The effect of the receding ice edge on the condition of copepods in the northwestern Weddell Sea: results from biochemical assays

We compared six biochemical measures of nutritional condition: citrate synthase activity (CS), malate and lactate dehydrogenase activity (MDH and LDH), RNA:DNA ratio, and percent body protein and lipid. Adult females of five species of calanoid copepod (Calanoides acutus, Calanus propinquus, Metridia gerlachei, Rhincalanus gigas and Paraeuchaeta antarctica) were collected in the marginal ice zone of the northwestern Weddell Sea at the time of the annual phytoplankton bloom that occurs in association with the receding ice edge during austral spring. Three zones within the marginal ice zone were sampled: heavy-ice-cover pre-bloom, ice-edge bloom and low-ice-cover post-bloom. Lipid generally increased greatly from ice-covered to open water zones, and its importance in the life of polar copepods cannot be overstated. Increases in protein from ice-covered to open water were also observed, but were of less significance. Each species exhibited significant changes in at least one enzyme activity level. Citrate synthase activity in C. acutus, C. propinquus and R. gigas, all herbivores, increased between pre- and post-bloom stations. C. propinquus and M. gerlachei, which feed during winter, had large increases in LDH activity between pre- and post-bloom stations. Rhincalanus gigas and P. antarctica, the two largest species studied, showed variations in MDH activity, with peak enzyme activity occurring in post-bloom stations. RNA:DNA ratio did not change in any species. The effects of size, shipboard handling and freezer storage were easily corrected statistically, and did not alter any conclusions. The patterns observed in copepod nutrition at the Antarctic ice edge were consistent with existing models of life history for each species. The observations reported here, in conjunction with previously reported data, suggested that measurement of metabolic enzyme activity, especially in concert with lipid, enables estimation of nutritional condition in adult copepods. Additional studies comparing metabolic activity and ecology of common species should yield more information on the ecology of rarer species.     

Gut evacuation rates of Antarctic copepods during austral spring

The results of gut evacuation experiments performed on Antarctic copepods during the austral spring are presented and discussed. Four species of large copepods commonly occurring in the Indian sector of the Antarctic Ocean were studied: Calanus propinquus, Calanoides acutus, Rhincalanus gigas and Pleuromamma robusta. For each species two experiments were carried out, one in daytime and one in night-time, except for Calanoides acutus, which was only studied at night. P. robusta showed pigment gut retention in all experiments. The results showed that all species studied had a longer gut passage time than that previously recorded and that gut evacuation rate appears to decrease during daytime. Accepted: 1 October 1998     

Aspects of the study of the life cycles of Antarctic copepods

Different approaches to the study of life cycle strategies of Antarctic copepods are described in an attempt to shed new light on our present knowledge. To date, most studies were carried out on abundance, horizontal and vertical distribution and stage composition during different seasons and in various regions. Hence, the seasonal pictures had to be compiled from different years and sampling regions. The physiological method includes measurements on e.g. egg production, feeding, respiration and excretion rates, C:N and O:N ratios, lipid and protein contents. However, both physiological and biochemical data are still rare. Results of field observations are given in this paper for investigations conducted within the last 15 years in the eastern Weddell Sea, while data of physiological parameters are based on a broader geographical region. In the eastern Weddell Sea, eight copepod species account for about 95% of copepod abundance and for more than 80% of copepod biomass. Within the calanoids, the small species Microcalanus pygmaeus dominates by numbers with 66%, while the large species Calanoides acutus and Calanus propinquus comprise together 52% of the biomass. Species abundance is lowest in winter and highest in summer/autumn, however, seasonal changes in the abundance of M. pygmaeus are small and this species occurs in similar quantities throughout the year. All copepod species show a distinct seasonal vertical distribution pattern and they occur in upper water layers in summer, in contrast to the other seasons. However, the depth layers of maximum concentration differ between species. The ontogenetic vertical migration is most pronounced in C. acutus and relatively weak in C. propinquus. The age structure also shows seasonal differences with the youngest population observed in summer for C. acutus, C. propinquus, Ctenocalanus citer or autumn for Metridia gerlachei, whereas the M. pygmaeus population is oldest during summer. The youngest copepodite stage and the males are not always present in C. acutus and C. propinquus. In contrast, all developmental stages and both sexes occur throughout the year in M. gerlachei, M. pygmaeus and C. citer. Gonad maturation in the dominant calanoid species proceeds well before the onset of phytoplankton production in the eastern Weddell Sea. However, the highest portion of females with ripe gonads and hence highest egg production rates coincide with the productive period in spring and summer. In autumn, ovaries of the three larger species C. acutus, C. propinquus and M. gerlacheiare all spent. In contrast, the percentage of ripe females of the two smaller species, C. citer and M. pygmaeus, stays high in autumn. Egg production rates are highly variable within one region and species. Many copepods accumulate large depots of lipid, mainly wax esters. In contrast, five species (C. propinquus, C. simillimus, Euchirella rostromagna, Stephos longipes and Paralabidocera antarctica) almost exclusively synthesise triacylglycerols and not wax esters. The lipid content exhibits distinct seasonal patterns, and is highest in autumn. A seasonal difference is also obvious in metabolic activities with lowest rates during the dark season. The adaptation to the pronounced seasonality in the Southern Ocean differs greatly between copepod species, and most Antarctic copepods stay active during the dark season. Calanoides acutus seems to be the only true diapause species. Calculations of summer developmental rates and winter mortality rates of the large species C. acutus and C. propinquus suggest that both species have a 1-year life cycle with few females overwintering and probably spawning a second time. In contrast, a 2-year life cycle is more likely in R. gigas. However, life cycle durations of all species studied are still uncertain and regional differences are very probable.     

