Trace elements in tissues of white-chinned petrels (Procellaria aequinoctialis) from Kerguelen waters,Southern Indian Ocean

The use of seabirds to assess marine contamination by trace elements in areas remote from pollutant emission points has already been done at various latitudes. Nevertheless, little information is available concerning the Southern Indian Ocean. Determining the contaminants levels, there appears necessary not only due to several deleterious effects reported in literature, but also as previous studies have highlighted elevated concentrations of cadmium (Cd) and mercury (Hg) in mollusks, crustaceans and fish. Within this context, the white-chinned petrel appears as a key species due to its lifespan, diet and trophic position. Thirty-three accidentally killed (collision with lights/bycatch in longline vessels) individuals collected in Kerguelen waters were analysed for Cd, copper (Cu), Hg, selenium (Se) and zinc (Zn) in liver, kidney, pectoral muscle, feathers and for mature males, testis. Elevated Hg concentrations (average 58.4 μg g^?1 dw in liver) are likely due to the presence of mesopelagic prey in the diet of Procellaria aequinoctialis. Cd concentrations (average of 65.7 μg g^?1 dw in kidney) can be attributed to a high level of fisheries offal consumption, as well as crustacean and squid ingestion. Correlation of Hg with Se indicates its detoxification by co-precipitation, and correlation of Cd with Zn suggests its displacement by Cd on metallothioneins binding sites. This work also indirectly confirms ecological data (range and diet composition) from the wintering period of the species, which is rather scarce. Seasonal diet change and moulting accounted more for the obtained results than sex of the birds.     

Population dynamics of Themisto gaudichaudii in Kerguelen Islands waters, Southern Indian Ocean

Fieldwork was carried out at Kerguelen Islands. Two groups of stations in a coastal area, the Morbihan gulf, were surveyed. At both stations, macroplankton biomass ranged from 2.3 mg dry weight m⁻³ to 89 mg dry weight m⁻³ and consisted mostly of Themisto gaudichaudii with values ranging from 1.9 mg dry weight m⁻³ to 50.6 mg dry weight m⁻³. Biomass was high for sub-Antarctic waters with marked seasonal and inter-zone differences. Biomass minima were observed at the end of the winter, from September to November, while maxima were recorded in summer and in early fall at the beginning of the year between January and April. T. gaudichaudii showed a recruitment of new size classes, mainly from November to January, followed by a rapid growth phase in summer, which slowed down during the southern winter period. Individuals breed after 1 year. Large individuals, older than 1 year, were not a significant presence in the gulf of Morbihan. The main pattern of the population dynamics were characterised by an univoltine life cycle with a very high biomass marked by a strong seasonal signal linked with the hydrological and trophic parameters of the Gulf.     

Influence of the diet on the bioaccumulation of heavy metals in zooplankton-eating petrels at Kerguelen archipelago,Southern Indian Ocean

Concentrations of cadmium, mercury, copper and zinc were measured in muscle, kidney and liver tissues and in the main prey of five species of zooplankton-eating petrels: blue petrel (Halobaena caerulea), thin-billed (Pachyptila belcheri) and Antarctic (P. desolata) prions, and South Georgian (Pelecanoides georgicus) and common (Pelecanoides urinatrix) diving petrels. Since some of these species are closely related species with respect to body size, timing of moult and life span, their diet has been examined to evaluate its influence on heavy-metal bioaccumulation. Inter-specific differences were significant for Hg concentrations in the liver and for Zn concentrations in both liver and kidney tissues. Blue petrels exhibited the highest Hg concentrations in the liver (3.9±2.02 µg.g^–1 wet weight). No significant differences were found in Cd concentrations between species. Exposure to heavy metals through the most important prey species in the diet during the breeding period was evaluated. The most evident result was the influence of fish prey on Hg levels. Although crustacean species exhibit different cadmium concentrations, the diet composition does not appear to be discriminant for Cd bioaccumulation within the small petrel community at Kerguelen.     

