderate proportions of 16:0. The unique feature of M. ovum lipids was the high amount of free fatty alcohols originating probably from the dietary wax esters. In May, free alcohols exhibited the highest mean proportion with 14.6% in age-group 0 animals. We present the first data describing a detailed free fatty alcohol composition in zooplankton. This composition was very different from the alcohol composition of M. ovum wax esters because of the predominance of the long-chain monounsaturated 22:1(n-11) alcohol accounting for almost 100% of total free alcohols in some samples. The detailed lipid composition clearly reflected feeding of M. ovum on the herbivorous calanoid species, Calanus glacialis and C. finmarchicus, the abundant members of the zooplankton community in Kongsfjorden. Other copepod species or prey items seem to be less important for M. ovum.     

Reproductive dynamics of endeavour prawns, Metapenaeus endeavouri and M. ensis, in Albatross Bay, Gulf of Carpentaria, Australia

 The spawning patterns of two penaeid prawns, Metapenaeus endeavouri (Schmitt) and M. ensis (De Haan), were examined from data collected at 45 stations between March 1986 and March 1992. An index of population fecundity based on the abundance, proportion and fecundity of sexually mature females was used as a measure of spawning output of the prawn stock. The population fecundity index for M. ensis was higher than that for M. endeavouri. The monthly population fecundity index for M. endeavouri varied markedly among years, while that for M. ensis was consistent among years. Spawning of M. endeavouri occurred year-round, while that of M. ensis was concentrated mainly in spring (September to November). For M. endeavouri, a minor spawning, derived from a relatively small number of summer spawners, occurred in the 20 to 30 m offshore waters in summer. In early summer (after May), the major spawning group consisted of large females from the winter-spawning cohort, and the spawning area shifted to depths of 30 to 60 m. In winter (July), the major spawning, derived from the winter-spawning cohort, occurred at depths of 20 to 40 m. For M. ensis, the major spawning, derived from the spring-spawning cohort, was observed in depths <50 m and was concentrated particularly in inshore waters (<20 m) in spring. In autumn, the spawning output was mainly from the autumn-spawning cohort, which comprised but a small number of individuals. In winter, the major spawning group again consisted of the large females from the spring-spawning cohort, and spawning increased in the oceanic waters (>50 m). These results suggest that mature female M. endeavouri and M. ensis move offshore (>40 m) by May and July, respectively, and return to shallow waters (<35 m) in July and November, respectively. The monthly reproduction patterns of both species in the “effective spawning” area showed that the major spawning season for M. endeavouri is August to October and that for M. ensis is September to December. Received: 19 February 1999 / Accepted: 18 June 2000     

On the lipid biochemistry of polar copepods: compositional differences in the Antarctic calanoids Euchaeta antarctica and Euchirella rostromagna

During austral summer of 1985 different developmental stages (CIII, CIV, CV, females, males) of the Antarctic copepod Euchaeta antarctica and females of Euchirella rostromagna were collected in the southeastern Weddell Sea to determine their lipid contents and compositions. For E. antarctica the analyses revealed a strong ontogenetic accumulation of lipids towards the older copepodids with highest lipid contents in late CV stages and adults. The females of E. rostromagna had moderate lipid levels. The most striking difference between these two species concerns their lipid class compositions. E. antarctica deposited predominantly wax esters, whereas in E. rostromagna the major lipid class consisted of triacylglycerols, an unusual storage lipid in polar marine copepods. Principal fatty acids in E. antarctica were the monounsaturates 18:1(n-9) and 16:1(n-7), especially in the lipid-rich stages, while the polyunsaturated fatty acids 20:5(n-3) and 22:6(n-3), usually membrane lipids, dominated in the lipid-poor stages. The wax ester moieties in E. antarctica consisted almost entirely of 14:0 and 16:0 fatty alcohols. Major components in E. rostromagna were the fatty acids 18:1(n-9), 16:0, 20:5(n-3) and 22:6(n-3). The potential of fatty acids and alcohols as typical trophic markers is rendered largely insignificant in the two species due to catabolic processes.     

