Trait‐based analysis of subpolar North Atlantic phytoplankton and plastidic ciliate communities using automated flow cytometer

Plankton are an extremely diverse and polyphyletic group, exhibiting a large range in morphological and physiological traits. Here, we apply automated optical techniques, provided by the pulse‐shape recording automated flow cytometer—CytoSense—to investigate trait variability of phytoplankton and plastidic ciliates in Arctic and Atlantic waters of the subpolar North Atlantic. We used the bio‐optical descriptors derived from the CytoSense (light scattering [forward and sideward] and fluorescence [red, yellow/green and orange from chlorophyll a, degraded pigments, and phycobiliproteins, respectively]) and translated them into functional traits to demonstrate ecological trait variability along an environmental gradient. Cell size was the master trait varying in this study, with large photosynthetic microplankton (> 20 μm in cell diameter), including diatoms as single cells and chains, as well as plastidic ciliates found in Arctic waters, while small‐sized phytoplankton groups, such as the picoeukaryotes (< 4 μm) and the cyanobacteria Synechococcus were dominant in Atlantic waters. Morphological traits, such as chain/colony formation and structural complexity (i.e., cellular processes, setae, and internal vacuoles), appear to favor buoyancy in highly illuminated and stratified Arctic waters. In Atlantic waters, small cell size and spherical cell shape, in addition to photo‐physiological traits, such as high internal pigmentation, offer chromatic adaptation for survival in the low nutrient and dynamic mixing waters of the Atlantic Ocean. The use of automated techniques that quantify ecological traits holds exciting new opportunities to unravel linkages between the structure and function of plankton communities and marine ecosystems

傳統相機與數碼相機

To project how ocean acidification will impact biological communities in the future, it is critical to understand the potential for local adaptation and the physiological plasticity of marine organisms throughout their entire life cycle, as some stages may be more vulnerable than others. Coralline algae are ecosystem engineers that play significant functional roles in oceans worldwide, and are considered vulnerable to ocean acidification. Using different stages of coralline algae, we tested the hypothesis that populations living in environments with higher environmental variability and exposed to higher levels of pCO2 would be less affected by high pCO2 than populations from a more stable environment experiencing lower levels of pCO2. Our results show that spores are less sensitive to elevated pCO2 than adults. Spore growth and mortality were not affected by pCO2 level, however elevated pCO2 negatively impacted the physiology and growth rates of adults, with stronger effects in populations that experienced both lower levels of pCO2 and lower variability in carbonate chemistry, suggesting local adaptation. Differences in physiological plasticity and the potential for adaptation could have important implications for the ecological and evolutionary responses of coralline algae to future environmental changes