Export 210 results:
Sort by: Author Title Type [ Year  (Desc)]
Kenitz, KM, Visser AW, Ohman MD, Landry MR, Andersen KH.  2019.  Community trait distribution across environmental gradients. Ecosystems. 22:968-980.   10.1007/s10021-018-0314-5   AbstractWebsite

Variability in community composition is often attributed to underlying differences in physical environments. However, predator-prey interactions can play an equally important role in structuring communities. Although environmental differences select for different species assemblages, less is known about their impacts on trait compositions. We develop a trait-based analysis of plankton communities of the southern California Current System across multiple trophic levels, from bacteria to mesozooplankton, and over a gradient of environmental conditions, from the oligotrophic open ocean to coastal upwelling. Across a factor of four differences in total community biomass, we observe similarities in the size structure along the environmental gradient, with the most pronounced departures from proportional variations in the biomasses found in the largest protists (> 40 mu m). Differences in the trait distributions emerge within a small range of size groups: greater biomass contribution of larger autotrophs (> 10 mu m) is observed only for the upwelling region.

Stukel, MR, Kelly TB, Aluwihare LI, Barbeau KA, Goericke R, Krause JW, Landry MR, Ohman MD.  2019.  The Carbon:(234)Thorium ratios of sinking particles in the California current ecosystem 1: relationships with plankton ecosystem dynamics. Marine Chemistry. 212:1-15.   10.1016/j.marchem.2019.01.003   AbstractWebsite

We investigated variability in the C:Th-234 ratio of sinking particles and its relationship to changing water column characteristics and plankton ecological dynamics during 29 Lagrangian experiments conducted on six cruises of the California Current Ecosystem Long-Term Ecological Research (CCE-LTER) Program. C:Th-234 ratios of sinking particles collected by a surface-tethered sediment trap ((CThST)-Th-:234) varied from 2.3 to 20.5 mu mol C dpm(-1) over a depth range of 47-150 m. C:Th-234(ST) was significantly greater (by a factor of 1.8) than C:Th-234 ratios of suspended > 51-mu m particles collected in the same water parcels with in situ pumps. C:Th-234 ratios of large (> 200-mu m) sinking particles also exceeded those of smaller sinking particles. C:Th-234(ST) decreased with depth from the base of the euphotic zone through the upper twilight zone. C:Th-234(ST) was positively correlated with several indices of ecosystem productivity including particulate organic carbon (POC) and chlorophyll (Chl) concentrations, mesozooplankton biomass, and the fraction of Chl > 20-mu m. Principal component analysis and multiple linear regression suggested that decaying phytoplankton blooms exhibited higher C:Th-234(ST) than actively growing blooms at similar biomass levels. C:Th-234(ST) was positively correlated with indices of the fractional contribution of fecal pellets in sediment traps when the proportion of fecal pellets was low in the traps, likely because of a correlation between mesozooplankton biomass and other indices of ecosystem productivity. However, when fecal pellets were a more important component of sinking material, C:Th-234(ST) decreased with increasing fecal pellet content. C:Th-234(ST) was also positively correlated with the Si:C ratio of sinking particles. Across the dataset (and across depths) a strong correlation was found between C:Th-234(ST) and the ratio of vertically-integrated POC to vertically-integrated total water column Th-234 (C-v:Th-234(tot)). A mechanistic one-layer, two-box model of thorium sorption and desorption was invoked to explain this correlation. Two empirical models (one using C-v:Th-234(tot); one using depth and vertically-integrated Chl) were developed to predict C:Th-234 ratios in this coastal upwelling biome. The former regression (log(10)(C:Th-234(ST)) = 0.43 x log(10)(C-v:Th-234(tot)) + 0.53) was found to also be a reasonable predictor for C:Th-234(ST) from diverse regions including the Southern Ocean, Sargasso Sea, Subarctic North Pacific, and Eastern Tropical North Pacific.

Gutierrez-Rodriguez, A, Stukel MR, dos Santos AL, Biard T, Scharek R, Vaulot D, Landry MR, Not F.  2019.  High contribution of Rhizaria (Radiolaria) to vertical export in the California Current Ecosystem revealed by DNA metabarcoding. Isme Journal. 13:964-976.   10.1038/s41396-018-0322-7   AbstractWebsite

Passive sinking of particulate organic matter (POM) is the main mechanism through which the biological pump transports surface primary production to the ocean interior. However, the contribution and variability of different biological sources to vertical export is not fully understood. Here, we use DNA metabarcoding of the 18S rRNA gene and particle interceptor traps (PITs) to characterize the taxonomic composition of particles sinking out of the photic layer in the California Current Ecosystem (CCE), a productive system with high export potential. The PITs included formalin-fixed and 'live' traps to investigate eukaryotic communities involved in the export and remineralization of sinking particles. Sequences affiliated with Radiolaria dominated the eukaryotic assemblage in fixed traps (90%), with Dinophyta and Metazoa making minor contributions. The prominence of Radiolaria decreased drastically in live traps, possibly due to selective consumption by copepods, heterotrophic nanoflagellates, and phaeodarians that were heavily enriched in these traps. These patterns were consistent across the water masses surveyed extending from the coast to offshore, despite major differences in productivity and trophic structure of the epipelagic plankton community. Our findings identify Radiolaria as major actors in export fluxes in the CCE.