Size-related reproductive biology of the infaunal bivalve<Emphasis Type="Italic"> Abra alba</Emphasis> (Bivalvia) in Kinsale Harbour (south coast of Ireland)

The reproductive behaviour of 248 specimens comprising four size classes of the infaunal bivalve Abra alba (Wood) was investigated between September 1994 and November 1995 in Kinsale Harbour. Small males returned a very small proportion of sexually mature and spawning animals. By contrast, no spawning females were found in this size class, suggesting that males develop and mature at a smaller size than females. Mean gonad maturity indices indicated that, except for the smallest size class, A. alba exhibits two spawning events in 1 year, i.e. a lesser spring and a major autumn spawning event. The spring event was well synchronised between males and females, while the autumn spawning was more broadly synchronised between the sexes. Only one spawning event was recorded for very large males and females, also occurring in spring. Spawning stages were recorded for both sexes over all size classes between February and November, indicating only a short period of sexual repose, if any. Oocyte diameters did not show a discrete size range from developing to spawning stages. All stages were seen to contain varying proportions of smaller, less mature oocytes, suggesting that large A. alba females do not develop and spawn en bloc, but release their gametes periodically. Maturity indices showed only a broad similarity with off-bottom temperatures.Communicated by O. Kinne, Oldendorf/Luhe     

Lipid metabolism of the Antarctic krill Euphausia superba and its ecological implications

 Various developmental stages (early larvae to adults) of Euphausia superba have been collected in different seasons in the Weddell Sea, the Lazarev Sea and off the Antarctic Peninsula to investigate the role of lipids and fatty acids in the life cycle of the Antarctic krill. The total-lipid data for E. superba exhibited seasonal variations, with low lipid levels in late winter/early spring and the highest levels in autumn. Seasonal changes were most pronounced in the immature and adult specimens, increasing from about 10% lipid of dry mass to more than 40%. The fatty-acid compositions of the younger stages were dominated by 20:5(n-3), 22:6(n-3) and 16:0. These are typical phospholipid fatty acids, which are major biomembrane constituents. The phospholipid composition was similar in the older stages. With increasing storage of triacylglycerols in the lipid-rich immature and adult stages, the fatty acids 14:0, 16:0 and 18:1(n-9) prevailed, comprising about 70% of total triacylglycerol fatty acids. The trophic-marker fatty acids 16:1(n-7) and 18:4(n-3), indicating phytoplankton ingestion, were less abundant. They reflected, however, the dependence of the larvae on phytoplankton as well as the seasonal changes in algal composition. The generally close linear relationships between fatty acids and lipid suggest that the fatty-acid compositions of the collected specimens were largely independent of the respective developmental stage, season and region. The linear fit indicates that triacylglycerol accumulation started at a level of about 5% of total lipid. Considering the various overwintering scenarios under discussion, the life cycle and reproductive strategies of krill are discussed in the context of the lipid metabolism and fatty-acid composition of E. superba. Lipid production is effective enough to accumulate large energy reserves for the dark season, but E. superba does not exhibit the sophisticated biosynthetic pathways known from other Antarctic euphausiids and copepods. Although important, lipid utilisation appears to be just one of several strategies of E. superba to thrive under the extreme Antarctic conditions, and this pronounced versatility may explain the success of this species in the Southern Ocean. Received: 16 June 2000 / Accepted: 18 December 2000     

Variation in the lipid content of wild-caught females of the marine shrimpPenaeus kerathurus during sexual maturation

Changes in total lipids, lipid classes and their fatty acid contents were studied in the ovaries and midgut glands ofPenaeus kerathurus Forskäl females during sexual maturation. The shrimp were captured in the Gulf of Cádiz (southwest Spain) in 1990. The lipid content and fatty acids, in relative terms, increased during ovarian development. The greatest changes occurred between Maturation Stages III and IV. Ovarian lipids were dominated by polar classes, whereas in the midgut gland the major classes were triacylglycerols and sterol esters. The amounts of major fatty acids in ovaries (16:0, 16:1n-7, 18:1n-9, 18:1n-7, 20:5n-3 and 22:6n-3) increased with increasing maturity, but declined slightly between Stages III and IV. The total polar lipid content of the midgut was 5.7% (by dry weight) and its fatty acid composition remained constant during the whole study period. Total lipid content of the midgut gland showed an upward trend during sexual maturation, except between Stages II and III, when a slight decrease was observed. Predominant fatty acids in the midgut gland (16:1n-7, 20:5n-3 and 22:6n-3) displayed a noteworthy decline between Stages II and III, corresponding with the marked increase in total lipid fatty acid content in the ovaries during the same period.     

