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Landry, MR, Peterson WK, Andrews CC.  1992.  Particulate flux in the water column overlying Santa Monica Basin. Progress in Oceanography. 30:167-195.   10.1016/0079-6611(92)90012-o   AbstractWebsite

Fluxes of particulate carbon, nitrogen, phytoplankton pigments, biogenic silica and dry mass were measured using free-floating and moored sediment trap arrays in the Santa Monica Basin during the period from October 1985 to August 1990 as part of the California Basin Study (CaBS) Program. In field testing for potential sources of sediment trap biases, we found little significant or consistent difference in rate estimates between short-term drifting traps and long-term moored traps, between preserved and unpreserved traps in short-term experiments, between different preservatives (mercury or formalin) in long-term experiments, between different designs of small cylindrical traps, and between deep-moored cylindrical traps and large conical traps. We did, however, find that sediment trap samples collected and analyzed on 0.45mum silver filters gave estimates of carbon and nitrogen fluxes about 25% higher than samples collected on GF/F glass-fiber filters. Concurrent trap deployments at two stations 18km apart revealed low mesoscale variability in flux estimates. Seasonal patterns in carbon and nitrogen flux were not evident in our data but strong seasonality, with spring maxima and summer minima, were observed for fluxes of phaeopigments and biogenic silica out of the euphotic zone. Time-averaged rates of particulate flux for long-term trap deployments from January to August 1990, were 121, 18.8, 1.5, 67 and 633mg m-2d-1 at 110-135m for carbon, nitrogen, phaeopigment, biogenic silica and mass, respectively. Flux estimates to the basin floor (835-860m) were 50, 6.5, 0.64, 41.6 and 575mg m-2d-1 for the same parameters. The former estimates are constrained by and in good agreement with independent assessments of new production from nitrate uptake in the euphotic zone.The latter agree with rates previously inferred from the sedimentary record using Pb-210 as a tracer. In addition, the difference in carbon estimates in the water column between the euphotic zone and the basin floor is consistent With the requirements for bacterial growth and metabolism at intermediate depths as measured by the thymidine method.

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.

Greene, CH, Landry MR.  1985.  Patterns of prey selection in the cruising calanoid predator Euchaeta elongata. Ecology. 66:1408-1416.   10.2307/1938003   AbstractWebsite

The invertebrate predators of marine and freshwater plankton assemblages typically employ encounter tactics that enable investigators to characterize them as either ambushers or cruisers. In this study, we examine the implications of cruising tactics on the prey selection patterns exhibited by the marine calanoid copepod Euchaeta elongata. Patterns and mechanisms of prey selection exhibited by Euchaeta were investigated in the laboratory with predation experiments and videotaped observations of predator and prey swimming behavior. Prey types offered to Euchaeta included each of the developmental stages of Calanus pacificus and the adults of Pseudocalanus sp. Calanus' vulnerability to Euchaeta predation steadily increased through the naupliar stages, reached a peak in the early copepodid stages, and declined rapidly after the molt to the fourth copepodite. Pseudocalanus adults were as vulnerable to Euchaeta predation as the early copepodites of Calanus. The behavioral mechanisms underlying the observed patterns of prey selection are discussed and compared with the results from other investigations of selective planktivory by marine calanoid copepods. It is concluded that prey selection by Euchaeta is largely determined by differences in prey vulnerability; some evidence for active behavioral choice was observed, however.

Landry, MR, Ohman MD, Goericke R, Stukel MR, Barbeau KA, Bundy R, Kahru M.  2012.  Pelagic community responses to a deep-water front in the California Current Ecosystem: overview of the A-Front Study. Journal of Plankton Research. 34:739-748.   10.1093/plankt/fbs025   AbstractWebsite

