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The partial pressure of CO 2 (pCO 2 ) and dissolved inorganic carbon (DIC) were monitored in shallow coastal waters located inside and outside giant kelp beds ( Macrocystis pyrifera ) located in the Kerguelen Archipelago (Southern Ocean). Photosynthesis and respiration by microplankton and kelp lead to marked pCO 2 and DIC diel cycles. Daily variations of pCO 2 and DIC are significant in the spring and summer, but absent in the winter, reflecting the seasonal cycle of biological activity in the kelp beds. If the kelp beds seem to favour the onset of phytoplankton blooms, most of the primary production inside the kelp beds is due to the kelp itself. The primary production of Macrocystis kelp beds in the Sub-Antarctic high-nutrient, low-chlorophyll (HNLC) waters off the Kerguelen Archipelago is elevated and closely linked to light availability. This production is significant from October to March and reaches its climax in December at the solar radiation maximum. more...

A short overview of the biodiversity of Antarctic marine bacteria is given with respect to morphology and metabolic activity. The importance of spatial and temporal variability is described. The physiological adaptation and ecological function of Antarctic marine bacterioplankton are discussed. more...

The distributions of phytoplankton biomass and bacterial populations were investigated at 37 statlons on the continental shelf of Terre Adelie (Antarctica) during Austral summer 1989. Despite a potentially favourable environment, phytoplankton biomass was relatively low. Surface chlorophyll a values ranged from 1.2 mg m-3 in the coastal area, with a maximum of 2.5 mg m-3 in the vicinity of the penguin rookeries, to only 0.2 mg m-3 70 km offshore. In the Pointe Geologie Archipelago, diatoms larger than 10 pm were predominant and represented more than 80 'h, of the total biomass. In offshore waters, these large cells represented only 38 % of the total biomass with 59 % of the biomass in the 1 to 10 fraction. Total bacterial abundance ranged from 9 4 X 10' to 1.0 x 10" cells m-3 and heterotrophic bacteria ranged from 1.4 x 106 to 7.7 X 10' colony forming units m-' Frequency of dividing cells ranged from 0.8 to 6.6 %. The highest numbers of heterotrophic bacteria were recorded in the immediate vicinity of penguin rookeries and the lowest in offshore waters. Bacterial biomass represents between 2 to 15 % of total microbial biomass in offshore waters and up to 30 O/ O in the coastal area. There was no direct correlation between bacterial and phytoplanktonic standing stocks. This lack of relationship can be explained by considering the differences in scale. It is suggested that in the coastal area where large diatoms are dominant, the bacteria are mainly dependant on organic matter introduced by bird manuring. On the other hand, in offshore waters where the dominant phytoplankton fraction under 10 pm represents a large part of the microbial loop, an indirect relationship between algae and bacteria may be expected. more...

Observations of the short-term changes of seawater bacterioplankton were carried out during the summer of 1988 in Antarctic coastal surface waters. The studies were designed to compare the variations of bacterioplankton in freemoving and enclosed seawater. Even when a diurnal cycle is present the data collected from the enclosed seawater experiments remain much more constant than the corresponding data in free-moving seawater. The wide range of parameters used in the two experiments reveals common properties which illustrate the major role of displacements of water masses at a fixed sampling station in the temporal changes observed in free-moving Antarctic coastal seawater. more...

The short-term effects of giant kelp Macrocystis pyrifera C.A. Agardh on the growth of subantarctic bacterial microflora were followed under various seasonal conditions in coastal seawater of the Kerguelen Archipelago. Artificial degradation experiments were carried out in 3-m 3 tanks (daily sampling allowed a regular survey of bacterial changes in the supplemented seawater). The results clearly revealed a significant response of the subantarctic bacterial community to macrophyte addition. Bacteria grew rapidly on freshly harvested or stranded kelp. Doubling time had a mean value of 40 h for total bacteria and 8 h for heterotrophic bacteria. Bacterial growth peaked within the first 3–5 days but declined thereafter. Both total and heterotrophic bacterial increases were higher in stranded or detritic kelp experiments than in freshly harvested kelp experiments. The amphipod Parathemisto gaudichaudii Guerin was used to assess the stimulating effect of macrofaunal breakdown on the bacterial decomposition of the kelp. more...

