Diatom species of the Australian sector of the Southern Ocean
The collection aims to showcase the range of Southern Ocean diatom species found in the major hydrological provinces of the Australian Sector of the Southern Ocean along the 140 degrees E. The collection includes specimens collected in the Sub-Antarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ).
Samples were collected with McLane Parflux time series sediment traps placed at several depths in the SAZ (47 degrees S site), PFZ (54 degrees S site) and AZ and (61 degrees S site) during the decade 1997-2007. The shortest sampling intervals were eight days and corresponded with the austral summer and autumn, whereas the longest interval was 60 days and corresponded with austral winter. Split aliquots were obtained for taxonomic analysis via scanning electron microscopy (SEM). For improved taxonomic imaging, samples were treated with hydrochloric acid and hydrogen peroxide to remove carbonates and organic matter, respectively. A micropipette was used to transfer the suspension of selected samples to a round-glass cover slip following standard decantation method outlined by Barcena and Abrantes (1998). Samples were air-dried and coated with gold for SEM analysis. SEM analysis was carried out using a JEOL 6480LV scanning electron microscope.
Taxonomy
Diatoms include all algae from the Class Bacillariophyceae and follow the standardised taxonomy of World Register of Marine Species (WoRMS).
Order Asterolamprales
Family Asterolampraceae
Asteromphalus hookeri Ehrenberg
Asteromphalus hyalinus Karsten
Order Achnanthales
Family Cocconeidaceae
Cocconeis sp.
Order Bacillariales
Family Bacillariaceae
Fragilariopsis curta (Van Heurck) Hustedt
Fragilariopsis cylindrus (Grunow) Krieger
Fragilariopsis kerguelensis (O'Meara) Hustedt
Fragilariopsis pseudonana (Hasle) Hasle
Fragilariopsis rhombica (O'Meara) Hustedt
Fragilariopsis separanda Hustedt
Nitzschia bicapitata Cleve
Nitzschia kolaczeckii Grunow
Nitzschia sicula (Castracane) Husted var. bicuneata (Grunow) Hasle
Nitzschia sicula (Castracane) Husted var. rostrata Hustedt
Pseudo-nitzschia heimii Manguin
Pseudo-nitzschia lineola (Cleve) Hasle
Pseudo-nitzschia turgiduloides Hasle
Order Chaetocerotanae incertae sedis
Family Chaetoceraceae
Chaetoceros aequatorialis var. antarcticus Cleve
Chaetoceros atlanticus Cleve
Chaetoceros dichaeta Ehrenberg
Chaetoceros peruvianus Brightwell
Chaetoceros sp.
Order Corethrales
Family Corethraceae
Corethron spp.
Order Coscinodiscales
Family Coscinodiscaceae
Stellarima stellaris (Roper) Hasle et Sims
Family Hemidiscaceae
Actinocyclus sp.
Azpeitia tabularis (Grunow) Fryxell et Sims
Hemidiscus cuneiformis Wallich
Roperia tesselata (Roper) Grunow
Order Hemiaulales
Family Hemiaulaceae
Eucampia antarctica (Castracane) Mangin
Order Naviculales
Family Plagiotropidaceae
Tropidoneis group
Family Naviculaceae
Navicula directa (Smith) Ralfs
Family Pleurosigmataceae
Pleurosigma sp.
Order Rhizosoleniales
Family Rhizosoleniaceae
Dactyliosolen antarcticus Castracane
Rhizosolenia antennata f. semispina Sundstrom
Rhizosolenia antennata (Ehrenberg) Brown f. antennata
Rhizosolenia cf. costata Gersonde
Rhizosolenia polydactyla Castracane f. polydactyla
Rhizosolenia simplex Karsten
Proboscia alata (Brightwell) Sundstrom
Proboscia inermis (Castracane) Jordan Ligowski
Order Thalassiosirales
Family Thalassiosiraceae
Porosira pseudodenticulata (Hustedt) Jouse
Thalassiosira ferelineata Hasle et Fryxell
Thalassiosira gracilis (Karsten) Hustedt
Thalassiosira lentiginosa (Janisch) Fryxell
Thalassiosira oestrupii (Ostenfeld) Hasle var. oestrupii Fryxell et Hasle
Thalassiosira oliveriana (O'Meara) Makarova et Nikolaev
Thalassiosira tumida (Janisch) Hasle
Order Thalassionematales
Family Thalassionemataceae
Thalassionema nitzschioides var. lanceolatum Grunow
Thalassiothrix antarctica Schimper ex Karsten
Data available: 73 SEM images of the most abundant diatom species found at the three sampling sites.