Landry, MR, Beckley LE, Muhling BA.  2019.  Climate sensitivities and uncertainties in food-web pathways supporting larval bluefin tuna in subtropical oligotrophic oceans. Ices Journal of Marine Science. 76:359-369.   10.1093/icesjms/fsy184   AbstractWebsite

Compared with high-latitude seas, the ecological implications of climate change for top consumers in subtropical regions are poorly understood. One critical area of knowledge deficiency is the nature of food-web connections to larvae during their vulnerable time in the plankton. Bluefin tuna (BFT) are highly migratory temperate species whose early life stages are spent in ultra-oligotrophic subtropical waters. Dietary studies of BFT larvae provide evidence of prey-limited growth coupled with strong selection for specific prey typescladocerans and poecilostomatoid copepodswhose paradoxical or poorly resolved trophic characteristics do not fit the conventional understanding of open-ocean food-web structure and flows. Current knowledge consequently leaves many uncertainties in climate change effects, including the possibility that increased nitrogen fixation by Trichodesmium spp. might enhance resiliency of BFT larvae, despite a projected overall decline in system productivity. To advance understanding and future predictions, the complementary perspectives of oceanographers and fisheries researchers need to come together in studies that focus on the trophic pathways most relevant to fish larvae, the factors that drive variability in spawning regions, and their effects on larval feeding, growth, and survival.

Decima, M, Stukel MR, Lopez-Lopez L, Landry MR.  2019.  The unique ecological role of pyrosomes in the Eastern Tropical Pacific. Limnology and Oceanography. 64:728-743.   10.1002/lno.11071   AbstractWebsite

Pyrosomes are an important but often overlooked component of marine zooplankton communities, with limited existing information regarding their ecological and trophic roles in pelagic ecosystems. We present the first estimates of grazing and trophic interactions of the large tropical pyrosome, Pyrostremma spinosum, in the Eastern Tropical Pacific. While patchy in distribution, Pyrostremma spinosum's grazing impact was substantial, up to 17.5% of chlorophyll a standing stock d(-1) in certain areas. In contrast, these organisms cleared a very small percentage of the abundant picoplankton Synechococcus spp. compared to the bulk zooplankton community. Stable isotopes (C-13 and N-15) indicated that particulate organic matter (POM) from the surface mixed layer (0-20 m) constitutes the isotopic food-web baseline for most of the zooplankton community, and zooplankton trophic interactions were size structured in some areas. Pyrosomes, doliolids, and appendicularians, along with the smallest size class of net-collected zooplankton, had isotopic values closest to pure herbivory, while intermediate size classes, copepods, and salps showed substantial omnivory/carnivory. Euphausiids, chaetognaths, and > 2 mm zooplankton were the main carnivorous zooplankton in the plankton food web. Stable isotopes indicated that Pyrostremma spinosum is trophically distinct from the rest of the zooplankton community, grazing just below the mixed layer (20-40 m), as opposed to feeding on surface POM. Pyrosomes represent an additional, distinct pathway for material transfer up the plankton food web, by directly consuming POM sources not substantially grazed upon by the rest of the mesozooplankton community.

Stukel, MR, Decima M, Landry MR, Selph KE.  2018.  Nitrogen and Isotope Flows Through the Costa Rica Dome Upwelling Ecosystem: The Crucial Mesozooplankton Role in Export Flux. Global Biogeochemical Cycles. 32:1815-1832.   10.1029/2018gb005968   AbstractWebsite

The Costa Rica Dome (CRD) is an open-ocean upwelling ecosystem, with high biomasses of picophytoplankton (especially Synechococcus), mesozooplankton, and higher trophic levels. To elucidate the food web pathways supporting the trophic structure and carbon export in this unique ecosystem, we used Markov Chain Monte Carlo techniques to assimilate data from four independent realizations of N-15 and planktonic rate measurements from the CRD into steady state, multicompartment ecosystem box models (linear inverse models). Model results present well-constrained snapshots of ecosystem nitrogen and stable isotope fluxes. New production is supported by upwelled nitrate, not nitrogen fixation. Protistivory (rather than herbivory) was the most important feeding mode for mesozooplankton, which rely heavily on microzooplankton prey. Mesozooplankton play a central role in vertical nitrogen export, primarily through active transport of nitrogen consumed in the surface layer and excreted at depth, which comprised an average 36-46% of total export. Detritus or aggregate feeding is also an important mode of resource acquisition by mesozooplankton and regeneration of nutrients within the euphotic zone. As a consequence, the ratio of passively sinking particle export to phytoplankton production is very low in the CRD. Comparisons to similar models constrained with data from the nearby equatorial Pacific demonstrate that the dominant role of vertical migrators to the biological pump is a unique feature of the CRD. However, both regions show efficient nitrogen transfer from mesozooplankton to higher trophic levels (as expected for regions with large fish, cetacean, and seabird populations) despite the dominance of protists as major grazers of phytoplankton. Plain Language Summary Most of the world's oceanic regions can be divided into (1) low-nutrient areas where small algae dominate and crustaceans, fish, and whales are scarce or (2) productive areas where large algae dominate, crustaceans and higher trophic levels are abundant, and substantial carbon is transported to depth as part of the biological pump. The Costa Rica Dome (CRD) is a unique natural laboratory for investigating the relationships between algae, zooplankton, and marine biogeochemistry because it is a productive region dominated by cyanobacteria (small algae) that nevertheless sustains large populations of crustaceans, fish, and whales. We used a novel data assimilation tool to constrain a food web model using at-sea rate measurements of plankton activity and nitrogen stable isotopes. We found that protists are an important intermediate trophic level linking cyanobacteria and mesozooplankton. Efficient recycling by the zooplankton community facilitates nitrogen transfer to fish, whales, and seabirds. In the CRD, vertically migrating zooplankton (which feed in the surface during the night but descend to depth during the day to escape predators) play a particularly important role in transporting nitrogen (and carbon dioxide) from the surface to the deep ocean, where it can be removed from the atmosphere.

