A study of the variations in lipid levels,lipid class composition and fatty acid composition in the first stages ofArtemia sp.

The lipid class composition and the fatty acid composition of total lipids of the cysts, newly hatched nauplii and 24-h-old metanauplii of a Spanish parthenogenetic diploid strain ofArtemia sp. were studied. Substantial differences in the total lipid level occurred among these stages, with a marked increase from the cyst to the nauplii being followed by a decrease in the metanaupliar stages. This variation affected the absolute levels (mg/g dry wt) of the total lipid classes and individual fatty acids, although the percent composition of the fatty acids in total lipid was essentially unchanged. An exception occurred during hatching in that the percentages of 16:0 and 16:1n-7 in total lipid decreased whereas that of 20: 5n-3 increased. The lipid classes showed higher variation than the fatty acids both in absolute and in relative terms, and in particular, the ratio of phosphatidylcholine:phosphatidylethanolamine decreased progressively from cysts to nauplii and metanauplii. The implications of these findings for the use ofArtemia sp. as a larval feed in aquaculture are considered.     

Changes in lipid content,lipid class composition and fatty acid composition of developing eggs and unfed larvae of cod (Gadus morhua)

Changes in the lipid class and fatty acid composition of developing eggs and unfed larvae of cod (Gadus morhua L.) were studied with the objective of determining probable requirements of cod larvae for dietary lipid. The eggs were collected on 24 March 1985 from holding tanks containing cod which had been caught off the northwest coast of Scotland. Phosphatidylcholine (PC) was the only lipid class to decline in absolute terms during embryogenesis. Catabolism of neutral lipid was initiated during the first week after hatching, and the rate of neutral lipid utilisation increased after the larvae had completely absorbed their yolk sacs. The quantity of triacylglycerol (TAG) remained constant during embryogenesis, but the percentage of 22:6(n-3) int TAG increased substantially during this period. It was calculated that ca. 33% of the 22:6(m-3) released during the process of PC catabolism was incorporated into TAG and sterol ester. The results suggest that PC, replete in appropriate essential fatty acids, should represent a major proportion of the lipid in artificial diets for fish and crustacean larvae.     

Seasonal changes in feeding, gonad development and lipid stores in Calanusfinmarchicus and C. hyperboreus from Malangen, northern Norway

 Seasonal dynamics of feeding activity, oil sac volume, gonad development, sex ratio and spawning periods in the two sibling species Calanusfinmarchicus and C. hyperboreus, the key zooplankton copepod organisms throughout the northern Atlantic waters, were studied simultaneously in Malangen, northern Norway, during 1992. We were also tracing differences in surface- and deep-dwelling components of these populations in terms of oil sac volume and gonad development during the time period when the G₁ is preparing for a subsequent generation (G₂) or hibernation. The main difference in the life cycle strategies of these species is the earlier maturation and spawning of C. hyperboreus. No feeding activity in either of the two species was found in February, but both commenced feeding in March, prior to the spring phytoplankton peak. The larger copepod, C. hyperboreus, had a more intensive energy deposition than C. finmarchicus. The period of active feeding was much shorter for the former species, only from March through July in copepodite stages CIV and CV, and even less in females – March and April. Basically, a similar pattern of seasonal changes in gonad length and lipids was observed in the two species. In June, oil sacs in the surface- and deep-dwelling specimens were about equal, during the rest of the year, lipids in the deep CVs exceeded those in the surface. We propose that as copepods accumulated sufficient lipid reserves, they started to descend, while others, containing less fat, stayed in the upper layers feeding. The mean length of the gonads in the surface-dwelling copepods was consistently less than in their deep counterparts from October to February, so that gonad development at the expense of accumulated reserves during resting stage was confirmed. C. finmarchicus males were found in considerable numbers only in February and March, and were only occasionally found in the upper layers (0–100 m), while adult male C. hyperboreus were present from October to March, but were never found in the surface layers. The differences in life cycle timing among the two species are discussed in relation to tradeoffs with regard to foraging strategies, generation numbers, bioenergetics and predator avoidance. Received: 31 March 1999 / Accepted: 23 November 1999     

Fatty acid compositions of neutral glycerides from the ovaries of the asteroids Ctenodiscus crispatus,Asterias lincki and Pteraster militaris from Balsfjorden,northern Norway

