(southwest Indian Ocean)

-

28

Results and Discussion

Levels of "available" Pin the island peats are low, generally<

3 J.tg g-¹ wet weight (Smith & Steyn 1982) and the concentra- tion added here represents a considerable fortification, up to levels found at areas manured by animals and showing enhanced plant vitality (Smith 1979b) and soil bacterial counts (Steyn & Smith 1981). Endogenous concentrations of Mo and Co are unknown; the amounts added in the investigation were within the range of those found by Alexander et al. (1978) to stimulate N fixation in Peltigera aphthosa.

None of the nutrient additions altered the pH (4.9-5.0) of the peat slurry. Endogenous ~H4 production did not occur for any of the peat subsamples. Fortification with P, Co or Mo, either separately or together, did not significantly (P ~ 0.05) enhance AR rates above those exhibited by the unamended peat subsamples (Fig. 1). Addition of glucose marked.ly stimu- lated AR. The addition of inorganic nutrients in combination with glucose appeared to cause a greater increase in nitrogenase activity than the addition of glucose alone;

however, the differences were not significant at P ~ 0.05.

A stimulation of AR (at 22oC) by glucose was also found for mesic meadow peats at Devon Island (75"N; Canadian high- Arctic); in the absence of glucose the peat samples failed to show evidence for N fixation (Jordan et al. 1978).

Contrary to the results of previous laboratory incubations (Smith 1984) unamended peat samples from the oligotrophic mire at Marion Island exhibited detectable, although low (0.5 nmol C2H2 g-• h-¹) AR rates. This may be due to the longer (12 rather than 3 h) incubation times employed in the study reported on here. However. glucose-fortified subsamples exhibited much lower (20-27 nmol C2H2 g-¹ h-¹⁾ reduction rates compared with those (404-932 nmol g-¹ h-¹) estimated previously on glucose-fortified samples from the same mire (Smith 1984).

The results suggest that heterotrophic bacteria potentially able to fix N are present in the mire peat. However, because of a lack of readily utilisable energy sources, fixation rates are very low. This agrees with the observation that bacterial growth in the island peats is primarily limited by the availa- bility of energy-rich substrates (Lindeboom 1979). Once the energy-substrate limitation to nitrogenase activity has been relieved, inorganic nutrients may have a secondary limiting

:;-

..c 40

':' 30

Ol

0 E c 20

-

^c ₀

u

_::l

u Q.)

:£ ^{2 f}

<5 1 t

0 Nil P Co Mo G P ---pcoPG G G G G G G Co Mo Mo Co P Co Mo Co P P P

Mo MoCoMoCo

Nutrient (s) added Mo

Fig. 1. Acetylene reduction by peat samples with and without added nutrients. Vertical lines in each bar indicate± 1 standard deviation of the mean (N=4). Note change of ordinate scale.

S. Afr. T. Nav. Antarkt., Deel 14, 1984 role but this could not be unequivocally demonstrated in this study. Low temperatures might be expected to further reduce nitrogenase activity, since field temperatures for most of the year are very much lower than that (20°C) employed in the laboratory incubations.

N fixation by methane-oxidizing bacteria cannot be detected by the AR assay procedure. C~ formation may have occurred under the anaerobic conditions imposed in this study but its subsequent utilisation would be strongly inhibited by the same conditions and by the presence of C₂H_2. Nothing b known regarding the role of methanc-oxidiz'!rs in the N cycle of sub- Antarctic terrestrial ecosystems; however, it is unlikely that either methane formation or oxidation are important meta- bolic pathways in the aerobic surface layer& of the oligo- trophic mire peats at Marion lsland.

Photo-autotrophic N fixation (especially by moss-cyanobac- teria associations; Smith and Russel 1982) is probably more important than heterotrophic fixation at Marion Island; in this respect the island ecosystem is similar to Arctic and sub-Arctic regions, where heterotrophic fixation is not generally regarded as an important source of reduced N (Alexander 1974; Jordan et al. 1978).

Acknowledgements

This investigation was sponsored by the South African Department of Transport.