Taylor, AG, Landry MR.  2018.  Phytoplankton biomass and size structure across trophic gradients in the southern California Current and adjacent ocean ecosystems. Marine Ecology Progress Series. 592:1-17.   10.3354/meps12526   AbstractWebsite

We used a combination of epifluorescence microscopy and flow cytometry to investigate variability of phytoplankton biomass and size structure with ocean richness, measured as autotrophic carbon (AC) or chlorophyll a (chl a). Samples were collected from mixed layers of 4 North Pacific ecosystems: the California Current (CCE), Equatorial Pacific, Costa Rica Dome, and subtropical gyre (station ALOHA). Both nano- (2-20 mu m) and microphytoplankton (20-200 mu m) in creased biomass as power functions with increasing richness, with a sharper slope leading to microphytoplankton dominance at high biomass. The AC: chl a ratio (mu g:mu g) was also well fit by a power function, varying from similar to 170 to 20 over the range of <0.06 to >11.7 mu g chl a l(-1). Prochlorococcus and diatoms were major biomass contributors at poorer and richer extremes, respectively, but mixed flagellates (prymnesiophytes, dinoflagellates, others) comprised a surprisingly consistent half of AC over the richness range. While pico- (<2 mu m) and nanophytoplankton co-dominated at low chl a, all picophytoplankton (Prochlorococcus, Synechococcus, picoeukaryotes) declined significantly in richer coastal waters. Their decrease was consistent with a previously proposed mechanism linking Prochlorococcus decline to increased productivity and grazing pressure on heterotrophic bacteria, termed here the enhanced microbial loop hypothesis. Generalized additive models further indicated that biotic variables explained more of picophytoplankton variability than abiotic variables in CCE coastal waters. Density-independent grazing may be a strong driver of picophytoplankton selection across trophic gradients, with implications for strategy trade-offs in growth rate and grazing resistance, and for representing mortality in marine ecosystem models. [GRAPHICS] Conceptual depiction of the Enhanced Microbial Loop hypo thesis at high chl a Conceptual depiction: Dennis Mc Thompson

Valencia, B, Decima M, Landry MR.  2018.  Environmental Effects on Mesozooplankton Size Structure and Export Flux at Station ALOHA, North Pacific Subtropical Gyre. Global Biogeochemical Cycles. 32:289-305.   10.1002/2017gb005785   AbstractWebsite

Using size-fractionated mesozooplankton biomass data collected over 23 years (1994-2016) of increasing primary production (PP) at station ALOHA (A Long-Term Oligotrophic Habitat Assessment), we evaluate how changing environmental conditions affect mesozooplankton size structure, trophic cycling, and export fluxes in the subtropical North Pacific. From generalized additive model analysis, size structure is significantly influenced by a nonlinear relationship with sea surface temperature that is mainly driven by the strong 1997-1998 El Nino and a positive and linear relationship with PP. Increasing PP has more strongly enhanced the biomass of smaller (0.2-0.5 mm) and larger (>5 mm) mesozooplankton, increasing evenness of the biomass spectra, while animals of 2-5 mm, the major size class for vertically migrating mesozooplankton, show no long-term trend. Measured PP is sufficient to meet feeding requirements that satisfy mesozooplankton respiration and growth rates, as determined by commonly used empirical relationships based on animal size and temperature, consistent with a tightly coupled food web with one intermediate level for protistan consumers. Estimated fecal pellet production suggests an enhanced contribution of mesozooplankton to passive particle export relative to the material collected in 150 m sediment traps. In contrast, the biomass of vertically migrants does not vary systematically with PP due to the varying responses of the different size classes. These results illustrate some complexities in understanding how varying environmental conditions can affect carbon cycling and export processes at the community level in open-ocean oligotrophic systems, which need to be confirmed and better understood by process-oriented mechanistic study.

