This is a general session covering topics in Plankton Ecology.
Lead Organizer: Kerri Finlay, University of Regina (kerri.finlay@uregina.ca)
Co-organizers:
Beatrix Beisner, University of Quebec at Montreal (beisner.beatrix@uqam.ca)
Angela Strecker, Western Washington University (angela.strecker@wwu.edu)
Presentations
09:00 AM
Life-cycle differentiation in a cosmopolitan calcifying microalga: a multiomic view (7735)
Primary Presenter: Chuan Ku, Academia Sinica (chuanku@gate.sinica.edu.tw)
Gephyrocapsa huxleyi (formerly Emiliania huxleyi), a key microalga influencing the global carbon cycle through photosynthesis and calcification, undergoes a haplodiplontic sexual life cycle involving the alternation between a calcifying non-flagellate diploid and a non-calcifying biflagellate haploid stage. To unravel the molecular basis of their morphological and physiological distinctions, we applied a multi-omic approach, involving de novo genome reconstructions and comparisons of transcriptomes, proteomes, and methylomes for a pair of isogenic haploid and diploid model strains. Genomic sequences of the two life stages revealed unexpected structural variations, including aneuploidy, chromosome-level recombination, and partial loss of heterozygosity in the diploid during asexual reproduction. This provides a plausible explanation for the observed high genomic structure and size variation but low genetic variation among natural populations. In addition to calcification and flagella, transcriptomic and proteomic differences of haploid and diploid cells modulate their differentiation in photosynthesis, sulfatases, DMSP degradation, DNA replication, and endomembrane system and transport. Haploid-diploid differential gene expression can be partially attributable to allelic imbalance (allele-specific expression) in the diploid. We also found that gene transcript abundance is correlated with patterns of DNA methylation, which occurs in CG and CHG contexts and can be inheritable, allele-specific, and differentiated between life-cycle phases. Our multiomic profiling and analyses offer insights into coccolithophore life-cycle differentiation, laying a robust foundation for investigating various biological processes in this phylogenetically distinct and ecologically crucial group of marine protists.
09:15 AM
PHYTOPLANKTON ASSEMBLAGE DYNAMICS IN RELATION TO ENVIRONMENTAL CONDITIONS IN A RIVERINE LAKE (8392)
Primary Presenter: Robert Burdis, Minnesota Department of Natural Resources (robert.burdis@state.mn.us)
Understanding drivers of phytoplankton assemblage structure is essential given the ecological, aesthetic, and health consequences that vary among taxonomic groups. In this study we examined phytoplankton assemblage structure over a three-year period in Lake Pepin, a natural riverine lake on the Upper Mississippi River. Phytoplankton samples along with a suite of limnological variables were collected from April to October, at 4 sites along a longitudinal gradient of the lake spanning 35 kilometers. To investigate potential relationships, mechanisms, and drivers between environmental conditions and phytoplankton assemblage structure a distance-based linear model was utilized. We found over 100 phytoplankton taxa and assemblage structure varied between years, months, and sites. 32.6% of the total variation in phytoplankton assemblages was explained by a combination of chemical, hydrological, and physical variables. Additionally, we noted a one-year absence of the common diatom, Stephanodiscus hantzschii, that may have been related to an unusual spring of warm water temperature and very low soluble reactive phosphorus concentrations that suggests a possible nutrient limitation for this species in a large river system. Insights into the relationships between environmental conditions and individual and co-occurring species of phytoplankton should aid in developing a greater predictability of assemblages and may enable large river scientists and managers to better anticipate and address water quality conditions under changing climate and hydrologic regimes.
09:30 AM
Trophic controls on thermal adaptation of phytoplankton size and stoichiometry (8172)
Primary Presenter: David Anderson, University of British Columbia (daan4786@zoology.ubc.ca)
Temperature impacts physiological function, driving evolutionary adaptation in physiological traits that influence ecosystem properties. Temperature also impacts ecological rates, altering the strength of trophic and competitive interactions. Yet, possible effects of temperature-driven shifts in ecological interactions on physiological adaptation are unclear. We investigate how ecological interactions shape thermal adaptation of phytoplankton cell size, a critical physiological trait that affects macromolecular composition, Phosphorus:Carbon ratio, competitive ability, and grazing susceptibility. We identify evolutionarily stable strategies in a nutrient-phytoplankton-zooplankton system. We find that trophic interactions strongly impact the evolutionarily stable cell size across temperatures. Without zooplankton, cell size and P:C ratio declines monotonically with temperature. With zooplankton, cell size and P:C ratio varies unimodally with temperature, due to temperature-dependent shifts in the grazer’s capacity to ease nutrient competition by controlling phytoplankton. Size-selective grazing does not qualitatively alter this result but can facilitate diversification of phytoplankton. In two species phytoplankton communities, a unimodal thermal response of P:C ratio emerges at the community level from shifts in the relative densities of a P-poor and P-rich species. We conclude that ecological interactions play critical roles in physiological adaptation to warming.