Samples were collected by several sediment traps placed at different depths in the Subantarctic Zone (47 degrees S site), Polar Frontal Zone (54 degrees S site) and Antarctic Zone (61 degrees S site) during the decade 1997-2007. The collection site and date for each species image can be found in Table 1 (see the word document in the download file).
From the abstract of some of the papers:
It has been suggested that increased springtime UVB radiation caused by stratospheric ozone depletion is likely to reduce primary production and induce changes in the species composition of Antarctic marine phytoplankton. Experiments conducted at Arthur Harbour in the Antarctic Peninsula revealed a reduction in primary productivity at both ambient and increased levels of UVB. Laboratory studies have shown that most species in culture are sensitive to high UVB levels, although the level at which either growth or photosynthesis is inhibited is variable. Stratospheric ozone depletion, with resultant increased springtime UVB irradiance, has been occurring with increasing severity since the late 1970's. Thus the phytoplankton community has already experienced about 20 years' exposure to increasing levels of UVB radiation. Here we present analyses of diatom assemblages from high-resolution stratigraphic sequences from anoxic basins in fjords of the Vestfold HIlls, Antarctica. We find that compositional changes in the diatom component of the phytoplankton community over the past 20 years cannot be distinguished from long-term natural variability, although there is some indication of a decline in the production of some sea-ice diatoms. We anticipate that our results are applicable to other Antarctic coastal regions, where thick ice cover and the timing of the phytoplankton bloom protect the phytoplankton from the effects of increased UVB radiation.
Growth rate, survival, and stimulation of the production of UV-B (280 to 320 nm) absorbing compounds were investigated in cultures of five commonly occurring Antarctic marine diatoms exposed to a range of UV-B irradiances. Experimental UV-B exposures ranged from 20 to 650% of the measured peak surface irradiance at an Antarctic coastal site (0.533 J per square metre per second). The five diatom species (Nitzschia lecointei, Proboscia alata, P. inermis, Thalassiosira tumida and Stellarima microtrias) appear capable of surviving two to four times this irradiance. In contrast to Phaeocystis cf. pouchetti, another major component of the Antarctic phytoplankton, the concentrations of pigments with discrete UV absorption peaks in diatoms were low and did not change significantly under increasing UV-B irradiance. Absorbance of UV-B by cells from which pigments had been extracted commonly exceeded that of the pigments themselves. Most of this absorbance was due to oxidisable cell contents, with the frustule providing the remainder. Survival of diatoms did not correlate with absorption by either pigments, frustules or oxidisable cell contents, indicating that their survival under elevated UV-B irradiances results from processes other than screening mechanisms.
Springtime UV-B levels have been increasing in Antarctic marine ecosystems since the 1970's. Effects on natural phytoplankton and sea-ice algal communities, however, remain unresolved. At the Marginal Ice Edge Zone, enhanced springtime UV-B levels coincide with a shallow, stratified water column and a major phytoplankton bloom. In these areas it is possible that phytoplankton growth and survival is adversely impacted by enhanced UV-B. In coastal areas, however, the sea ice, which attenuates most of the UV-B before it reaches the water column, remains until December/January, by which time UV-B levels have returned to long-term seasonal averages. Phytoplankton from these areas are unlikely to show long-term changes resulting from the hole in the ozone layer. Fjords of the Vestfold Hills, eastern Antarctica, have anoxic basins which contain high-resolution, unbioturbated sedimentary sequences. Diatom assemblages from these sequences reflect the diatom component of the phytoplankton and sea-ice algal assemblages at the time of deposition. Twenty-year records from these sequences show no consistent record of change in species composition, diversity or species richness. Six-hundred-year records from the same area also show changes in species abundance greater than those seen in the last 20 years. From these records it can be seen that recent changes in diatom abundances generally fall within the limits of natural variability and there is little evidence of recent changes that might be associated with UV-B-induced change.