Lipid dynamics and feeding of dominant Antarctic calanoid copepods in the eastern Weddell Sea in December

Lipid content, fatty acid composition, and feeding activity of the dominant Antarctic copepods, Calanoides acutus, Calanus propinquus, and Metridia gerlachei, were studied at a quasi-permanent station in the eastern Weddell Sea in December 2003. During 3 weeks of the spring phytoplankton development, total lipid levels of females and copepodite stages V (CVs) of C. acutus were almost doubled. Meanwhile, only a slight increase in total lipid content occurred in M. gerlachei, and no clear trend was observed in lipids of C. propinquus females. The pronounced increase of lipids in C. acutus was due to an accumulation of wax esters. The proportion of wax esters in the lipids of M. gerlachei was clearly lower, while triacylglycerols played a more important role. In C. propinquus, triacylglycerols were the only neutral lipid class. There were no pronounced changes in the feeding activity of M. gerlachei, whereas the feeding activity of C. acutus had rapidly increased with the development of the phytoplankton bloom in December, which explains its rapid lipid accumulation. The combination of gut content and fatty acid trophic marker analyses showed that C. acutus was feeding predominantly on diatoms. The typical diatom fatty acid marker, 16:1(n-7), slightly decreased and the tracer for flagellates, 18:4(n-3), increased in females and CVs of C. acutus. This shift indicates the time, when the significance of flagellates started to increase. The three copepod species exhibited different patterns of lipid accumulation in relation to their trophic niches and different duration of their active phases. The investigations filled a crucial data gap in the seasonal lipid dynamics of dominant calanoid copepods in the Weddell Sea in December and support earlier hypotheses on their energetic adaptations and life cycle strategies.     

Feeding patterns of post-larval and juvenile notothenioids in the southern Weddell Sea (Antarctica)

Summary The food of 163 juvenile specimens of 13 species of notothenioid fishes collected in the southern Weddell Sea (Antarctica) was analyzed. Investigated fish size range was 3–13 cm SL. Principal food items were calanoid copepods Metridia gerlachei, Calanoides acutus, and Calanus propinquus; all developmental stages of Euphausia crystallorophias, and post-larval nototheniid fish Pleuragramma antarcticum. Diet of juvenile channichthyids is limited to few species of euphausiids and fish in the size > 10 mm, but does not include significant numbers of copepods. Pelagic stages of nototheniids feed on copepods and/or larval euphausiids smaller than 10 mm. At similar size, nototheniids and bathydraconids take smaller prey items than channichthyids.     

