Anna C. Palmisano

Distribution patterns of benthic microalgal standing stock at McMurdo Sound, Antarctica

SummaryDuring the austral summer of 1975–76 and winter of 1977 benthic and water column chlorophyll a and phaeopigments were measured at several sites along the east and west sides of McMurdo Sound, Antarctica. Estimates of in situ primary productivity were made at some McMurdo Sound locations. Additionally, water column samples were collected at 5 stations in the Ross Sea during January, 1976. Standing stock data are analyzed to identify seasonal and spatial patterns. Variability in algal standing stock was related to ambient light levels and appeared to be mediated by ice and snow cover whereby the highest algal standing stock was present under high light conditions (low ice and snow cover, shallow water, summer). Differences in published benthic invertebrate densities appear to be closely allied to differences in benthic primary production, and less so to in situ planktonic ice microalgal production.

Changes in the lipid composition of Antarctic sea-ice diatom communities during a spring bloom: an indication of community physiological status

The lipid composition of natural populations of diatoms in the sea ice at McMurdo Sound was determined during the austral spring bloom of 1985, using an Iatroscan TLC-FID system. The major lipid classes in all samples were polar lipids (including phospholipid, glycolipid and chlorophyll) and triacylglycerol, with lesser proportions of free fatty acids. Total lipid increased through November and early December, reaching a maximum (3300 mg mZ at Cape Armitage and 1800 mg m-2 at Erebus Ice Tongue) c. one week after the chlorophyll a maxima. This increase was largely attributable to a corresponding increase in triacylglycerol. At the lipid maxima, uiacylglycerol/polar lipid ratios in the range 1 .O to 2.5 were observed. The dynamic variations in lipid class abundances indicate that profound changes in the physiology of sea- ice diatoms are occurring throughout the spring bloom. A range of sterols (CX-C3J were detected; 24- methylenecholesterol, brassicasterol and 24-ethylcholesterol were the major sterols at the Cape Armitage and Erebus sites. The similarity of the sterol profiles to those of Antarctic freshwater algal communities strongly indicates diatoms as a more probable source of C, sterols in the freshwater lakes than cyanobacteria or other algal groups. The hydrocarbons isolated from sea-ice diatoms at all sites were dominated by two unsaturated components, n-C,,:, and a diunsaturated isoprenoid C, alkene. Until this study, no biological source had been validated for the isoprenoid Cz:2 diene, even though it has been detected in many estuarine and coastal sediments.

Occurrence of novel C30 sterols in Antarctic sea-ice diatom communities during a spring bloom

Abstract The sterol compositions of natural populations of diatom communities in the sea-ice at McMurdo Sound, Antarctica were determined during the austral spring bloom of 1985, using capillary GC and GC-MS. A range of sterols (C26-C30) were detected in the sea-ice diatom communities; 24-methylenecholesterol, brassicasterol and 24-ethylcholesterol were the major sterols at the Cape Armitage, Erebus, Cape Evans and Wohlschlag Bay sites. The similarity of the sterol profiles to those observed in previous studies of Antarctic freshwater algal communities strongly indicates that diatoms, rather than cyanobacteria or other algal groups previously proposed, are a more probable source of C29 sterols in these extreme environments. Two novel 4-methyl-C30 sterols were also detected: a C30 sterol showing a similar mass spectrum to 4-methyl-24-ethyl-5α-cholest-22-en-3β-ol derived from the prymnesiophyte microalga Pavlova lutheri, but which was chromatographically resolved from this compound; and a stanol presumed to be derived from the C30 sterol. 4-Methyl C30 sterols have not been reported previously in diatoms; their presence, and the occurrence of 4-methyl C28 and C29 sterols, may be due to temperature-induced adaptations in sterol biosynthetic pathways.