References

ALEXANDER, V. 1974. A synthesis of the ffiP Tundra Biome circumpolar study of nitrogen fixation. In: Soil Organisms and Decomposition in Tundra, eds. A.J. Holding, O.W. Heal & S.F.

Aanagan. Tundra Biome Steering Committee, Stockholm, pp 109- 121.

ALEXANDER, V., BILUNGTON, M. & SCHELL, O.M. 1978.

Nitrogen fixation in Arctic and alpine tundra. In: Vegetation and Production Ecology of an Alaskan Arctic Tundra, ed. L.L. Tieszen.

Ecological Studies 29, Springer Verlag, pp 539-558.

JORDAN, D.C., McNICOL, P.J. & MARSHALL, M.R. 1978.

Biological nitrogen fixation in the terrestrial environment of a high Arctic ecosystem (Truelove Lowland, Devon Island, N.W.T.).

Can. J. Microbiol. 24: 643-649.

MA TSUGUCHI, T., SHIMOMURA, T. & LEE, S.K. 1979. Factors regulating acetylene reduction assay for measuring heterotrophic nitrogen fixation in waterlogged soils. Soil Sci. Plant Nut. 25:

323-336.

POSTGATE, J. 1978. Nitrogen fixation. Studies in Biology no. 92.

Edward Arnold, London.

SMITH, V.R. 1979a. Evaluation of a resin-bag procedure for deter- mining plant available Pin organic, volcanic soils. Plant and Soil 53:

245-249.

SMITH, V. R. 1979b. The influence ofseabird manuring on the phos- phorous status ofMarion Island (sub-Antarctic) soils. Oecologia41:

123-126.

SMITH, V.R. 1984. Effects of abiotic factors on acetylene reduction by cyanobacteria epiphytic on moss at a sub-Antarctic island.

Applied and Environmental Microbiology48: 594-600.

SMITH, V.R. 1985. Heterotrophic acetylene reduction in soils at Marion Island. ln: Eds. W.R. Siegfried, P.R. Condy and R.M.

Laws. Antarctic nutrient cycles and food webs. Proceedings of the Fourth SCAR Symposium on Antarctic Biology, Wilderness, September 1983. Heidelberg; Springer-Verlag pp 11-21.

SMITH, V. R. & STEYN, M. G. 1982. Soil microbial counts in relation to site characteristics at a Subantarctic island. Microbial Ecology 8:

253-266.

SMITH, V.R. & RUSSELL, S. (1982). Acetylene reduction by bryophytecyanobacteria associations on a sub-Antarctic island.

Polar Bioi. 1: 153-157.

STEYN, M.G. & SMITH, V.R. 1981. Microbial populations in Marion Island soils. S. Afr. J. Antarcl. Res. 10/11: 14-18.

. .

S. Afr. J. Antarct. Res., Vol. 14, 1984 29

Hydrology and bio-oceanography of the Prince Edward Islands (southwest Indian Ocean)

Results are presented from a hydrographic survey of the Prince Edward Island group (46°45'S; 3'?55' E) during September 1982. These provide additional information about the hydro- dynamics of this little-studied region. The distribution of conservative properties (temperature, salinity, density and oxygen) showed little vertical stratification, indicating that water around the islands is well mixed. It is postulated that topo- graphical effects and the close proximity of the islands to the Antarctic Polar Front may combine to influence significantly biogeographic affiliations nearby. Such effects may also operate in concert with ephemeral run-off from the islands (particularly of nitrates) to affect marine productivity in the region.

Introduct ion

Some of the main bio-oceanographic features prevalent in the sub-Antarctic, south-western Indian Ocean have been outlined by American (Gordon & Goldberg 1970), Japanese (Fukuchi 1980) and French (Plancke 1977) surveys. Neverthe- less, detailed investigations of the region as a whole are sparse (El-Sayed et al. 1979a). This is particularly true for the Prince Edward Island Group (46°45'S; 37°55'E) where only two detailed (El-Sayed 1979; Parker & Allanson 1982) and one superficial survey (Deacon 1937; 1983) have been reported to date.