Understanding the trophic role of the Antarctic ctenophore,Callianira antarctica,using lipid biomarkers

To better understand the trophic role of ctenophores in Antarctica during austral fall and winter, a major species of cydippid ctenophore, Callianira antarctica, was collected during April/May (fall) and August/September (winter) 2002 in the vicinity of Marguerite Bay. Lipid content, lipid classes, fatty acids, fatty alcohols and sterols were analyzed in animals, together with lipid biomarkers in krill and copepod species representing potential ctenophore prey. Lipid content in ctenophores collected in winter was slightly higher than from animals in fall (4.8 and 3.5% of dry weight, respectively). Polar lipids were the dominant lipid class in ctenophores, accounting for over half of the lipid content, with significant amounts of free fatty alcohols (more than 10% of total lipid content) detected. Lipid-class composition, however, differed significantly between seasons, with significant amounts of neutral lipid (wax esters and triacylglycerols) only detected in animals from fall. Although the dominant lipid classes in ctenophores varied between fall and winter, individual lipids (i.e., fatty acids, alcohols and sterols) showed only minor changes between seasons. Specifically, long-chain polyunsaturated fatty acids [20:5(n-3) and 22:6(n-3)] found in high abundance in larval krill were also elevated in ctenophores collected in winter. Very high amounts of monounsaturated fatty alcohols, particularly 20:1(n-9) and 22:1(n-11), known to be important components of wax esters in calanoid copepods, were also observed. Multivariate analysis using the suite of lipids found indicated that copepods are an important diet item for ctenophores in the study area. Results further suggest that C. antarctica feed actively year-round, with larval krill providing a food resource during austral winter.     

Effects of the ice-edge bloom and season on the metabolism of copepods in the Weddell Sea,Antarctica

The metabolic responses of several species of Antarctic copepods to primary productivity and changes between seasons were investigated. To examine the influence of the spring ice-edge bloom on the metabolism of copepods, oxygen consumption rates were determined on specimens from three zones of widely different ice coverage and chlorophyll biomass: pack ice (pre-bloom), ice edge (bloom) and open water (post-bloom). Summer metabolic rates were compared with published winter rates. Field work was done in the Weddell Sea in the region of 60 °S, 36°W in late November and December 1993. Oxygen consumption rates were determined by placing individuals in syringe respirometers and monitoring the oxygen partial pressure for 10–20 hours. Higher metabolic rates were observed in the primarily herbivorous copepods, Calanoides acutus, Rhincalanus gigas and Calanus propinquus in regions of higher primary production: ice edge and open water. The carnivorous Paraeuchaeta antarctica showed a similar pattern. The omnivorous copepods Metridia gerlachei and Gaetanus tenuispinus showed no changes in metabolism between zones. Data on routine rates of copepods from the winter were available for C. propinquus and P. antarctica. In P. antarctica, rates were higher in the summer. Calanus propinquus showed a higher metabolic rate in the summer than in the winter, but the difference was not significant at the 0.05 level. It was concluded that copepods near the ice zone in the ice zone in the Antarctic rely on the spring ice-edge bloom for growth and completion of their life cycle.     

Qualitative models of the life cycles of Calanoides acutus,Calanus propinquus,and Rhincalanus gigas

Summary The life cycle of Calanoides acutus, Calanus propinquus, and Rhincalanus gigas was analyzed in samples collected by five expeditions from 1963 to 1984 in the Scotia and Weddell Seas. The result of this analysis, and of published data suggest that C. acutus and C. propinquus have a one year life cycle. Males of C. acutus are present in the population for a short period of time during late winter and fertilization occurs in deep waters. C. propinquus mates in the surface and males are present in the population throughout the summer. Part of its population may remain in the surface waters in winter. R. gigas has a more flexible, one or two year life cycle. Late summer spawning may occur in this species.This is contribution No. 95 of the Alfred-Wegener-Institut für Polar- und Meeresforschung     

A comparison of carbon-specific respiration rates in gelatinous and non-gelatinous zooplankton: A search for general rules in zooplankton metabolism

Using 470 data from the literature the dry weight-specific respiration rates of gelatinous zooplankton (cnidarians, ctenophores and salps) and non-gelatinous zooplankton (mainly crustacea) were converted to carbon-specific values. The resulting carbon-specific respiration rates showed no significant differences between the two groups of zooplankton, indicating similar oxygen requirements per gram of carbon biomass. From this finding, it can be suggested that the differences in the rates of oxygen consumption measured in the two types of zooplankton in the sea can be explained by the carbon biomass ratio between gelatinous and non-gelatinous zooplankton. Furthermore, the low rate of metabolism of gelatinous species compared with that of non-gelatinous animals of the same volume can be attributed predominantly to the relatively low organic matter content in the former. It is recommended that all weight-specific metabolism rates be expressed using carbon as body mass unit (e.g. mg O₂ gC⁻¹ d⁻¹) which enables more accurate comparisons between individuals exhibiting different dry weight/carbon ratios.     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Distribution of six major copepod species around South Georgia in early summer

