Age and growth of the Antarctic dragonfish Parachaenichthys charcoti (Pisces, Bathydraconidae) from the southern Scotia Arc

The Antarctic dragonfish Parachaenichthys charcoti is commonly found in shelf waters of islands in the southern Scotia Arc. Its northern congener P. georgianus is distributed on the shelves of South Georgia and the South Sandwich Islands. Biological information on P. charcoti is limited and restricted largely to reproductive traits and feeding habits. The present study fills this gap, providing the first data on age and growth of this species by otolith reading. Age was estimated in juveniles and adults by counting annuli on otoliths. Age of early juveniles was determined by microincrement counts (considered to be daily rings). Age estimates of juveniles and adults ranged from 1 to 9?years, with a high percentage agreement between readings and low values of counting variability indices APE (3.3?%) and CV (4.7?%). Age of early juveniles ranged from 160 to 204?days, all showing an evident check at 32–35?days of age, tentatively linked to the first larval exogenous feeding. The estimated values of von Bertalanffy growth parameters L _∞ and k were 53.55?cm and 0.22, respectively, and the index of growth performance P was 2.33. Hatching in P. charcoti takes place in late winter, from August to September. Compared to other notothenioids inhabiting the Seasonal Pack-ice Zone, P. charcoti is a relatively fast growing species with moderate longevity, sharing several biological characteristics with its sister species P. georgianus.     

Metabolic energy utilization during development of Antarctic naked dragonfish (Gymnodraco acuticeps)

We have capitalised on the availability of eggs and adults of the naked dragonfish Gymnodraco acuticeps (Sub-order Notothenioidei, F. Bathydraconidae) near McMurdo Station, Antarctica to examine metabolic energy utilization at different stages of its life cycle. Average egg respiration rates were found to increase from 2.17±1.02 nmol O₂ h⁻¹ ind⁻¹ at about 17 h post-fertilization (hpf) to 5.72±0.56 nmol h⁻¹ ind⁻¹ at about 24 hpf, during which time the eggs underwent first cleavage. The respiration rates of embryos from 2–20 days post-fertilization (dpf) averaged 4.11±1.47 nmol O₂ h⁻¹ ind⁻¹. About 10 months post-fertilization, oxygen consumption rates of 27.14±3.92 nmol O₂ h⁻¹ ind⁻¹ were recorded immediately prior to hatching, with a peak of 112.41±31.38 nmol O₂ h⁻¹ ind⁻¹ at the time of hatch. Larvae aged 46–63 days post-hatch had an average respiration rate of 64.4±15.11 nmol O₂ h⁻¹ ind⁻¹. Mass-specific respiration rates of hatched larvae (approximately 1–2 months old) were calculated using dry weights (DW) and averaged 16.1±3.4 nmol O₂ h⁻¹ mg⁻¹ DW. Adult dragonfish respiration rates (corrected for a 100 g fish and using a 0.8 scaling exponent) averaged 0.91±0.36 mmol O₂ kg⁻¹ h⁻¹ after a 48 h acclimatization period, which is not indicative of significant metabolic cold adaptation. The energy contents of dragonfish eggs and larvae were also measured by microbomb calorimetry and used, along with the respiration data, in an initial approach to estimate an energy budget. In order to balance the budget, the bulk of the available post-gastrulation respiratory energy (during 213 days of embryonic incubation) must be consumed at a relatively low average rate (7.1 nmol O₂ h⁻¹ ind⁻¹), which supports the possibility that advanced dragonfish embryos overwinter in a relatively quiescent metabolic state while awaiting a suitable stimulus (such as the return of the sun) to initiate hatching.     

Haemogregarina georgianae n. sp., a new haemogregarine parasite from the Antarctic teleost Parachaenichthys georgianus

Haemogregarina georgianae n. sp. occurs frequently in the bathydraconid teleost Parachaenichthys georgianus from the western Antarctic portion of the Southern Ocean. The haemogregarine and its developmental stages in the vertebrate have been found in erythrocytes of the fish: both microschizogony and macroschizogony have been seen in fish caught during the austral summer. Morphological evidence suggests the merozoites from macroschizogony give rise to the microschizont, and that the microschizont merozoites give rise to gametocytes. Comparison of H. georgianae with other haemogregarines known from teleosts shows that it has a previously undescribed morphology.     