Like many islands in the Southern Ocean, the Prince Edward Group is characterised by a large land-based predator population, supposedly dependent on the surrounding oceans forfood (Williams et al. 1975; Anon. 1978; Skinner et al. 1978;

Van Zinderen Bakker 1978). The obvious importance of the marine ecosystem to these predators (El-Sayed 1977; Anon.

1978) has prompted considerable interest in the biological oceanography and productivity of a little-studied region. This paper presents some results from 23 hydrological stations occupied in the nearshore waters of the Prince Edward Island Group during September 1982. It forms part of an overall investigation into predator-prey relationships at selected localities in the Southern Ocean (Miller 1982a; 1982b).

Results and Discussion

A lack of vertical stratification in the conservative properties of temperature, salinity, density (ot) and oxygen, demonstrated a well-mixed water mass around the islands (e.g. Fig. 1). However, shoal minima in salinity were visible at two stations in the lee of Marion Island. These may be attri- buted to effects of freshwater run-off from the numerous rivers draining the island (Van Zinderen Bakker 1978).

A cell of water in the south possessing the characteristics of Antarctic surface water (T=2,31°C; S=33,87 %..; ot=27,06) suggests that periodic advection of Antarctic surface water

D.G . M. Miller Sea Fisheries Research Institute Private B ag X2 , R oggebaai 8012

B. P. Boden and L. Parker D ept. Zoology and E nt omology Rhodes University , Grahamstown 6140

into the region may explain previously reported appearances of an Antarctic fauna! component (Grindley & Lane 1979) in what is usually considered to be a sub-Antarctic neighbour- hood. In conjunction with a topographical influence on neigh- bouring hydro-dynamic eventS (Planke 1977; Allan!>On et al.

1985). the sporadic proximity of the Antarctic Pola"r Front to the Prince Edward islands may result in considerable inter- change across the Front and hence preclude the persistence of a permanently rigid biogeographic boundary (Deacon 1983;

Miller 1985).

Nutrient salt concentrations and productivity were low, although directly comparable with available data for the region (Table 1). The mean silicate concentration, however, was higher than previously reported although the peak value was considerably lower than that obtained by David (1979).

Elevated reactive nitrate concentrations were observed close to the southeastern seaboard of Marion Island (Fig. 2). Thus it is theorised that both substantial nutrient salt run-off from breeding bird colonies on the island (Burger et al. 1978; Sieg- fried et al. 1978; Williams et al. 1978) and the advection of extra-insular water may affect nutrient salt levels close inshore. Such effects are likely to be ephemeral and the result of interaction between hydrological and meteorological phenomena (Allanson er al. 1985). Acting either individually or in concert these may significantly influence both the produc- tivity of inshore waters and the fauna! character of insular plankton.

Acknowledgements

We would like to thank all our colleagues aboard the R/S Africana and at the Sea Fisheries Research institute for their

Table I

Mean and observed ranges of reactive nutrient salts and chlorophyll-a at the Prince Edward Island, compared with results from other survey~

of the region prior to 1982.

Parameter Mean Range Data Source

PO~ (J.Lg-at/L) 1,43 1,07-1,94 This survey

0,59 0,38- 1,10 Parker & Allanson 1982 1,20 1,17- 1,74 David 1979

N03 (J.Lg-at/1) 18,95 14,79-24,44 This survey

21,19 17,29-22.57 Parkcr&AIIanson 1982 19,62 17,60-22,90 David 1979

Si02(J.Lg-at/1) 6,12 4,84-9,30 This survey

2,50 0,29-5,59 Parker & Allanson 1982 4,16 0,50- 18,90 David 1979

Chl-a (mglm³) 0,28 0.01-0,50 This survey

0,93 0,48- 1,82 Parker & Allanson 1982

0,12

-

Plancke 1977

0,45 0,09- 1,47 El-Sayed et at. 1979b

30

20

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60

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120

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STATIONS 02

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0.4

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2.0 .4.0 6.0

TEMPERATURE (°C)

100

200

300

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....

