Photosynthetic response to a winter heatwave in leading and trailing edge populations of the intertidal red alga Corallina offi-cinalis(Rhodophyta)

Marine heatwaves(MHWs)caused by anthropogenic climate change are becoming a key driver of change at the ecosystem level.Thermal conditions experienced by marine organisms across their distribution,particularly towards the equator,are likely to approach their physiological limits,resulting in extensive mortality and subsequent changes at the population level.Populations at the margins of their species’distribution are thought to be more sensitive to climate-induced environmental pressures than central populations,but our understanding of variability in fitness-related physiological traits in trailing versus leading-edge populations is limited.In a laboratory simulation study,we tested whether two leading(Iceland)and two trailing(Spain)peripheral populations of the intertidal macroalga Corallina officinalis display different levels of maximum potential quantum efficiency(Fv/Fm)resilience to current and future winter MHWs scenarios.Our study revealed that ongoing and future local winter MHWs will not negatively affect leading-edge populations of C.officinalis,which exhibited stable photosynthetic efficiency throughout the study.Trailing edge populations showed a positive though non-significant trend in photosynthetic efficiency throughout winter MHWs exposure.Poleward and equatorward populations did not produce significantly different results,with winter MHWs having no negative affect on Fv/Fm of either population.Additionally,we found no long-term regional or population-level influence of a winter MHWs on this species’photosynthetic efficiency.Thus,we found no statistically significant difference in thermal stress responses between leading and trailing populations.Nonetheless,C.officinalis showed a trend towards higher stress responses in southern than northern populations.Because responses rest on a variety of local population traits,they are difficult to predict based solely on thermal pressures.

Behavioral and physiological photoresponses to light intensity by intertidal microphytobenthos

Abstract 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 different 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 different light intensities; high light induced downward migration to avoid photoinhibition, and low and medium light （50-250 ~tmol/（m2. 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 yidd （Fv/Fm） 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 （rETRmax）, minimum saturating irradiance （E0 and light utilization coefficient （a）, was observed in MPB after exposure to prolonged illumination under low and medium light. Lat A effectively inhibited the migration of MPB in all light treatments and induced lower Fv/Fm under high light （500 and 100 μmol/（m2·s）） and prolonged illumination at 250 μmol/（m2·s）, but did not significantly influence Fv/Fm under low light （0-100 μmol/（m2·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 a） and lower maximum photosynthetic capacity （lower rETRm^x） than migratory MPB under light intensities above 250μmol/（m2. 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.