92 research outputs found
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 advancementsâand if efforts to reduce nutrient pollution and control climate change become global prioritiesâthere 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 ÎŒm 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 NO3â 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 6500â9000 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 mixoplanktonâubiquitous microbes that employ phototrophy and phagotrophy synergistically in one cellâreshapes 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 organismsâas well as the complexity of their interactionsâhas 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 whalesâCelebrating 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, âto a degree that will enable man to exercise satisfactory control of the environment and make useful predictionsâ (Institute of Marine Resources annual report, 1968, cited in Shor 1978:143) and âto predict the formation and transfer of nutrients through the full cycle of life in the oceanâ (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 significanceâsuch as
general ocean circulation, the carbon
cycle, the structure and dynamics
of ecosystems, and harmful algal
bloomsâare 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 processesâ
such as climate change, CO2 enhancement,
ocean acidification, pollution,
and eutrophicationâwhose 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 changesâboth
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
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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 2008â2009. For the first 2 weeks of the coastal Omani bloom, C. polykrikoides abundance was near monospecific proportions, with cell densities ranging from 4.6âĂâ103 to 9âĂâ106 cells Lâ1 and very high levels of chlorophyll a (78.0 ÎŒg Lâ1) 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 3â, 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 SeĂČl 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)
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