Decima, M, Landry MR, Bradley CJ, Fogel ML.  2017.  Alanine delta(15) N trophic fractionation in heterotrophic protists. Limnology and Oceanography. 62:2308-2322.   10.1002/lno.10567   AbstractWebsite

We evaluated differences in the N-15 isotopic enrichment factors of trophic amino acids (AA) for protistan (microzooplankton) and metazoan (mesozooplankton) consumers, testing the hypothesis that delta N-15 of alanine (ala) increases in both consumer types, while glutamic acid (glu) enriches mainly in mesozooplankton. AA delta N-15 values were measured for dinoflagellate and ciliate grazers and their respective algal prey (Oxyrrhis marina/Dunaliella tertiolecta and Favella sp./Heterocapsa triquetra) in four two-stage chemostat experiments, including treatments with different nitrogen : phosphorous nutrient ratios and light/dark recycling conditions. Propagation of AA N-15 enrichment to a metazoan consumer was also assessed in two-and three-stage chemostat experiments simulating simple "classical" (Calanus pacificus and the diatom Thalassiosira weissflogii) and "multivorous" (C. pacificus, O. marina, and D. tertiolecta) food chains. We found small or negligible 15 N-enrichment of glu for both protistan grazers, while ala enrichment was consistently greater and similar to that in metazoan consumers. Ala and glu delta N-15 values were both highly elevated in C. pacificus relative to prey, and enrichment was higher with autotrophic diets. These laboratory results suggest that ala may be used as an alternate, accurate isotopic proxy for quantifying protistan contributions to trophic structure in aquatic systems.

Li, QP, Franks PJS, Landry MR.  2017.  Recovering growth and grazing rates from nonlinear dilution experiments. Limnology and Oceanography. 62:1825-1835.   10.1002/lno.10536   AbstractWebsite

Biological rate measurements provide critical information for understanding key processes and modeling future states of marine ecosystems. Experimentally derived rates can be challenging to interpret when methodological assumptions are untested or potentially violated under variable natural conditions, such as the assumed linear grazing response of the dilution technique for estimating rates of phytoplankton growth and microzooplankton grazing impact. Here, we show that grazing nonlinearity can be related to the ratio of initial phytoplankton biomass to the half-saturation parameter in the Holling II model, while not being affected by varying grazer biomass during dilution experiments. From this, we present theory to recover growth and grazing rates from multi-treatment dilution experiments with nonlinear grazing results. We test our analyses with data collected during the California Current Ecosystem-Long-Term Ecological Research (CCE-LTER) program. We show that using a linear regression in 2-treatment dilution experiments may lead to underestimates of microzooplankton grazing rates, particularly in high-phytoplankton-biomass coastal regions where grazing can be saturated. Using the Holling II grazing model and a correction factor, growth and grazing rates from 2-treatment experiments can also be estimated, as illustrated by application to Lagrangian watertracking studies of growth and grazing dynamics in the CCE.

Zhang, SW, Chan KYK, Shen Z, Cheung SY, Landry MR, Liu HB.  2017.  A cryptic marine ciliate feeds on progametes of Noctiluca scintillans. Protist. 168:1-11.   10.1016/j.protis.2016.08.005   AbstractWebsite

The dinoflagellate Noctiluca scintillans (Noctiluca) has the ability to reproduce sexually, which may help to increase or restore its population size during periods of blooms or environmental stress. Here, we documented for the first time a marine ciliate Strombidium sp. that feeds on Noctiluca's progametes undergoing stages 5 to 9 of nuclear division. This ciliate frequently swam on or around gametogenic and some vegetative Noctiluca cells. The ciliates associated with gametogenic cells had significantly lower swimming speed and changed direction more frequently than those associated with vegetative cells, which overall increased their time spent around the food patches (progametes). This trophic interaction constitutes an upside-down predator -prey link, in which ciliates within the typical size range of Noctiluca prey, become the predators. Based on the phylogenetic tree (maximum-likelihood), there are 14 environmental clones similar to Strombidium sp. found in other coastal waters, where Noctiluca presence or blooms have been reported. This novel predator-prey relationship could therefore be common in other Noctiluca habitats. Additional studies are needed to assess the magnitude of its impacts on Noctiluca population dynamics and plankton bloom succession. (C)2016 Elsevier GmbH. All rights reserved.

Stukel, MR, Aluwihare LI, Barbeau KA, Chekalyuk AM, Goericke R, Miller AJ, Ohman MD, Ruacho A, Song H, Stephens BM, Landry MR.  2017.  Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction. Proceedings of the National Academy of Sciences of the United States of America. 114:1252-1257.   10.1073/pnas.1609435114   AbstractWebsite

Enhanced vertical carbon transport (gravitational sinking and subduction) at mesoscale ocean fronts may explain the demonstrated imbalance of new production and sinking particle export in coastal upwelling ecosystems. Based on flux assessments from U-238:Th-234 disequilibrium and sediment traps, we found 2 to 3 times higher rates of gravitational particle export near a deep-water front (305 mg C.m(-2).d(-1)) compared with adjacent water or to mean (nonfrontal) regional conditions. Elevated particle flux at the front wasmechanistically linked to Fe-stressed diatoms and high-mesozooplankton fecal pellet production. Using a data assimilative regional ocean model fit to measured conditions, we estimate that an additional similar to 225 mg C.m(-2).d(-1) was exported as subduction of particle-rich water at the front, highlighting a transport mechanism that is not captured by sediment traps and is poorly quantified by most models and in situ measurements. Mesoscale fronts may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems.