The short term degradation of ‘Arabian light’ crude oil was followed under various seasonal conditions in coastal seawater at Iles Kerguelen. Artificial degradation experiments were carried out in 3 m3 tanks. In situ experiments were conducted in free-floating, semi-enclosed chambers permitting direct contact between the crude oil and the marine environment. Daily sampling allowed a regular survey of the bacterial changes of the oil contaminated seawater. All samples were analysed for total bacteria, heterotrophic viable microflora and hydrocarbon utilizing microflora. At the end of experiments, the remaining oil was carefully collected for rough quantitative estimation of hydrocarbon degradation. All the results clearly revealed a significant increase in the three types of bacterial microflora after the addition of crude oil. However, the data suggest that the initial state of the bacterial communities is important. Thus, the seasonal variations in the bacterial responses to hydrocarbon addition can be related to the differences in the natural bacterial populations involved. In all cases the wall effects observed in batch systems were reduced with in situ incubations. more...

Untreated sewage has been released from Port-aux Francais station, Kerguelen Island, into the Southern Ocean for more than 50 years. We investigated the spatial distribution of faecal bacteria indicators during a one-year survey conducted in seawater off Morbihan Bay near the French permanent station of the Kerguelen Island (4921 0 S, 7030 0 E). Seawater samples were taken bimonthly from nine stations evenly distributed around the sewage outfalls of the station. Escherichia coli and enterococci were estimated using specific microplates (Miniaturized method for the enumeration of E. coli or enterococci in surface and waste waters, ‘‘MU/EC or MU/SF methods’’, BIO-RAD). In order to evaluate the role of seasonal changes of environmental parameters on the survival of enteric bacteria, total and saprophytic bacterial abundances were also estimated in all seawater samples. High densities of faecal bacteria (maximum 10 4 cells 100 ml � 1 ) were found in seawater surrounding the sewage outfall. However, enteric bacterial counts decreased rapidly with increasing distance from the outfall. In all samples collected further than 2 km from the outfall, the bacterial indicators were absent or present in small numbers ( more...

In the last few years, increased attention has been focused on enzymes produced by cold-adapted micro-organisms. It has emerged that psychrophilic enzymes represent an extremely powerful tool in both protein folding investigations and for biotechnological purposes. Such enzymes are characterised by an increased thermosensitivity and, most of them, by a higher catalytic efficiency at low and moderate temperatures, when compared to their mesophilic counterparts. The high thermosensitivity probably originates from an increased flexibility of either a selected area of the molecular edifice or the overall protein structure, providing enhanced abilities to undergo conformational changes during catalysis at low temperatures. Structure modelling and recent crystallographic data have allowed to elucidate the structural parameters that could be involved in this higher resilience. It was demonstrated that each psychrophilic enzyme adopts its own adaptive strategy. It appears, moreover, that there is a continuum in the strategy of protein adaptation to temperature, as the previously mentioned structural parameters are implicated in the stability of thermophilic proteins. Additional 3D crystal structures, site-directed and random mutagenesis experiments should now be undertaken to further investigate the stability-flexibility-activity relationship. more...

During a 1-year period, systematic observations of the Antarctic coastal marine bacterioplankton were recorded. Three field stations were sampled weekly in 1989 in “Terre Adelie” area. The survey included physicochemical (temperature and particulate organic matter) and bacteriological (total and heterotrophic counts, estimation of bacterial production) measurements. The bacterial community structure was investigated by carrying out 27 morphological and biochemical tests on 254 strains isolated during each season. Gram-negative non-fermentative rods were always dominant. However, an obvious difference exists between the communities inhabiting ice-free and ice-covered seawater. The potential metabolic abilities which were relatively significant in the summer community were severely reduced in the winter community. A general increase in bacterial biomass and production was observed in surface water after sea ice formation. The results suggest a close coupling between heterotrophic bacterioplankton and the input of allochthonous organic carbon, for example from the overlying sea-ice communities or from nearby penguin rookeries. more...

Previous Antarctic studies have pointed out the ecological importance of ornithogenic soils. However, few data exist to determine the impact of the bird's manuring on surrounding seawater microbial populations. In order to evaluate the influence of birds manuring, the relationships between the spatial distributions of seawater bacterial microflora and some related biological (chlorophyll pigments) and physicochemical (seston, NH4 + & NO3 −) parameters were studied during the Antarctic summer 1988 in the Terre Adelie land area. The clearly decreasing gradient from the shore towards the open sea previously reported for bacterial microflora (from 104 to 1 CFU ml−1 for heterotrophic bacteria and from 105 to 5.0103 cells ml−1 for total bacteria) was also observed for organic and mineral nutrients (from 1.09 mg Cl−1 to 0.1 mg Cl−1 for POC and from 196 to 17 μmole l−1 for NH 4 + ) but not for chlorophyll pigments. The absence of any observable phytoplankton enrichment in the coastal area suggests a direct interaction between the birds manuring and the bacterial seawater microflora. more...