Day and night mesopelagic fish assemblages off the Kerguelen Islands (Southern Ocean)

Mesopelagic fish assemblages were investigated in the Polar Frontal Zone off the Kerguelen Islands during summer 1995, in parallel with a king penguin tracking study. During the day, the upper offshore water layers (0–200 m) have low potential prey diversity and abundance with only three fish species: a lanternfish, Krefftichthys anderssoni, a member of the Muraenolepididae, Muraenolepis marmoratus, and the early stages of the nototheniid, Lepidonotothen squamifrons. The mesopelagic fish community, including the typical myctophids, first appears in the deeper layer (300 m). At night, the surface layer (50 m) is invaded by the mesopelagic Myctophidae Electrona antarctica, Gymnoscopelus braueri, G. piabilis, G. fraseri, G. nicholsi, Protomyctophum bolini and P. tenisoni. Deeper (>100 m), a cline of species assemblages from the coast to offshore is observed. Accepted: 4 August 1999     

The reproductive biology of Euchaeta antarctica Giesbrecht (Copepoda: Calanoida) at South Georgia

The reproductive biology of the predatory calanoid copepod Euchaeta antarctica Giesbrecht was investigated in two interconnected fjord systems at South Georgia. Counts of the number of spermatophores attached to adult females and the number of egg sacs encountered, indicated probable peaks of reproduction in summer and winter. Patterns of spermatophore placement were examined and compared with data for E. norvegica (Boeck) from boreal waters. Elemental analysis indicated a high proportion of carbon and a low proportion of nitrogen in adult females and egg sacs from both sites.High winter carbon levels in adults seem related to their predatory feeding habits allowing high food intake throughout the year whereas in egg sacs it probably reflects extended development times and/or non-feeding naupliar stages.Mean adult female and egg clutch dry weights were higher in Cumberland East Bay during winter than in Moraine Fjord during summer. These differences are discussed in the context of relationships between fjord morphology and production levels.     

Feeding and diel vertical migration cycles of Metridia gerlachei (Giesbrecht) in coastal waters of the Antarctic Peninsula

Diel vertical migration and feeding cycles of adult female Metridia gerlachei in the upper 290 m of a 335-m water column were measured during a total of 65 h in two periods of early summer (Dec 20–21 and Dec 25–26, 1991). Samples collected in eight depth strata by 35 MOCNESS tows (333-m mesh) were analyzed for abundance and mean individual gut pigment content. Most of the copepod population was concentrated in a 50-m depth interval at all times. Feeding began simultaneously with nocturnal ascent from a depth of 200–250 m at 18:00 h (local time), when the relative change in ambient light intensity was greatest. Ingestion rate increased exponentially (k_i = 0.988 h^–1) at double the gut evacuation rate (k_e = 0.488 h^–1) as the population moved upward at 22.3–26.5 m h^–1 through increasing concentrations of particulate chlorophyll-a. Although the bulk of the population did not move to depths shallower than 50 m, and began its downward migration at a rate of 20.8–31.7 mh^–1 in complete darkness, individual females continued to make brief excursions into chlorophyll-rich surface waters (4–8 g l^–1) during the first few hours of population descent. Ingestion rate diminished abruptly by one order of magnitude (k_i = 0.068 h^–1) at dawn ( 0330 h). Within four more hours, the population had reached its daytime depth and gut pigment content remained constant at a minimum value until the next migration cycle. No feeding appeared to take place at depth during the day. Ingestion by M. gerlachei females removed < 4% of daily primary production, with only 20% of this amount being removed from surface waters by active vertical transport.     

