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1.
The foraging strategies of king penguins from Heard and Macquarie islands were compared using satellite telemetry, time-depth
recorders and diet samples. Trip durations were 16.8±3.6 days and 14.8±4.1 days at Macquarie and Heard islands, respectively.
At Macquarie Island, total distances travelled were 1281±203 km compared to 1425±516 km at Heard Island. The total time the
penguins spent at sea was 393±66 h at Macquarie Island and 369±108 h at Heard Island. The penguins from Macquarie Island performed
more deep dives than those from Heard Island. King penguins from Macquarie Island travelled 1.5±0.2 km h−1 day−1 compared to 1.3±0.1 km h−1 day−1. At Macquarie Island, 19% of dives were upto 70–90 m depth compared to 35% at Heard Island. The main dietary prey species
were the fish Krefftychthis anderssoni and the squid Moroteuthis ingens in both groups. The differences in the at-sea distribution and the foraging behaviour of the two groups of penguins were
possibly related to differences in oceanography and bathymetric conditions around the two islands. Dietary differences may
be due to interannual variability in prey availability since the two colonies were studied during incubation but in different
years. 相似文献
2.
The seasonal variation in the foraging behaviour of king penguins (Aptenodytes patagonicus) was studied at Heard Island (53°05′S, 73°30′E) during 1992/1993. On seven occasions throughout the breeding cycle, time-depth-light
recorders were deployed on breeding adults to record the dive activities and foraging. Foraging locations changed with season:
in autumn and spring 1992, adults foraged between 48–52°S and 74–78°E, about 370 km NNE of Heard Island close to the Polar
Front. Two penguins tracked in winter travelled 2220 km east of Heard Island (95°E) along the northern ice limit, and 1220 km
south of Heard Island to approximately 65°S, respectively. In spring (October), the penguins again foraged further north than
during winter. The foraging area utilised in October overlapped the area where the penguins foraged in March/April. The penguins'
diving behaviour also varied seasonally: the modal depth of deep dives (>50 m) increased from about 100 m in February to 220 m
in October. Mean dive depths increased from 70 ± 52 m in March 1992 to 160 ± 68 m in August 1992. Penguins dived deep (>50 m)
only during daylight hours (16 h in February, 9 h in July). Mean dive durations ranged from 2.9 ± 1.1 min in March 1992 to
5.1 ± 1.2 min in August 1992. Associated with changes in foraging location and dive behaviour was a change in diet composition:
during summer the penguins ingested mainly myctophid fish (>90%) while in winter the most important diet item was squid.
Accepted: 19 October 1998 相似文献
3.
Antarctic terrestrial ecosystems are nutrient-poor and depend for their functioning in part on external nutrients. However,
little is known about the relative importance of various sources. We measured external mineral nutrient sources (wind blown
material, precipitation and guano) at three locations, the cold temperate oceanic Falkland Islands (51°76′S), and the Maritime
Antarctic Signy (60°71′S) and Anchorage Islands (67°61′S). These islands differ in the level of vegetation development through
different environmental constraints and historical factors. Total mineral nitrogen input differed considerably between the
islands. During the 3 month summer period it amounted to 18 mg N m−2 on the Falkland Islands and 6 and 102 mg N m−2 at Signy and Anchorage Islands, respectively. The high value for Anchorage was a result of guano deposition. By measuring
stable isotopic composition (δ15N) of the different nitrogen sources and the dominant plant species, we investigated the relative utilisation of each source
by the vegetation at each island. We conclude that external mineral nitrogen inputs to Antarctic terrestrial ecosystems show
great spatial variability, with the local presence of bird (or other vertebrate) colonies being particularly significant. 相似文献
4.
William H. Wilson Daniel Lane David A. Pearce J. Cynan Ellis-Evans 《Polar Biology》2000,23(9):657-660
Water samples from a range of fresh-water Antarctic lakes on Signy Island (South Orkney Islands: 60°45′S, 45 °38′W) were
examined for the presence of virus-like particles (VLPs) during the 1998/1999 field season. It was discovered that VLPs were
ubiquitous, morphologically diverse and abundant, with high concentrations ranging from 4.9 × 106 ml−1 to 3.1 × 107 ml−1. Likely hosts include bacteria, cyanobacteria and eukaryotic algae. In addition, an unusually large virus morphotype was
observed with a head diameter 370 × 330 nm and a tail 1.3 μm long.