In October 2008, we investigated pelagic community composition and biomass, from bacteria to fish, across a sharp frontal gradient overlying deep waters south of Point Conception, California. This northsouth gradient, which we called A-Front, was formed by the eastward flow of the California Current and separated cooler mesotrophic waters of coastal upwelling origin to the north, from warm oligotrophic waters of likely mixed subarcticsubtropical origin to the south. Plankton biomass and phytoplankton growth rates were two to three times greater on the northern side, and primary production rates were elevated 5-fold to the north. Compared with either of the adjacent waters, the frontal interface was strongly enriched and uniquely defined by a subsurface bloom of large diatoms, elevated concentrations of suspension-feeding zooplankton, high bioacoustical estimates of pelagic fish and enhanced bacterial production and phytoplankton biomass and photosynthetic potential. Such habitats, though small in areal extent, may contribute disproportionately and importantly to regional productivity, nutrient cycling, carbon fluxes and trophic ecology. As a general introduction to the A-Front study, we provide an overview of its design and implementation, a brief summary of major findings and a discussion of potential mechanisms of plankton enrichment at the front.

Hood, RR, Laws EA, Armstrong RA, Bates NR, Brown CW, Carlson CA, Chai F, Doney SC, Falkowski PG, Feely RA, Friedrichs MAM, Landry MR, Moore JK, Nelson DM, Richardson TL, Salihoglu B, Schartau M, Toole DA, Wiggert JD.  2006.  Pelagic functional group modeling: Progress, challenges and prospects. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 53:459-512.   10.1016/j.dsr2.2006.01.025   AbstractWebsite

In this paper, we review the state of the art and major challenges in current efforts to incorporate biogeochemical functional groups into models that can be applied on basin-wide and global scales, with an emphasis on models that might ultimately be used to predict how biogeochernical cycles in the ocean will respond to global warming. We define the term "biogeochemical functional group" to refer to groups of organisms that mediate specific chemical reactions in the ocean. Thus, according to this definition, "functional groups" have no phylogenetic meaning-these are composed of many different species with common biogeochemical functions. Substantial progress has been made in the last decade toward quantifying the rates of these various functions and understanding the factors that control them. For some of these groups, we have developed fairly sophisticated models that incorporate this understanding, e.g. for diazotrophs (e.g. Trichodesmium), silica producers (diatoms) and calcifiers (e.g. coccolithophorids and specifically Emiliania huxleyi). However, current representations of nitrogen fixation and calcification are incomplete, i.e., based primarily upon models of Trichodesmium and E huxleyi, respectively, and many important functional groups have not yet been considered in open-ocean biogeochemical models. Progress has been made over the last decade in efforts to simulate dimethylsulfide (DMS) production and cycling (i.e., by dinoflagellates and prymnesiophytes) and denitrification, but these efforts are still in their infancy, and many significant problems remain. One obvious gap is that virtually all functional group modeling efforts have focused on autotrophic microbes, while higher trophic levels have been completely ignored. It appears that in some cases (e.g., calcification), incorporating higher trophic levels may be essential not only for representing a particular biogeochemical reaction, but also for modeling export. Another serious problem is our tendency to model the organisms for which we have the most validation data (e.g., E huxleyi and Trichodesmium) even when they may represent only a fraction of the biogeochemical functional group we are trying to represent. When we step back and look at the paleo-oceanographic record, it suggests that oxygen concentrations have played a central role in the evolution and emergence of many of the key functional groups that influence biogeochemical cycles in the present-day ocean. However, more subtle effects are likely to be important over the next century like changes in silicate supply or turbulence that can influence the relative success of diatoms versus dinoflagellates, coccolithophorids and diazotrophs. In general, inferences drawn from the paleo-oceanographic record and theoretical work suggest that global warming will tend to favor the latter because it will give rise to increased stratification. However, decreases in pH and Fe supply could adversely impact coccolithophorids and diazotrophs in the future. It may be necessary to include explicit dynamic representations of nitrogen fixation, denitrification, silicification and calcification in our models if our goal is predicting the oceanic carbon cycle in the future, because these processes appear to play a very significant role in the carbon cycle of the present-day ocean and they are sensitive to climate change. Observations and models suggest that it may also be necessary to include the DMS cycle to predict future climate, though the effects are still highly uncertain. We have learned a tremendous amount about the distributions and biogeochemical impact of bacteria in the ocean in recent years, yet this improved understanding has not yet been incorporated into many of our models. All of these considerations lead us toward the development of increasingly complex models. However, recent quantitative model intercomparison studies suggest that continuing to add complexity and more functional groups to our ecosystem models may lead to decreases in predictive ability if the models are not properly constrained with available data. We also caution that capturing the present-day variability tells us little about how well a particular model can predict the future. If our goal is to develop models that can be used to predict how the oceans will respond to global warming, then we need to make more rigorous assessments of predictive skill using the available data. (c) 2006 Elsevier Ltd. All rights reserved.