Egg-release behaviour in Antarctic krill

The process of egg release is a complex and crucial step in the life cycle of euphausiids, especially with regards mortality and recruitment success. We examined this process in Antarctic krill (Euphausia superba) in terms of the functioning of the female genital apparatus and associated swimming behaviour. A tethering technique combined with video analysis was used to make observations of three females during the release process. We found eggs were steadily extruded over a period of up to 10 h, during which time the krill released between 1,600 and 4,000 eggs and the ovary reduced by a half in length and a third in height. Eggs were mainly released individually or, less commonly, in batches of between 2 and 4 eggs. Release rates were between 5 and 30 eggs min⁻¹. The steady release of eggs fits well with histological evidence that mature oocytes must pass individually through tight genital ducts with narrow apertures, before coming in to close contact with the sperm plug for fertilisation, and then expulsion from the thelycum as fertilised eggs. During spawning, the female alternated between slow and rapid rates of pleopod beating with egg release occurring at the moment of beat acceleration. At the point of release, the descent of the egg was accelerated through downward beats of the 7th thoracic leg. The cyclic pattern in pleopod beat-rate during spawning may alter swimming performance and contribute to the widely reported sex- and maturity-based biases within krill swarms.     

New perspectives on the dispersal mechanisms of the Antarctic brooding bivalve Mysella charcoti (Lamy, 1906)

. Brooding is a widespread phenomenon among Antarctic bivalves. Although it should represent a handicap to dispersion, many brooding species have achieved a wide distribution in Antarctic and subantarctic waters, suggesting that they have alternative and effective methods of dispersal. Evidence of such an alternative method is presented here for the bivalve Mysella charcoti, unexpectedly found alive and healthy in feces expelled by Notothenia coriiceps (Nototheniidae: Pisces). The finding indicates that the snug-fitting shell of Mysella functions as a barrier to digestive enzymes. Withstanding passage through the digestive tract of fish allows Mysella to be passively dispersed (within the home range of the fish) and colonize new habitats or re-colonize shallow-water substrates severely impacted by ice scours.     

Cholinergic and adrenergic tone on the heart of the Antarctic dragonfish, Gymnodraco acuticeps, living at sub-zero temperatures

Heart rate and ventral aortic blood pressures were recorded from the Antarctic dragonfish,Gymnodraco acuticeps, a member of the family Bathydraconidae. At −1.0 °C, the resting heart rate was 17.4 beats per minute and the ventral aortic pressure was 3.4 kPa. Cholinergic and adrenergic tone on the heart was determined by administration of the muscarine and ß-adrenoreceptor antagonists, atropine and sotalol, respectively. Neither antagonist influenced ventral aorta blood pressure; however, injection of atropine resulted in a significant increase in heart rate, and sotalol a decrease in heart rate. The cholinergic tone accounted for 30% of intrinsic heart rate and the adrenergic tone 26% of intrinsic heart rate. Comparison of these cardiac data with those for other teleosts from a wide range of thermal environments revealed no significant correlation for either cholinergic or adrenergic tone with body temperature (i.e. thermal independence); however, the resting and intrinsic heart rate of teleosts were strongly correlated with temperature.     

Energy balance and cold adaptation in the octopus Pareledone charcoti

A complete energy balance equation is calculated for the Antarctic octopus Pareledone charcoti at 0 degrees C. Energy used in respiration, growth, and excretion of nitrogenous and faecal waste, was recorded along with the total consumption of energy through food, for three specimens of P. charcoti (live weights: 73, 51 and 29 g). Growth rates were very slow for cephalopods, with a mean daily increase in body weight of only 0.11%. Assimilation efficiencies were high, between 95.4 and 97.0%, which is consistent with previous work on octopods. The respiration rate in P. charcoti was low, with a mean of 2.45 mg O(2) h(-1) for a standard animal of 150 g wet mass at 0 degrees C. In the North Sea octopus Eledone cirrhosa, respiration rates of 9.79 mg O(2) h(-1) at 11.5 degrees C and 4.47 mg O(2) h(-1) at 4.5 degrees C for a standard animal of 150 g wet mass were recorded. Respiration rates between P. charcoti and E. cirrhosa were compared using a combined Q(10) value between P. charcoti at 0 degrees C and E. cirrhosa at 4.5 degrees C. This suggests that P. charcoti are respiring at a level predicted by E. cirrhosa rates at 4.5 and 11.5 degrees C extrapolated to 0 degrees C along the curve Q(10)=3, with no evidence of metabolic compensation for low temperature.     