Accepted: 15 May 2000 相似文献
5.
The diet of Cape petrel Daption capense was investigated at Laurie Island, South Orkney Islands (60°46′S, 44°42′W), Antarctica, in the period January–February 1996. Stomach contents of adults and regurgitate of chicks were sampled during
the post-hatching period. The analysis showed that during the whole sampling period Antarctic krill and fish represented the
predominant preys in terms of frequency of occurrence, forming nearly 35.8% and 64% by mass, respectively. The species Electrona antarctica was the most frequent fish prey. Amphipods were present in lower numbers and cephalopods were detected in the diet, but in
a very small proportion. Diet composition in terms of frequency of occurrence, mass and number is compared with results of
previous studies.
Received: 27 September 1996 / Accepted: 22 February 1997 相似文献
6.
Consumption of marine resources by seabirds and seals at Heard Island and the McDonald Islands 总被引:1,自引:1,他引:0
Summary The seabird and seal community at Heard Island and the McDonald Islands comprised an estimated total biomass of 27893 tonnes of which the 15 breeding species of seabirds made up 70%. The total annual consumption of marine resources was estimated to be approximately 521 000 t, of which 81% was consumed by seabirds Approximately 165 000 t of fish, 41 600 t of squid and 312 000 t of crustaceans are consumed annually by this seabird and seal community. The annual energy flux to this community was estimated to be 2.17·1012 kJ and approximately 56 000 t of carbon are consumed annually. Breeding populations of King Penguins and Antarctic Fur Seals are increasing, that of the Southern Elephant Seal is decreasing; there are no data on the population trend for Macaroni Penguins, the predominant consumer species. Commercial fisheries are presently operating at the nearby Iles Kerguelen, and similar activities may prove to be commercially viable at Heard Island. The fishery is for Champsocephalus gunnari, a major prey species of penguins and Antarctic Fur Seals at Heard Island during the summer breeding season. 相似文献
7.
Sixty nine hammerhead sharks, Sphyrna lewini, were tagged at Malpelo Island (Colombia) with ultrasonic transmitters during March 2006, 2007 and 2008, as part of a study
to understand their residency at the island and their horizontal and vertical movements. Five sharks visited Cocos Island,
627 km distant from Malpelo. One of the sharks that appeared at Cocos Island also visited the Galapagos Islands, 710 km from
Cocos, a month later. There is connectivity of Sphyrna lewini between Malpelo, Cocos and the Galapagos Islands, but the frequency of movements between the islands appears to be relatively
low (<7% of the tagged sharks). The most common depth at which the sharks swam coincided with the thermocline (rs = 0.72, p < 0.01). The depth of the thermocline varied depending on the time of the year. Nocturnal detections of the sharks were more
frequent during the cold season than during the warm season (W = 60, p < 0.01). We also found that hammerheads spent significantly more time on the up-current side of the island (Kruskal-Wallis = 31.1008;
p < 0.01). This study contributes to the knowledge of hammerhead sharks not only in Malpelo Island but also at a regional level
in the Eastern Tropical Pacific. 相似文献
8.
The diet composition of king penguins (Aptenodytes patagonicus) at Heard Island (53°05′S; 73°30′E) was determined from stomach contents of 98 adults captured as they returned to the island
throughout 1992. During the two growth seasons, the diet was dominated by the myctophid fish Krefftichthys anderssoni (94% by number, 48% by mass). The paralepidid fish Magnisudis prionosa contributed <1% by numbers but 17% by mass. Mackerel icefish (Champsocephalus gunnari) accounted for 17% by mass of chick diet in late winter, when chicks were malnourished and prone to starvation, although
its annual contribution to the penguins' diet was only 3%. Squid was consumed only between April and August; Martialia hyadesi was the commonest squid taken, comprising 40–48% of the winter diet. The remainder of the diet consisted of the squid Moroteuthis ingens and fish other than K. anderssoni. The energy content of the diet mix fed to the chicks varied seasonally being highest during the growth seasons (7.83 ± 0.25 kJ g−1) and lowest in winter (6.58 ± 0.19 kJ g−1). From energetic experiments we estimated that an adult penguin consumed 300 kg of food each, of which its chick received
55 kg during the 1992 season. The chicks received large meals at the beginning of winter (1.2 ± 0.3 kg) and during the middle
of the second growth season (1.2 ± 0.3 kg), and their smallest meals in late winter (0.4 ± 0.1 kg). The gross energy required
to rear a king penguin chick was estimated to be 724 MJ. The potential impact of commercial fisheries on the breeding activities
of king penguins is discussed.