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

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.

Landry, MR, Brown SL, Neveux J, Dupouy C, Blanchot J, Christensen S, Bidigare RR.  2003.  Phytoplankton growth and microzooplankton grazing in high-nutrient, low-chlorophyll waters of the equatorial Pacific: Community and taxon-specific rate assessments from pigment and flow cytometric analyses. Journal of Geophysical Research-Oceans. 108   10.1029/2000jc000744   AbstractWebsite

[1] Phytoplankton growth and microzooplankton grazing rates were investigated using the seawater dilution technique during a French Joint Global Ocean Flux Study cruise focusing on grazing processes in the high-nutrient, low-chlorophyll equatorial Pacific at 180degrees ( Etude du Broutage en Zone Equatoriale, October - November, 1996). Raw rate estimates based on spectrofluorometric and high-performance liquid chromatography pigment analyses were typically in close agreement, but most showed substantial imbalances in growth and grazing. Flow cytometric (FCM) analyses were used both as an alternate approach for distinguishing populations and as a means for adjusting pigmentbased growth estimates for changes in cellular chlorophyll content and biovolume. Total chlorophyll a (Tchl a) gave mean community growth rates of 0.76 d(-1) at 30 m and 0.27 d(-1) at 60 m. Grazing rates averaged 0.56 and 0.15 d(-1) at the two depths, respectively, and 69% of phytoplankton growth overall. For the prokaryotic picophytoplankter, Prochlorococcus ( PRO), rate estimates from dv-chl a and FCM cell counts generally indicated balanced growth and grazing and therefore close grazing control by microzooplankton. At the equator, rate estimates from dv-chl a averaged 0.6 - 0.7 d(-1) at 30 m and 0.25 - 0.26 at 60 m and were consistent with inferences based on diel pigment variations in the 30 - 70 m depth range. Phytoplankton production estimates from experimentally determined rates and microscopical assessments of autotrophic carbon at 30 m ( mean = 19 mg C m(-3) d(-1)) agreed well with contemporaneous measurements by 14 C uptake. Diatom growth rate estimates (1.0 - 1.6 d(-1)), constrained by contemporaneous measurements of silicate uptake, implied a relatively small biomass (10 - 45 nmol C L-1) with high rates of turnover and recycling.

Landry, MR, Selph KE, Taylor AG, Decima M, Balch WM, Bidigare RR.  2011.  Phytoplankton growth, grazing and production balances in the HNLC equatorial Pacific. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:524-535.   10.1016/j.dsr2.2010.08.011   AbstractWebsite

We investigate the hypothesis that phytoplankton growth and grazing processes are strongly balanced in high-nutrient low-chlorophyll (HNLC) waters of the equatorial Pacific using euphotic-zone estimates of rates and biomass determined for 30 stations during EB04 (December 2004) and EB05 (September 2005). As predicted by the balance hypothesis, depth-averaged instantaneous rates of phytoplankton growth and grazing losses to micro- and mesozooplankton show a net growth difference of zero. Contemporaneous estimates of phytoplankton biomass and specific rates from flow cytometry, microscopy and taxon-specific accessory pigments allow determination of constrained production-consumption trophic balances for the phytoplankton community as a whole and for major component populations. The magnitude of growth-based production (867 mg C m(-2) d(-1)) is consistent with measured (14)C primary production, given methodological differences. 70% of production is utilized by protistan herbivores within the microbial community; 30% is consumed by mesozooplankton. Among picophytoplankton (Prochlorococcus, Synechococcus and small eukaryotes), representing 40% of community biomass and 27% of daily biomass growth, microzooplankton consume almost all production. Among groups of larger eukaryote taxa, including diatoms but dominated by dinoflagellate biomass, micro-grazers consume 51-62% of production, with the remainder available to mesozooplankton. Some leakage from the balance is expected as export of sinking phytoplankton cells and aggregates, but is constrained to no more than a few percent of daily production from alternate determinations of mesozooplankton grazing. The demonstrated balance of growth and grazing processes in the equatorial Pacific is inconsistent with recent claims from inverse models that a large flux associated with ungrazed picophytoplankton production dominates euphotic zone carbon export in the region. (C) 2010 Elsevier Ltd. All rights reserved.