Fatty acid analyses of lipids in the asteroids Ctenodiscus crispatus (Retzius), Asterias lincki (Müller and Troschel) and Pteraster militaris (O. F. Müller) collected in Balsfjorden, near Tromsø, northern Norway in 1978–1980, were performed to further our understanding of the asteroids' reproductive biology. Fatty acid compositions were determined in phospholipids, triacylglycerols and alkyldiacylglycerols isolated from ovaries of frozen C. crispatus. The major polyunsaturates in phospholipids were 20:4(n-6) followed by 20:5(n-3). Both the triacylglycerols and alkyldiacylglycerols were relatively deficient in polyunsaturates but had 20:1(n-13) and 18:1(n-7) as major components. Both these liqid classes had additionally 15% of their fatty acids as a variety of odd-numbered and branched-chain fatty acids. The fatty acid composition of neutral glycerides, largely alkyldiacylglycerols, from heat-dried ovaries of C. crispatus was not materially different from that of alkyldiacylglycerols isolated from the ovaries of frozen individuals. The fatty acid composition of neutral glycerides, largely alkyldiacylglycerols, from heat-dried ovaries of P. militaris was similar to that for C. crispatus in that 20:1(n-13) and 18:1(n-7) were major components, and odd-numbered together with branched-chain fatty acids accounted for about 15% of the total fatty acids. The fatty acid composition of neutral glycerides, consisting of equal amounts of triacylglycerols and alkyldiacylglycerols, from heat-dried ovaries of A. lincki differed from those of the previous two species in that 20:1(n-9) and 18:1(n-9) were major components and odd-numbered together with branched-chain fatty acids accounted for less than 5% of the total fatty acids. The results are discussed mainly in terms of lipid biosynthetic mechanisms within the asteroids and the interplay between internal biosynthetic activities and dietary fatty acids, particularly those from bacterial sources, is considered.     

Changes in the digestive gland of Euphausia superba during short-term starvation: lipid class,fatty acid and sterol content and composition

During a period of short-term (19 d) starvation, total lipid in the digestive gland of Euphausia superba Dana decreased from 21 to 9% dry weight. Total lipid per digestive gland decreased significantly during starvation compared to Day 0 individuals, falling from 1960 (±172) to 385 (±81) g. Polar lipid was the major lipid class utilised during starvation, falling from 1510 (±225) to 177 (±46) g per digestive gland (76 to 45%). Absolute levels of triacylglycerol fell from 300 (±41) to 76 (±5) g; however, relative levels remained unchanged. The relative level of free fatty acid increased significantly with starvation (4 to 39%) with absolute levels ranging from 79 (±1) to 156 (±20) g per digestive gland. Absolute levels of all fatty acids per digestive gland declined continually until the end of the starvation period. The long-chain polyunsaturated acids eicosapentaenoic (20:53) and docosahexaenoic (22:63), decreased with starvation from 37 to 26% and 15 to 10%, respectively whereas the saturated fatty acid, palmitic acid (16:0), increased from 15 to 20%. Cholesterol, the major sterol in this organ, increased from 17 (±20) to 44 (±13) g per digestive gland by Day 3, and by Day 19 had returned to levels found in the digestive gland of Day 0 individuals. Desmosterol followed a similar pattern to cholesterol, increasing from 3 (±1) g per digestive gland on Day 0 to 11 (±4) g on Day 3, and falling to 2 (±1) g on Day 19. Other sterols in the digestive gland, predominantly of algal origin, fell from the levels found in Day 0 individuals to near zero amounts by Day 6. The digestive gland of E. superba plays a dynamic role during shortterm starvation in terms of lipid content and composition. The relative levels of polar lipids, free fatty acids and cholesterol in the digestive gland may provide reliable indices of the nutritional condition of E. superba in the field. Sterols in the digestive gland are indicative of recent dietary composition of krill, and may also be used to quantify dietary input from individual phytoplanktonic species.     