Received: 20 October 1997 / Accepted: 27 April 1998 相似文献
9.
Density and biomass of the larvae of a small, alien chironomid midge, Limnophyes minimus, whose parthenogenetic adult females do not feed, were quantified for ten major lowland plant communities at sub-Antarctic
Marion Island (46°52′S 37°51′E) and compared with the density and biomass of indigenous macro-invertebrates in the same communities.
An estimate of litter consumption by larvae of this midge was also made. L. minimus reached high densities in most of the plant communities sampled, with the highest density being recorded in the Cotula plumosa biotically influenced community (annual mean of 4,365 individuals m−2) and the lowest in the Crassula moschata salt spray community (annual mean of 41 individuals m−2). Estimates of litter ingestion indicated that L. minimus larvae are capable of consuming between 0.07 and 8.54 g(dry mass) m−2 per year, depending on the community. In some communities this litter consumption amounted to an order of magnitude more
than that consumed by Pringleophaga marioni (Lepidoptera, Tineidae). Although the larvae of this moth species are thought to represent the bottleneck to nutrient recycling
on the island, this study showed that midge larvae may also contribute substantially to this process. As a consequence, the
considerable changes that have been predicted to occur in Marion Island's terrestrial ecosystem as a consequence of enhanced
predation by mice on P. marioni larvae may be retarded or obscured by the contribution of the midge larvae to nutrient cycling. Hence, it is suggested that
greater attention be given to the small and inconspicuous elements of the alien sub-Antarctic faunas because such species
may have profound consequences for ecosystem functioning on these islands.
Received: 17 November 1997 / Accepted: 23 February 1998 相似文献
10.
Summer plankton beneath the McMurdo Ice Shelf at white Island,McMurdo Sound,Antarctica 总被引:3,自引:3,他引:0
The zooplankton of the under-shelf-ice ecosystem at White Island (78°10′ S, 167°30′ E), McMurdo Sound, Antarctica was investigated during December 1976 and January 1977. The water column was sampled through
a hole in the McMurdo Ice Shelf over a water depth of 67 m. Seawater temperatures under the ice shelf ranged from −1.91 to
1.96°C. Dissolved oxygen levels ranged from 5.0–6.05 ml l-1 in early December to 4.65–4.8 ml l-1 in late January. Current speeds of up to 0.13 m s-1 were recorded at a depth of 50 m and a predominantly northward flow was detected. Light levels under the shelf ice were low
with less than 1% of the incident light being transmitted to a depth of 3 m. No chlorophyll a was detected within the water column throughout the investigation. Mean zooplankton biomass values in the water column ranged
from 12 to 447 mg wet weight m-3 and were similar to values recorded elsewhere from Antarctic inshore waters, but were very much higher than those recorded
from under seasonal sea ice in McMurdo Sound. Thirty-two zooplankton species were recorded including 1 ostracod, 21 copepods
(10 calanoids, 3 cyclopoids and 8 harpacticoids), 4 amphipods, 2 euphausiids, a chaetognath and 3 pteropods. Larvae of polychaetes
and fish were found on some occasions. The species composition in general was similar to that recorded from McMurdo Sound
and other Antarctic inshore localities. Among the Copepoda, however, there were a number of species, especially among the
Harpacticoidea, that have not been found previously in McMurdo Sound and the Ross Sea, but that are known to be associated
with ice in other localities in Antarctica. Two recently described species are known only from White Island. They were present
in the water column but were most abundant in the surface water of the tide crack where they were the most abundant zooplankters.
The tide crack, which probably is an extension of the under-ice habitat, is apparently a significant nursery area for amphipods
and copepod species.
Received: 23 November 1994/Accepted 7 May 1995 相似文献
11.