Steinberg, DK, Landry MR.  2017.  Zooplankton and the ocean carbon cycle. Annual Review of Marine Sciences, Vol 9. 9:413-444., Palo Alto: Annual Reviews   10.1146/annurev-marine-010814-015924   Abstract

Marine zooplankton comprise a phylogenetically and functionally diverse assemblage of protistan and metazoan consumers that occupy multiple trophic levels in pelagic food webs. Within this complex network, carbon flows via alternative zooplankton pathways drive temporal and spatial variability in production-grazing coupling, nutrient cycling, export, and transfer efficiency to higher trophic levels. We explore current knowledge of the processing of zooplankton food ingestion by absorption, egestion, respiration, excretion, and growth (production) processes. On a global scale, carbon fluxes are reasonably constrained by the grazing impact of microzooplankton and the respiratory requirements of mesozooplankton but are sensitive to uncertainties in trophic structure. The relative importance, combined magnitude, and efficiency of export mechanisms (mucous feeding webs, fecal pellets, molts, carcasses, and vertical migrations) likewise reflect regional variability in community structure. Climate change is expected to broadly alter carbon cycling by zooplankton and to have direct impacts on key species.

Valencia, B, Landry MR, Decima M, Hannides CCS.  2016.  Environmental drivers of mesozooplankton biomass variability in the North Pacific Subtropical Gyre. Journal of Geophysical Research-Biogeosciences. 121:3131-3143.   10.1002/2016jg003544   AbstractWebsite

The environmental drivers of zooplankton variability are poorly explored for the central subtropical Pacific, where a direct bottom-up food-web connection is suggested by increasing trends in primary production and mesozooplankton biomass at station ALOHA (A Long-term Oligotrophic Habitat Assessment) over the past 20 years (1994-2013). Here we use generalized additive models (GAMs) to investigate how these trends relate to the major modes of North Pacific climate variability. A GAM based on monthly mean data explains 43% of the temporal variability in mesozooplankton biomass with significant influences from primary productivity (PP), sea surface temperature (SST), North Pacific Gyre Oscillation (NPGO), and El Nino. This result mainly reflects the seasonal plankton cycle at station ALOHA, in which increasing light and SST lead to enhanced nitrogen fixation, productivity, and zooplankton biomass during summertime. Based on annual mean data, GAMs for two variables suggest that PP and 3-4 year lagged NPGO individually account for similar to 40% of zooplankton variability. The full annual mean GAM explains 70% of variability of zooplankton biomass with significant influences from PP, 4 year lagged NPGO, and 4 year lagged Pacific Decadal Oscillation (PDO). The NPGO affects wind stress, sea surface height, and subtropical gyre circulation and has been linked to mideuphotic zone anomalies in salinity and PP at station ALOHA. Our study broadens the known impact of this climate mode on plankton dynamics in the North Pacific. While lagged transport effects are also evident for subtropical waters, our study highlights a strong coupling between zooplankton fluctuations and PP, which differs from the transport-dominated climate influences that have been found for North Pacific boundary currents.

Pasulka, AL, Levin LA, Steele JA, Case DH, Landry MR, Orphan VJ.  2016.  Microbial eukaryotic distributions and diversity patterns in a deep-sea methane seep ecosystem. Environmental Microbiology. 18:3022-3043.   10.1111/1462-2920.13185   AbstractWebsite

Although chemosynthetic ecosystems are known to support diverse assemblages of microorganisms, the ecological and environmental factors that structure microbial eukaryotes (heterotrophic protists and fungi) are poorly characterized. In this study, we examined the geographic, geochemical and ecological factors that influence microbial eukaryotic composition and distribution patterns within Hydrate Ridge, a methane seep ecosystem off the coast of Oregon using a combination of high-throughput 18S rRNA tag sequencing, terminal restriction fragment length polymorphism fingerprinting, and cloning and sequencing of full-length 18S rRNA genes. Microbial eukaryotic composition and diversity varied as a function of substrate (carbonate versus sediment), activity (low activity versus active seep sites), sulfide concentration, and region (North versus South Hydrate Ridge). Sulfide concentration was correlated with changes in microbial eukaryotic composition and richness. This work also revealed the influence of oxygen content in the overlying water column and water depth on microbial eukaryotic composition and diversity, and identified distinct patterns from those previously observed for bacteria, archaea and macrofauna in methane seep ecosystems. Characterizing the structure of microbial eukaryotic communities in response to environmental variability is a key step towards understanding if and how microbial eukaryotes influence seep ecosystem structure and function.