Spatial variability in lipid composition of calanoid copepods from Fram Strait,the Arctic

The calanoid copepods Calanus hyperboreus and C. finmarchicus were investigated in view of their lipid and wax ester content and their fatty acid and alcohol composition. Analyses were performed in females and copepodid stages V and IV from the Fram Strait region between Greenland and Spitsbergen in 1984. This region offers different food conditions like diatom blooms in the North East Water Polynya, food shortage in areas with very close ice cover, high phytoplankton biomass in the marginal ice zone and lower biomass in the open Atlantic water. Lipids contained generally more than 70% wax esters. Highest levels were found in C. hyperboreus with more than 90%. This percentage was not very variable, in spite of large differences in dry weight and lipid content. Copepods with particularly high weight and lipid content were found in the North East Water Polynya. The lightest individuals were found under the pack ice. Lipid proportions per unit dry weight were higher in C. hyperboreus than in C. finmarchicus, whose lowest values were found in the open Atlantic water. Spatial variability in fatty acid composition was much higher than in alcohol composition. The principle alcohols, 20:1 and 22:1, generally accounting for more than 80% of total alcohols. In the North East Water Polynya, the predominant monounsaturated fatty acid was 16:1, while under the ice 20:1 and 22:1 dominated. In the marginal ice zone and in the open water, the 18:4 acid reached percentages up to 30% of total fatty acids. These changes were related to the different food conditions. C. hyperboreus appears to be best adapted to the cold water and unfavourable conditions of polar regions because of its high lipid and wax ester store with long-chain wax esters of high calorific value.     

Seasonal study of planktonic copepods and their benthic resting eggs in northern California coastal waters

Few investigations have examined the occurrence of zooplankton resting eggs in the sea bed of waters deeper than 20 m. In this study the distribution and abundance of planktonic copepods and their benthic resting eggs in coastal waters off northern California, U.S.A., were determined and related to environmental parameters (temperature, salinity, depth, and sediment grain size). Sediment cores, net tows, and CTD profiles were obtained in April and October 1989, and February, April, and October 1990. Water depths in the study area ranged from approximately 60 to 120 m. The mean abundance of eggs was as high as 1.2×10⁵ m^-2 for Acartia clausi Giesbrecht and 1.9×10⁵ m^-2 for Tortanus discaudatus Thompson and Scott. These egg concentrations are comparable to those reported previously for shallower more protected regions. The abundance of eggs in the sediments decreased with increasing depth of the water column. For the region as a whole, eggs were least abundant in muddy sediments. The mean abundance of eggs in the sea bed also varied seasonally and annully. Benthic resting eggs of A. clausi were more abundant in April 1989 than in April 1990, and adults of the species were never found in the plankton samples. The lack of adults is not unusual since results of previous studies indicate that A. clausi is a cold-water species, and in this region water temperatures are colder in summer, than in winter, due to upwelling. Temperature and salinity data indicated that the upwelling season had commenced by the time of the April 1990, but not the April 1989 sampling. Thus, the reduced abundance of benthic eggs in April 1990 may have been due to egg-hatching in response to reduced temperatures. The results suggest that the presence of A. clausi in coastal waters off northern California is linked to recruitment from benthic resting eggs.     

Seasonal and long-term variations in the body size of planktonic copepods in the northern Baltic Sea

Seasonal and long-term variations in the body size of planktonic copepods were studied in the northern Baltic Sea. The influence of temperature, salinity and phytoplankton concentration to the body size of Eurytemora affinis, Acartia bifilosa and Limnocalanus macrurus (Calanoida) was examined at three sea areas, differing in their hydrographical and trophic conditions (an archipelago area and an enclosed bay on the SW coast of Finland in 1992 and at an open sea station in the Gulf of Bothnia in 1991). There was an inverse relationship between copepod body length and temperature, while there was a direct effect of phytoplankton concentration. According to multiple regression analysis, the relative importance of these factors varied according to species, developmental stage and study area. In the archipelago area, copepod body size was mainly determined by temperature, while in the open Gulf of Bothnia, phytoplankton concentration was usually more important. Interannual variation in the summer body length of E. affinis and A. bifilosa was examined using samples collected over 18 years (1967 to 1984) in the archipelago area. In this analysis, the inverse relationship between water temperature and copepod body size disappeared; in E. affinis the average female length correlated positively with summer temperature. We suggest that the length and timing of the study period greatly influence the investigator's view of the factors regulating copepod body size.     