The carbon-flux via algal bloom events involves bacteria as an important mediator. The present study, carried out during the
spring inter-monsoon month of April 2008 onboard CRV Sagar Manjusha-06 in the Eastern Arabian Sea, addresses the bloom-specific
flow of carbon to bacteria via chromophoric dissolved organic matter (CDOM). Eleven stations monitored were located in the
coastal, shelf and open-ocean areas off Ratnagiri (16°59′N, 73°17′E), Goa (15°30′N, 73°48′E) and Bhatkal (13°58′N, 74°33′E)
coasts. Visible bloom of “saw-dust” color in the Ratnagiri shelf were microscopically examined and the presence of cyanobacteria
Trichodesmium erythraeum and T. thieabautii with cell concentrations as high as 3.05 × 106 trichomes L−1 was recorded. Total bacterial counts (TBC) varied between 94.09 × 108 cells L−1 in the bloom to 1.34 × 108 cells L−1 in the non-bloom area. Chromophoric dissolved organic matter (CDOM) concentrations averaged 2.27 ± 3.02 m−1 (absorption coefficient 325 nm) in the bloom to 0.28 ± 0.07 m−1 in the non-bloom waters respectively. CDOM composition varied from a higher molecular size with lower aromaticity in the
bloom to lower molecular size and increased aromaticity in the non-bloom areas respectively. Strong positive relationship
of TBC with Chlorophyll a (R
2 = 0.65, p < 0.01) and CDOM concentrations (R
2 = 0.8373, p = 0.01) in the bloom area indicated hydrolysis and/or uptake of CDOM by bacteria. Absorption by mycosporine-like amino acid
palythene (λ
max = 360 nm) was recorded in the filtrate of bloom. Morphotypes of Trichodesmium-associated bacteria revealed a higher frequency of Gram-positive rods. The role of bacteria in relation to changing CDOM
nature and as a factor in affecting oxygen content of the water column is discussed in context of the Arabian Sea. 相似文献
12.
A macrozoobenthic community study was conducted in an East Greenlandic fjord (Young Sound, 74°18′N; 20°15′W) during the ice-free
period from July to August in 1996. Grab samples as well as underwater photography were used for quantifying the macrozoobenthos
at water depths between 20 and 85 m. Abundance decreased with depth from 2700 ind. · m−2 at 20 m to 900 ind. · m−2 at 85 m. At a time series station at 35 m, abundance increased from 700 ind. · m−2 in mid-July to 1400 ind. · m−2 in mid-August. Polychaetes dominated in grab samples but bivalves constituted an important part of the benthic fauna, especially
at the shallow part of the depth gradient. Photographs revealed high abundances of large epifaunal species, especially brittle
stars. Diversity was generally high, with around 45 species per 201 individuals, as calculated by Hurlbert's rarefaction term.
A gradual change in community structure with depth was observed, which could be related to variation in sediment composition
and disturbance intensity.
Accepted: 20 May 2000 相似文献
13.
Annual and interannual variability in phytoplankton at a permanent station off Kerguelen Islands, Southern Ocean 总被引:4,自引:4,他引:0
From November 1992 to February 1995 a quantitative and qualitative phytoplankton study was conducted at a permanent station
(Kerfix) southwest off the Kerguelen Islands, in the vicinity of the Polar Front (50°40′S–68°25′E). Phytoplankton populations
are low in this area both during summers and winters. They consist, in order of decreasing cell abundance, of pico- and nanoflagellates
(1.5–20 μm), coccolithophorids (<10 μm), diatoms (5–80 μm) and dinoflagellates (6–60 μm). Flagellates form the dominant group
throughout the year and attain the highest summer average of 3.0 × 105 cells l−1. Next in abundance year-round are coccolithophorids with the dominant Emiliania huxleyi (highest summer 1992 average 1.9 × 105 cells l−1), diatoms (summer 1992 average 1.0 × 105 cells l−1) and dinoflagellates (average 3.8 × 104 cells l−1). Winter mean numbers of flagellates and picoplankton do not exceed 8.4 × 104 cells l−1; those of the three remaining algal groups together attain 2 × 104 cells l−1. Summer peaks of diatoms and dinoflagellates are mainly due to the larger size species (>20 μm). The latter group contributes
most to the total cell carbon biomass throughout the year. Dominant diatoms during summer seasons include: Fragilariopsis kerguelensis, Thalassionema nitzschioides, Chaetoceros dichaeta, C. atlanticus, Pseudonitzschia heimii, and P. barkleyi/lineola. This diatom dominance structure changes from summer to summer with only F. kerguelensis and T. nitzschioides retaining their first and second positions. Any one of the co-dominant species might be absent during some summer period.
The variable diatom community structure may be due to southward meandering of the Polar Front bringing “warmer” species from
the north, and to the mixing of the water masses in this area. The entire community structure characterized both during summer
and winters by the dominance of flagellates can be related to deep mixing (ca. 40–200 m) of the water column as the probable
controlling factor.