Reproduction of<Emphasis Type="Italic"> Ophiactis resiliens</Emphasis> (Echinodermata: Ophiuroidea) in New South Wales with observations on recruitment

Reproduction of the ophiuroid Ophiactis resiliens Lyman 1879, a common species in the shallow waters around Australia, was examined over 1 year in two populations near Sydney, New South Wales. Gametogenesis was documented by histological examination of the gonads. Vitellogenesis in females and spermatocyte proliferation in males started in February and March. O. resiliens had an annual spawning period from May to September/October with peak gamete release from May to July. Thereafter, spawning occurred in some specimens through November. Gravid gonads were present for approximately 2 months longer in O. resiliens from Clovelly Bay than in those from Little Bay. At both sites spawning was episodic and gametogenesis continued through most of the spawning season. Most specimens (50–100%) collected from November to March had indeterminate/recovery stage gonads, the sex of which, could not be determined. The timing of gametogenic renewal during these months varied among individuals. O. resiliens has a 3-month planktonic stage and the presence of juveniles, 0.5 –1.5 mm disk diameter, in the coralline algal turf at Little Bay from February to May, suggests that settlement occurs in summer and autumn at this site. In contrast, juveniles were rarely encountered in coralline turf at Clovelly.     

Sexual and asexual reproduction of<Emphasis Type="Italic"> Allostichaster capensis</Emphasis> (Echinodermata: Asteroidea) in Golfo Nuevo

Sexual and asexual reproduction of the fissiparous starfish Allostichaster capensis were examined for 24 months at Bahía Kaiser, Golfo Nuevo, Chubut, Argentina. Gonad indices revealed an annual reproductive cycle, with peak development occurring in late winter (August). Spawning occurred in spring (September). Pyloric caeca indices displayed a clear annual cycle and a reciprocal relationship with gonad indices, showing the storage function of pyloric caeca. The starfish population appears to be largely maintained by fission, as only two females were found. A. capensis also showed an annual cycle of fission, with the highest frequency in spring and summer (from November to January), just after spawning. Incidence of fission was correlated with environmental factors such as photoperiod, seawater temperature, and salinity.Communicated by P.W. Sammarco, Chauvin     

Biochemical changes during the reproductive cycle of the deep-sea decapod <Emphasis Type="Italic">Nephrops norvegicus</Emphasis> on the south coast of Portugal

The objectives of the present study were to characterize the changes in the proximate chemical composition, lipid classes, fatty-acid profiles, glycogen and cholesterol contents of the muscle, ovary and hepatopancreas of Nephrops norvegicus (L.), during the reproduction cycle of this species. The gonadosomatic index increased significantly in May and June and during maturation, suggesting that spawning may start in late spring or summer. The hepatosomatic index also increased throughout the ovarian maturation, suggesting that the hepatopancreatic resources are not depleted. Positive correlations between lipid levels in the ovary and the gonadosomatic index (r=0.51, P<0.05) and the hepatopsomatic index (r=0.27, P<0.05) were found. In fact, ovarian lipid levels increased with maturation, but no concomitant decrease occurred in hepatopancreatic lipids. The muscle showed very low lipid levels (mainly polar lipids), presenting a significant increase during May and June (P<0.05). Higher proportions of neutral lipids, mainly triacylglycerols, were observed in the ovary and the hepatopancreas. Since both ovarian and hepatopancreatic cholesterol increased with maturation, the mobilization of hepatopancreatic cholesterol stores to build up ovarian cholesterol was not clear. On the other hand, protein and glycogen contents in the muscle, ovary and hepatopancreas did not vary as a function of ovary maturity stage. Among the various tissues analysed, the glycogen was mainly stored in the hepatopancreas and to a lesser extent in the muscle. In both ovary and hepatopancreas the major fatty acids were 16:0, 18:1(n-7), 18:1(n-9), 20:5(n-3) and 22:6(n-3), and significant increases (P<0.05) in the levels of monounsaturated and polyunsaturated fatty acids were observed in the ovary during sexual maturation, which indicates these compounds are the major sources of energy during embryonic and early larval development. It was evident that reproduction has profound effects upon the biochemistry of this species, because there are large associated energy costs, owing to the increase in biosynthetic work, which will support the lecithotrophic strategy of the embryos and first larval stages.     