Annual and interannual variability in phytoplankton at a permanent station off Kerguelen Islands, Southern Ocean

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     

The complete history of salmonid introductions in the Kerguelen Islands, Southern Ocean

Since the early 1950s, several species of salmonids have been introduced more or less successfully in the Kerguelen Islands, a 7,215 km² archipelago located in the Southern Ocean (49°S, 70°E) and previously devoid of any freshwater fish. The aim of this work was to establish a documented chronicle of these events from available archives, to better understand the causes of the colonization failure or success for the different species. The history that emerged from the analysis of the archives appeared much more complex than previously published. Stocks of various origins were used, and numerous attempts were made at different sites involving variable numbers of fish released at different life stages. Between 1951 and 1991, 22 importation attempts took place, involving about 2 million individuals. Of the 8 species introduced (Salmo trutta, S. salar, Oncorhynchus mykiss, O. tshawytscha, O. kisutch, Salvelinus namaycush, S. fontinalis and S. alpinus), only 3 failed to establish local populations (O. mykiss, O. tshawytscha and S. namaycush). Overall, 23 watersheds were stocked. At present, 45 watersheds are colonized by one or several species. S. trutta, S. fontinalis, S. alpinus and O. kisutch were capable of migrating toward new habitats. The brown trout (S. trutta) was the only species to colonize a large number of watersheds (32 in about 10 generations). Its success can be explained by the diversity of origins, the number and importance of introduction and transfer attempts, the diversity of release sites and the peculiarities of its life cycle.     

Optical fractionation of chlorophyll and primary production for coastal waters of the Southern Ocean

Our objective was to quantify the potential variability in remotely sensed chlorophyll a (Chl a) and primary productivity in coastal waters of the Southern Ocean. From data collected throughout the springs/summers of 1991–1994, we calculated the proportion of water column Chl a and primary productivity within the upper optical attenuation length (K ⁻¹ _par) and the satellite-weighted depth. The temporal variability was resolved every 2–3 days and was observed to be greater within years than between years. Three-year averages (n=223) revealed that 10.2 ± 3.6% of total Chl a and 14.8 ± 6.5% of production occurred within satellite-weighted depth in predominantly Case I waters. The average values were twice as high within K ⁻¹ _par, 24.1 ± 8% of total Chl a and 34 ± 9% of production respectively. Masked in these long-term averages are very large changes occurring on short time scales of seasonal blooms. We observed that the patterns of Chl a vertical distribution within blooms are also subject to taxonomic influence and dependent upon the physiological state of the phytoplankton. Highest proportions of water column Chl a in the first optical depth were measured during the rapid onset of surface cryptophyte blooms each year, i.e. 50% within K ⁻¹ _par and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% of biomass within K ⁻¹ _par and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyses suggest that satellite-dependent models of Chl a and subsequent chlorophyll-dependent primary production will be challenging to develop for the near-shore Southern Ocean, especially given the potentially high natural variability in the vertical distribution of Chl a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences. Accepted: 27 August 1999     

Morphological Characteristics of Sailfish Pike Channichthys velifer (Channichthyidae) from the Kerguelen Islands (Southern Ocean)

Journal of Ichthyology - Based on a representative sample set (41 specimens), features of external morphology, seismosensory system, and axial skeleton of the sailfish pike Channichthys velifer...     

Distribution of surface zooplankton and seabirds across the Southern Ocean

Surface zooplankton and seabird densities and community composition in the Atlantic (between Cape Town and Sanae) and Pacific (between New Zealand and the Ross Sea) sectors of the Southern Ocean are described and related to oceanographic features. Samples were collected during two return voyages aboard the MV Benjamin Bowring as part of the Transglobe Expedition (1979–1981). High abundances of surface zooplankton and seabirds were consistently observed within the main frontal systems of the Southern Ocean. Generally, on a mesoscale significant correlations between surface temperature and the distribution of zooplankton or seabirds were observed. On a macroscale, the geographical positions of the zooplankton and seabird communities coincided with specific water masses. The results of this study suggest that appropriate food availability rather than water temperature is important for the determination of seabird distribution. The ecological importance of the recently described frontal zone associated with the northern boundary of the maximum winter expansion of sea ice is confirmed by biological data obtained in this study.     