Biology and functional morphology of the pallial organs of the Antarctic bivalve Mysella charcoti (Lamy, 1906) (Galeommatoidea: Lasaeidae)

Mysella charcoti is an Antarctic lasaeid bivalve and the most frequently encountered mollusc in Admiralty Bay, King George Island, South Shetlands. The behaviour of the species in aquaria, combined with analyses of the gross and microscopic morphologies and functioning of the organs in the mantle cavity of living and preserved specimens have allowed an understanding of important aspects of its biology. The role of the foot and its ciliature during the processes of dislodgement and burrowing within the sediment are described. The species is a free-living, shallow-burrower, with a predominantly deposit-feeding habit and derives part of its food from the labile settled organic deposits carried into the mantle cavity by the anterior–posterior current of water. Pedal sweep-feeding was not detected. M. charcoti is the first known lasaeid with ctenidia formed of the descending lamellae of the inner demibranchs only, a feature probably related to its highly specialised brooding habit.     

Predatory behaviour and metabolic costs in the Antarctic muricid gastropod Trophon longstaffi

Aquarium-based observations of the feeding behaviour of the Antarctic muricid gastropod Trophon longstaffi over a 3-year period revealed that individuals were capable of feeding on both bivalve (Laternula elliptica and Yoldia eightsi) and brachiopod (Liothyrella uva) prey. Feeding activity was remarkably infrequent, with most individuals taking between 0.67 and 2.66 items per year, but two individuals ate nothing for 30 months and another ate nothing over the entire 36-month period. The time taken to attack and consme prey was extremely slow, with 20 days to complete an attack on the brachiopod Liothyrella uva and 29 days for the bivalve Laternula elliptica. Y. eightsi were mostly attacked by a wedging method. Most attacks were by drilling and the positioning of large, highly distinctive drillholes was broadly stereotypic. Metabolic rates for T. longstaffi ranged from 46.2 µg O₂ h^-1 for a 1.7-g tissue dry mass individual to 18.1 µg O₂ h^-1 for a 0.98-g tissue dry mass specimen. These rates are amongst the lowest so far reported for a gastropod mollusc but are within the range previously recorded for polar invertebrates. We suggest that T. longstaffi is well adapted for the low temperature, but highly seasonal, Antarctic conditions, with a low energy strategy and the ability to withstand highly extended periods of limited food availability.     

Assessing the Semelparity Hypothesis: Egg-guarding and Fecundity in the Malaysian Treehopper Pyrgauchenia tristaniopsis

According to the semelparity hypothesis, iteroparous insects should provide either no maternal care or less care than related semelparous species. We present field data on reproductive output and maternal care in the Southeast Asian treehopper Pyrgauchenia tristaniopsis (Mt. Kinabalu, Borneo) relevant to a preliminary assessment of the hypothesis. In a mark‐recapture experiment, more females than expected under semelparity were found to have oviposited a second clutch (37%). Female longevity was a of 75 d. Both these estimates were highly conservative. Oviposition was successive resulting in a of 46 eggs per clutch. Females provided care for eggs only, occasionally scraping their legs along the sides of the clutch apparently attempting to deter Brachygrammatella sp. egg parasitoids (Trichogrammatidae). Females straddled their clutch for a of 27 d, i.e. until 8 d after the beginning of first instar hatching. First instars hatched successively over a period of 11 d. When a female deserted her clutch, it contained about 37% yet unhatched eggs. Egg‐guarding effectively reduced egg mortality: the earlier a female was experimentally removed from her clutch the higher the egg mortality. Displacement experiments demonstrated that egg‐guarding is a behaviour actively maintained despite disturbances and specifically directed towards the egg clutch but not to the feeding site. We interpret our findings as being in accordance with the weaker claim of the semelparity hypothesis, i.e. the iteroparous P. tristaniopsis provided less maternal care than semelparous membracid species. Continued female feeding is discussed as a mechanism to display some level of care despite iteroparity.     

The relationship between foraging behaviour and energy expenditure in Antarctic fur seals

By using time-depth recorders to measure diving activity and the doubly-labelled water method to determine energy expenditure, the relationship between foraging behaviour and energy expenditure was investigated in nine Antarctic fur seal females rearing pups. At-sea metabolic rate (MR) (mean of 6.34 ± 0.4 W. kg^-1; 4.6 times predicted BMR) was positively correlated to foraging trip duration (mean of 4.21 ± 0.54 days; r²= 0.5, P < 0.04). There were no relationships between MR and the total number of dives, the total time spent diving or the total vertical distance travelled during the foraging trip. There was, however, a close negative sigmoidal relationship (r²= 0.93) between at-sea MR and the proportion of time at sea spent diving. This measure of diving behaviour may provide a useful, inexpensive means of estimating foraging energy expenditure in this species and possibly in other otariids. The rate of diving (m.h^-1) was also negatively related to at-sea MR (r²= 0.69, P < 0.005). Body mass gain during a foraging trip had a positive relationship to the time spent at sea (r²= 0.58, P < 0.02) and the total amount of energy expended while at sea (r²= 0.72, P < 0.004) such that, while females undertaking long trips have higher metabolic rates, the energetic efficiency with which females gain mass is independent of the time spent at sea. Therefore, within the range of conditions observed, there is no apparent energetic advantage for females in undertaking foraging trips of any particular duration.     

