Phytoplankton in the aqueous ecological theater: Changing conditions, biodiversity, and evolving ecological concepts

Phytoplankton communities, from lakes to oceans, are changing with anthropogenic nutrient loading and climate change. So, too, are the tools by which phytoplankton are quantified and characterized, yielding a torrent of new data and new types of data that can be related to ecosystem function. New insights have been gained about the physiology of resource acquisition by phytoplankton, allowing new relationships between phytoplankton biodiversity and function to be developed. Despite years of emphasis on the use of inorganic substrates in support of phytoplankton nutrition, it is now well understood that phytoplankton rely on a broad suite of substrates, both dissolved and particulate. Simple characterizations of limiting nutrients are not sufficient to understand how phytoplankton biodiversity is changing, or may change, in future conditions. Ecological theory is also advancing. Ecological stoichiometry brings the seemingly divergent concepts of nutrient limitation and trophic interactions together by recognizing that different organisms both within and between trophic groups have fundamentally different elemental requirements, that food web structure is a function of not only food quantity but also food quality, and that these interactions result in a complex suite of feedbacks that shape community composition. Trait-based (functional response) approaches are increasingly applied in characterizing ecosystem function and response, and new models are also emerging allowing new genomic data to be incorporated in models of ecosystem function. Climate change and altered nutrient loads should continue to motivate both new dynamic balance model architectures and new experimental investigations that support them. This article uses the metaphor of ecological theater to convey contemporary trends and themes against the backdrop of a changing world. There is potential for the outcome of the aqueous play to be characterized as tragedy with more harmful taxa emerging, but with continued science advancements—and if efforts to reduce nutrient pollution and control climate change become global priorities—there can be optimism in the face of tragedy

Nitrogen uptake and NH4+ regeneration by pelagic microplankton and marine snow from the North Atlantic

Comparative rates of nitrogen uptake and NH4+ regeneration by plankton of \u3c153 and \u3c5 μm in size were determined in the Sargasso Sea and Gulf Stream, and by plankton associated with marine snow in the Gulf Stream during May 1982. Rates of total nitrogen uptake of Sargasso Sea phytoplankton exceeded those of the Gulf Stream phytoplankton by factors ranging from 1.8 to 5.6. Rates of microplankton NH4+ regeneration equaled or exceeded rates of NH4+ uptake in the Sargasso Sea, but in the Gulf Stream were negligible in all but one case. Significant rates of NH4+ regeneration were measured for Gulf Stream marine snow, and, in all but one case, exceeded those of NH4+ uptake. Rates of NO3– and urea uptake by the snow were less than half those of NH4+. Protozoan densities were enumerated on aliquots of the same snow particles and compared with previously reported bacterial estimates; enrichment factors of the cultivable ciliates and flagellates were 6500–9000 relative to ambient seawater. These organisms were also grazing and reproducing rapidly. Bacterial densities were also moderately enriched, but their productivity was lower than surrounding seawater bacteria. Thus, the large bacterivorous population associated with marine snow may have accounted for a substantial fraction of the observed NH4+ regeneration

From webs, loops, shunts, and pumps to microbial multitasking: evolving concepts of marine microbial ecology, the mixoplankton paradigm, and implications for a future ocean

Emerging knowledge of mixoplankton—ubiquitous microbes that employ phototrophy and phagotrophy synergistically in one cell—reshapes our knowledge of the flow of materials and energy, with wide-reaching impacts on marine productivity, biodiversity, and sustainability. Conceptual models of microbial interactions have evolved from food-chains, where carbon-fixing phytoplankton are conceived as being grazed solely by zooplankton that, in turn, support fisheries and higher trophic levels, to microbial webs, loops, and shunts, as knowledge about abundance, activity, and roles of marine microbial organisms—as well as the complexity of their interactions—has increased. In a future world, plankton that depend on a single strategy for acquiring nutrition (photo-autotrophy or phago-heterotrophy) may be disadvantaged with increasing temperatures and ocean acidification impacting vital rates, thermal stratification decreasing water column nutrient exchange, and anthropogenic pollution shifting amounts, forms, and proportions of nutrients. These conditions can lead to stoichiometric imbalances that may promote mixoplanktonic species with an increasing likelihood of harmful blooms. Such changes in plankton species composition alters the interconnectivity of oceanic microbes with direct consequences on biogeochemical cycling, trophic dynamics, and ecosystem services. Here, the implications of the mixoplankton paradigm relative to traditional concepts of microbial oceanography in a globally-changing, anthropogenically-impacted world are explored

Advancing science from plankton to whales—Celebrating the contributions of James J. McCarthy

