Light Intensity Modulates the Response of Two Antarctic Diatom Species to Ocean Acidification

It is largely unknown how rising atmospheric COconcentrations and changes in the upper mixed layer depth, with its subsequent effects on light availability will affect phytoplankton physiology in the Southern Ocean. Linking seasonal variations in the availability of CO2 and light to abundances and physiological traits of key phytoplankton species could aid to understand their abilities to acclimate to predicted future climatic conditions. To investigate the combined effects of CO2 and light on two ecologically relevant Antarctic diatoms (Fragilariopsis curta and Odontella weisflogii) a matrix of three light intensities (LL = 20, ML = 200, HL = 500 µmol photons m-2 s−1) and three pCO2 levels (low = 180, ambient = 380, high = 1000 µatm) was applied assessing their effects on growth, particulate organic carbon (POC) fixation and photophysiology. Under ambient pCO2, POC production rates were highest already at low light in Fragilariopsis, indicating saturation of photosynthesis, while in Odontella highest rates were only reached at medium irradiances. In both species ocean acidification did not stimulate, but rather inhibited, growth and POC production under low and medium light. This effect was, however, amended under high growth irradiances. Low pCO2 levels inhibited growth and POC production in both species at low and medium light, and further decreased absolute electron transport rates under high light. Our results suggest that Southern Ocean diatoms were sensitive to changes in pCO2, showing species-specific responses, which were further modulated by light intensity. The two diatom species represent distinct ecotypes and revealed discrete physiological traits that matched their seasonal occurrence with the related physical conditions in Antarctic coastal waters

Spatio-temporal patterns in the coral reef communities of the Spermonde Archipelago, 2012–2014, II: Fish assemblages display structured variation related to benthic condition

The Spermonde Archipelago is a complex of ~70 mostly populated islands off Southwest Sulawesi, Indonesia, in the center of the Coral Triangle. The reefs in this area are exposed to a high level of anthropogenic disturbances. Previous studies have shown that variation in the benthos is strongly linked to water quality and distance from the mainland. However, little is known about the fish assemblages of the region and if their community structure also follows a relationship with benthic structure and distance from shore. In this study, we used eight islands of the archipelago, varying in distance from 1 to 55 km relative to the mainland, and 3 years of surveys, to describe benthic and fish assemblages and to examine the spatial and temporal influence of benthic composition on the structure of the fish assemblages. Cluster analysis indicated that distinct groups of fish were associated with distance, while few species were present across the entire range of sites. Relating fish communities to benthic composition using a multivariate generalized linear model confirmed that fish groups relate to structural complexity (rugosity) or differing benthic groups; either algae, reef builders (coral and crustose coralline algae) or invertebrates and rubble. From these relationships we can identify sets of fish species that may be lost given continued degradation of the Spermonde reefs. Lastly, the incorporation of water quality, benthic and fish indices indicates that local coral reefs responded positively after an acute disturbance in 2013 with increases in reef builders and fish diversity over relatively short (1 year) time frames. This study contributes an important, missing component (fish community structure) to the growing literature on the Spermonde Archipelago, a system that features environmental pressures common in the greater Southeast Asian region

Spatio-temporal patterns in coral reef communities of the Spermonde Archipelago, 2012-2014, I: Comprehensive reef monitoring of water and benthic indicators reflect changes in reef health

Pollution, fishing, and outbreaks of predators can heavily impact coastal coral reef ecosystems, leading to decreased water quality and benthic community shifts. To determine the main environmental drivers of coral reef status in the Spermonde Archipelago, Indonesia, we monitored environmental variables and coral reef benthic community structure along an on-to-offshore gradient annually from 2012 to 2014. Findings revealed that concentrations of phosphate, chlorophyll a-like fluorescence, suspended particulate matter, and light attenuation significantly decreased from on-to-offshore, while concentrations of dissolved O2 and values of water pH significantly increased on-to-offshore. Nitrogen stable isotope signatures of sediment and an exemplary common brown alga were significantly enriched nearshore, identifying wastewater input from the city of Makassar as primary N source. In contrast to the high temporal variability in water quality, coral reef benthic community cover did not show strong temporal, but rather, spatial patterns. Turf algae was the dominant group next to live coral, and was negatively correlated to live coral, crustose coralline algae (CCA), rubble and hard substrate. Variation in benthic cover along the gradient was explained by water quality variables linked to trophic status and physico-chemical variables. As an integrated measure of reef status and structural complexity, the benthic index, based on the ratio of relative cover of live coral and CCA to other coral reef organisms, and reef rugosity were determined. The benthic index was consistently low nearshore and increased offshore, with high variability in the midshelf sites across years. Reef rugosity was also lowest nearshore and increased further offshore. Both indices dropped in 2013, increasing again in 2014, indicating a period of acute disturbance and recovery within the study and suggesting that the mid-shelf reefs are more resilient to disturbance than nearshore reefs. We thus recommend using these two indices with a selected number of environmental variables as an integral part of future reef monitoring

Impact of ocean acidification and high solar radiation on productivity and species composition of a late summer phytoplankton community of the coastal Western Antarctic Peninsula