Received: 13 November 1997 / Accepted: 11 May 1998 相似文献
14.
Hans Mose Jensen Lorna Pedersen AnnDorte Burmeister Benni Winding Hansen 《Polar Biology》1999,21(5):269-278
The distribution of phytoplankton biomass and primary production were studied during summer 1993 at 16 stations from 65 to
72°N off West Greenland, ranging more than 900 km. Hydrography, nutrients and chlorophyll a profiles revealed a significant change in structure from south to north. Nitrate was depleted in the euphotic zone at most
stations except close to the ice edge (West Ice) or close to outflow from large glaciers. The vertical distribution of phosphate
followed that of nitrate, but was never depleted. Despite two stations with relatively high surface concentrations, silica
showed the same distribution as the other two nutrients. In the south, chlorophyll a concentration and primary production were lower than north of Disko Bay (69°N), associated with a well-mixed versus a salinity-generated
stratification, respectively. In Vaigat, a high-production station was identified, (st. 910, 69°52′69N–51°30′61W) with a chlorophyll a concentration in the euphotic zone of >13 μg l−1 and an area primary production of 3.2 g C m−2 day−1. This is seldom encountered in arctic waters and was presumably due to nutrient-rich melt-water originating from the Iluliíssat
Glacier. The overall primary production for the studied area was 67–3207 mg C m−2 day−1 (mean ± SD=341± 743 mg C m−2 day−1), which is within the range of the few results published for West Greenland and eastern Canadian Arctic waters.
Accepted: 24 October 1998 相似文献
15.
The light-mantled sooty albatross is a medium-sized albatross with a circumpolar distribution in the Southern Ocean. The known
breeding sites are restricted to Islands in sub-Antarctic latitudes close to the Antarctic convergence between 46° and 53°S.
In the austral summer season 2008/2009 we discovered a new breeding colony with at least two confirmed and three probable
nests at Fildes Peninsula, King George Island, South Shetland Islands, Antarctica (62°12′S, 59°01′W). The new breeding colony
of light-mantled sooty albatross described here represents the southernmost breeding place of any albatross species ever recorded. 相似文献
16.
Solute mobilities in cuticular membranes of six species (Hedera helix, Malus domestica, Populus alba, Pyrus communis, Stephanotis floribunda, Strophantus gratus) were measured using plant hormones, growth regulators and other organic model compounds varying in molar volumes from 99
to 349 mL · mol−1 The dependence of mobilities (k*) on molar volume (V
x
) was exponential and could be described with equations of the type log
k*=log
k*0−′
V
x
. The y-intercepts (log
k*0) represent mobilities of a hypothetical solute of zero molar volume. The parameter β′ is a measure of size selectivity of
cuticular membranes and no differences among the six species were observed. At 25 °C the average β′ was 0.0095 mol · mL−1. Solute mobility decreased by about a factor of 8.9 when molar volume increased by 100 mL · mol−1 and the mobility of a compound with V
x
= 100 mL · mol−1 was about 700-fold higher than the mobility of a compound with V
x
= 400 mL · mol−1. Size selectivity decreased with increasing temperatures and for Strophantusβ′-values of 1.6 × 10−2 to 8.0 × 10-4 mol · mL−1 were obtained for 10 and 30 °C, respectively. The-intercepts (log k*0) differed among plant species by 3 orders of magnitude and since size selectivity was the same for all species, solute mobilities
for solutes having zero molar volumes were the sole cause for differences among species in solute mobilities and permeabilities.
We argue that these differences in k*0 are related to tortuosity of the diffusion path. These results were used to derive an equation which predicts rates of cuticular
penetration on the basis of k*0, the average size selectivity of 9.5 × 10−3 mol · mL−1 and the driving forces of penetration.
Received: 25 November 1997 / Accepted: 9 March 1998 相似文献
17.
