Grazing interactions between Oxyrrhis marina and Synechococcus strains grown in single nitrogen sources

The goal of this study was to assess the interaction between abiotic and biotic factors on diverse Synechococcus strains isolated from the coastal California Current (CC9311, CC9605, CC9902) and the oceanic Sargasso Sea (WH8102 and mutants: JMS40 and SIO7B). Previous research has demonstrated that abiotic factors, such as nutrient source or concentration, can alter cellular structure and chemistry. These cell characteristics in turn influence biotic factors such as predation by protozoan grazers. Synechococcus strains isolated from coastal and open ocean waters were grown to nitrogen (N) depletion in N-reduced medium. After reaching stationary phase, strains were transferred to media containing nitrate, ammonium, urea, proline, alanine, glycine, or glutamine to assess the growth rates for each strain on these individual N sources. Compared to growth rates prior to N-limited stationary phase, all strains increased their growth rate in the single N source media. Synechococcus strains appear to have diverse abilities to grow on a broad range of N sources; however, the pattern of N use was not related to coastal or oligotrophic clade association. The majority of strains showed maximal growth on glycine, rather than on nitrate, ammonium, or urea. However, coastal strain CC9902 and mutants of the Sargasso Sea strain WH8102 either did not grow on or were actively inhibited by several amino acids. Further analysis of cell size, shape, and carbon:nitrogen (C:N) ratios of N source-grown coastal strain CC9311 and oceanic strain WH8102 demonstrated that cell physiological and morphological characteristics, in addition to growth rates, varied among N sources within a strain, as well as between strains. Coastal strain CC9311 and oceanic strain WH8102 were used in 30-minute grazing experiments with the heterotrophic dinoflagellate Oxyrrhis marina. Overall, grazing on coastal strain CC9311 was consistently higher than grazing on open ocean strain WH8102. However, within each strain grazing behavior also varied depending on N sources for strain growth. Physiological and morphological analysis of prey, in concert with grazing experiments, suggested that N source alters prey morphology and physiology, and the predator O. marina responds to these cell alterations. While many characteristics such as C and N content, cell size, and cell shape were inter-related, grazing on coastal strain CC9311 was strongly linked to cell shape (highest on more rounded cells) and C and N content (higher on cells with higher nutrient content). In contrast to coastal strain CC9311, few clear relationships could be discerned between ocean strain WH8102 N source-grown cell characteristics and the feeding behavior of the heterotrophic dinoflagellate, O. marina. While previous work has shown that O. marina readily eats coastal strain CC9311, this study showed O. marina grazing rate is also affected by prey growth condition, reflected in the physiology and morphology of the cell. Further studies expanding the breadth of protozoan predators and Synechococcus strains would aid in the understanding of the microzooplankton\u27s role in top-down control of Synechococcus populations under different nutrient regimes and in more general issues of how resource use might affect predation

Microalgal community structure and primary production in Arctic and Antarctic sea ice : A synthesis

Sea ice is one the largest biomes on earth, yet it is poorly described by biogeochemical and climate models. In this paper, published and unpublished data on sympagic (ice-associated) algal biodiversity and productivity have been compiled from more than 300 sea-ice cores and organized into a systematic framework. Significant patterns in microalgal community structure emerged from this framework. Autotrophic flagellates characterize surface communities, interior communities consist of mixed microalgal populations and pennate diatoms dominate bottom communities. There is overlap between landfast and pack-ice communities, which supports the hypothesis that sympagic microalgae originate from the pelagic environment. Distribution in the Arctic is sometimes quite different compared to the Antarctic. This difference may be related to the time of sampling or lack of dedicated studies. Seasonality has a significant impact on species distribution, with a potentially greater role for flagellates and centric diatoms in early spring. The role of sea-ice algae in seeding pelagic blooms remains uncertain. Photosynthesis in sea ice is mainly controlled by environmental factors on a small scale and therefore cannot be linked to specific ice types. Overall, sea-ice communities show a high capacity for photoacclimation but low maximum productivity compared to pelagic phytoplankton. Low carbon assimilation rates probably result from adaptation to extreme conditions of reduced light and temperature in winter. We hypothesize that in the near future, bottom communities will develop earlier in the season and develop more biomass over a shorter period of time as light penetration increases due to the thinning of sea ice. The Arctic is already witnessing changes. The shift forward in time of the algal bloom can result in a mismatch in trophic relations, but the biogeochemical consequences are still hard to predict. With this paper we provide a number of parameters required to improve the reliability of sea-ice biogeochemical models.Peer reviewe