Summary An intensive net sampling survey was conducted around the island of South Georgia during November/December 1981. The distribution and copepodite stage structure of the dominant copepods Calanoides acutus, Calanus simillimus, C. propinquus, Rhincalanus gigas, Metridia lucens and Metridia gerlachei were compared. The herbivorous species had completed their spring vertical migration and their summer generations were developing during the survey. At every station, Calanoides acutus was noticeably more advanced than Rhincalanus gigas in its reproductive cycle. The species were also more advanced in their development in the SE oceanic part of the survey area than in the NW. However, copepod development rates are rapid at this time of year, and this apparent regional difference may be due mainly to temporal variation during the four weeks of the survey. A truly regional variation in timing of reproduction was found when development was compared between shelf and oceanic waters. Spawning of Rhincalanus gigas and particularly of Calanoides acutus was later over the shelf. The age structure of the epi-mesopelagic metridinids also differed between shelf and oceanic waters, but no age differences were found for either Calanus simillimus or C. propinquus, both of which live and spawn higher in the water column than the other species. The presence of the South Georgia shelf also limited the overall abundance of the two deeper living metridinids. However, the length of time between spawning (and production of large numbers of early copepodids) and sampling had the largest influence on observed species abundance within the survey area.     

Feeding patterns of dominant Antarctic copepods: an interplay of diapause,selectivity, and availability of food

Gut contents and feeding activity of five dominant Antarctic copepods (Calanus propinquus, Calanoides acutus, Rhincalanus gigas, Metridia gerlachei and Microcalanus pygmaeus) were studied from samples collected during several cruises of the RV Polarstern to the eastern Weddell Sea. In summer, feeding activity, estimated as percentage of copepods with food in the guts, was high in all the species, and diatoms dominated all gut contents. In winter, C. acutus was trophically inactive, and C. propinquus and R. gigas considerably decreased their feeding activity, while a decrease in feeding of M. gerlachei and M. pygmaeus was less pronounced. Unidentified mass dominated gut contents in winter, supplemented by phytoplankton and protozoans. Prior to the spring bloom, feeding activity of C. acutus was low, with unidentified food predominating, while carnivory was important in actively feeding C. propinquus. Rhincalanus gigas tended to be more carnivorous than C. acutus, however with less feeding activity than C. propinquus. Seasonal changes in feeding patterns are discussed.     

Summer-winter differences in copepod distribution around South Georgia

Zooplankton was sampled on a synoptic grid of stations centered on South Georgia during the austral summer of 1981/82 and winter 1983. Within the top 1000 m layer at oceanic stations, copepods averaged 48% of the total biomass in summer and winter, but outnumbered all other taxa combined by a factor of 10. In winter the mean zooplankton biomass within the top 1000 m was 68% of its summer level. Copepod biomass was 77% of its summer level. During both surveys, the large and abundant Calanoides acutus and Rhincalanus gigas dominated the copepod biomass and, with several other species, showed a marked downwards seasonal migration out of the top 250 m layer in winter. Antarctic epipelagic species predominated around the island during summer but tended to be replaced by sub-Antarctic and cosmopolitan species during the winter. Factors likely to influence our estimates of overall copepods abundance and changes in species composition include seasonality of reproduction, net mesh selection and differences in water mass distribution. The observed trends are attributed mainly to variation in the position of the Polar Front which lay north of the island during the summer survey yet lay across the survey area in winter. This resulted in a greater influence of sub-Antarctic water around South Georgia in winter and the displacement of Antarctic species.     

Inter-annual variation in summer zooplankton community structure in Prydz Bay, Antarctica, from 1999 to 2006