Ontogenic variations in fatty acid and alcohol composition of the pelagic amphipod <Emphasis Type="Italic">Themisto libellula</Emphasis> in Kongsfjorden (Svalbard)

The fatty acid and alcohol composition of the pelagic amphipod, Themisto libellula, was monitored during the 5 first months of its life cycle (4–20 mm length) in an Arctic fjord, Kongsfjorden, Svalbard. Fatty acids of the three major lipid classes, polar lipids (PL), triacylglycerol (TAG), and wax esters (WE), were analyzed to highlight ontogenic changes in their diet and metabolism. The PL composition of T. libellula did not show any strong variations along their growth except during the first month where an important increase of 20:5(n-3) (EPA) and 22:6(n-3) (DHA) was observed. The TAG composition revealed a clear gradient corresponding to a diet shift from omnivorous juveniles toward carnivorous sub-adults and adults. Indeed, fatty acid trophic markers of diatoms were dominant in the juveniles, whereas 20:1(n-9) and 22:1(n-11), the Calanus sp. trophic markers, overwhelmed in the older stages. The WE composition highlighted the same general trend, however, differences were found with the TAG and are discussed as a result of differences in turnover rates and assimilation pathways between the two lipid classes.     

Seasonal lipid dynamics of the copepods <Emphasis Type="Italic">Pseudocalanus minutus</Emphasis> (Calanoida) and <Emphasis Type="Italic">Oithona similis</Emphasis> (Cyclopoida) in the Arctic Kongsfjorden (Svalbard)

Seasonal lipid dynamics of various developmental stages were investigated in Pseudocalanus minutus and Oithona similis. For P. minutus, the dominance of 16:1(n−7), 16:4(n−3) and 20:5(n−3) fatty acids indicated a diatom-based nutrition in spring, whereas 22:6(n−3), 16:0, 18:2(n−6) and 18:1(n−9) pointed to a flagellate-based diet during the rest of the year as well as omnivorous/carnivorous low-level feeding during winter. The shorter-chain fatty alcohols 14:0 and 16:0 prevailed, also reflecting biosynthetic processes typical of omnivores or carnivores. Altogether, the lipid signatures characterized P. minutus as an opportunistic feeder. In contrast, O. similis had consistently high amounts of the 18:1(n−9) fatty acid in all stages and during all seasons pointing to a generally omnivorous/carnivorous/detritivorous diet. Furthermore, the fatty alcohol 20:1(n−9) reached high percentages especially in adult females and males, and feeding on Calanus faecal pellets is suggested. Fatty alcohols, as wax ester moieties, revealed significant seasonal variations in O. similis and a seasonal trend towards wax ester accumulation in autumn in P. minutus. P. minutus utilized its lipid deposits for development in the copepodite stages III and IV and for gonad maturation in CV and females during the dark season. However, CVs and females depended on the spring phytoplankton bloom for final maturation processes and reproduction. O. similis fueled gonad maturation and egg production for reproduction in June by wax esters, whereas reproduction in August/September co-occurred with the accumulation of new depot lipids. Both species revealed significantly higher wax ester levels in deeper (>50 m) as compared to surface (0–50 m) dwelling individuals related to a descent prior to overwintering.     