Liu, X, Xiao WP, Landry MR, Chiang KP, Wang L, Huang BQ.  2016.  Responses of phytoplankton communities to environmental variability in the East China Sea. Ecosystems. 19:832-849.   10.1007/s10021-016-9970-5   AbstractWebsite

We investigated seasonal and spatial patterns of phytoplankton variability in the East China Sea in order to understand biomass and compositional responses to environmental factors in the contemporary ocean. We used satellite imagery from 2002 to 2013 to define the mean seasonal climatology of sea surface temperature and chlorophyll a. Phytoplankton and environmental measurements were synthesized for the study region and four seasons from 11 cruises conducted from 2006 to 2012. The results of CHEMTAX analyses on group-specific phytoplankton composition were consistent with those of microscopy and flow cytometry observations, revealing three patterns of seasonal variability. Canonical correspondence analysis and generalized additive models (GAMs) were used to resolve the spatiotemporal variations of major phytoplankton groups and their relationships to month, temperature, salinity, nutrients, mixed layer depth, and bottom depth. Monsoon forcing drove the distributional patterns of environmental factors and was critical to explaining phytoplankton dynamics at the seasonal scale. Compared to autumn and winter, significantly higher chlorophyll a concentrations were observed during spring and summer, associated with the spring bloom and the Changjiang (Yangtze) River plume, respectively. Diatoms dominated biomass over the East China Sea, especially during the summer months influenced by the Changjiang (Yangtze) River plume, whereas dinoflagellates were especially important during spring blooms. GAMs analysis showed the differences in their responses to environmental variability, with a clear mid-range salinity optimum (similar to 31) and a more pronounced temperature effect for dinoflagellates. The photosynthetic bacteria, Prochlorococcus and Synechococcus, both increased strongly with warming, but Prochlorococcus showed stronger sensitivity to variations in physical environmental parameters, whereas Synechococcus was more responsive to chemical (nutrient) variability, with broader tolerance of low-salinity conditions.

Stukel, MR, Benitez-Nelson CR, Decima M, Taylor AG, Buchwald C, Landry MR.  2016.  The biological pump in the Costa Rica Dome: an open-ocean upwelling system with high new production and low export. Journal of Plankton Research. 38:348-365.   10.1093/plankt/fbv097   AbstractWebsite

The Costa Rica Dome is a picophytoplankton-dominated, open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone. To investigate the efficiency of the biological pump in this unique area, we used shallow (90-150 m) drifting sediment traps and Th-234: U-238 deficiency measurements to determine export fluxes of carbon, nitrogen and phosphorus in sinking particles. Simultaneous measurements of nitrate uptake and shallow water nitrification allowed us to assess the equilibrium balance of new and export production over a monthly timescale. While f-ratios (new: total production) were reasonably high (0.36+/-0.12, mean+/-standard deviation), export efficiencies were considerably lower. Sediment traps suggested e-ratios (export/C-14-primary production) at 90-100 m ranging from 0.053 to 0.067. ThE-ratios (Th-234 disequilibrium-derived export) ranged from 0.038 to 0.088. C: N and N: P stoichiometries of sinking material were both greater than canonical (Redfield) ratios or measured C: N of suspended particulates, and they increased with depth, suggesting that both nitrogen and phosphorus were preferentially remineralized from sinking particles. Our results are consistent with an ecosystem in which mesozooplankton play a major role in energy transfer to higher trophic levels but are relatively inefficient in mediating vertical carbon flux to depth, leading to an imbalance between new production and sinking flux.

Goes, JI, Gomes HD, Selph KE, Landry MR.  2016.  Biological response of Costa Rica Dome phytoplankton to Light, Silicic acid and Trace metals. Journal of Plankton Research. 38:290-304.   10.1093/plankt/fbv108   AbstractWebsite

The Costa Rica Dome (CRD) is a unique open-ocean upwelling system, with picophytoplankton dominance of phytoplankton biomass and suppressed diatoms, yet paradoxically high export of biogenic silica. As a part of Flux and Zinc Experiments cruise in summer (June-July 2010), we conducted shipboard incubation experiments in the CRD to examine the potential roles of Si, Zn, Fe and light as regulating factors of phytoplankton biomass and community structure. Estimates of photosynthetic quantum yields revealed an extremely stressed phytoplankton population that responded positively to additions of silicic acid, iron and zinc and higher light conditions. Size-fractioned Chl a yielded the surprising result that picophytoplankton, as well as larger phytoplankton, responded most to treatments with added silicic acid incubated at high incident light (HL + Si). The combination of Si and HL also led to increases in cell sizes of picoplankton, notably in Synechococcus. Such a response, coupled with the recent discovery of significant intracellular accumulation of Si in some picophytoplankton, suggests that small phytoplankton could play a potentially important role in Si cycling in the CRD, which may help to explain its peculiar export characteristics.