09:45 AM
BOTTOM-UP DRIVEN DIEL VERTICAL MIGRATION: SIZE AND SPECIES MATTERS (7990)
Primary Presenter: Bart De Stasio, Lawrence University (destasib@lawrence.edu)
Diel vertical migration (DVM) of zooplankton in lakes and oceans is primarily thought to be driven by a top-down process of visual planktivory in illuminated surface waters. During the day zooplankton move to deep, dark depths to avoid predators and then ascend at night to feed on algae that thrive in surface waters. Different patterns occur where invertebrate predation can cause reverse DVM, but this still is a top-down process. Less work has examined how bottom-up forces such as productivity in surface waters and across depths affect DVM. Our study examined how lake trophic status and chlorophyll depth distributions drive zooplankton DVM. Six Wisconsin lakes varying in trophic status from oligotrophic (2 µg/L chlorophyll) to meso-eutrophic (> 10 µg/L) were sampled during mid-day and moonless nights. Replicate Schindler trap samples of zooplankton were collected from surface to bottom and basic limnological profiles of temperature, dissolved oxygen, chlorophyll and light flux were obtained. Zooplankton were enumerated by depth and Daphnia body sizes were measured. Both typical and reverse DVM were observed, and patterns differed based on species and on size, with greater migration amplitude for larger Daphnia. Migration amplitude was also greater in lakes with more chlorophyll a. Lakes with deep chlorophyll layers showed DVM different than expected by top-down driven processes. Overall, trophic status and chlorophyll depth profile patterns are underappreciated factors affecting zooplankton DVM.
10:00 AM
RESPONSE OF ZOOPLANKTON TO UNUSUAL INCREASE IN TEMPERATURE AND SEA ICE MELTING IN COASTAL ANTARCTICA DURING AUSTRAL SUMMER (7703)
Primary Presenter: Venkataramana Vankara, National Centre for Polar and Ocean Research (venkataramana.987@gmail.com)
Zooplankton play a critical role in energy transfer across the Antarctic food web, where copepods are known to constitute the primary food supply for upper trophic level species, particularly at higher latitudes. Zooplankton samples were collected at five depth intervals, covering the area between the surface and 1000 m, by using a standard multiplankton sampler (mouth area: 0.25m2; mesh size: 200 µm) in the coastal Antarctica during January and February 2017. The sea surface temperature was slightly warmer than expected in the neritic zone, resulting in mixed layer depth was shallower in the neritic zone than in the ice-free domain of coastal Antarctica. Freshening of the surface water prevented both phytoplankton and zooplankton biomass in the seasonal ice zone, resulting in high zooplankton diversity in the subsurface layer. The high zooplankton biovolume in the neritic zone and ice fee zone was likely due to the presence of higher Chl-a concentrations than in the seasonal ice zone. Calanoids and cyclopoids composed the majority of the overall zooplankton biovolume, accounting for more than 81% of the total zooplankton count. Calanus simillimus and Calanus australis are important in the oceanic region, where Stephos longipes is an indicator species in the shelf region associated with floating sea ice. We assumed that the combination of provincial features, such as sea surface temperature, food availability, sea ice cover and freshening, would likely have the greatest impact on zooplankton abundance and species diversity in the coastal waters of eastern Antarctica.
10:15 AM
HOW THE PHENOLOGY AND OVERWINTERING STRATEGIES OF COPEPODS ARE DISRUPTED BY CLIMATE CHANGE (7812)
Primary Presenter: Ida Krogsgaard Svendsen, Linnaeus University (ida.krogsgaardsvendsen@lnu.se)
We are living in a rapidly changing world due to the current climate crisis, which is altering our world faster than the natural climatic fluctuations on Earth. These changes impact all ecosystems and increase the importance of research to understand the consequences of climate change. In our study, we investigated the effects of global warming on the phenology and overwintering strategy of copepods. This knowledge is highly relevant because copepods play a crucial role in the food web. Our study site consists of a bay that has been heated for over 50 years, simulating the potential effects of climate change, and an unaffected control bay for comparison with current environmental conditions. We directly collected zooplankton samples from the field and conducted additional incubation studies using sediment from both bays. These studies aimed to examine the hatching of dormant eggs in the sediment. Copepods exhibit different types of eggs: subitaneous eggs, which hatch immediately, and dormant eggs, which are adapted to survive extended periods of unfavorable environmental conditions, such as winter. From our field samples, we observed that the heated bay generally produces more hatchlings and adult copepods, along with a higher chlorophyll content, compared to the control bay. In the incubation studies, more dormant eggs hatched in the sediment from the control bay than from the heated bay. These results suggest that the life histories of copepods are adapting to the elevated temperatures, seemingly disfavoring the use of dormant eggs.
CS26B - Plankton Ecology
Description
Time: 9:00 AM
Date: 5/6/2024
Room: Meeting Room MN