Hailing from Sweet Home, Oregon, where his father introduced him to the fascinations of pondwater (McCarthy 2018), Jim McCarthy graduated from Gonzaga University, and in the late 1960s joined the Food Chain Research Group at the Scripps Institution of Oceanography, where he received his doctorate in 1971. The Food Chain Research Group, which was becoming recognized as the premier research group on plankton, was at that time directed by such distinguished scientists as John Strickland and Dick Eppley, among others. The goal of the Food Chain Group was to understand plankton dynamics and trophodynamics, “to a degree that will enable man to exercise satisfactory control of the environment and make useful predictions” (Institute of Marine Resources annual report, 1968, cited in Shor 1978:143) and “to predict the formation and transfer of nutrients through the full cycle of life in the ocean” (Shor 1978:140). It was there that Jim became immersed in all aspects of nutrients, plankton, and the marine food web

Models : tools for synthesis in international oceanographic research programs

Author Posting. © Oceanography Society, 2010. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 23, no. 3 (2010): 126-139, doi: 10.5670/oceanog.2010.28Through its promotion of coordinated international research programs, the Intergovernmental Oceanographic Commission (IOC) has facilitated major progress on some of the most challenging problems in oceanography. Issues of global significance—such as general ocean circulation, the carbon cycle, the structure and dynamics of ecosystems, and harmful algal blooms—are so large in scope that they require international collaboration to be addressed systematically. International collaborations are even more important when these issues are affected by anthropogenic processes— such as climate change, CO2 enhancement, ocean acidification, pollution, and eutrophication—whose impacts may differ greatly throughout the global ocean. These problems require an entire portfolio of research activities, including global surveys, regional process studies, time-series observations, laboratorybased investigations, and satellite remote sensing. Synthesis of this vast array of results presents its own set of challenges (Hofmann et al., 2010), and models offer an explicit framework for integration of the knowledge gained as well as detailed investigation of the underlying dynamics. Models help us to understand what happened in the past, and to make predictions of future changes—both of which support the development of sound policy and decision making. We review examples of how models have been used for this suite of purposes, focusing on areas where IOC played a key role in organizing and coordinating the research activities.Support from the National Science Foundation, National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, and National Institute of Environmental Health Sciences. DS acknowledges CLISAP (Integrated Climate System Analysis and Prediction) at the KlimaCampus of the University of Hamburg. PG acknowledges SCOR/ LOICZ Working Group 132

Simulating Effects of Variable Stoichiometry and Temperature on Mixotrophy in the Harmful Dinoflagellate Karlodinium veneficum

Results from a dynamic mathematical model are presented simulating the growth of the harmful algal bloom (HAB) mixotrophic dinoflagellate Karlodinium veneficum and its algal prey, Rhodomonas salina. The model describes carbon-nitrogen-phosphorus-based interactions within the mixotroph, interlinking autotrophic and phagotrophic nutrition. The model was tuned to experimental data from these species grown under autotrophic conditions and in mixed batch cultures in which nitrogen:phosphorus stoichiometry (input molar N:P of 4, 16, and 32) of both predator and prey varied. A good fit was attained to all experimentally derived carbon biomass data. The potential effects of temperature and nutrient changes on promoting growth of prey and thus K. veneficum bloom formation were explored using this simulation platform. The simulated biomass of K. veneficum was highest when they were functioning as mixotrophs and when they consumed prey under elevated N:P conditions. The scenarios under low N:P responded differently, with simulations showing larger deviation between mixotrophic and autotrophic growth, depending on temperature. When inorganic nutrients were in balanced proportions, lower biomass of the mixotroph was attained at all temperatures in the simulations, suggesting that natural systems might be more resilient against Karlodinium HAB development in warming conditions if nutrients were available in balanced proportions. These simulations underscore the need for models of HAB dynamics to include consideration of prey; modeling HAB as autotrophs is insufficient. The simulations also imply that warmer, wetter springs that may bring more N with lower N:P, such as predicted under climate change scenarios for Chesapeake Bay, may be more conducive to development of these HABs. Prey availability may also increase with temperature due to differential growth temperature responses of K. veneficum and its prey

Mesoscale and Nutrient Conditions Associated with the Massive 2008 Cochlodinium polykrikoides Bloom in the Sea of Oman/Arabian Gulf

Cochlodinium polykrikoides formed large blooms in the coastal waters of Oman from October 2008 through mid-January 2009, and satellite images from Aqua-MODIS and region-wide reports suggest that this bloom was found throughout the Arabian Gulf and Sea of Oman for more than 10 months. The unusual occurrence of this species appears to have supplanted the more regularly occurring bloom species, Noctiluca scintillans, in 2008–2009. For the first 2 weeks of the coastal Omani bloom, C. polykrikoides abundance was near monospecific proportions, with cell densities ranging from 4.6 × 103 to 9 × 106 cells L−1 and very high levels of chlorophyll a (78.0 μg L−1) were also recorded. The regional progression of the bloom likely began with stronger than normal upwelling along the Iranian and northern Omani coasts during the southwest monsoon in late summer, followed by discharge of unusually warm coastal plume water along the coast of Oman with the reversal of monsoonal winds in late October. The occurrence and persistence of high densities of C. polykrikoides in Oman coastal water were also significantly influenced by an elevated nutrient load and warmer than normal temperatures. Concentrations of nutrients, especially NH4 +, urea, PO4 3−, and organic nitrogen and phosphorus, were manyfold higher than observed in the year prior or since. These findings suggest that mesoscale features were important in bloom dynamics more regionally, but locally the bloom was sustained by nutrient enrichment supplemented by its mixotrophic capabilities