Inter-annual variations in zooplankton community structure in Prydz Bay were investigated using multivariate analysis based on samples collected with a 330-μm mesh, 0.5-m² Norpac net during the austral summer from 1999 to 2006. Two distinct communities, an oceanic and a neritic community, were consistently identified in all surveys. Oceanic communities had higher diversity and were indicated by species such as Haloptilus ocellatus, Heterorhabdus austrinus, Thysanoessa macrura, Rhincalanus gigas, Scolecithricella minor and Oikopleura sp.. Neritic communities were indicated by Euphausia crystallorophias and Stephos longipes and were characterized by fewer but more abundant species. In 1999 and 2006, a transitional community was also distinguished near the continental shelf edge, where ice coverage was more extensive than either the oceanic or neritic regions. Significant inter-annual variations in community structure (mainly involving species abundance rather than species composition) were found in both oceanic and neritic communities, being more obvious in the latter. The timing and amplitude of sea ice retreat (polynya appearance), and its effect on food availability, had strong influences on zooplankton community structure. In oceanic communities during years with earlier ice retreat, the extra time available for phytoplankton blooms to accumulate resulted in a higher proportion of large copepods (Calanoides acutus, Calanus propinquus, Metridia gerlachei) (especially the younger copepodites) in the zooplankton assemblage. In neritic communities, zooplankton such as the ice krill E. crystallorophias, and large copepods (C. acutus, C. propinquus, M. gerlachei), also showed higher abundance and earlier developmental stages in years with larger polynya. On the other hand, in years with later ice retreat, smaller polynya, and less time for phytoplankton blooms to form, the abundance of large copepods was lower and older age classes were more common.     

Winter distribution and overwintering strategies of the Antarctic copepod species Calanoides acutus,Rhincalanus gigas and Calanus propinquus (Crustacea,Calanoida) in the Weddell Sea

During the Winter Weddell Gyre Study in September–October 1989, the horizontal and vertical distribution, stage composition and feeding condition of the three antarctic copepod species Calanoides acutus, Rhincalanus gigas and Calanus propinquus were studied. The data indicate that C. acutus and R. gigas have the bases of their distributional ranges (sensu Makarov et al. 1982) in the Antarctic Circumpolar Current (ACC) and in the Warm Deep Water (WDW) entering the Weddell Gyre (WG). C. propinquus lived mainly in the cold WG south of the ACC. C. acutus overwintered mainly in the WG as stage IV copepodites (C). The species mainly inhabited the layers below the T_max stratum and down to 2000 m, but C V and females occurred slightly higher than C III and IV. Males prevailed over females and were confined to a rather narrow layer between 500 and 1000 m. Feeding experiments suggested all deep-living stages to be resting. However, if this species spawns in late autumn the younger C I–II can stay in the Winter Water (WW). R. gigas inhabited mainly the T_max stratum. In the eastern part of the WG, R. gigas breed in the WDW in autumn and hibernate as C I–III and C V–VI in the first and second winter, respectively. In the ACC zone, however, its life cycle is different and winter breeding of overwintered adults occurs. Most of the C. propinquus population overwintered in the WG as C III–V, inhabiting the WW. In the upper water layers in the interior of the WG, C III dominated with upto 18,000 individuals 1,000 m³. Shallow living C. propinquus were in the active, feeding state. Persistence of active feeding zooplankton populations in the WW of the WG can be an important factor influencing processes of phytoplankton development and the particle flux.     

Temporal changes in the relationship between condition indices and proximate composition of juvenile Coregonus artedi

The Fulton‐condition factor ( K ) and per cent whole‐body water content were examined to determine whether these indices can estimate the proximate composition of juvenile lake herring Coregonus artedi exposed to a simulated Lake Superior winter over a 225 day laboratory experiment. The K was positively correlated to whole‐body crude lipid, crude protein, and gross energy content and negatively correlated to whole‐body water content for each sampling period of the experiment (days 75, 150 and 225). In contrast, there was only a weak positive correlation between K and whole‐body ash content. While per cent water content was negatively correlated with crude lipid, crude protein and gross energy content for each of the three sampling periods, the correlation between this predictor and ash content was only weakly negative. The indices can be used to accurately estimate temporal changes in proximate composition of juvenile lake herring during winter periods.     

SEASONALITY OF SELECTED NUTRITIONAL CONSTITUENTS OF EDIBLE DELMARVA SEAWEEDS

Edible seaweeds have not been thoroughly explored for food, medicinal, or industrial purposes in the United States. This study compared selected proximate constituents of three edible seaweed species (Ulva lactuca L., Fucus vesiculosus L., and Gracilaria tikvahiae McLachan) at two sites for possible future development as a food crop on the Delmarva Peninsula. Sampling was conducted bimonthly at Chincoteague Memorial Park, Virginia, and Indian River Inlet, Delaware, from 2005 to 2008. Proximate constituents of moisture, ash, dietary fiber, proteins, and fat were measured seasonally and calorific values were calculated. Data were analyzed using correlation, paired samples t‐tests and one‐ and two‐way ANOVA. Significant variations in the proximate constituents were found among seasons, species, and between sites. The brown seaweed (Fucus) at both sites had higher fiber, fat, and ash (mineral) content than the green (Ulva) or the red (Gracilaria). Ulva and Gracilaria had higher protein content than Fucus. Seaweeds from Delaware had more fat, ash, and protein than from Virginia, potentially because of the more polluted, nutrient rich environment at the Delaware site. Positive correlations between seaweed fat and protein content may indicate an increase in the synthesis of both components under optimal growth conditions. Species' physiology differences and the water quality at the two sites likely impacted proximate constituent values. This study contributed new information to the existing body of knowledge in the areas of nutrition and ecology of seaweeds and their potential as a cash crop.     