Freibott, A, Taylor AG, Selph KE, Liu HB, Zhang WC, Landry MR.  2016.  Biomass and composition of protistan grazers and heterotrophic bacteria in the Costa Rica Dome during summer 2010. Journal of Plankton Research. 38:230-243.   10.1093/plankt/fbv107   AbstractWebsite

We investigated biomass and composition of heterotrophic microbes in the Costa Rica Dome during June-July 2010 as part of a broader study of plankton trophic dynamics. Because picophytoplankton (, 2 mm) are known to dominate in this unique upwelling region, we hypothesized tight biomass relationships between size-determined predator-prey pairs (i.e. picoplankton-nano-grazers, nanoplankton-micro-grazers) within the microbial community. Integrated biomass of heterotrophic bacteria ranged from 180 to 487 mg C m(-2) and was significantly correlated with total autotrophic carbon. Heterotrophic protist (H-protist) biomass ranged more narrowly from 488 to 545 mg C m(-2), and was comprised of 60% dinoflagellates, 30% other flagellates and 11% ciliates. Nano-sized (<20 mu m) protists accounted for the majority (57%) of grazer biomass and were positively correlated with picoplankton, partially supporting our hypothesis, but nanoplankton and micro-grazers (>20 mu m) were not significantly correlated. The relative constancy of H-protist biomass among locations despite clear changes in integrated autotrophic biomass, Chl a, and primary production suggests that mesozooplankton may exert a tight top-down control on micro-grazers. Biomass-specific consumption rates of phytoplankton by protistan grazers suggest an instantaneous growth rate of 0.52 day(-1) for H-protists, similar to the growth rate of phytoplankton and consistent with a trophically balanced ecosystem dominated by piconanoplankton interactions.

Baines, SB, Chen X, Twining BS, Fisher NS, Landry MR.  2016.  Factors affecting Fe and Zn contents of mesozooplankton from the Costa Rica Dome. Journal of Plankton Research. 38:331-347.   10.1093/plankt/fbv098   AbstractWebsite

Mineral limitation of mesozooplankton production is possible in waters with low trace metal availability. As a step toward estimating mesozooplankton Fe and Zn requirements under such conditions, we measured tissue concentrations of major and trace nutrient elements within size-fractioned zooplankton samples collected in and around the Costa Rica Upwelling Dome, a region where phytoplankton growth may be co-limited by Zn and Fe. The geometric mean C, N, P contents were 27, 5.6 and 0.21 mmol gdw(-1), respectively. The values for Fe and Zn were 1230 and 498 nmol gdw(-1), respectively, which are low compared with previous measurements. Migrant zooplankton caused C and P contents of the 2-5 mm fraction to increase at night relative to the day while the Fe and Zn contents decreased. Fe content increased with size while Zn content decreased with size. Fe content was strongly correlated to concentrations of two lithogenic tracers, Al and Ti. We estimate minimum Fe: C ratios in large migrant and resident mixed layer zooplankton to be 15 and 60 mu mol mol(-1), respectively. The ratio of Zn: C ranged from 11 mu mol mol(-1) for the 0.2-0.5 mm size fraction to 33 mu mol mol(-1) for the 2-5 mm size fraction.

Decima, M, Landry MR, Stukel MR, Lopez-Lopez L, Krause JW.  2016.  Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web. Journal of Plankton Research. 38:317-330.   10.1093/plankt/fbv091   AbstractWebsite

We investigated standing stocks and grazing rates of mesozooplankton assemblages in the Costa Rica Dome (CRD), an open-ocean upwelling ecosystem in the eastern tropical Pacific. While phytoplankton biomass in the CRD is dominated by picophytoplankton (<2-mu m cells) with especially high concentrations of Synechococcus spp., we found high mesozooplankton biomass (similar to 5 g dry weight m(-2)) and grazing impact (12-50% integrated water column chlorophyll a), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll a and mesozooplankton biomass, variability in herbivory was substantial, with lower rates in the central dome region and higher rates in areas offset from the dome center. While grazing rates were unrelated to total phytoplankton, correlations with cyanobacteria (negative) and biogenic SiO2 production (positive) suggest that partitioning of primary production among phytoplankton sizes contributes to the variability observed in mesozooplankton metrics. We propose that advection of upwelled waters away from the dome center is accompanied by changes in mesozooplankton composition and grazing rates, reflecting small changes within the primary producers. Small changes within the phytoplankton community resulting in large changes in the mesozooplankton suggest that the variability in lower trophic level dynamics was effectively amplified through the food web.

Baines, SB, Chen X, Vogt S, Fisher NS, Twining BS, Landry MR.  2016.  Microplankton trace element contents: implications for mineral limitation of mesozooplankton in an HNLC area. Journal of Plankton Research. 38:256-270.   10.1093/plankt/fbv109   AbstractWebsite

Mesozooplankton production in high-nutrient low-chlorophyll regions of the ocean may be reduced if the trace element concentrations in their food are insufficient to meet growth and metabolic demands. We used elemental microanalysis (SXRF) of single-celled plankton to determine their trace metal contents during a series of semi-Lagrangian drift studies in an HNLC upwelling region, the Costa Rica Dome (CRD). Cells from the surface mixed layer had lower Fe:S but higher Zn:S and Ni:S than those from the subsurface chlorophyll maximum at 22–30 m. Diatom Fe:S values were typically 3-fold higher than those in flagellated cells. The ratios of Zn:C in flagellates and diatoms were generally similar to each other, and to co-occurring mesozooplankton. Estimated Fe:C ratios in flagellates were lower than those in co-occurring mesozooplankton, sometimes by more than 3-fold. In contrast, Fe:C in diatoms was typically similar to that in zooplankton. RNA:DNA ratios in the CRD were low compared with other regions, and were related to total autotrophic biomass and weakly to the discrepancy between Zn:C in flagellated cells and mesozooplankton tissues. Mesozooplankton may have been affected by the trace element content of their food, even though trace metal limitation of phytoplankton was modest at best.