Spawning pattern and type of fecundity in relation to ovarian allometry in the round herring <Emphasis Type="Italic">Etrumeus teres</Emphasis>

Spawning pattern (assessed by seasonal changes in ovarian developmental stages) and type of fecundity (assessed by analysis of oocyte-size frequency distributions) of the round herring Etrumeus teres were studied in relation to ovarian growth and seasonal changes in the gonadosomatic (GSI), hepatosomatic (HSI) and liposomatic (LSI) index as well as the somatic condition of spawners (CS) in a spawning ground of southern Japan. Except for summer, mature and recently spawned ovaries occurred all year round. Oogonia and primary oocytes were present in all ovaries, and cortical alveoli stage (CA) oocytes occurred in all mature, hydrated and partially spent (PS) females (PS: females containing post-ovulatory follicles). Before hydration, a clutch of larger yolked oocytes, undergoing synchronous growth (range 0.7–1.1 mm), was present in mature ovaries which was completely separated from a more heterogeneous clutch of oogonia, primary and secondary oocytes (<0.150 mm) and oocytes in the CA stage (range 0.15–0.60 mm). As vitellogenesis progressed, the yolked clutch increased in size but the CA oocytes remained arrested. The latter entered into the secondary growth phase when hydration started in the advanced batch. Ovarian growth was isometric in all developmental stages, validating the use of GSI, which showed a consistent monthly evolution among years. Spawning stopped in summer (July and August) and peaked in winter and spring. HSI correlated positively with GSI on both a monthly mean basis (r = 0.76) and individual fish basis (liver weight explained 67–83% of the variability in ovary weight when females were grouped into 1-unit GSI intervals) suggesting a significant role of liver in vitellogenesis. LSI and CS also showed marked seasonal changes peaking from summer to middle autumn. Overall results suggest that E. teres is a multiple spawner with a group-synchronous ovarian development and indeterminate annual fecundity, with the three processes linked to an isometric growth of the ovary. We propose that such a reproductive pattern is an adaptation to produce batches of large pelagic eggs through a protracted spawning season.     

Reproductive cycle of the subarctic brooding asteroid Leptasterias polaris

The reproductive cycle of the large brooding seastar Leptasterias polaris Müller and Troschel was examined over an 18-month period in the St. Lawrence Estuary, Québec, Canada. There is a distinct annual cycle with spawning over several months in the autumn. The female has an unusual cycle in that the ovary only slightly decreases in size during spawning, and the size structure of the oocyte population is remarkably stable throughout the year. The major annual change observed in the oocyte population is the development of a small number of 600-to 800- oocytes prior to spawning and their loss during spawning. This stability, combined with the lack of evidence of phagocytosis, suggests that oocyte development takes place over many years. By contrast, the developmental cycle of the testis is similar to that of most echinoderms. The large reservoir of oocytes probably guarantees a steady annual recruitment, and brooding during the winter probably minimizes metabolic costs for the female and ensures the release of the juveniles when conditions are favourable in the spring and summer.     

Biannual spawning periods and resultant divergent patterns of growth in the estuarine goby Pseudogobius olorum: temperature-induced?

Samples of juveniles and adults of the goby Pseudogobius olorum were collected from seven sites in the shallows of the upper Swan Estuary, Western Australia, using a 3 mm-mesh seine net on one or two occasions in each month between September 1983 and April 1985. The mean gonadosomatic index of female fish rose from very low values in winter (June–August) to a sharp peak in mid-spring (October), reflecting the rapid maturation of ovaries over, this period. Ovaries with post-ovulatory follicles and ovaries that were undergoing degeneration were present, in November and December, but were then either rare or absent in those members of the corresponding cohort which survived into January and February. Female fish with advanced oocytes and mature ovaries were not found in December and January, but were present in February to April. The above trends exhibited by ovarian maturity indices, together with the appearance of larvae and small fish in both spring and autumn, demonstrate that P. olorum spawns in both spring and autumn and at best to only a limited extent in summer. Length-frequency and gonadal data show that the progeny of the spring-spawning group frequently spawn in the following autumn, when they are 5 mo old, and that those of the autumn-spawning group frequently spawn in the following spring, when they are 7 mo old. Some representatives of these two spawning groups survive through the winter and summer, respectively, to breed in a second season. Growth of the progeny of the spring-spawning group was relatively rapid between late spring and mid-autumn, whereas that of the autumn-spawning group was negligible during winter, but then inceased markedly in spring. It is proposed that the biannual spawning periods in each year by P. olorum in the Swan Estuary developed as a result of a rise in water temperature over the last few thousand years. Such a rise would have brought forward further into spring and extended later into autumn the periods when the water temperatures lie within the range (20 to 25°C) at which P. olorum typically spawns. However, mid-summer is now characterised by water temperatures >25°C, which are considered less conducive to reproductive success.     