Inter-annual variability in the breeding performance of seabirds in relation to oceanographic anomalies that affect the Crozet and the Kerguelen sectors of the Southern Ocean

Global warming is expected to increase the frequency and intensity of inter-annual variation in Sea-Surface Temperatures (SST) associated with a latitudinal shift of frontal structures in the Southern Ocean. However, the long-term consequences of these major climatic events on the biotic environment remain poorly understood. We studied the effect of SST anomalies in the southern Indian Ocean on the breeding success of eight seabird species, and found these temperature anomalies to have different effects depending on the foraging habitat of the species. The breeding success of four seabird species foraging mainly south of the Polar Front in Antarctic waters was significantly depressed by warm SST occurring mainly in winter and spring, prior to breeding. Conversely, warm SST anomalies were associated with a higher breeding success for species foraging mainly north of the Polar Front, while no significant effect was found for two species that forage on the Kerguelen plateau. These different responses to changes in the SST were also observed for two closely related species (sooty albatross Phoebetria fusca and light-mantled sooty albatross P. palpebrata ) breeding at Kerguelen. These observations highlight the importance of multi-species long-term monitoring programs for understanding the ecological consequences of environmental variability. Our results suggest that the predicted southward shift of the Polar Front caused by oceanic warming could lead to an important decrease in the breeding performance of top predator seabirds depending on the location and changes of their foraging habitat in relation the Polar Front.     

Spatio-temporal distribution of mesozooplankton in a sub-Antarctic coastal basin of the Kerguelen Archipelago (southern Indian Ocean)

Seventeen surveys were performed fortnightly from January to December 1990 and covered a grid of 16 stations in the large Morbihan Bay at Kerguelen Island. Temperature and salinity were measured at four or five standard depths. Chlorophyll, carbon and nitrogen contents of surface water particulate matter were determined along with mesozooplanktonic biomass and abundance of copepods. The dominant species (90%) of mesozooplankton wasDrepanopus pectinatus, and two other taxa,Oithona spp. andCalanus simillimus, accounted for 8.6 and 0.4% respectively. A Multiple Correspondence Analysis was used to determine the influence of abiotic (temperature and salinity) and biotic factors (potential food supply) on the spatio-temporal distribution of copepods and, more specifically, on that of the growth stages ofD. pectinatus. No specific hydrological features were found. The distribution of copepods was fairly homogeneous in the whole bay while the quantitative changes were influenced by the seasonal rhythm. Only a slight trend of increasing values for the biotic or abiotic parameters and the neriticD. pectinatus was observed from the central to the inner back area of the bay.     

Cadmium, copper and zinc in octopuses from Kerguelen Islands, Southern Indian Ocean

 Concentrations of cadmium, copper and zinc were measured in 34 octopuses over a large range of size and weight, caught in the Kerguelen shelf waters. Compared with levels normally encountered in European cephalopods, Cd concentrations in both species were very high: 30.7–47.1 and 27.3–54.4 μg/g dry weight in Graneledone sp. and Benthoctopus thielei, respectively; Cu concentrations were generally low while Zn concentrations exhibited similar levels. Distribution of Cd in tissues showed that the high levels of Cd in Kerguelen octopuses resulted from very high levels of the metal in the digestive gland (369 and 215 μg/g dry wt in Graneledone sp. and Benthoctopus thielei, respectively). The digestive gland accumulated about 90% of the total Cd in the whole animal. Due to the very high concentrations of Cd in the Kerguelen octopuses, we hypothesize that these species play an important role in the process of Cd transfer throughout the food chain to top vertebrate predators in this area. Received: 2 June 1997 / Accepted: 30 October 1997     

Surface-water cooling and salinity decrease during the Middle Miocene climate transition at Southern Ocean ODP Site 747 (Kerguelen Plateau)

