ALGAL ASSEMBLAGES IN ANTARCTIC PACK ICE AND IN ICE-EDGE PLANKTON1

A significant amount of the primary production in the Southern Ocean and other ice-covered oceans takes place in localized ice edge plankton blooms. The dynamics of these blooms appear to be closely related to seasonal melting of sea ice. Algal cells released from the ice are a possible source of ice edge planktonic assemblages, but evidence for this “seeding” has been equivocal. We compared algal assemblages in ice and water in the Weddell Sea during the austral spring of 1983 at a receding ice edge with a well-developed ice edge bloom. The high degree of similarity between ice and water column assemblages, the spatial and temporal patterns in the distribution and abundances of species, and preliminary evidence for the viability and growth of ice-associated species provide evidence for seeding from sea ice of some species in Antarctica.     

LIPIDS IN BLUE-GREEN ALGAL MATS (MODERN STROMATOLITES) FROM ANTARCTIC OASIS LAKES1

Lipids comprising the stenols, stanols, polar lipid fatty acids, alkanes and alkenes of blue-green algal-(diatomaceous)-microbial mats and cores (modern cold water stromatolites) collected from three Antarctic lakes were identified and compared with those of other algae. The major stenols were: (cholesta-5, 22-dien-3β-ol, cholest-5-en-3β-ol, 24-methylcholesta-5, 22-dien-3β-ol, 24-methyl-cholest-5-en-3β-ol, 24-ethylcholesta-5, 22-dien-3β-ol, and 24-ethylcholest-5-en-3β-ol). The presence of C28 Δ^{3, 22} stenols, as well as other C28 stenols, was suggestive of diatom input. C29 stenols may have originated from blue-grern algae. However, the high concentrations of stenols present and the lack of Δ⁷ stenols was atypical for known stenol components of several blue-green algal species previously reported. The occurrence of these stenols and other lipid markers strongls implicate diatoms as well as blue-green algae as important biogenetic sources of lipids and has established the potential for studies of lipid diagenesis in these unique cold, freshwater stromatolites .     

REMOVAL OF ORGANIC AND INORGANIC MATTER FROM ANTARCTIC LAKES BY AERIAL ESCAPE OF BLUEGREEN ALGAL MATS1

Field studies on three perennially ice-covered Antarctic oasis lakes with little or no outflow disclosed a unique biological phenomenon. Benthic algal mats dominated by the prokaryotic Phormidium frigidum Fritsch and several pennate diatoms growing in shallower, more brightly illuminated areas beneath 4 to 5.5 m of ice accumulate and entrap bubbles of photosynthetically produced oxygen. Clumps of this gas-filled mat tear loose from the gravelly substrate, lift off and float to the bottom of the lake ice. Some of these floating mat pieces become frozen into newly forming ice with the onset of winter. Through the combination of ablation of ice from the upper surface and the formation of new ice from below, algal mat pieces reach the upper lake surface in 5–10 years. Here, they are lyophilized by polar winds and dispersed in at least a partially viable state. The process of mat lift-off and escape is important in removing nutrients and salts from these lakes and helps to perpetuate their oligotrophic state. Neutron activation and X-ray dispersive analyses of elements in the algal mats along with other analyses, field observations, and calculations suggest that significant quantities of organic matter, select minerals and salts are lost from the lakes annually through this process whose magnitude has not been recognized previously.     

南极三种弹尾目记述(英文)

本文描述了采自南极的三种弹尾目 ,其中详细描述了新种南极隐跳Cryptopygusnanjiensis头、胸、腹部诸如 :触角、角后器、足、弹器、腹管以及毛序等鉴别特征 ,并将两种已知种Tullbergiamediantarcti ca和Frieseawoyciechowskii与模式种进行了比较。新种及观察的已知种标本存放在中科院上海昆虫研究所的标本馆中     

