Behavioral and physiological photoresponses to light intensity by intertidal microphytobenthos

Behavioral and physiological responses to light are the two major mechanisms by which natural microphytobenthic assemblages adapt to the intertidal environment and protect themselves from light stress. The present study investigated these photoresponses with diff erent light intensities over 8 h of illumination, and used a specific inhibitor(Latrunculin A, Lat A) for migration to compare migratory and non-migratory microphytobenthos(MPB). Photosynthetic activity was detected using rapid light curves and induction curves by chlorophyll fluorescence. It showed distinct variation in migratory responses to diff erent light intensities; high light induced downward migration to avoid photoinhibition, and low and medium light(50–250 μmol/(m^2 ·s)) promoted upward migration followed by downward migration after certain period of light exposure. No significant difference in non-photochemical quenching(NPQ) or PSII maximal quantum yield(F v/F m) was detected between low and medium light irradiance, possibly indicating that only high light influences the photosynthetic capability of MPB. Decreased photosynthetic activity, indicated by three parameters, the maximum relative electron transport rate(r ETR_(max)), minimum saturating irradiance(E _k) and light utilization coefficient(α), was observed in MPB after exposure to prolonged illumination under low and medium light. Lat A ef fectively inhibited the migration of MPB in all light treatments and induced lower F v/F _m under high light(500 and 100 μmol/(m^2 ·s)) and prolonged illumination at 250 μmol/(m^2 ·s), but did not significantly influence F _v/F m under low light(0–100 μmol/(m^2 ·s)) or NPQ. The increase of NPQ in Lat A treatments with time implied that the MPB assemblages can recover their physiological photoprotection capacity to adapt to light stress. Non-migratory MPB exhibited lower light use efficiency(lower α) and lower maximum photosynthetic capacity(lower r ETR_(max)) than migratory MPB under light intensities above 250 μmol/(m ~2 ·s) after 4.0 h illumination.

Limnology and ecology of lakes along the S?ya Coast, East Antarctica

The Soya Coast in East Antarctica has several ice-free areas where many small （〈1 km2） and shallow （〈50 m depth） glacial lakes display various limnological features. Geological, biological, and ecological studies conducted by the Japanese Antarctic Research Expeditions since 1957 are reviewed herein. Most of the lakes along the coast are oligotrophic; however, water quality is highly variable depending on differences in lake morphology and history. Geophysical and paleolimnological studies suggest that most of the lakes appeared after the Last Glacial Maximum （LGM） and have since maintained a lacustrine condition. The ubiquitous occurrence of benthic microbial assemblages with low phytoplankton biomasses is a common feature of other Antarctic lakes. However, diverse benthic assemblages such as moss pillars and large pinnacle microbial structures are found in the lake basins. Frequent and continuous limnological studies have revealed three typical water circulation patterns, underwater light climate features （too much light, which includes UV radiation during the ice free season）, and the structure of benthic assemblages based on their photosynthetic physiology. The phenomenon of mass floatation of benthic assemblages was observed in a lake during the ice-covered season; this was explained by seasonal environmental conditions. Thus, a hypothesis was formulated based on ecological matter cycling, eutrophication, and lake succession processes.