Ecological investigations on the zooplankton community of Balsfjorden,northern Norway: Lipids in the euphausiids Thysanoessa raschi and T. inermis during spring

Dry body weights, lipid levels and lipid compositions were measured in I-and II-group Thysanoessa raschi (M. Sars) and T. inermis (Krøyer) collected in April-May, 1980 in Balsfjorden, north Norway. Dry body weights were mininal in late April but had doubled by mid-May for I-group T. raschi and for I- and II-group T. inermis. II-group T. raschi had increased its dry weight by less than 50% by mid-May. Lipid accounted for approximately 10% of the dry body weight throughout the period, with free fatty acids and phospholipids being the dominant classes. An exception occurred for II-group T. inermis in mid-May, when wax esters were present in substantial amounts. Wax esters were present only in small amounts at other times and triacylglycerols were negligible. The free fatty acids in I-group T. raschi and I-group T. inermis in late April were deficient in polyunsaturates; by mid-May the free fatty acids were rich in polyunsaturates. II-group T. raschi and II-group T. inermis had free fatty acids rich in polyunsaturates throughout the period of study. The wax esters present in II-group T. inermis in mid-May consisted mainly of 16:0 and 14:0 alcohols esterified to 18:1 fatty acid. The traces of wax esters present in T. raschi did not contain significant amounts of phytol. Results are discossed with respect to the metabolic activities of the two euphausiids and their trophic positions in terms of different dietary inputs.     

Seasonal variations in hepatopancreas fatty acid profiles of two colour forms of shore crabs, Carcinus maenas

 The relationship between intermoult duration (coloration), sex, size and seasonal variations in fatty acid (FA) profiles was studied in a population of shore crabs, Carcinus maenas, inhabiting the Isefjord, Denmark. For male shore crabs, the total hepatopancreas FA content was high in July and December (12.7 to 16.0 mg g⁻¹ dry weight, dw) but lower in May and September (7.3 to 10.0 mg g⁻¹). This indicates that male shore crabs are in relatively good condition before winter, when the crabs migrate off shore, but in relatively poor condition when they return to shallow waters during spring. The hepatopancreas FA content also decreased over the mating season. After the mating season the hepatopancreas FA content of males had decreased to approximately 60% of that prior to the mating season. Female shore crabs had significantly higher hepatopancreas FA levels than males in May (11.7 mg g⁻¹ dw), September (12.6 mg g⁻¹ dw) and December (17.9 mg g⁻¹ dw) but lower levels in July (9.5 mg g⁻¹ dw). This indicates that the spawning season is the most energy-demanding part of the female reproductive cycle. For all seasons, the hepatopancreas FA content of green shore crabs was significantly higher than that of red shore crabs. For both colour forms, the amount of polyunsaturated fatty acids (PUFAs) was significantly higher than that of saturated fatty acids (SAFAs) and monounsaturated fatty acids (MUFAs), with the relative proportion of PUFAs increasing when the total hepatopancreas FA content decreased. For both genders and colour forms, the most dominating SAFA was palmitic acid (16:0). Palmitoleic acid (16:1ω7), vaccenic acid (18:1ω7) and oleic acid (18:1ω9) were the three MUFAs found in highest concentrations. The most dominating PUFA was eicosapentaenoic acid (EPA, 20:5ω3). Docosahexaenoic acid (DHA, 22:6ω3) and arachidonic acid (AA, 20:4ω6) were also abundant in all samples. The results demonstrated that season, sex, size and intermoult duration all influence the amount of FAs present in the hepatopancreas of shore crabs. Received: 23 September 1999 / Accepted: 29 April 2000     

Short-term temporal variation in population structure of two harpacticoid copepods,Zausodes arenicolus and Paradactylopodia brevicornis

Aspects of the population biology of two harpacticoid copepod species [Zausodes arenicolus Wilson and Paradactylopodia brevicornis (Claus)] living in Tampa Bay, Florida, USA, were studied on time scales of hours to days during November 1983. Fluctuations in population agestructure, adult sex-ratio, and proportion of ovigerous females were determined for these two species in a control plot and in an experimental plot defaunated by raking. For both species, immigrants into the defaunated plot differed significantly from conspecifics in the control plot in all characteristics examined. The disturbed plot contained a larger proportion of young juveniles of both species compared to the unmanipulated site after 4 h but not after 8 h. In Z. arenicolus, adult males returned to the experimental plot more quickly than adult females. For both species, rapid and significant changes in population age-structure, adult sex-ratio, and the proportion of adult females with eggs occurred within the control plot. It is suggested that this variation was too large and occurred too rapidly to be accounted for solely by in situ processes in the absence of large-scale immigration and/or emigration of individuals. Potential implications of these results for population studies of harpacticoid copepods and other benthic invertebrates are discussed.     

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.     