TEMPERATURE REQUIREMENTS FOR GROWTH AND SURVIVAL OF ANTARCTIC RHODOPHYTA1

The temperature requirement for growth and the upper survival temperatures (USTs) of 15 Antarctic red algal species collected on King George Island (South Shetland Islands) and Signy Island (South Orkney Islands) were determined. Two groups with different temperature requirements were identified. 1) A “eurythermal” group includes Rhodymenia subantarctica, Phyllophora ahnfeltioides, Gymnogongrus antarcticus, and Rhodochorton purpureum, growing between 0° and 10°C with optimum values at (0°) 5°(l0°)C. The USTs of these species and of Porphyra endiviifolium, Delesseria lancifolia, and Bangia atropurpurea were between 22° and 16°C. These species survived temperatures in a similar range as most endemic Arctic or Arctic/cold-temperate species but exhibited a lower temperature demand for growth, suggesting an earlier contact with low temperatures than Arctic species. 2) A stenothermal group includes Pantoneura plocamioides, Myriogramme mangini, Ballia callitricha, Phyllophora antarctica, Gigartina skottsbergii, Georgiella confluens, and Plocamium cartilagineum growing at 0° or ≤5°C with optimum values at 0° or 5°C. The USTs of these species and of Phycodrys austrogeorgica were between 14° and 7°C. The species of this group must have had an even earlier contact with the Antarctic cold-water environment than species of the “eurythermal” group. Gigartina skottsbergii, Georgiella confluens, Plocamium cartilagineum, and Pantoneura plocamioides were probably exposed longer to low temperatures than the other species of this group or Antarctic green and brown algae because they show the lowest temperature requirements so far determined in seaweeds. The results are discussed in the context of present local temperature regimes at the localities where the isolates were collected. Moreover, an attempt was made to explain the geographic distribution of individual species by the temperature requirements determined in this study. Only a few of the distribution limits are determined by temperature growth and/or survival characteristics. In many species (Rhodymenia subantarctica, Ballia callitricha, Gigartina skottsbergii, Bangia atropurpurea, Rhodochorton purpureum, and Plocamium cartilagineum), the development of temperature ecotypes is evident.     

CELL SURVIVAL CHARACTERISTICS AND MOLECULAR RESPONSES OF ANTARCTIC PHYTOPLANKTON TO ULTRAVIOLET-B RADIATION1

Twelve species of Antarctic diatoms were studied to assess UV sensitivity in relation to cellular and molecular aspects of DNA damage and repair. Responses of cell survival, induction of DNA damage, and DNA repair capacity were determined. There was a wide range of interspecific UV-sensitivity among diatoms. D₃₇ values (average fluence to kill one cell) ranged from 681 J · m^?2 (most sensitive) to 25,338 J · m^?2 (most resistant). Molecular analysis (by radioimmunoassay) of UV-induced DNA damage [induction of cys-syn cyclobutane dimers and pyrimidine (6-4) pyrimidone photoproducts] also revealed considerable variability among species [0.98–84 lesions · (10⁸ daltons DNA)^?1 induced by exposure to 2500 J · m^?2]. Repair of DNA damage ranged from 0.18 to 2.72 lesions removed · (10⁸ daltons DNA)^?1 in 6 h; removal represented 0.72–73.5% of initial damage. Comparison of cellular responses associated with photoenhanced repair and nucleotide excision (“dark”) repair indicated that light-mediated correction of UV damage was an important factor in cell survival. There was a relationship between the number of photoproducts induced and cell survival, but not between repair efficiency and survival. The data also indicate a general dependence of photoproduct induction and D₃₇ values on cell size and shape (expressed as the surface area: volume ratio which ranged from 0.07 to 0.66 between species) and suggest that these factors are indicators of UV sensitivity. Smaller cells with greater surface area: volume ratios sustained more damage per unit of DNA, had lower D₃₇ values, and were more sensitive to UV exposure. The wide species variations observed in molecular and cellular responses to UV exposure emphasize the ecological implications of changes in natural UV regimes. These changes can act as determinants of cell size and taxonomic structure within phytoplankton communities and have as yet unknown effects on trophic interactions within the Antarctic ecosystem.     