Comparative studies on the feeding behaviour of high Antarctic amphipods (Crustacea) in laboratory

Summary Feeding behaviour of Epimeria robusta K.H. Barnard, 1930 (Paramphithoidae), Gnathiphimedia mandibularis K.H. Barnard, 1930 (Acanthonotozomatidae) and Paraceradocus gibber Andres, 1984 (Gammaridae) was observed in aquaria. The observations and the analysis of gut contents of preserved specimens demonstrate that these species have different feeding behaviour and food preferences. Additional information is given from an examination of the functional morphology of the mouth-parts.     

Kin selection may influence fostering behaviour in Antarctic fur seals (Arctocephalus gazella)

Fostering confers obvious advantages to the offspring but is seemingly costly to the caregiver. Such behaviour is particularly paradoxical in seals where the energetic investment in milk is very high and has led to the suggestion that this behaviour may have evolved through either kin selection or reciprocity. We used a combination of genetic and behavioural data to investigate whether kin selection plays a role in the fostering behaviour observed in a well-studied population of Antarctic fur seals (Arctocephalus gazella) from Bird Island, South Georgia. Genotypic data from eight highly polymorphic microsatellite markers were used to estimate relatedness among mother-pup pairs, foster mother-pup pairs and the total population. Mean relatedness was found to be significantly higher for foster mother-pup pairs than that observed for the total population, suggesting that kin selection could have a role in the maintenance of fostering behaviour in this species.     

Territoriality and breeding behaviour of adult male Antarctic Fur seal, Arctocephalus gazella

The social organization and behaviour of 35 individually recognizable territorial male Antarctic Fur seals ( Arctocephalus guzellu ), were studied during the breeding season at South Georgia. Adults of both sexes remain at sea throughout the winter. Among the first bulls ashore were those which had the longest territorial tenures. The mean period of tenure for 13 bulls seen to copulate was 34.3±9.0 days. New bulls continued to arrive and fight for territories on the breeding beach throughout the study period. Many were successful and mean territory size declined from about 60 m² in mid-November to 22 m³ in December. More than 3000 boundary displays between known bulls were recorded and analysed. These were largely ritualized although in 14% of displays bites were exchanged. Outright fighting was infrequent in relation to the total number of inter-male encounters. 94% of of the fights occurred on the first day a pair of bulls became neighbours. Less than 50% of bulls holding territory were seen to copulate and the mean copulation frequency for these bulls was 10. During late December, by which time most females had mated, adult males ceased to maintain their territories actively and many abandoned them completely. Features of the social organization are compared with those of other otariid seals and the interrelationships between period of tenure, territory size, form of boundary display and copulation frequency are discussed in relation to environmental and social influences. Within fur seals and sea lions, differences in social organization during the breeding season do not seem to be related to phylogenetic differences.     

Sex ratio and adult behaviour of the Antarctic midge Belgica antarctica (Diptera, Chironomklae)

Abstract. 1. The sex ratio in populations of the Antarctic chironomid Belgica antarctica approximates 1:1 at eclosion.
2. Male predominance in surface populations of the short-lived adult persists throughout the summer. The mean ratio, based on data from surface aggregations (austral summer 1977–78) and from sticky traps (1978–79) is about 6:1, with a steady seasonal decline from 10–20:1 to 2–5:1.
3. Males live slightly longer than females but the difference does not account for observed ratios.
4. Samples of adult populations taken from subsurface sites have sex ratios nearer to equality than surface populations.
5. It is concluded that the male-dominated surface populations are equivalent to the male swarms typical of winged Chironomidae.
6. Capture of airborne adults shows that aerial transport as well as water-surface rafting may play a role in dispersal of adults.     