Calbet, A, Landry MR.  2004.  Phytoplankton growth, microzooplankton grazing, and carbon cycling in marine systems. Limnology and Oceanography. 49:51-57.   10.4319/lo.2004.49.1.0051   AbstractWebsite

We present an analysis of the global impact of microplanktonic grazers on marine phytoplankton and its implications for remineralization processes in the microbial community. The data were obtained by an extensive literature search that yielded 788 paired rate estimates of autotrophic growth (mu) and microzooplankton grazing (m) from dilution experiments. From studies in which phytoplankton standing stock was measured in terms of carbon equivalents, we show that the production estimate from dilution experiments is a reasonable proxy (r = 0.89) for production determined by the standard C-14 method. The ratio m: mu, the proportion of primary production (PP) consumed by micrograzers, shows that microzooplankton consumption is the main source of phytoplankton mortality in the oceans, accounting for 67% of phytoplankton daily growth for the full data set. This ratio varies modestly among various marine habitats and regions, with data averages ranging from 60% for coastal and estuarine environments to 70% for the open oceans, and from similar to59% for temperate-subpolar and polar systems to 75% for tropical-subtropical regions. Given estimates for the metabolic requirements of micrograzers and assuming they consume most bacterial production, regionally averaged estimates of the protistan respiration are 35-43% of daily PP for the first level of consumer or 49-59% of PP for three trophic transfers. The estimated contributions of microbial grazers to total community respiration are of the same magnitude as bacterial respiration. Consequently, potential ecosystem differences in micrograzer activity or trophic structure are a large uncertainty for biogeochemical models that seek to predict the microbial community role in carbon cycling from bacterial parameters alone.

Landry, MR, Selph KE, Decima M, Gutierrez-Rodriguez A, Stukel MR, Taylor AG, Pasulka AL.  2016.  Phytoplankton production and grazing balances in the Costa Rica Dome. Journal of Plankton Research. 38:366-379.   10.1093/plankt/fbv089   AbstractWebsite

We investigated phytoplankton production rates and grazing fates in the Costa Rica Dome (CRD) during summer 2010 based on dilution depth profiles analyzed by flow cytometry and pigments and mesozooplankton grazing assessed by gut fluorescence. Three community production estimates, from C-14 uptake (1025+/-113 mg C m(-2) day(-1)) and from dilution experiments analyzed for total Chla (990+/-106 mg C m(-2) day(-1)) and flow cytometry populations (862+/-71 mg C m(-2) day(-1)), exceeded regional ship-based values by 2-3-fold. Picophytoplankton accounted for 56% of community biomass and 39% of production. Production profiles extended deeper for Prochlorococcus (PRO) and picoeukaryotes than for Synechococcus (SYN) and larger eukaryotes, but 93% of total production occurred above 40 m. Microzooplankton consumed all PRO and SYN growth and two-third of total production. Positive net growth of larger eukaryotes in the upper 40 m was balanced by independently measured consumption by mesozooplankton. Among larger eukaryotes, diatoms contributed similar to 3% to production. On the basis of this analysis, the CRD region is characterized by high production and grazing turnover, comparable with or higher than estimates for the eastern equatorial Pacific. The region nonetheless displays characteristics atypical of high productivity, such as picophytoplankton dominance and suppressed diatom roles.