PHOTOADAPTATION,GROWTH AND PRODUCTION OF BOTTOM ICE ALGAE IN THE ANTARCTIC1

Biomass, chemical composition, growth rates and the photosynthetic response of natural populations of sea ice algae in McMurdo Sound, Antarctica were followed over most of the spring bloom to examine temporal variability under a relatively constant incident irradiance (ca. 1500–1700 μE · m^-2· s^-1 at solar noon). Collection were restricted to bottom 20 cm of the ice sheet in an area with little or no snow (0–5 cm). At low temperature and irradiance these algae normally exhibited low assimilation numbers (ca. 0.1–0.4 mg C · mg Chl^-1· h^-1). Average growth rates (0.02–0.45 d^-1), based on changes in standing stocks, were also low. Biomass, biochemical composition, growth rates, assimilation numbers and photosynthetic efficiencies (mg C · mg Chl^-1· h^-1 (μE · m^-2· s^-1)^-1) displayed large fluctuations over periods of several days during the growth season. On the other hand, I_k which is an index of photoadaptation, and I_m, the optimal irradiance for photosynthesis, were relatively constant with less than twofold variation throughout our study. Substantial nutrient fluxes (3.3–8.0 mmol Si or N · m^-2· d^-1) were necessary to satisfy the minimum nutrient demand for the observed biomass levels and population growth rates; over the 41 days of our study, integrated nutrient demand represented 69–150 mmol N or Si · m^-2, Only 5–25% of this total demand could be met by all of the nutrients in the ice sheet, if they were readily available. However, adequate amounts were present in the top few meters of the water column. With small nutrient gradients in surface waters below the sea ice, vertical eddy diffusivities on the order of 3.8–9.3 cm²· s^- should supply sufficient nutrients to meet algal demand.     

A DINOFLAGELLATE CYST FROM ANTARCTIC SEA ICE1

The small (< 15 μm) hypnozygote of an autotrophic athecate dinofiagellate found in association with Antarctic sea ice had an external covering composed of approximately 60 plates, each of which was bounded by sutural ridging and possessed an intratabular process. A cingulum and sulcus were also evident. The ultrastructure of the cyst was increasingly dominated by storage bodies as the cyst matured, and the cell wall thickened from 0.2 to 0.8 μm over 2 months. This cyst has been encountered often but usually at low abundances (10³?10⁴ cells·L^?1); however, the maximum abundances observed (10⁶ cells·L^?1) indicate that the formation of this cyst may play an important part in the ecology of sea ice communities.     

INVESTIGATION OF 4-METHYL STEROLS FROM CULTURED DINOFLAGELLATE ALGAL STRAINS

The marine dinoflagellates Prorocentrum micans, Gonyaulax polyedra, Gymnodinium sp., and Alexandrium tamarense, collected from the Adriatic Sea during red-tide blooms, were cultured to investigate the 4-methyl sterol constituents. To ascertain a possible influence of cell age on the 4-methyl sterol content, for one strain (Gymnodinium sp.)we investigated the composition of these constituents at exponential and stationary growing phases. The lipid material extracted with acetone from the lyophilized algal samples was fractionated by thin-layer chromatography. The 4-methyl sterols recovered from the layer were converted into the corresponding OTMS derivatives. Nine of 11 constituents were identified by gas chromatography and gas chromatography-mass spectrometry; only two minor constituents were characterized by their gas chromatographic parameters. All free methyl sterols identified in the algal samples had been detected previously in various dinoflagellates. The 4-methyl sterol fractions generally contained very few constituents. Except for the Gymnodinium sp. sample, collected at the exponential growing phase (GyD2 exp), which contains 4,24-dimethylcholestan-3-ol as a unique constituent, dinosterol was the major component. Moreover, 4,24-ethylcholestan-3-ol was also an important constituent of both Prorocentrum and Gonyaulax strains, whereas considerable amounts of dinostanol characterized all the Gymnodinium sp. strains. In addition, the latter contained several minor constituents such as 4-methylcholestan-3-ol, 4,24-dimethylcholesta-22-en-3-ol, and 4-methyl-24-ethylcholestan-3-ol. 4-Methyl-24-methylene-cholestan-3-ol was a constituent of the Gymnodinium sp. sample, collected at the stationary growing phase (GyD2 stat)only, whereas 4-methylgorgostanol was identified only in the Alexandrium tamarense Gt4 strain. Except for 4-methyl-24-ethylcholesta-8(14)-en-3-ol, all the methyl sterol constituents from our algae show a saturated polynuclear system. The pathways by which side-chain modifications occur in dinoflagellate 4-methyl sterols are considered, and a map of the fragmentation pattern of the trimethylsilyl-4-methyl sterols under electronic impact is also reported.     

CRYPTOENDOLITHIC ALGAL COMMUNITIES OF THE COLORADO PLATEAU1

Eighteen taxa, including representatives of both eukaryotic and prokaryotic genera, were isolated from below the surface of eight sandstones in four semi-desert and cold temperate biomes of northern Arizona, southern Utah and Western New Mexico. The algae occurred as uniform well defined bands in light-colored sandstones and also as scattered patches in dark sandstones. The algal communities varied in generic composition, chlorophyll a content, and location within the different sandstones. Biomass, estimated by chlorophyll a content, was approximately two to twenty-fold greater than reported for cryptoendolithic algal bands in a cold desert habitat. The widespread distribution of certain algae in endolithic habitats of the Colorado Plateau and their presence in rocks at quite distant locations suggests that the endolithic habitat may he utilized by algae whenever it provides more favorable conditions than the surrounding surfaces.     