The Western Antarctic Peninsula (WAP), one of the most productive regions of the Southern Ocean, is currently undergoing rapid environmental changes such as ocean acidification (OA) and increased daily irradiances from enhanced surface‐water stratification. To assess the potential for future biological CO2 sequestration of this region, we incubated a natural phytoplankton assemblage from Ryder Bay, WAP, under a range of pCO2 levels (180 μatm, 450 μatm, and 1000 μatm) combined with either moderate or high natural solar radiation (MSR: 124 μmol photons m−2 s−1 and HSR: 435 μmol photons m−2 s−1, respectively). The initial and final phytoplankton communities were numerically dominated by the prymnesiophyte Phaeocystis antarctica, with the single cells initially being predominant and solitary and colonial cells reaching similar high abundances by the end. Only when communities were grown under ambient pCO2 in conjunction with HSR did the small diatom Fragilariopsis pseudonana outcompete P. antarctica at the end of the experiment. Such positive light‐dependent growth response of the diatom was, however, dampened by OA. These changes in community composition were caused by an enhanced photosensitivity of diatoms, especially F. pseudonana, under OA and HSR, reducing thereby their competitiveness toward P. antarctica. Moreover, community primary production (PP) of all treatments yielded similar high rates at the start and the end of the experiment, but with the main contributors shifting from initially large to small cells toward the end. Even though community PP of Ryder Bay phytoplankton was insensitive to the changes in light and CO2 availability, the observed size‐dependent shift in productivity could, however, weaken the biological CO2 sequestration potential of this region in the future

ScienceTainment - How to communicate science entertaining

The Internet and its features offer great opportunities for scientists to present their work to the public. Using new media channels like Youtube, TedTalks or blogs, scientists can offer their research in a creative, entertaining and intelligible way to the public

Elucidating the role of light and CO2 on Antarctic coastal phytoplankton ecophysiology

The effects of climate change, including ocean acidification (OA), on future Southern Ocean phytoplankton communitya s species composition and consequent impacts on primary production and carbon export are largely unknown. Further, changes in light availability induced by decreased vertical mixing of surface waters can lead to higher light availability enhancing potentially phytoplankton productivity in Antarctic coastal and shelf areas. Therefore, a suite of laboratory and field experiments with the two ecologically relevant Antarctic diatom species as well as a natural phytoplankton community from the Western Antarctic Peninsula were conducted under different pCO2 levels and irradiance regimes. In the two diatom species Fragilariopsis curta and Odontella weisflogii, OA did not stimulate, but inhibited growth and carbon fixation under low and medium light whereas this effect was amended under high growth irradiances. Under different dynamic light regimes, however, OA stimulated carbon fixation in the two diatoms. Yet, reduced photosynthetic efficiencies in both species indicated that photosensitivity was enhanced under OA. In CO2-light incubation experiments with a natural community of the West Antarctic Peninsula, OA led to a decline of overall diatom abundances, including Fragilariopsis and Odontella, triggering thereby the dominance of the prymnesiophyte Phaeocystis antarctica, an inefficient vector for carbon export. In summary, these findings highlight that, under different irradiance regimes, OA is likely to induce a species shift, away from diatoms, within phytoplankton communities and to alter primary productivity of the coastal Southern Ocean with important implications for biogeochemical cycles in the future

Die Auswirkungen von Licht und CO2 auf die Ökophysiologie von antarktischem Phytoplankton

The effects of climate change, including ocean acidification (OA), on future Southern Ocean phytoplankton communitya s species composition and consequent impacts on primary production and carbon export are largely unknown. Further, changes in light availability induced by decreased vertical mixing of surface waters can lead to higher light availability enhancing potentially phytoplankton productivity in Antarctic coastal and shelf areas. Therefore, a suite of laboratory and field experiments with the two ecologically relevant Antarctic diatom species as well as a natural phytoplankton community from the Western Antarctic Peninsula were conducted under different pCO2 levels and irradiance regimes. In the two diatom species Fragilariopsis curta and Odontella weisflogii, OA did not stimulate, but inhibited growth and carbon fixation under low and medium light whereas this effect was amended under high growth irradiances. Under different dynamic light regimes, however, OA stimulated carbon fixation in the two diatoms. Yet, reduced photosynthetic efficiencies in both species indicated that photosensitivity was enhanced under OA. In CO2-light incubation experiments with a natural community of the West Antarctic Peninsula, OA led to a decline of overall diatom abundances, including Fragilariopsis and Odontella, triggering thereby the dominance of the prymnesiophyte Phaeocystis antarctica, an inefficient vector for carbon export. In summary, these findings highlight that, under different irradiance regimes, OA is likely to induce a species shift, away from diatoms, within phytoplankton communities and to alter primary productivity of the coastal Southern Ocean with important implications for biogeochemical cycles in the future

Light intensity modulates the response of two Antarctic diatom species to ocean acidification

It is largely unknown how rising atmospheric CO2 concentrations and changes in the upper mixed layer depth, with its subsequent effects on light availability will affect phytoplankton physiology in the Southern Ocean. Linking seasonal variations in the availability of CO2 and light to abundances and physiological traits of key phytoplankton species could aid to understand their abilities to acclimate to predicted future climatic conditions. To investigate the combined effects of CO2 and light on two ecologically relevant Antarctic diatoms (Fragilariopsis curta and Odontella weisflogii) a matrix of three light intensities (LL=20, ML=200, HL=500 µmol photons m-2 s-1) and three pCO2 levels (low=180, ambient=380, high=1000 µatm) was applied assessing their effects on growth, particulate organic carbon (POC) fixation and photophysiology. Under ambient pCO2, POC production rates were highest already at low light in Fragilariopsis, indicating saturation of photosynthesis, while in Odontella highest rates were only reached at medium irradiances. In both species ocean acidification did not stimulate, but rather inhibited, growth and POC production under low and medium light. This effect was, however, amended under high growth irradiances. Low pCO2 levels inhibited growth and POC production in both species at low and medium light, and further decreased absETRs under high light. Our results suggest that Southern Ocean diatoms were sensitive to changes in pCO2, showing species-specific responses, which were further modulated by light intensity. The two diatom species represent distinct ecotypes and revealed discrete physiological traits that matched their seasonal occurrence with the related physical conditions in Antarctic coastal waters