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600

700

8ooi

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0.0

S. Afr. T. Nav. Antarkt., Deel 14, 1984

J J I I I I

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I

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STATIONS 03 13 19 23

10.0 TEMPERATURE (°C)

20.0

Fig. 1. Vertical distribution of remperarure at stations around the Prince Edward Islands demonstrating absence of any formal stratification.

assistance and encouragement. Financial assistance from the South African National Committee for Oceanographic Research, South African Scientific Committee for Antarctic Research and the Sea Fisheries Research Institute is also gratefully acknowledged.

References

ALLANSON, B.R., BODEN, B.P., PARKER, L. & RAE. C.D.

1985. A contribution to the oceanology of the Prince Edward islands. In: Eds. W.R. Siegfried, P.R. Condy and R.M. Laws.

Antarctic nutrient cycles and food webs. Proceedings of Fourth SCAR Symposium on Antarctic Biology. Wilderness, September 1983. Heidelberg; Springer-Verlag: pp 38-45.

BURGER, A.E., LINDEBOOM, H.J. & WILLIAMS, A.J. 1978.

The mineral energy of selected species of birds to the Marion Island terrestrial ecosystem. S. Afr. J. Antarct. Res. 8: 59-74.

DAVID, P. 1979. Les elements nutritifs des eaux bordant les iles Marion et Crozet (Sud-ouest de !'Ocean Indien). CNFRA. 44:

61-78.

DEACON, G.E.R. 1937. The hydrology of the Southern Oceans.

Discovery Rept. 15: 1-124.

DEACON, G.E.R. 1983. Kerguelen, Antarctic and subantarctic.

Deep Sea Res. 30: 77-81.

EL-SAYED, S.Z. (ed.). 1977. Biological investigations of marine

Antarctic systems and stocks (BIOMASS), Vol. 1, Research Pro- posals. SCAR!SCOR Group of Specialists on the Living Resources of the Southern Ocean. 79 pp.

EL-SA YED, S.Z. 1979. Recherches sur la productivite primaire au cours de la campagne MD.08. CNFRA. 44: 79-82.

EL-SAYED, S.Z., BENON, P., DAVID, P., GRINDLEY, J.R. &

MURAIL, J.F. 1979a. Some aspects of the water column studied during the "Marion-Dufresne" Cruise 08. CNFRA. 44: 127-134.

EL-SAYED, S.Z., STOCKWELL, D.A., RHEIM, H.A., TAGUCHI, S. &MEYER, M.A.1979b. Ontheproductivityofthe Southwestern Indian Ocean. CNFRA. 44: 81-110.

FUKUCHI, M. 1980. Phytoplankton chlorophyll stocks in the Antarctic Ocean. J. Oceanogr. Soc. Japan 36: 73-84.

GORDON, A.L., & GOLDBERG, R.D.1970. Circumpolarcharac- teristics of Antarctic waters. Antarct. Map Folio Ser. (Am. geogr.

Soc.) 13: 1-5.

GRINDLEY, J.R. & LANE, SUSAN B. 1979. Zooplankton around Marion and Prince Edward Islands. CNFRA. 44: 111-125.

MILLER, D.G.M. 1982a. Results of a combined hydroacoustic and midwater trawling survey of the Prince Edward Island Group.

S. Afr. J. Antarct. Res. 12:3-10.

MILLER, D.G.M. 1982b. Results of a combined hydroacoustic and midwater trawling survey of the Gough Island region. S. Afr. J.

Antarct. Res. 12: 17-22.

MILLER, D.G.M.1985. Marinemacroplanktonoftwosub-Antarctic

S. Afr. J. Antarct. Res., Vol. 14, 1984

s 30

AO I

50

47 19.09

19.95

•

19.69

•

1~91 1~90

NITRATE

•

(N )Jg.otjt}

D

^<20

ME~;~m~l1 > 2

o

30' •o'

18.51

•

17.98

•

so'

31

18.94

• •

18.05

• •

• •

18.50

•

^19.63

•

19.92

•

38° 10¹ E

Fig. 2. Horizontal distributiOn of integrated reactive nitrate (0-200m) highlighting an area of higher concentration near the south-east tip of Marion Island.

islands. In: Proceedings of 4th SCAR Symposium on Antarctic Biology. Wilderness. September 1983. Springer-Verlag: pp 355- 361.