EVOLUTION OF THE ANTARCTIC MARINE BENTHIC ALGAL FLORA

There are many logistic difficulties associated with studying Antarctic marine algae and, as a consequence, the taxonomic information available is far from comprehensive and any generalizations should be regarded with caution. The Antarctic marine benthic flora is characterized by a low species richness. Biogeographical characteristics of the flora are outlined. There is a high degree of endemism, possibly around 35–40%. Other major floristic elements are a group of species with a distribution extending to Tierra del Fuego and subantarctic islands, a group spread through temperate regions of the Southern Hemisphere, and a cosmopolitan group. Ecological observations show that ice has a major effect on the occurrence and distribution of algae, and ecophysiological studies indicate that Antarctic macroalgae possess various adaptations to ice, low temperatures, and strongly seasonal light conditions. Possible trends in the evolution of the Antarctic benthic marine flora, including a reduction in species richness and the origins of biogeographical links with subantarctic and temperate regions of the Southern Hemisphere, are discussed in the context of tectonic and climatic changes over the past 100 million years. A comparison is made with studies on the evolution of shallow-water marine fauna.     

GROWTH RESPONSES OF SEVERAL DIATOM SPECIES ISOLATED FROM VARIOUS ENVIRONMENTS TO TEMPERATURE

Eight diatom species (Chaetoceros pseudocurvisetus Mang ., Stephanodiscus hantzschii Grun ., Skeletonema costatum ( Grev.) Cleve , Asterionella formosa Hass ., Thalassiosira nordenskioeldii Cleve , Detonula confervacea ( Cleve) Gran , Chaetoceros sp., and Nitzschia frigida Grun.) were isolated from various temperature environments ranging from temperate to the Arctic, and their growth responses to temperature were determined. Each species grew over a different temperature range. The lower and upper limits of each species varied from −1.8° to 20° C and from 2° to 30° C, respectively. The width of the growth range of each species. also varied from 3.8° to 25° C, and the growth of these species was observed, as a whole, between a wide temperature range from −1.8° to 30° C .
Within the growth temperature ranges, the growth rate of each species increased with temperature until reaching a maximum, which was followed by a steep decrease up to the upper limit of the growth range. As a result, each species showed a maximum rate at the temperature very near to the upper limit, which was generally higher than the isolation temperature. The specific growth rates were compared among the eight species. The interspecific maximum rate at each temperature exhibited an exponential increase with a Q₁₀ = 1.48. The relative growth rates of each species were calculated by normalizing the specific growth rates with the interspecific maximum rate at each respective temperature. The higher relative growth rates tended to occur at the isolation temperature of each species, suggesting that temperature is a significant control on species distributions in nature .     

SEDIMENTATION STUDIES OF RED ALGAL SPORES1

More than 1000 spores from 11 species of red algae were collected; their differences in size and sinking rates were measured using a new micro-video technique. A relationship between size and sinking rate was shown with larger spores generally sinking faster than smaller ones. Variability in spore size, or lack thereof, is a species characteristic. Cryptopleura violacea (J. G. Ag.) Kylin and Neoagardhiella baileyi (Kutz.) Wynne and Taylor were found to produce a wide range of spore sizes. Such variability in size may be related to differences in spore formation. Centrifugation was used to separate the contents of spores to show differences in them. The ecological implications of these observations are considered.     

IMPACT OF ULTRAVIOLET-B RADIATION ON PHOTOSYSTEM II ACTIVITY AND ITS RELATIONSHIP TO THE INHIBITION OF CARBON FIXATION RATES FOR ANTARCTIC ICE ALGAE COMMUNITIES1