Influence of cadmium accumulation and dietary status on fatty acid composition in two colour forms of shore crabs, Carcinus maenas

 The effects of cadmium exposure and dietary status on cadmium accumulation, fatty acid (FA) content and profiles were investigated in two colour forms of the shore crab Carcinus maenas. Groups of shore crabs were either starved or fed with blue mussels, Mytilus edulis, during a 40 d exposure period to 2 or 6 μM Cd²⁺ (as CdCl₂). Starved green individuals accumulated more cadmium in haemolymph and hepatopancreas than did red crabs and green crabs fed during the experiments. In the red colour form, no difference in cadmium accumulation was observed between starved and fed individuals. In both colour forms, hepatopancreas contained more FA than gills and muscle. The FAs often present in the largest amounts in the tissues were 16:0, 16:1ω7, 18:1ω7, 18:1ω9, 20:4ω6, 20:5ω3 and 22:6ω3. However, saturated (SAFA) and mono-unsaturated fatty acids (MUFAs) were dominant in hepatopancreas, whereas poly-unsaturated fatty acids (PUFAs) were dominant in gills and muscles. At the beginning of the experiment, the total FA content in the hepatopancreas was 111.6 mg g⁻¹ (dry weight) for red crabs and 78.4 mg g⁻¹ for green shore crabs. During the experiment, however, the FA content decreased in red crabs. This decrease was more pronounced for starved individuals than for fed individuals. Also, the decrease in FA content was more pronounced in crabs exposed to 6 μM cadmium compared to crabs exposed to 2 μM or crabs not exposed to cadmium. No change in FA content was observed in green shore crabs, irrespective of diet and cadmium exposure. For both colour forms, no change in FA content was observed for gills and muscle. In red crabs, a decrease was observed for all FAs in the hepatopancreas. This decrease, however, was more pronounced for SAFAs and MUFAs than for PUFAs, indicating that the metabolism of FAs during starvation and cadmium exposure is selective. The experiments indicate that green colour forms of shore crabs are more tolerant of natural stress such as starvation and anthropogenic stress, e.g. cadmium exposure, than are red colour forms of shore crabs. Received: 23 September 1999 / Accepted: 29 April 2000     

Reproduction of asteroids from Balsfjorden,Northern Norway: Analyses of lipids in the gonads of Ctenodiscus crispatus,Asterias lincki and Pteraster militaris

Seasonal lipid analyses were performed on the gonads and residual bodies of Ctenodiscus crispatus (Retzius) and Asterias lincki (Müller & Troschel), collected from Balsfjorden, northern Norway during March 1978–February 1980. The ovaries of both species had high percentages of total lipid (in the region of 60% of the dry weight) that were relatively constant throughout the season. Testes from both species had in the region of 20% of their dry weight as lipid, again with little seasonal variation. The majority of the total lipid in the ovaries of C. crispatus was accounted for by alkyldiacylglycerols and there was little seasonal variation in lipid class composition. Phospholipid accounted for the bulk of the lipid in the testes of C. crispatus, where alkyldiacylglycerols were present but in minor amounts. A slight degree of seasonal variation occurred in the composition of testis lipid in that maximal percentages of triacylglycerols and alkyldiacylglycerols occurred in January–April. The ovaries of A. lincki contained both triacylglycerols and alkyldiacylglycerols as major neutral lipids. Significant seasonal variation occurred in lipid class composition in the ovaries in that neutral lipids showed transient minima in February–April. The testes of A. lincki had substantial amounts of both triacylglycerols and alkyldiacylglycerols: maximal percentages of these lipids occurred in January–March. Analyses of gonads of near-mature Pteraster militaris (O. F. Müller) revealed that the ovaries were rich in lipid that was predominantly alkyldiacylglycerols, whereas the testes had much lower levels of lipid accounted for mainly by phospholipids. The residual bodies of all three asteroids had significant but small amounts of alkyldiacylglycerols in their lipids. A. lincki had triacylglycerols as a major lipid class in its body lipids, whereas in C. crispatus the major body lipid was phospholipid. Little seasonal variation was seen in the composition of the residual body lipid of either C. crispatus or A. lincki. The results are consistent with an aseasonal reproductive pattern in C. crispatus, although a main breeding activity occurred in mid-winter. A. lincki is a more seasonal breeder, but also had maximal activity in winter. Irrespective of their breeding habits, all three asteroids produced eggs rich in alkyldiacylglycerols. A major role for this lipid in the development of the large lecithotrophic eggs of asteroids is indicated.     