Krause, JW, Stukel MR, Taylor AG, Taniguchi DAA, de Verneil A, Landry MR.  2016.  Net biogenic silica production and the contribution of diatoms to new production and organic matter export in the Costa Rica Dome ecosystem. Journal of Plankton Research. 38:216-229.   10.1093/plankt/fbv077   AbstractWebsite

We determined the net rate of biogenic silica (bSiO(2)) production and estimated the diatom contribution to new production and organic matter export in the Costa Rica Dome during summer 2010. The shallow thermocline significantly reduces bSiO(2) dissolution rates below the mixed layer, leading to significant enhancement of bSiO(2) relative to organic matter (silicate-pump condition). This may explain why deep export of bSiO(2) in this region is elevated by an order of magnitude relative to comparable systems. Diatom carbon, relative to autotrophic carbon, was low (<3%); however, the contribution of diatoms to new production averaged 3 and 13% using independent approaches. The 4-old discrepancy between methods may be explained by a low average C:Si ratio (similar to 1.4) for the net produced diatom C relative to the net produced bSiO(2). We speculate that this low production ratio is not the result of reduced C, but may arise from a significant contribution of non-diatom silicifying organisms to bSiO(2) production. The contribution of diatoms to organic matter export was minor (5.7%). These results, and those of the broader project, suggest substantial food-web transformation of diatom organic matter in the euphotic zone, which creates enriched bSiO(2) relative to organic matter within the exported material.

Taylor, AG, Landry MR, Freibott A, Selph KE, Gutierrez-Rodriguez A.  2016.  Patterns of microbial community biomass, composition and HPLC diagnostic pigments in the Costa Rica upwelling dome. Journal of Plankton Research. 38:183-198.   10.1093/plankt/fbv086   AbstractWebsite

We investigated biomass, size-structure, composition, depth distributions and spatial variability of the phytoplankton community in the Costa Rica Dome (CRD) in June-July 2010. Euphotic zone profiles were sampled daily during Lagrangian experiments in and out of the dome region, and the community was analyzed using a combination of digital epifluorescence microscopy, flow cytometry and HPLC pigments. The mean depth-integrated biomass of phytoplankton ranged 2-fold, from 1089 to 1858 mg C m(-2) (mean+/-SE = 1378+/-112 mg C m(-2)), among 4 water parcels tracked for 4 days. Corresponding mean (+/-SE) integrated values for total chlorophyll a (Chl a) and the ratio of autotrophic carbon to Chl a were 24.1+/-1.5 mg Chl a m(-2) and 57.5+/-3.4, respectively. Absolute and relative contributions of picophytoplankton (similar to 60%), Synechococcus (>33%) and Prochlorococcus (17%) to phytoplankton community biomass were highest in the central dome region, while >20 mu m phytoplankton accounted for <= 10%, and diatoms, <2%, of biomass in all areas. Nonetheless, autotrophic flagellates, dominated by dinoflagellates, exceeded biomass contributions of Synechococcus at all locations. Order-of-magnitude discrepancies in the relative contributions of diatoms (overestimated) and dinoflagellates (underestimated) based on diagnostic pigments relative to microscopy highlight potential significant biases associated with making community inferences from pigments.

Gutierrez-Rodriguez, A, Selph KE, Landry MR.  2016.  Phytoplankton growth and microzooplankton grazing dynamics across vertical environmental gradients determined by transplant in situ dilution experiments. Journal of Plankton Research. 38:271-289.   10.1093/plankt/fbv074   AbstractWebsite

The Costa Rica Dome (CRD) represents a classic case of the bloom-forming capacity of small phytoplankton. Unlike other upwelling systems, autotrophic biomass in the CRD is dominated by picocyanobacteria and small eukaryotes that outcompete larger diatoms and reach extremely high biomass levels. We investigated responses of the subsurface phytoplankton community of the CRD to changes associated with vertical displacement of water masses, coupling in situ transplanted dilution experiments with flow cytometry and epifluorescence microscopy to assess group-specific dynamics. Growth rates of Synechococcus (SYN) and photosynthetic picoeukaryotes (PEUK) were positively correlated with light (R-pearson_SYN = 0.602 and R-pearson_PEUK = 0.588, P<0.001). Growth rates of Prochlorococcus (PRO), likely affected by photoinhibition, were not light correlated (R-pearson_PRO = 0.101, P = 0.601). Overall, grazing and growth rates were closely coupled in all picophytoplankton groups (R-spearman_PRO = 0.572, R-spearman_SYN = 0.588, R-spearman_PEUK = 0.624), and net growth rates remained close to zero. Conversely, the abundance and biomass of larger phytoplankton, mainly diatoms, increased more than 10-fold in shallower transplant incubations indicating that, in addition to trace-metal chemistry, light also plays a significant role in controlling microphytoplankton populations in the CRD.