Under-ice phytoplankton blooms inhibited by spring convective mixing in refreezing leads

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 90–109, doi:10.1002/2016JC012575.Spring phytoplankton growth in polar marine ecosystems is limited by light availability beneath ice-covered waters, particularly early in the season prior to snowmelt and melt pond formation. Leads of open water increase light transmission to the ice-covered ocean and are sites of air-sea exchange. We explore the role of leads in controlling phytoplankton bloom dynamics within the sea ice zone of the Arctic Ocean. Data are presented from spring measurements in the Chukchi Sea during the Study of Under-ice Blooms In the Chukchi Ecosystem (SUBICE) program in May and June 2014. We observed that fully consolidated sea ice supported modest under-ice blooms, while waters beneath sea ice with leads had significantly lower phytoplankton biomass, despite high nutrient availability. Through an analysis of hydrographic and biological properties, we attribute this counterintuitive finding to springtime convective mixing in refreezing leads of open water. Our results demonstrate that waters beneath loosely consolidated sea ice (84–95% ice concentration) had weak stratification and were frequently mixed below the critical depth (the depth at which depth-integrated production balances depth-integrated respiration). These findings are supported by theoretical model calculations of under-ice light, primary production, and critical depth at varied lead fractions. The model demonstrates that under-ice blooms can form even beneath snow-covered sea ice in the absence of mixing but not in more deeply mixed waters beneath sea ice with refreezing leads. Future estimates of primary production should account for these phytoplankton dynamics in ice-covered waters.National Science Foundation (NSF) Grant Numbers: PLR-1304563 , PLR-1303617; KEL; NSF Graduate Research Fellowship Program Grant Number: DGE-06459622018-07-0

Early Spring Phytoplankton Dynamics in the Western Antarctic Peninsula

The Palmer Long-Term Ecological Research program has sampled waters of the western Antarctic Peninsula (wAP) annually each summer since 1990. However, information about the wAP prior to the peak of the phytoplankton bloom in January is sparse. Here we present results from a spring process cruise that sampled the wAP in the early stages of phytoplankton bloom development in 2014. Sea ice concentrations were high on the shelf relative to nonshelf waters, especially toward the south. Macronutrients were high and nonlimiting to phytoplankton growth in both shelf and nonshelf waters, while dissolved iron concentrations were high only on the shelf. Phytoplankton were in good physiological condition throughout the wAP, although biomass on the shelf was uniformly low, presumably because of heavy sea ice cover. In contrast, an early stage phytoplankton bloom was observed beneath variable sea ice cover just seaward of the shelf break. Chlorophyll a concentrations in the bloom reached 2 mg m^(−3) within a 100–150 km band between the SBACC and SACCF. The location of the bloom appeared to be controlled by a balance between enhanced vertical mixing at the position of the two fronts and increased stratification due to melting sea ice between them. Unlike summer, when diatoms overwhelmingly dominate the phytoplankton population of the wAP, the haptophyte Phaeocystis antarctica dominated in spring, although diatoms were common. These results suggest that factors controlling phytoplankton abundance and composition change seasonally and may differentially affect phytoplankton populations as environmental conditions within the wAP region continue to change

Distribution of Phaeocystis antarctica-dominatedsea ice algal communities and their potential to seed phytoplankton across the western Antarctic Peninsula in spring

The western Antarctic Peninsula has experienced extreme changes in the timing of sea ice melt and freeze up, shortening the duration of the seasonal sea ice cycle. While previous research demonstrated connections between multiple pelagic trophic levels and the physics of the sea ice, few studies have assessed the sea ice ecosystem or its linkage to the ocean ecosystem in this region. Through a field survey and shipboard experiments, our study focused on characterizing the spring ice algal bloom and elucidating its role in seeding phytoplankton communities post-ice melt in high and low light conditions. Field data revealed that algal communities in slush layers, often formed from the flooding of seawater (infiltration layers), dominated biomass distributions in the sea ice throughout the region, and showed distinct photophysiological characteristics from interior or bottom ice communities. Sea ice algal biomass reached 120 mg chl a m−2 and was often dominated by Phaeocystis antarctica. Shipboard growth experiments showed that prior light history (ice or water column), rather than community composition (phytoplankton and ice algae were composed of similar taxa), primarily drove physiological responses to high and low light. P. antarctica generally dominated the community in growth experiments at the end of the 6 d incubation period. Settling column experiments suggested that P. antarctica’s higher sinking rates relative to other taxa may explain its minor contributions to the summer phytoplankton community in single-cell form and its absence in colonial form, observed in the long-term ecological record of this region