One goal of the Icecolors 1993 study was to determine whether or not photosystem II (PSII) was a major target site for photoinhibition by ultraviolet-B radiation (Q_UVB, 280–320 nm) in natural communities. Second, the degree to which Q_UVBinhibition of PSII could account for Q_UVBeffects on whole cell rates of carbon fixation in phytoplankton was assessed. On 1 October, 1993, at Palmer Station (Antarctica), dense samples of a frazil ice algal community were collected and maintained outdoors in the presence or a bsence of Q_UVBand l or ultraviolet-A (Q_UVB, 320–400 nm) radiation. Samples were then collected at intervals over the day to track the time course of UV inhibition of primary production. The ice algae were assessed for changes in pigment composition and rates of carbon fixation. The quantum yield of PSII (Ø_IIc°) was measured by P ulse A mplitude M odulated fluorometry. Over the day, Ø_IIc° declined due to increasing time-integrated dose exposure of Q_UVB. The Q_UVB-driven inhibition of Ø_IIc° increased from 4% in the early morning hours to a maximum of 23% at the end of the day. The Q_UVB photoinhibition of PSII quantum yield did not recover by 6 h after sunset. In contrast, photoinhibition by Q_UVA and photosynthetically available radiation (Q_PAR, 400–700 nm) recovered during the late afternoon. Flourescence-based estimates of carbon fixation rates were linearly correlated (P =0.002, r²=0.45) with measured carbon fixation. Fluorescence overestimated the observed Q_UVB inhibition in measured carbon fixation rates by 8% in the morning hours; however, the discrepancy increased during the afternoon. Therefore, researchers should be cautious in using fluorescence measurements to infer ultraviolet inhibition for rates of carbon fixation until there is a greater understanding of the coupling of carbon metabolism to PSII activity for natural populations. Despite these current limitations, fluorescence-based technologies represent powerful tools for studying the impact of the ozone hole on natural populations on spatial/ temporal scales not possible using conventional productivity techniques.     

SEASONAL PATTERN OF DIEL PERIODICITY IN PHOTOSYNTHESIS BY POLAR PHYTOPLANKTON: SPECIES-SPECIFIC RESPONSES1

The diel patterns of light-saturated and light-limited photosynthesis were measured for three diatom species in McMurdo Sound, Antarctica during the transition from late austral winter to summer. Maximum photosynthetic capacity occurred around mid-day during September, when there was a well defined light/dark cycle, and progressively shifted to about midnight by late october when irradiance was continuous. There was a concomitant shift in minimum photosynthetic capacity from midnight to midday. Rates of light-saturated and -limited photosynthesis covaried, and the magnitude of seasonal and diel changes in photosynthetic characteristics were similar. The linear relationship between light-saturated and -limited photosynthesis suggests that the shapes of the photosynthesis-irradiance curves remained relatively constant over the day and througout the season. The unique diel patterns of photosynthesis of these polar phytoplankton appear to be a response to the persistently low, yet continuous irradiance of the polar summer.     

STRATEGIES AND KINETICS OF PHOTOACCLIMATION IN THREE ANTARCTIC NANOPHYTOFLAGELLATES1

Three Antarctic nanophytoflagellates (two cryptophyte species and a Pyramimonas sp.) were compared for their capacity to phiotoacclimate and for their kinetic responses in changing photic environments. Division rate, cell size cellular fluorescence, and chlorophyll a content were measured steady and transient states of semi-continuous cultures maintain at 1.0° C. Of all parameters tested, cell size was most affected by irradiance. Acclimation kinetics were modeled using a first-order equation. Rates of change in cell size following shifts in irradiance were comparable with rates of change in chemical composition reported for temperate algae. Response rates of cellular in vivo red and orange fluorescence were lower. In many cases, however, responses could not be described by the first-order kinetic model. Division rates remained high for approximately 3 days following a shift down in irradiance, after which new division rates were established. The nanoflagellates studied here appear to respond to small irradiance perturbations at low rates. However, they may fail to adapt and abrupt changes in photon flux density (PFD). When shade-adapted (25 μmol, m^?2, m^?2, s^?1) cells were exposed to high PFD (400 μmol, m^?2, s^?1) for 1–3 days, cell were incapable of readapting division rate and pigment content to the initial irradiance condition (25 μmol, m^?2, s^?1) for about 1 month following the shift-down step. The ecological role of the kinetics of photoacclimation in nanophytoflagellate growth performance in Antarctic ecosystems is discussed.     