The authors investigated the development of the harpacticoid copepod population in relation to the variations in organic matter and meteorology. Sediment sampling was performed over a 2-year period in the shallow waters (3 m deep) of Banyuls Bay (Western Mediterranean). Each year presents two distinct periods: winter to early spring, and from late spring until fall. During the first period of the annual cycle, the organic carbon and nitrogen cycles are fairly dissociated; the quantity of copepods appears to be dependent upon the climatic and physical conditions. During the second period, the climatic conditions are very similar from year to year, without heavy rains or strong storms, and the values observed both for the organic matter and the copepod population are also similar. The hypothesis is proposed that organic matter can be considered a limiting factor to population increase. more...

One major difficulty in the interpretation of short-term variations in bacterioplankton is that variability in time is closely entwined with variability in space. In order to clarify this problem, two series of investigations were carried out in Antarctic and subAntarctic coastal surface waters during the summer of 1986. Each series included temporal (on hourly and daily scales) and spatial surveys, using standard parameters such as total and viable counts, and estimations of the frequency of dividing cells. Our results showed spectacular gradients in bacterial concentrations. To explain the observed decreases from the shore to the open sea, we suggest a relation with: (1) the degradation processes of macrophytes in the subAntarctic area, and (2) the presence of penguin faeces in the Antarctic area. These organic matter sources appear responsible for the formation of bacterial patches along the gradients. Storm-induced modifications of the spatial distribution of bacterioplankton appeared sufficient to explain the hourly changes in bacterial concentrations; this fact was confirmed by measurements of some nutrient parameters (POC, pigment, seston). On daily scales, other phenomena, probably linked to trophic food chains ( e.g. bacterial growth, grazing), must be considered to explain the bacterioplankton changes. more...

Previous antarctic studies have pointed out the ecological importance of ornithogenic soils. However, few data exist to determine the impact of such guanoenriched soils on surrounding seawater microbial populations. In order to evaluate the influence of birds, the relationships of spatial distribution of seawater bacterial microflora to penguin repartition were studied during the antarctic summer 1986 in Terre Adelie land area and in January 1984 in the subantarctic Kerguelen Archipelago. With bacterial estimates as high as 1.7×108 cells ml-1 for total counts and 2.3×107 CFU ml-1 for aerobic heterotrophic populations, ornithogenic soil analyses confirmed previous results from similar sites. In seawater a clear decreasing gradient from the shore towards the open sea was found. All bacterial parameters studied (epifluorescence direct counts, frequency of dividing cells estimation and viable counts) were correlated significantly with penguin populations. Complementary numerical taxonomy confirmed the major role played by the bird manuring in such antarctic ecosystems. more...

A large mussel bed occurs in one of the largest fjords in Kerguelen archipelago. In January 1986, seawater and bivalves were collected at four tidal levels to determine whether a specific heterotrophic bacterial community could be observed in the mussels, especially in the stomach and in the fecal pellets, and to compare these microflora to seawater bacterial communities. The investigation was carried out using morphological and biochemical tests. Test results were analysed by a numerical taxonomic method. Almost all the heterotrophic mesophile isolates, grown on Zobell medium, were non-fermentative Gram-negative rods. The bacterial communities in the mussel fecal pellets were clearly different from the other communities studied. This specific bacterial microflora was characterized by the existence of Vibrionaceae. more...

The abundances of the heterotrophic bacteria in relation to the degradation of the stranded kelp bed of Macrocystis pyrifera of the Morbihan Bay (Kerguelen Archipelago) were studied. During a one year period between the austral autumns 1982 and 1983 systematic observations of viable and direct counts of bacteria were recorded for three stations along a transect including kelp bed, intertidal and offshore waters. Quantitatively the microflora was very similar to that found in more temperate regions. Seasonal fluctuations were correlated with successive periods of deposit and degradation of the stranded kelp debris. After each new deposit, a very fast growing phase of the microbial population were observed. Doubling time (approximately 1.5 days) and biovolumes of the total bacteria showed rapid increases (from 0.16 to 0.38 μm3). At the same time the ratio direct counts/viable counts showed a significant decrease and reached values close to 1. Decreasing number of bacteria were observed along the transect studied but the impact of kelp deposits on bacterial growth reached also offshore waters. more...

High densities (56000–146000 individuals m2) of Allotanais hirsutus were observed in the intertidal zone of Morbihand Bay at Kerguelen Island. A new method, involving 14C-labelled tracers, was used in a preliminary in situ investigations of the ingestion of bacteria by A. hirsutus. Feeding activity appeared to be influenced by the tide, being higher during retreating and rising tides than during the slack. The average rate of total bacterial carbon incorporated by A. hirsutus was 12.8 × 10−3 µg C µg individual (dw−1) h−1, indicating that bacteria could contribute significantly to the diet of the dense population of A. hirsutus. more...