The gametogenic cycle of<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> (Mollusca: Cephalopoda) as observed on the Atlantic coast of Andalusia (south of Spain)

The present study reports the gametogenic cycle of the common octopus, Octopus vulgaris Cuvier, 1797 in the Atlantic coast of Andalusia between May 2001 and May 2002. A total of 673 specimens of total weight ranging from 30 to 3,732 g were analysed. The gonad development was defined by means of histological methods and gonadosomatic indexes. Four gametogenic stages were identified in males (I immature, II maturing, III mature, IV spawning) and in females (I immature, II maturing, III pre-spawning, IV spawning). The sex ratio obtained was not significantly different from 1:1 (P>0.01). Mature males were found during the whole year, September being the month when the highest rate of sexually active individuals occurred (48%). In females, the gametogenic cycle commenced in December and ended in November, and spawning occurred between April and October, with two maximum peaks in August and September (48% in each). Size at sexual maturity was 850 g of total body weight for males and 1,250 g of total body weight for females. Males mature earlier than females.Communicated by S.A. Poulet, Roscoff     

Population structure and accumulation of lipids in the ctenophore Mertensia ovum

We studied the abundance, length-frequency distribution and body composition (lipid accumulation) of the ctenophore Mertensia ovum in Kongsfjorden, Svalbard (79°N) between May 2001 and April 2002. The highest abundances were found during summer in the outer and middle areas of the fjord, possibly caused by the concentration of advected zooplankton. Polymodal length-frequencies indicated a life span of 2 years, with 0, 1 and 2-groups being present in summer. Total lipid for a standardized animal decreased from May to August, and increased to the highest level in September. Relative lipid content was always highest in the 0-group, probably reflecting reduction of lipid levels due to increased energy costs during reproduction for the older age groups. Lipids probably are used to fuel prolonged reproduction from May to August until spawning ends by September. The overwintering age groups (0 and 1) subsequently build up lipid reserves for the next years’ spawning.     

Long-term changes in populations of subtidal bivalves (Abra alba and A. prismatica) from the Bay of Morlaix (Western English Channel)

Two populations of Abra alba (Wood) and one of A. prismatica (Montagu) (Mollusca: Bivalvia) were studied over a 10 yr period (1977–1987) in two muddy fine-sand subtidal communities of the Bay of Morlaix, France. The survey provided an example of long-term changes in the three Abra spp. populations, which displayed synchronized changes, with a regular annual cycle and increasing densities during 1979–1980 related to the higher concentration of organic matter resulting from the Amoco Cadiz oil spill in March 1978. A. alba rapidly adapts its demographic strategy to eutrophic conditions by increasing its reproductive potential, growth, and abundance. During times of eutrophication, A. alba has three spawning periods and three recruitments per year as opposed to two spawning periods and two recruitments per year during oligotrophic conditions. Growth of the juveniles of this species is insignificant until spring for individuals recruited in the autumn, whereas individuals which settle during spring or summer display immediate rapid growth. A. prismatica has a low capacity to adapt to eutrophic conditions. It has one annual period of sexual maturation at the end of the summer, with spawning in September–October and settlement beginning in mid-November. Growth of the juveniles after settlement is also insignificant until April. These results enable comparison of the demographic strategies of these two sympatric species.