Hybridisation between South polar skua (C. maccormicki) and Brown skua (C. antarctica lonnbergi) in the area of the Antarctic Peninsula is known at least since the beginning of the last century but no survey has been
done so far. This paper reviews information on the species composition of skua colonies of more than 10 pairs in the Antarctic
Peninsula region, and the incidence of mixed pairs. Morphometrics, population size and breeding success were examined in detail
at King George Island. The northward distribution of South polar skuas extended to King George Island (62°11′ S 59°00′ W),
with a small outlying population on Signy Island (60°45′ S 45°36′ W), whereas Brown skuas did not breed further south than
Anvers Island archipelago (64°46′ S 64°03′ W). The proportion of mixed pairs was highest at the northern end of the ∼500-km-wide
hybrid zone. Body size distribution of sympatric skuas from King George Island is clearly bimodal but overlaps considerably
and hybrids cannot be identified. Skua population sizes at Potter Peninsula/King George Island remained stable between 1994
and 2004. Numbers of mixed breeding pairs fluctuated more strongly than those of pure species pairs. Breeding success of Brown
skuas varied the least. 相似文献
18.
The flea Glaciopsyllus antarcticus is endemic to the Antarctic continent, where it is known to parasitise a number of seabird species. This paper reports the
occurrence of the flea and two species of lice from snow petrel (Pagodroma nivea) colonies in central Dronning Maud Land, Antarctica, and extends considerably the recorded distribution of the flea. Flea
adults, pupae and larvae were recovered from 10 of 11 samples of organic material collected from snow petrel nests at Svarthamaren
(71°53′S, 05°10′E) in the Mühlig-Hofmannfjella. Specimens of two philopterid lice species, Saemundssonia antarctica and Pseudonirmus charcoti, were recovered from three of these samples. Specimens of the Antarctic flea and of the louse S. antarctica were recovered from carcasses of snow petrel chicks collected both at Svarthamaren and Robertskollen (71°28′S, 03°15′W) in the northern Ahlmannryggen; the louse Pseudonirmus charcoti was recovered from Robertskollen only.
Received: 30 January 1996 / Accepted: 28 April 1997 相似文献
19.
During January 1989, phytoplankton biomass and species composition were studied in a north / south transect at the Weddell / Scotia
Confluence (47°W), between 57° and 61°30′S. Results showed a diatom bloom in the Scotia Sea (chlorophyll a 1.9 μg l−1, particulate organic carbon 239 μg l−1), dominated by Fragilariopsis cylindrus, Dactyliosolen antarcticus and Chaetoceros dichaeta. Low chlorophyll a / phaeopigments ratios (about 1.4) and silicate concentrations (15 μmol l−1) suggested that this was an advanced bloom phase, probably linked to high grazing pressure. Minimum chlorophyll a values of 0.1–0.2 μg l−1 and particulate organic carbon 46 μg l−1 were found at the Weddell / Scotia Front and in a subsurface layer of the Weddell Sea Water. In the southern part of the
transect (61°30′S), in the Weddell Sea, a second surface maximum was found (chlorophyll a 0.9 μg l−1, particulate organic carbon 120 μg l−1), but with a different species composition, with Cryptomonas sp. dominant. Our results show a succession within the diatom community in the Weddell / Scotia Confluence Waters when comparing
the three EPOS legs. In the Weddell Sea from spring to summer, nanoflagellates, with only a minor contribution from diatoms,
persist over a long period with little change in the community structure. We suggest that the frontal system, together with
the receding ice edge and the grazing pressure of either krill or protozooplankton, are mainly responsible for the phytoplankton
distribution patterns found.
Received: 3 July 1996 / Accepted: 3 November 1996 相似文献
20.
Sub-Antarctic bottom-dwelling caridean shrimps Nauticaris marionis were collected in April/May between 1984 and 1997 over the shelf region of the Prince Edward Islands (37 °50′E, 46 °45′S).
N. marionis is a partially protandric hermaphrodite. Hatching probably occurs just before April each year, but may persist until May.
During the 1st year N. marionis seem to survive in undetected localities, moult into juveniles, and then settle amongst the benthos from the plankton beginning
probably after November. Diel vertical migration then occurs up to an unknown larger size. The vast majority of juveniles
develop into males, most of which transmutate into females by April/May of their 3rd year. Reproduction can occur before all
male secondary characteristics have been lost. A minority of individuals develop directly into females without passing through
a male phase. Individuals older than 5 years are undetectable using samples of the sizes analysed, but they may well persist
in the population. The von Bertalanffy growth parameters for N. marionis are tentatively identified as k=0.2353/year, L
∞=12.6 mm, t
0=−0.2828 years and WW
∞=2.03 g. Sex-reversal in N. marionis at Marion Island may be affected by the changing environment as sexual differentiation is probably determined during the
planktonic stage.
Accepted: 3 January 2000 相似文献