Distribution of Phaeocystis antarctica-dominatedsea ice algal communities and their potential to seed phytoplankton across the western Antarctic Peninsula in spring

The western Antarctic Peninsula has experienced extreme changes in the timing of sea ice melt and freeze up, shortening the duration of the seasonal sea ice cycle. While previous research demonstrated connections between multiple pelagic trophic levels and the physics of the sea ice, few studies have assessed the sea ice ecosystem or its linkage to the ocean ecosystem in this region. Through a field survey and shipboard experiments, our study focused on characterizing the spring ice algal bloom and elucidating its role in seeding phytoplankton communities post-ice melt in high and low light conditions. Field data revealed that algal communities in slush layers, often formed from the flooding of seawater (infiltration layers), dominated biomass distributions in the sea ice throughout the region, and showed distinct photophysiological characteristics from interior or bottom ice communities. Sea ice algal biomass reached 120 mg chl a m−2 and was often dominated by Phaeocystis antarctica. Shipboard growth experiments showed that prior light history (ice or water column), rather than community composition (phytoplankton and ice algae were composed of similar taxa), primarily drove physiological responses to high and low light. P. antarctica generally dominated the community in growth experiments at the end of the 6 d incubation period. Settling column experiments suggested that P. antarctica’s higher sinking rates relative to other taxa may explain its minor contributions to the summer phytoplankton community in single-cell form and its absence in colonial form, observed in the long-term ecological record of this region

Data from: Early spring phytoplankton dynamics in the western Antarctic Peninsula

The Palmer Long-Term Ecological Research program has sampled waters of the western Antarctic Peninsula (wAP) annually each summer since 1990. However, information about the wAP prior to the peak of the phytoplankton bloom in January is sparse. Here we present results from a spring process cruise that sampled the wAP in the early stages of phytoplankton bloom development in 2014. Sea ice concentrations were high on the shelf relative to non-shelf waters, especially toward the south. Macronutrients were high and non-limiting to phytoplankton growth in both shelf and non-shelf waters, while dissolved iron concentrations were high only on the shelf. Phytoplankton were in good physiological condition throughout the wAP, although biomass on the shelf was uniformly low, presumably because of heavy sea ice cover. In contrast, an early stage phytoplankton bloom was observed beneath variable sea ice cover just seaward of the shelf break. Chlorophyll a concentrations in the bloom reached 2 mg m−3 within a 100 to 150 km band between the SBACC and SACCF. The location of the bloom appeared to be controlled by a balance between enhanced vertical mixing at the position of the two fronts and increased stratification due to melting sea ice between them. Unlike summer, when diatoms overwhelmingly dominate the phytoplankton population of the wAP, the haptophyte Phaeocystis antarctica dominated in spring, although diatoms were common. These results suggest that factors controlling phytoplankton abundance and composition change seasonally and may differentially affect phytoplankton populations as environmental conditions within the wAP region continue to change

Early Spring Phytoplankton Dynamics in the Western Antarctic Peninsula

The Palmer Long-Term Ecological Research program has sampled waters of the western Antarctic Peninsula (wAP) annually each summer since 1990. However, information about the wAP prior to the peak of the phytoplankton bloom in January is sparse. Here we present results from a spring process cruise that sampled the wAP in the early stages of phytoplankton bloom development in 2014. Sea ice concentrations were high on the shelf relative to nonshelf waters, especially toward the south. Macronutrients were high and nonlimiting to phytoplankton growth in both shelf and nonshelf waters, while dissolved iron concentrations were high only on the shelf. Phytoplankton were in good physiological condition throughout the wAP, although biomass on the shelf was uniformly low, presumably because of heavy sea ice cover. In contrast, an early stage phytoplankton bloom was observed beneath variable sea ice cover just seaward of the shelf break. Chlorophyll a concentrations in the bloom reached 2 mg m−3 within a 100–150 km band between the SBACC and SACCF. The location of the bloom appeared to be controlled by a balance between enhanced vertical mixing at the position of the two fronts and increased stratification due to melting sea ice between them. Unlike summer, when diatoms overwhelmingly dominate the phytoplankton population of the wAP, the haptophyte Phaeocystis antarctica dominated in spring, although diatoms were common. These results suggest that factors controlling phytoplankton abundance and composition change seasonally and may differentially affect phytoplankton populations as environmental conditions within the wAP region continue to change

Cruise Bottle File

Bottle file in WOCE WHP Exchange Format. Contains data from samples collected from Niskin bottles and CTD sensor data from cruise NBP1409