Antarctic hairgrass expansion in the South Shetland archipelago and Antarctic Peninsula revisited

Populations of both native higher Antarctic plants, Deschampsia antarctica and Colobanthus quitensis, increased during the last decades. However, for D. antarctica, previous population studies on the South Shetland Islands and the Antarctic Peninsula have been too sporadic, patchy, and methodologically different to allow general conclusions. Our aim was to compare sites with D. antarctica along a north–south latitudinal transect with an integral census method to assess the possible impact of climatic change on grass population dynamics. During two summer seasons (2009–2010), plant populations were censed on Fildes and Coppermine Peninsula and several localities on the west coast of the Antarctic Peninsula. Largest plant populations were found on Fildes Peninsula with vegetation cover (VC) of 44–46%. Six out of eleven stands of D. antarctica on Coppermine Peninsula were new records, with increasing plant number and VC (0.1–22%). In the Antarctic Peninsula, contrarily to our expectation, only at Forbes Point, D. antarctica VC was relatively high (ca. 2%) and a new stand of C. quitensis was found. At three previously reported sites, plants had disappeared. Our monitoring confirms that northern D. antarctica populations are expanding, but that this expansion is not continuous along the Antarctic Peninsula and inconsistent with the gradient of relative temperature increase in north–south direction. We suggest that other abiotic and biotic factors are influencing the colonization and expansion of vascular plants in this particular ecosystem.     

Observations on the feeding behaviour of the Antarctic Gammarid Eusirus perdentatus Chevreux, 1912 (Crustacea: Amphipoda) in aquaria

Summary The feeding behaviour of adult Eusirus perdentatus was observed in aquaria. These observations and the analysis of gut contents of preserved specimens demonstrate that this species is a carnivorous predator feeding on polychaetes, amphipods and other small crustaceans. Apparently the localization and capture of prey in aquaria follows a fixed pattern.     

Carbohydrate structure and serological behaviour of "antifreeze" glycoproteins from an Antarctic fish.

The carbohydrate moiety of the “antifreeze” glycoprotein from $\text{Trematomus borchgrevinki}$ was found to be β-D-galactosyl 1–3 N-acetyl galactosamine by gasliquid chromatography. The glycoprotein inhibited anti-T antibody from human serum and $\text{Arachis hypogoea}$ lectin, but was inactive against $\text{Vicia graminea}$. Native “antifreeze” glycoprotein did not inhibit the agglutinins from $\text{Helix pomatia}$ or $\text{Cepaea hortensis}$, although after Smith degradation showed a strong inhibition towards them. Inhibition of the latter agglutinin demonstrates the carbohydrate-protein linkage to be α-linked. The presence of the Thomsen-Friedenreich antigen (T-antigen) on the “antifreeze” glycoprotein and its relation to tumour cell surfaces is briefly discussed.     

Aspects of the foraging behaviour of the Antarctic Tern Sterna vittata gaini at Harmony Point, South Shetland Islands

During January and February of 2002 and 2003, we studied the diet of the Antarctic Tern Sterna vittata gaini at two colonies in Nelson Island, South Shetland Islands, by identifying the prey fed to chicks by breeders. The fish Notothenia coriiceps was the main prey in both seasons, followed by the myctophid Electrona antarctica, Antarctic krill Euphausia superba and gammarid amphipods. The contribution of fish to the diet increased as chicks grew older. Fish and amphipods were brought to chicks during the day, whereas adults brought Antarctic krill at sunrise and sunset. Both the duration of the feeding trips and the number of trips per foraging bout varied according to the type of prey caught. Preliminary information suggests that, among other causes, the foraging strategy is strongly influenced by the predation pressure of skuas on chicks. Results are compared with the only two previous study on the diet of the Antarctic Tern at the South Shetland Islands.     

Feeding behaviour in the Antarctic fairy shrimp, <Emphasis Type=Italic>Branchinecta gaini</Emphasis>

Direct observations of feeding behaviour in Branchinecta gaini are described. B. gaini possess sophisticated food manipulation behaviours, using their abdominal appendages to ‘scrape’ at and carry away food items. Scraping behaviour was employed by animals for both detrital feeding and the cannibalisation of dead conspecifics. In the absence of like observations from other non-raptatory species of Branchinecta, it appears that adults of B. gaini occupy an intermediary position between species that feed exclusively on vegetative and detrital material and those (e.g. B. gigas, B. ferox, B. raptor) that are known to be carnivorous. In an Antarctic context, particularly, specialisation towards carnivory would have little adaptive value, while expansion of diet breadth via increased manipulative and digestive flexibility would, on the other hand, be advantageous. These behaviours, moreover, mean that B. gaini plays an active role in the breakdown and recycling of its own nutrient base.