Acclimation to various temperature and pCO2 levels does not impact the competitive ability of two strains of Skeletonema marinoi in natural communities

Understanding the long-term response of key marine phytoplankton species to ongoing global changes is pivotal in determining how oceanic community composition will respond over the coming decades. To better understand the impact of ocean acidification and warming, we acclimated two strains of Skeletonema marinoi isolated from natural communities to three pCO2 (400 μatm, 600 μatm and 1000 μatm) for 8 months and five temperature conditions (7°C, 10°C, 13°C, 16°C and 19°C) for 11 months. These strains were then tested in natural microbial communities, exposed to three pCO2 treatments (400 μatm, 600 μatm and 1000 μatm). DNA metabarcoding of the 16S and 18S gene for prokaryotes and eukaryotes respectively was used to show differences in abundance and diversity between the three CO2 treatments. We found there were no significant differences in acclimated S. marinoi concentrations between the three pCO2 treatments, most likely due to the high variability these strains experience in their natural environment. There were significant compositional differences between the pCO2 treatments for prokaryotes suggesting that indirect changes to phytoplankton-bacteria interactions could be a possible driver of bacterial community composition. Yet, there were no differences for eukaryotic community composition, with all treatments dominated by diatoms (but not the acclimated S. marinoi) resulting in similar biodiversity. Furthermore, strain-specific differences in community composition suggests interactions between prokaryotic and eukaryotic taxa could play a role in determining future community composition.publishedVersio

Diatoms in a sediment core from a flood pulse wetland in Malaysia record strong responses to human impacts and hydro‐climate over the past 150 years

Rapid development and climate change in southeast Asia is placing unprecedented pressures on freshwater ecosystems, but long term records of the ecological consequences are rare. Here we examine one basin of Tasik Chini (Malaysia), a UNESCO?designated flood pulse wetland, where human disturbances (dam installation, iron ore mining, oil palm and rubber cultivation) have escalated since the 1980s. Diatom analysis and organic matter geochemistry (?13Corg and C/N ratios) were applied to a sediment sequence to infer ecological changes in the basin since c. 1900 CE. As the Tasik Chini wetland is a rare ecosystem with an unknown diatom ecology, contemporary diatom habitats (plant surfaces, mud surfaces, rocks, plankton) were sampled from across the lake to help interpret the sedimentary record. Habitat specificity of diatoms was not strongly defined and, although planktonic and benthic groupings were distinctive, there was no difference in assemblages among the benthic habitat surfaces. An increase in the proportion of benthic diatom taxa suggests that a substantial decrease in water level occurred between c. 1938 and 1995 CE, initiated by a decline in rainfall (supported by regional meteorological data), which increased the hydrological isolation of the sub?basin. Changes in the diatom assemblages were most marked after 1995 CE when the Chini dam was installed. After this time both ?13Corg and C/N decreased, suggesting an increase in autochthonous production relative to allochthonous river flood pulse inputs. Oil palm plantations and mining continued to expand after c. 1995 CE and we speculate that inputs of pollutants from these activities may have contributed to the marked ecological change. Together, our work shows that this sub?basin of Tasik Chini has been particularly sensitive to, and impacted by, a combination of human and climatically induced changes due to its hydrologically isolated position

Changing water quality and thermocline depth along an aquaculture gradient in six tropical crater lakes

Understanding how lakes respond to changes in nutrient loading along a productivity gradient can help identify key drivers of aquatic change, thereby allowing appropriate mitigation strategies to be developed. Physical, chemical and biological water column measurements combined with long-term water monitoring data for six closely located crater lakes, in Southeast Asia, were compared to assess the response of lakes along a productivity gradient equating to a transect of increasing aquaculture intensity. Increasing chlorophyll a (phytoplankton biomass) in the upper waters appeared to modify the thermocline depth and light availability causing a shift from a deep chlorophyll maximum at low aquaculture intensity to the emergence of algal dead zones lower in the water column with high aquaculture intensity. High phosphorus loading and light limitation from enhanced algal biomass, associated with high aquaculture intensity, exacerbated nitrogen drawdown, leading to the prevalence of potentially nitrogen-fixing cyanobacteria. Seasonal overturn during the cooler season resulted in low dissolved oxygen concentrations in the epilimnion, potential harmful algal blooms, a reduction in the habitable depth for fish and ultimately increased mortality amongst farmed fish

DataSheet_1_Acclimation to various temperature and pCO2 levels does not impact the competitive ability of two strains of Skeletonema marinoi in natural communities.docx

Understanding the long-term response of key marine phytoplankton species to ongoing global changes is pivotal in determining how oceanic community composition will respond over the coming decades. To better understand the impact of ocean acidification and warming, we acclimated two strains of Skeletonema marinoi isolated from natural communities to three pCO2 (400 μatm, 600 μatm and 1000 μatm) for 8 months and five temperature conditions (7°C, 10°C, 13°C, 16°C and 19°C) for 11 months. These strains were then tested in natural microbial communities, exposed to three pCO2 treatments (400 μatm, 600 μatm and 1000 μatm). DNA metabarcoding of the 16S and 18S gene for prokaryotes and eukaryotes respectively was used to show differences in abundance and diversity between the three CO2 treatments. We found there were no significant differences in acclimated S. marinoi concentrations between the three pCO2 treatments, most likely due to the high variability these strains experience in their natural environment. There were significant compositional differences between the pCO2 treatments for prokaryotes suggesting that indirect changes to phytoplankton-bacteria interactions could be a possible driver of bacterial community composition. Yet, there were no differences for eukaryotic community composition, with all treatments dominated by diatoms (but not the acclimated S. marinoi) resulting in similar biodiversity. Furthermore, strain-specific differences in community composition suggests interactions between prokaryotic and eukaryotic taxa could play a role in determining future community composition.</p