Role of temperature on lipid/fatty acid composition in Pacific cod (Gadus macrocephalus) eggs and unfed larvae

During early development, oviparous fish species must use finite lipid and fatty acid (FA) reserves for both catabolism and structural components. In cold environments, developing fish have the additional constraint of maintaining membrane fluidity for metabolic efficiency (homeoviscous adaptation), resulting in further demand on lower melting point FAs like n-3 polyunsaturated fatty acids (PUFAs). To examine whether marine fish embryos physiologically adapt to changing temperature environments, we incubated Pacific cod (Gadus macrocephalus) eggs at 5 temperatures (0, 2, 4, 6, and 8 °C) in the laboratory and sampled them repeatedly during development to measure changes in lipid/FA composition. Pacific cod embryos increased n-3 PUFA content during the egg stage in all temperature treatments, with the possible exception of 0 °C, where poor survival and hatch success limited our ability for continued sampling. At the beginning of the hatch cycle, free-swimming embryos shifted from lipogenesis to lipid catabolism. The rates of lipogenesis and catabolism were temperature dependent, and the distinct increase in unsaturated fatty acids at temperatures <8 °C was consistent with homeoviscous adaptation theory. However, with the possible exception of embryos at 0 °C, the relative amounts of essential fatty acids (e.g., EPA, DHA, AA) were conserved in a similar manner across incubation temperatures. Collectively, these data suggest Pacific cod are capable of homeoviscous adaptation but cannot tolerate temperatures approaching 0 °C despite their possible ability to biosynthesize PUFAs from other energetic sources.     

Seasonal variation in the white muscle biochemical composition of deep-sea macrourids in the North-east Atlantic

The peculiar limpet-like morphology of the genus Colobocentrotus is unique among the regular echinoids. This shape has been interpreted as an adaptation to life in areas of extreme wave exposure. In this study the attachment strength of C. atratus is compared with that of three sympatric species, Echinometra mathaei, Heterocentrotus trigonarius and Stomopneustes variolaris, which have more typical echinoid morphology and live in different microhabitats. For each species, the adhesion of individual sea urchins was measured as well as the tenacity of single tube foot and the mechanical properties of the tube foot stems. Colobocentrotus always presented the highest measured values, although not always significantly different from those of the other species. Of the mechanical properties of the stem measured, the stem extensibility was the only property that was significantly different among species. In general the stems of all the species studied became more extensible and more difficult to break with increasing strain rate, providing an adaptative advantage to the sea urchin when subjected to rapid loads such as waves. In terms of single tube foot tenacity, C. atratus tube feet attached with a tenacity (0.54 MPa) two times higher than the one of E. mathaei, H. trigonarius and S. variolaris (0.21–0.25 MPa). Individual sea urchins of the four species, however, attached with a similar strength (0.2–0.26 MPa). The calculation of safety factors showed that it is the very high number of adoral tube feet of C. atratus and not the overall shape of the animal that allows this species to withstand very high water velocities. However, C. atratus streamlined morphology may be a functional adaptation to reduce the impact of other hydrodynamic forces (such as wave impingement forces) or to cope with other selective environmental stresses (such as dessication), and thus to inhabit extremely exposed areas of the intertidal.     

Changes in the content and fatty acid composition of lipid in an isolated population of the capelin Mallotus villosus during sexual maturation and spawning

Changes in the wet weights and lipid contents of muscle, liver and gonad were determined in male and female Mallotus villosus in Balsfjorden, northern Norway, in 1981, from January, when gonadal development becomes noticeable, until May when the fish are spawning. Fatty acid compositions of tissue lipids were also determined. Over 4 mo prior to spawning, the weight of muscle in female capelin decreased by 32% while the weight of the ovary increased exponentially by 830%. In males the weight of the muscle remained constant and that of the testis decreased slightly. The lipid contents of the muscle of both males and females decreased by 76% over the period and an inverse relationship existed between the water and lipid contents of muscle in both sexes. Male liver weight remained constant over the period of study whereas female liver weight increased transiently by 300% between January and March. 38% of the lipid lost from female muscle was accounted for by lipid deposited in ovary whereas negligible amounts of the lipid lost from male muscle was accounted for by lipid in the testis. Gonadal lipid was always richer in polyunsaturated fatty acids than muscle lipid and, immediately prior to spawning, 42% of the fatty acids in ovarian lipid were polyunsaturated. Muscle lipid of males and females showed a progressive increase in the percentage of the long-chain monoenes 20:1 and 22:1 between January and May. It is concluded that male capelin catabolise more of their muscle lipid reserves than females in the 4 mo prior to spawning and that most of the lipid catabolism in males is associated with physical activity. Conversely, females deposit much more of their muscle lipid in gonads than males, although considerable selectivity occurs in the mobilisation of fatty acids from muscle lipid into ovarian lipid. Additionally, biosynthesis of gonadal constituents accounts for a considerable proportion of the lipid catabolised in females.     