Ocean acidification with (de)eutrophication will alter future phytoplankton growth and succession

Human activity causes ocean acidification (OA) though the dissolution of anthropogenically generated CO2 into seawater, and eutrophication through the addition of inorganic nutrients. Eutrophication increases the phytoplankton biomass that can be supported during a bloom, and the resultant uptake of dissolved inorganic carbon during photosynthesis increases water-column pH (bloom-induced basification). This increased pH can adversely affect plankton growth. With OA, basification commences at a lower pH. Using experimental analyses of the growth of three contrasting phytoplankton under different pH scenarios, coupled with mathematical models describing growth and death as functions of pH and nutrient status, we show how different conditions of pH modify the scope for competitive interactions between phytoplankton species. We then use the models previously configured against experimental data to explore how the commencement of bloom-induced basification at lower pH with OA, and operating against a background of changing patterns in nutrient loads, may modify phytoplankton growth and competition. We conclude that OA and changed nutrient supply into shelf seas with eutrophication or de-eutrophication (the latter owing to pollution control) has clear scope to alter phytoplankton succession, thus affecting future trophic dynamics and impacting both biogeochemical cycling and fisheries

Nitrogen dynamics and phytoplankton community structure: the role of organic nutrients

Publication history: Accepted - 7 June 2017; Published online - 15 June 2017.Dissolved organic nitrogen (DON) is recognised as an important N source for phytoplankton. However, its relative importance for phytoplankton nutrition and community composition has not been studied comprehensively. This study, conducted in a typical Scottish fjord, representative of nearpristine coastal environments, evaluates the utilisation of DON and dissolved inorganic nitrogen (DIN) by different microbial size fractions and the relationship of phytoplankton community composition with DON and other parameters. The study demonstrated that DON was important in supporting phytoplankton throughout the yearly production cycle. The higherthan-expected urea uptake rates and large fraction of the spring bloom production supported by DON suggested that organic N not only contributes to regenerated production and to the nutrition of the small phytoplankton fraction, but can also contribute substantially to new production of the larger phytoplankton in coastal waters. Multivariate statistical techniques revealed two phytoplankton assemblages with peaks in abundance at different times of the year: a spring group dominated by Skeletonema spp., Thalassiosira spp., and Pseudo-nitzschia spp. group delicatissima; and a summer/autumn group dominated by Chaetoceros spp., Scrippsiella spp., and Pseudonitzschia spp. group seriata. The multivariate pattern in community composition and abundance of these taxa was significantly correlated with the multivariate pattern of DON, urea, dissolved free amino acids, DIN, temperature, salinity, and daylength, with daylength and urea being particularly important, suggesting both physical and chemical controls on community composition.The authors wish to acknowledge the National Environment Research Council (NERC) for funding and the officers and crew of RV Seòl Mara for assisting with sample collection. This is contribution number 5318 from the University of Maryland Center for Environmental Science

Harmful algal blooms and eutrophication : examining linkages from selected coastal regions of the United States

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Harmful Algae 8 (2008): 39-53, doi:10.1016/j.hal.2008.08.017.Coastal waters of the United States (U.S.) are subject to many of the major harmful algal bloom (HAB) poisoning syndromes and impacts. These include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), ciguatera fish poisoning (CFP) and various other HAB phenomena such as fish kills, loss of submerged vegetation, shellfish mortalities, and widespread marine mammal mortalities. Here, the occurrences of selected HABs in a selected set of regions are described in terms of their relationship to eutrophication, illustrating a range of responses. Evidence suggestive of changes in the frequency, extent or magnitude of HABs in these areas is explored in the context of the nutrient sources underlying those blooms, both natural and anthropogenic. In some regions of the U.S., the linkages between HABs and eutrophication are clear and well documented, whereas in others, information is limited, thereby highlighting important areas for further research.Support was provided through the Woods Hole Center for Oceans and Human Health (to DMA), National Science Foundation (NSF) grants OCE-9808173 and OCE-0430724 (to DMA), OCE-0234587 (to WPC), OCE04-32479 (to MLP), OCE-0138544 (to RMK), OCE-9981617 (to PMG); National Institute of Environmental Health Sciences (NIEHS) grants P50ES012742-01 (to DMA) and P50ES012740 (to MLP); NOAA Grants NA96OP0099 (to DMA), NA16OP1450 (to VLT), NA96P00084 (to GAV and CAH), NA160C2936 and NA108H-C (to RMK), NA860P0493 and NA04NOS4780241 (to PMG), NA04NOS4780239-02 (to RMK), NA06NOS4780245 (to DWT). Support was also provided from the West Coast Center for Oceans and Human Health (to VLT and WPC), USEPA Grant CR826792-01-0 (to GAV and CAH), and the State of Florida Grant S7701617826 (to GAV and CAH)