The lipid compositions of high-Antarctic notothenioid fish species with different life strategies

Lipid and fatty acid compositions of five notothenioid fishes from the Antarctic Weddell and Lazarev Seas were investigated in detail with regard to their different modes of life. The pelagic Aethotaxis mitopteryx was the lipid-richest species (mean of 61.4% of dry mass, DM) followed by Pleuragramma antarcticum (37.7%DM). The benthopelagic Trematomus lepidorhinus had an intermediate lipid content of 23.2%DM. The benthic Bathydraco marri (20.8%DM) and Dolloidraco longedorsalis (14.5%DM) belonged to the lipid-poorer species. Triacylglycerols were the major lipid class in all species. Important fatty acids were 16:0, 16:1(n-7), 18:1(n-9), 18:1(n-7), 20:5(n-3) and 22:6(n-3). The enhanced proportions of the long-chain monounsaturated fatty acids, 20:1 and 22:1, in the lipid-rich pelagic fishes clearly reflected the ingestion of the two copepod species, Calanoides acutus and Calanus propinquus, which are the only known Antarctic zooplankters rich in these fatty acids. Although wax esters are the major storage lipid in many prey species, they were absent in all notothenioid fishes studied. Thus, wax esters ingested with prey are probably converted to triacylglycerols via fatty acids or metabolised by the fishes. The enhanced lipid accumulation with increasingly pelagic lifestyle has energetic advantages, especially with regard to improved buoyancy. It is still unknown to what extent these lipids are utilised as energy reserves, since it has been suggested that not only the benthic but also the pelagic Antarctic fishes are rather sluggish, with a low scope for activity and hence low metabolic requirements. Accepted: 14 May 2000     

Seasonal Variation in the Chemical Composition of Tropical Australian Marine Macroalgae

The proximate chemical composition (ash, soluble carbohydrate, lipid and protein) was determined in 30 common species of tropical Australian marine macroalgae from Darwin Harbour (12^∘26′S, 130^∘51′E), in summer (hot and wet) and winter (cool and dry). There was a wide diversity of species in both seasons (19 species in summer and 20 species in winter). In most species, the major component was soluble carbohydrate (chlorophytes range 2.5–25.8% dry weight (dw), phaeophytes range 8.4–22.2% dw, rhodophytes range 18.7–39.2% dw) with significantly higher (p < 0.05) percentages only in winter season rhodophytes. Highest percentages of protein were found in rhodophytes collected in the summer (range 4.8–12.8% dw), with significantly lower percentages (p < 0.05) during winter. All species had lipid contents within the range 1.3–7.8% dw, with highest percentages in summer phaeophytes, but no significant differences between species or season. Most species had moderate to high ash contents (24.2–89.7% dw), with the highest percentages during summer. Compared with summer samples, macroalgae collected in winter had higher energy value and slightly lower percentages of inorganic matter. The variation of algal groups and chemical composition may influence the availability of the food source for the majority of herbivores, which in turn is likely to effect their ecology and community structure.     

Common relationships among proximate composition components in fishes

Relationships between the various body proximate components and dry matter content were examined for five species of fishes, representing anadromous, marine and freshwater species: chum salmon Oncorhynchus keta, Chinook salmon Oncorhynchus tshawytscha, brook trout Salvelinus fontinalis, bluefish Pomatomus saltatrix and striped bass Morone saxatilis. The dry matter content or per cent dry mass of these fishes can be used to reliably predict the per cent composition of the other components. Therefore, with validation it is possible to estimate fat, protein and ash content of fishes from per cent dry mass information, reducing the need for costly and time‐consuming laboratory proximate analysis. This approach coupled with new methods of non‐lethal estimation of per cent dry mass, such as from bioelectrical impedance analysis, can provide non‐destructive measurements of proximate composition of fishes.