RATES OF PHOTOADAPTATION IN SEA ICE DIATOMS FROM MCMURDO SOUND,ANTARCTICA1

Sea ice microalgae are released from their relatively stable light environment to the water column seasonally, and any subsequent growth in a vertically mixed water column may depend, in part, on their photoadaptation rates. In this study we followed the time course of photoadaptation in natural sea ice algal communities from bottom ice and surface ice by measuring their photophysiological response to an artificial shift in the ambient irradiance field. Microalgae from under-ice habitats, were incubated under full sunlight (LL-HL) and microalgae from surface ice habitats were incubated under artificial light to mimic under-ice irradiance (HL-LL). During 3- to 4-day time course studies, opposite shifts in chlorophyll: carbon, α, P^B_m, and I_k were observed, depending on the direction of the irradiance change. First-order rate constants (k) ranged from 0.0067 to 0.29 h^?1 for photosynthetic parameters, although P^B_m did not always show a clear change over time. Rates of photoadaptation for ice algae are comparable to k values reported for temperate phytoplankton, suggesting that sea ice algae may be equally capable of adapting to the light conditions experienced in a vertically mixed water column. This study presents the first evidence that sea ice microalgae are physiologically capable of adapting to a planktonic life and thus could serve as a seed population for polar marine phytoplankton blooms.     

THE INFLUENCE OF SALINITY AND TEMPERATURE COVARIATION ON THE PHOTOPHYSIOLOGICAL CHARACTERISTICS OF ANTARCTIC SEA ICE MICROALGAE1

The responses of sea ice microalgae to variation in ambient irradiance (0 to 150 μE · m^?2· s^?1), temperature (–6° to + 6° C), and salinity (0 to 100 ppt) were tested to determine whether these variables act independently or in concert to influence rates of microalgal photosynthesis. The photosynthetic efficiency and maximum photosynthetic rate for sea ice microalgae increased as a function of incubation temperature between -6° and + 6° C. Furthermore, photosynthetic efficiency, maximum photosynthetic rate, and quantum yield were greatest at salinities between SO and 50 ppt. In contrast, the mean specific absorption coefficients were lowest near seawater salinities, and the saturating irradiance, I_s, appeared to be inversely proportional to salinity. Results also suggest that the effects of salinity on the growth of sea ice microalgae are independent of those elicited by temperature or light, and that the functional relationship between salinity and light or temperature is multiplicative. This information is essential to the proper formulation of algorithms used to describe algal growth in environments where light, temperature, and salinity are changing simultaneously, such as within sea ice or within the water column at the marginal ice edge zone.     

A COMPARISON OF THE ATTACHED ALGAL COMMUNITIES OF A NATURAL AND AN ARTIFICIAL SUBSTRATE1

A study of communities of attached algae in Lake Mize Florida, wax made during July 1969, July-August 1970 and April 1971. The substrates exposed during the study included glass slides mid the terrestrial form of the amphibious sedge, Eleocharis baldwinii (Torr.) Chapman. Counts were used to determine the relative abundance and densities of the species present on the 2 substrates under different environmental conditions. Such analyses indicated that at any given lime and place, a number of factors influenced the composition of the periphyton. Generally, lightly adhering, resupinate species attained higher densities on glass slides than filamentous and loosely associated metaphytonic species. The epiphytic flora of E. baldwinii contained a large number of both strong attachers and the metaphyton. The vertical range of many attached species was also greater on E. baldwinii than on glass slides.     

FLUORESCENCE INDUCTION AND PHOTOSYNTHETIC RESPONSES OF ARCTIC ICE ALGAE TO SAMPLE TREATMENT AND SALINITY1

The measurement of Photosynthetic rates of algae growing on the undersurface of 1. 7 m thick ice in the Canadian Arctic (Resolute Passage. N.W.T.) presents several problems. During the preparation of samples for physiological measurements, the ice algae may he exposed to salinity and temperature shocks. Fluorescence induction (the rise in in vivo Chl a fluorescence intensity during a period of millineconds) and photosynthesis-irradiance (PI) experiments examined the potential effects of salinity and temperature on the physiology of ice algae. Experimental suspensions were routinely prepared by scraping one part ire crystals (11–14%₀ salinity) and attached algae from the bottom ice into four parts filtered seawater (32%₀ salinity). giving a final salinity of 28–31%₀. Post-dilution of melted ice scrapings with seawater suppressed photosynthetic ¹⁴C-fixation and decreased A_DCMU (the area above the fluorescence induction curve measured in the presence of the inhibitor DCMC: an estimate of photosynthetic capacity) by a factor of 3–16. due to the low salinity of the melted ice scrapings. Fluorescence induction and PI experiments showed that the ice algae had a salinity optimum near 30%₀, close to the ambient seawater salinity, Experiments in which the Chl a concentration was manipulated showed that A_DCMU, P^a_m (Chl a-normalized rate of photosynthesis at light saturation), and a (photosynthetic efficiency) declined with increasing Chl a concentration. Ice algae tolerated heating (l.5°C-min^-1) up to 17° C, above which A_DCMU’decreased with sample temperature.