Characteristic features of body composition and metabolism in some interzonal copepods

Protein, lipid, phosphorus, and organic carbon contents, as well as electron transport system (ETS) activity, lactatedehydrogenase activity, and gut evacuation rate, were measured in four interzonal species of Pacific copepods:Calanus australis, C. pacificus, Eucalanus inermis, andE. elongatus f.hyalinus, collected at the upwelling areas off Peru (8°S) and California (27°N), and in the middle of the North Pacific (30°N), from February to April 1987. The two Eucalanidae species —E. inermis andE. elongatus — have distinctive biochemical and elemental body composition and rates of main physiological processes. Relative protein, lipid, phosphorus, and organic carbon contents (µg mg^–1 wet weight) in these species were, respectively, ca. 1/7 to 1/10, 1/5 to 1/20, 1/5 to 1/10, and 1/5 those inCalanus spp. Likewise, oxygen uptake rate per unit of wet weight (based on ETS activity) inE. inermis andE. elongatus was 5 to 10% of that in calanids; a similar difference was found in phosphorus excretion rate. In addition, gut evacuation rates inE. inermis andE. elongatus were ca. one-fifth of those inCalanus spp. Based on these data, we considered the eucalanids as belonging to a distinctive physiological group, figuratively named jelly-body copepods. In contrast with calanids, active lactatedehydrogenase has been found in the bodies ofE. inermis andE. elongatus, apparently allowing them to survive for a long time in layers of extremely low oxygen content (<0.2 ml l^–1). The adaptive value of physiological features in these eucalanids and typical calanids is compared.     

Annual population development and production by small copepods in Disko Bay,western Greenland

The population of small copepod species (approximately <1 mm) were investigated during an annual cycle in Disko Bay, western Greenland. The small species considered were Acartia longiremis, Pseudocalanus spp., Oithona spp., Oncaea spp., Microsetella spp., and Microcalanus spp. Most of the small species were present in the surface waters year round and numerically dominated the community, and in biomass from late summer and throughout winter. Oithona spp. was numerically the main contributor, while Pseudocalanus spp. dominated in terms of biomass. In the uppermost 50 m, maximum abundance, biomass and secondary production were observed in late September after the phytoplankton production practically had terminated and the winter initiated. The free spawning Acartia longiremis showed a strong seasonal fluctuation in biomass and egg production, in contrast to the egg carrying species Pseudocalanus spp. and Oithona spp. These had a long spawning season and maintained a more stable biomass year round. Secondary production was estimated by three different ways: (1) based on the obtained specific egg production rates, (2) a temperature dependent equation, and (3) a multilinear regression taking temperature, body weight and chlorophyll into consideration. The contribution of the small species was insignificant when compared to the large Calanus species during the spring- and post-bloom. However, during late summer and winter, where Calanus had left the upper water strata for hibernation, the small species played a crucial role in the pelagic carbon cycling.     

Seasonal variation and diversity of rotifers in Ehoma lake, Nigeria

The zooplankton and physicochemistry of Ehoma lake were studied from March 2005 to August 2006 in order to evaluate seasonal trend in species composition and abundance in relation to water quality. Forty two (42) species of rotifers dominated by Keratella tropica tropica were encountered. Species richness declined by nearly 50% from dry season values during the rainy season. Species richness was higher in the littoral zone during the dry season, the reverse was the case during the rainy season. Species abundance followed similar trend as species richness. Abundance was closely associated with dissolved oxygen, biological oxygen demand and width of the lake and these in turn varied significantly between seasons. Shannon-Weaver diversity varied from 2.2 to 3.8 bit ind(-1) and significantly between seasons (p<0.05). Anuraeopsis navicula navicula and Euchlanis dilatata dilatata Ehrenbreg were the only species gained during the flood periods.