Changes in photosynthetic carbon assimilation in Antarctic sea-ice diatoms during spring bloom: variation in synthesis of lipid classes

Abstract Carbon assimilation into three lipid classes (neutral lipids, glycolipids, and phospholipids) as well as into protein, low-molecular weight metabolites, polysaccharides, and total lipids was determined during a spring bloom of sea-ice diatoms in McMurdo Sound, Antarctica. The most dramatic changes in incorporation of NaH 14 CO 3 were found in the neutral-lipid fraction. During late November, when chl a · m −2 showed an overall increase, 7–11% of the total carbon assimilated was incorporated into neutral lipids. Incorporation dropped to 0.1 % in early December as chl a · m −2 leveled off, then recovered to 13 % in late December, as a secondary sea-ice diatom bloom became established. The dynamic changes in photosynthetic carbon assimilation into neutral lipids suggested that profound changes in physiological state occurred in sea-ice diatom communities during the spring bloom.

LIPOPHILIC PIGMENTS FROM CYANOBACTERIAL (BLUE‐GREEN ALGAL) AND DIATOM MATS IN HAMELIN POOL, SHARK BAY, WESTERN AUSTRALIA

Lipophilic pigments were examined in microbial mat communities dominated by cyanobacteria in the intertidal zone and by diatoms in the subtidal and sublittoral zones of Hamelin Pool, Shark Bay, Western Australia. These microbial mats have evolutionary significance because of their similarity to lithified stromatolites from the Proterozoic and Early Paleozoic eras. Fucoxanthin, diatoxanthin, diadinoxanthin, β‐carotene, and chlorophylls a and c characterized the diatom mats, whereas cyanobacterial mats contained myxoxanthophyll zeaxanthin, echinenone, β‐carotene, chlorophyll a and, in some cases, sheath pigment. The presence of bacteriochlorophyll a with in the mats suggest a close association of photosynthetic bacteria with diatoms and cyanobacteria. The high carotenoids: chlorophyll a ratios (0.84–2.44 wt/wt) in the diatom mats suggest that carotenoids served a photoprotective function in this high light environment. By contrast, cyanobacterial sheath pigment may have largely supplanted the photoprotective role of carotenoids in the intertidal mats.

Analysis of lipophilic pigments from a phototrophic microbial mat community by high performance liquid chromatography

As assay for lipophilic pigments in phototrophic microbial mat communities using reverse phase-high performance liquid chromatography was developed which allows the separation of 15 carotenoids and chloropigments in a single 30 min program. Lipophilic pigments in a laminated mat from a commercial salina near Laguna Guerrero Negro, Baja California Sur, Mexico reflected their source organisms. Myxoxanthophyll, echinenone, canthaxanthin, and zeaxanthin were derived from cyanobacteria; chlorophyll c, and fucoxanthin from diatoms; chlorophyll a from cyanobacteria and diatoms; bacteriochlorophylls a and c, bacteriophaeophytin a, and gamma-carotene from Chloroflexus spp.; and beta-carotene from a variety of phototrophs. Sensitivity of detection was 0.6-6.1 ng for carotenoids and 1.7-12 ng for most chloropigments. This assay represents a significant improvement over previous analyses of lipophilic pigments in microbial mats and promises to have a wider application to other types of phototrophic communities.

Lipophilic pigments from the benthos of a perennially ice-covered Antarctic lake.

The benthos of a perennially ice-covered Antarctic lake, Lake Hoare, contained three distinct ‘signatures’ of lipophilic pigments. Cyanobacterial mats found in the moat at the periphery of the lake were dominated by the carotenoid myxoxanthophyll; carotenoids: chlorophyll a ratios in this high light environment ranged from 3 to 6.8. Chlorophyll c and fucoxanthin, pigments typical of golden-brown algae, were found at 10 to 20 m depths where the benthos is aerobic. Anaerobic benthic sediments at 20 to 30 m depths were characterized by a third pigment signature dominated by a carotenoid, tentatively identified as alloxanthin from planktonic cryptomonads, and by phaeophytin b from senescent green algae. Pigments were not found associated with alternating organic and sediment layers. As microzooplankton grazers are absent from this closed system and transformation rates are reduced at low temperatures, the benthos beneath the lake ice appears to contain a record of past phytoplankton blooms undergoing decay.