PARKER, L. & ALLANSON, B.R. 1982. Some aspects of the oceanology of the Prince Edward Islands, south of South Africa.

Unpublished poster. SCOR Joint Oceanographic Assembly Symposium. Halifax. 3 pp.

PLANKE, JACQUELINE. 1977. Phytoplankton biomass and productivity in the subtropical convergence area and shelves of the western Indian subantarctic islands. In: Adaptations within Antarctic ecosystems, ed. G.A. Llano,; pp. 51-73. Smithsonian Institution, Washington D.C.

SIEGFRIED, W.R., WILLIAMS, A.J., BURGER, A.E. &

BERRUTI, A. 1978. Mineral and energy contributions of eggs of

selected species of seabirds to the Marion Island terrestrial ecosys- tem. S. Afr. J. Antarct. Res. 8:75-87.

SKINNER, LD., CONDY, P.R., VAN AARDE, R.J., BESTER, M:N. & ROBINSON, T.J.1978. ThemammalsofMarion Island: A review. S. A fr. J. Antarct. Res. 8: 35-42.

VAN ZINDEREN BAKKER Snr, E.M. 1978. Origin and general ecology of the Marion Island ecosystem. S. Afr. J. Amarct. Res.

8: 13-21.

WILLlAMS, A.J., BURGER, A.E. & SIEGFRIED, W.R. 1975.

Ornithological research on Marion Island. S. Afr. J. Antarct. Res.

5:48-50.

WILLIAMS, A.J., BURGER, A.E. & BERRUTI, A. 1978. Mineral and energy contributions of carcasses of selected species of seabirds to the Marion Island terrestrial ecosystem. S. Afr. J. Antarct. Res.

8: 53-59.

30

20

.40

60

801

E :r: 10

....

do w 0

120

16

180, A

STATIONS 02

•

0.4

•

08

•

11 + 20 0 21 A

•

2.0 .4.0 6.0

TEMPERATURE (°C)

100

200

300

.400

E :r: 500

....

w do

0

600

700

8ooi

900 8

0.0

S. Afr. T. Nav. Antarkt., Deel 14, 1984

J J I I I I

""

',t'

/j

I •

i j

I: j I I . J . . i

J • . I ' I •I

~ ·~

~ f

i \

\ ;~

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• f

I J I : I I . J I j.

I

I ''

!

\,;

I

STATIONS 03 13 19 23

10.0 TEMPERATURE (°C)

20.0

Fig. 1. Vertical distribution of remperarure at stations around the Prince Edward Islands demonstrating absence of any formal stratification.

assistance and encouragement. Financial assistance from the South African National Committee for Oceanographic Research, South African Scientific Committee for Antarctic Research and the Sea Fisheries Research Institute is also gratefully acknowledged.

References

ALLANSON, B.R., BODEN, B.P., PARKER, L. & RAE. C.D.

1985. A contribution to the oceanology of the Prince Edward islands. In: Eds. W.R. Siegfried, P.R. Condy and R.M. Laws.

Antarctic nutrient cycles and food webs. Proceedings of Fourth SCAR Symposium on Antarctic Biology. Wilderness, September 1983. Heidelberg; Springer-Verlag: pp 38-45.

BURGER, A.E., LINDEBOOM, H.J. & WILLIAMS, A.J. 1978.

The mineral energy of selected species of birds to the Marion Island terrestrial ecosystem. S. Afr. J. Antarct. Res. 8: 59-74.

DAVID, P. 1979. Les elements nutritifs des eaux bordant les iles Marion et Crozet (Sud-ouest de !'Ocean Indien). CNFRA. 44:

61-78.

DEACON, G.E.R. 1937. The hydrology of the Southern Oceans.

Discovery Rept. 15: 1-124.

DEACON, G.E.R. 1983. Kerguelen, Antarctic and subantarctic.

Deep Sea Res. 30: 77-81.

EL-SAYED, S.Z. (ed.). 1977. Biological investigations of marine

Antarctic systems and stocks (BIOMASS), Vol. 1, Research Pro- posals. SCAR!SCOR Group of Specialists on the Living Resources of the Southern Ocean. 79 pp.