Paleoceanographic variability at southern high latitude Ocean Drilling Program (ODP) Site 747 was investigated in this study through the interval which spans the Middle Miocene Climate Transition (MMCT). Between 15.0 and 12.2 million years ago (Ma), foraminiferal δ¹⁸O records derived from both benthic (Cibicidoides spp.) and planktonic taxa (Globorotalia praescitula and Globigerina bulloides) reveal a history of changes in water column thermal and salinity structure and a strong imprint of seasonality. Prior to the MMCT, in the interval between 14.35 and 13.9 Ma, G. bulloides displays relatively high δ¹⁸O values similar to those of G. praescitula, interpreted to indicate weakening of the thermocline and/or increased seasonality with cooler early-spring and/or late-fall temperatures. Following this interval, G. bulloides δ¹⁸O values diverge significantly from benthic and G. praescitula values, with G. bulloides values remaining relatively low for at least 600 kyr following the benthic foraminiferal δ¹⁸O shift during the MMCT at ~ 13.9 Ma. This divergence in δ¹⁸O records occurs in direct association with the Mi3 cooling and glaciation event and may suggest: (1) a strengthening of the vertical temperature gradient, with greater cooling of deep waters than surface waters, (2) changes in the depth habitat of G. bulloides, (3) changes in the dominant season of G. bulloides calcification, (4) modification of surface-water δ¹⁸O values in association with enhanced sea-ice formation, (5) increased surface-water carbonate ion concentration, and/or (6) a significant decrease in surface-water salinity across the MMCT. The first of these possible scenarios is not likely, particularly in light of recent Mg/Ca evidence for significant surface-water cooling in the Southern Ocean associated with the MMCT. Of the remaining possibilities, we favor a change in surface salinity to explain the observed trends in δ¹⁸O values and hypothesize that surface salinity may have decreased by up to 2 salinity units at ~ 13.9 Ma. In this scenario, the development of a lower-salinity Antarctic surface layer coincided with regional cooling of both surface and deep waters of the Southern Ocean during the Mi3 glaciation of East Antarctica, and contributed into the dominance of Neogloboquadrina spp. between 13.8 and 13.2 Ma. Additionally, the distinct patterns observed in planktonic foraminiferal δ¹⁸O records spanning the MMCT correspond with changes in the vertical δ¹³C gradient between planktonic and benthic foraminiferal records and major changes in planktonic foraminiferal assemblages at Site 747, providing further evidence of the environmental significance of this climatic transition.     

Physical-biological coupling in the waters surrounding the Prince Edward Islands (Southern Ocean)

The results of a macro-scale oceanographic survey conducted in the upstream and downstream regions of the Prince Edward Islands in austral autumn (April/May) 1989 are presented. During the investigation, the Subantarctic Front, upstream of the islands, was shown to lie initially south at 46°38′S, while downstream, the front remained in a northern position of approximately 46°S. Surface expressions of the front show that the Subantarctic Front forms a zonal band, while the subsurface expressions (200 m) show a distinct meander in both regions. In the upstream region of the islands, the northern branch of the Antarctic Circumpolar Current, the Subantarctic Front, influenced by the shallow bathymetry, was deflected around the northern edge of the islands. Water masses in this region were shown to modify gradually from Subantarctic Surface Water (7°C, 33.75) to Antarctic Surface Water (5°C, 33.70) as the Polar Frontal Zone was crossed. Downstream of the islands a wake was formed resulting in the generation of broad, cross-frontal meanders. As a consequence, warm Subantarctic Surface Water from north of the Subantarctic Front was advected southwards across the Polar Frontal Zone, while cooler waters, which had been modified in the transitional band of the Polar Frontal Zone, were advected northwards. In the downstream region a warm eddy consisting of Subantarctic Surface Water was observed. Its generation is possibly due to baroclinic instabilities in the meandering wake. Zooplankton species composition and distribution patterns during the investigation were consistent with the prevailing oceanographic regime. Four distinct groupings of stations were identified by numerical analysis. These corresponded to stations found north of the Subantarctic Front, within the warm eddy, located in the Polar Frontal Zone, and those stations associated with the meander. The groupings were separated by the Subantarctic Front, which appears to represent an important biogeographic boundary to the distribution of warm-water zooplankton species. Warm eddies in the downstream region of the islands may represent an effective mechanism for transporting warm water species across the Subantarctic Front. Accepted: 19 August 1998