Physiological responses of a small Antarctic diatom (Chaetoceros sp.) to simulated environmental constraints associated with sea-ice formation

Abstract

The physiological responses of a small unicellular Chaetoceros species, isolated from the Weddell Sea, Antarctica, to changes in temperature, salinity and irradiance simulating those that occur during new-ice formation were investigated. The combination of increased salinity, increased quantum irradiance and decreased temperature significantly reduced growth and photosynthetic rates compared to the control, although cellular metabolism was not inhibited. The cells retained the capacity to photoacclimate, which was observed in the variations in cellular chlorophyll a concentrations and carbon allocation patterns. In terms of photosynthesis, a doubling of quantum irradiance apparently compensated for the adverse effects of increased salinity and lowered temperature. It is thus hypothesized that at least some species of the late season phytoplankton population survive incorporation into ice and continue to photosynthesize and grow under the extreme conditions encountered during sea-ice formation. This potentially prolonges the Antarctic vegetation period well into late austral autumn and winter, enhancing the total primary production available for higher trophic levels.

Eukaryotic microbiota in the surface waters and sea ice of the Southern Ocean: aspects of physiology, ecology and biodiversity in a ?two-phase? ecosystem

“…Two diatom species from sea ice have been shown to photosynthesize in culture at a temperature of-8°C and a salinity of 145 (Aletsee and Jahnke, 1992). Interestingly, several studies have suggested that algal tolerance to high salinities increases with lower temperatures (Aletsee and Jahnke, 1992;Gleitz and Thomas, 1992). The capacity of different phytoplankton species to acclimate to low temperatures and high salinities will determine their survival during ice formation, and subsequently which species are able to colonize the ice (Gleitz and Thomas, 1993;Grossmann and Gleitz, 1993).…”

Carbon acquisition and growth of Antarctic sea ice diatoms in closed bottle incubations

“…reduced temperature and light at increased salinities (Palmisano & Sullivan 1982, Aletsee & Jahnke 1992, Gleitz & Thomas 1992. However, productivity of sea ice algae during winter is greatly hindered by adverse environmental conditions, and daily nrnrllrrtinn ratnc arP i i~i i a l l y 1 tn 2 o r d e r s of m a~n i t u d e r * .…”

Melting out of sea ice causes greater photosynthetic stress in algae than freezing in1

“…For example, these microalgae are exposed to a wide range of salinities during their growing season. As pelagic algae become incorporated into the growing sea‐ice lattice in winter, they are confined into microscopic channels and pockets within the ice that contain hypersaline brine (Gleitz and Thomas 1992). Brine channels provide a niche for sea‐ice algae where salinity can exceed 100‰ (Gleitz et al.…”

“…There have been relatively few studies on the physiological impact on microalgae during sea‐ice formation, in comparison to the decay and melting of sea ice (Gleitz and Thomas 1992). During the process of ice formation, the salinity of the interstitial brine can increase to >60‰ (Vargo et al.…”

“…Similarly, salinity acclimation requires energy for both maintenance of ionic pumps and synthesis of osmolytes. Production of low‐molecular‐weight osmolytes (such as proline) balances the ionic pressure during changes in salinity and assists with cryopreservation (Gleitz and Thomas 1992).…”