EL-SA YED, S.Z. 1979. Recherches sur la productivite primaire au cours de la campagne MD.08. CNFRA. 44: 79-82.

EL-SAYED, S.Z., BENON, P., DAVID, P., GRINDLEY, J.R. &

MURAIL, J.F. 1979a. Some aspects of the water column studied during the "Marion-Dufresne" Cruise 08. CNFRA. 44: 127-134.

EL-SAYED, S.Z., STOCKWELL, D.A., RHEIM, H.A., TAGUCHI, S. &MEYER, M.A.1979b. Ontheproductivityofthe Southwestern Indian Ocean. CNFRA. 44: 81-110.

FUKUCHI, M. 1980. Phytoplankton chlorophyll stocks in the Antarctic Ocean. J. Oceanogr. Soc. Japan 36: 73-84.

GORDON, A.L., & GOLDBERG, R.D.1970. Circumpolarcharac- teristics of Antarctic waters. Antarct. Map Folio Ser. (Am. geogr.

Soc.) 13: 1-5.

GRINDLEY, J.R. & LANE, SUSAN B. 1979. Zooplankton around Marion and Prince Edward Islands. CNFRA. 44: 111-125.

MILLER, D.G.M. 1982a. Results of a combined hydroacoustic and midwater trawling survey of the Prince Edward Island Group.

S. Afr. J. Antarct. Res. 12:3-10.

MILLER, D.G.M. 1982b. Results of a combined hydroacoustic and midwater trawling survey of the Gough Island region. S. Afr. J.

Antarct. Res. 12: 17-22.

MILLER, D.G.M.1985. Marinemacroplanktonoftwosub-Antarctic

S. Afr. J. Antarct. Res., Vol. 14, 1984

s 30

AO I

50

47 19.09

19.95

•

19.69

•

1~91 1~90

NITRATE

•

(N )Jg.otjt}

D

^<20

ME~;~m~l1 > 2

o

30' •o'

18.51

•

17.98

•

so'

31

18.94

• •

18.05

• •

• •

18.50

•

^19.63

•

19.92

•

38° 10¹ E

Fig. 2. Horizontal distributiOn of integrated reactive nitrate (0-200m) highlighting an area of higher concentration near the south-east tip of Marion Island.

islands. In: Proceedings of 4th SCAR Symposium on Antarctic Biology. Wilderness. September 1983. Springer-Verlag: pp 355- 361.

PARKER, L. & ALLANSON, B.R. 1982. Some aspects of the oceanology of the Prince Edward Islands, south of South Africa.

Unpublished poster. SCOR Joint Oceanographic Assembly Symposium. Halifax. 3 pp.

PLANKE, JACQUELINE. 1977. Phytoplankton biomass and productivity in the subtropical convergence area and shelves of the western Indian subantarctic islands. In: Adaptations within Antarctic ecosystems, ed. G.A. Llano,; pp. 51-73. Smithsonian Institution, Washington D.C.

SIEGFRIED, W.R., WILLIAMS, A.J., BURGER, A.E. &

BERRUTI, A. 1978. Mineral and energy contributions of eggs of

selected species of seabirds to the Marion Island terrestrial ecosys- tem. S. Afr. J. Antarct. Res. 8:75-87.

SKINNER, LD., CONDY, P.R., VAN AARDE, R.J., BESTER, M:N. & ROBINSON, T.J.1978. ThemammalsofMarion Island: A review. S. A fr. J. Antarct. Res. 8: 35-42.

VAN ZINDEREN BAKKER Snr, E.M. 1978. Origin and general ecology of the Marion Island ecosystem. S. Afr. J. Amarct. Res.

8: 13-21.

WILLlAMS, A.J., BURGER, A.E. & SIEGFRIED, W.R. 1975.

Ornithological research on Marion Island. S. Afr. J. Antarct. Res.

5:48-50.

WILLIAMS, A.J., BURGER, A.E. & BERRUTI, A. 1978. Mineral and energy contributions of carcasses of selected species of seabirds to the Marion Island terrestrial ecosystem. S. Afr. J. Antarct. Res.

8: 53-59.