Selph, KE, Landry MR, Taylor AG, Gutierrez-Rodriguez A, Stukel MR, Wokuluk J, Pasulka A.  2016.  Phytoplankton production and taxon-specific growth rates in the Costa Rica Dome. Journal of Plankton Research. 38:199-215.   10.1093/plankt/fbv063   AbstractWebsite

During summer 2010, we investigated phytoplankton production and growth rates at 19 stations in the eastern tropical Pacific, where winds and strong opposing currents generate the Costa Rica Dome (CRD), an open-ocean upwelling feature. Primary production (C-14-incorporation) and group-specific growth and net growth rates (two-treatment sea-water dilution method) were estimated from samples incubated in situ at eight depths. Our cruise coincided with a mild El Nino event, and only weak upwelling was observed in the CRD. Nevertheless, the highest phytoplankton abundances were found near the dome center. However, mixed-layer growth rates were lowest in the dome center (similar to 0.5-0.9 day(-1)), but higher on the edge of the dome (similar to 0.9-1.0 day(-1)) and in adjacent coastal waters (0.9-1.3 day(-1)). We found good agreement between independent methods to estimate growth rates. Mixed-layer growth rates of Prochlorococcus and Synechococcus were largely balanced by mortality, whereas eukaryotic phytoplankton showed positive net growth (similar to 0.5-0.6 day(-1)), that is, growth available to support larger (mesozooplankton) consumer biomass. These are the first group-specific phytoplankton rate estimates in this region, and they demonstrate that integrated primary production is high, exceeding 1 g C m(-2) day(-1) on average, even during a period of reduced upwelling.

Buitenhuis, ET, Li WKW, Lomas MW, Karl DM, Landry MR, Jacquet S.  2012.  Picoheterotroph (Bacteria and Archaea) biomass distribution in the global ocean. Earth Syst. Sci. Data. 4:101-106.   10.5194/essd-4-101-2012   Abstract

We compiled a database of 39,766 data points consisting of flow cytometric and microscopical measurements of picoheterotroph abundance, including both Bacteria and Archaea. After gridding with 1°spacing, the database covers 1.3% of the ocean surface. There are data covering all ocean basins and depths except the Southern Hemisphere below 350m or from April until June. The average picoheterotroph biomass is 3.9 ± 3.6 μg C l−1 with a 20-fold decrease between the surface and the deep sea. We estimate a total ocean inventory of about 1.3 × 10^29 picoheterotroph cells. Surprisingly, the abundance in the coastal regions is the same as at the same depths in the open ocean. Using an average of published open ocean measurements for the conversion from abundance to carbon biomass of 9.1 fg cell−1, we calculate a picoheterotroph carbon inventory of about 1.2 Pg C. The main source of uncertainty in this inventory is the conversion factor from abundance to biomass. Picoheterotroph biomass is 2 times higher in the tropics than in the polar oceans.

Buitenhuis, ET, Li WKW, Vaulot D, Lomas MW, Landry MR, Partensky F, Karl DM, Ulloa O, Campbell L, Jacquet S, Lantoine F, Chavez F, Macias D, Gosselin M, McManus GB.  2012.  Picophytoplankton biomass distribution in the global ocean. Earth Syst. Sci. Data. 4:37-46.   10.5194/essd-4-37-2012   Abstract

The smallest marine phytoplankton, collectively termed picophytoplankton, have been routinely
enumerated by flow cytometry since the late 1980s during cruises throughout most of the world ocean. We compiled a database of 40,946 data points, with separate abundance entries for Prochlorococcus, Synechococcus and picoeukaryotes. We use average conversion factors for each of the three groups to convert the abundance data to carbon biomass. After gridding with 1 degree spacing, the database covers 2.4% of the ocean surface area, with the best data coverage in the North Atlantic, the South Pacific and North Indian basins, and at least some data in all other basins. The average picophytoplankton biomass is 12 ± 22 μg C l−1 or 1.9 g C m−2. We estimate a total global picophytoplankton biomass of 0.53–1.32 Pg C (17–39% Prochlorococcus, 12–15% Synechococcus and 49–69% picoeukaryotes), with an intermediate/best estimate of 0.74 Pg C. Future efforts in this area of research should focus on reporting calibrated cell size and collecting data in undersampled regions.

Brown, SL, Landry MR, Barber RT, Campbell L, Garrison DL, Gowing MM.  1999.  Picophytoplankton dynamics and production in the Arabian Sea during the 1995 Southwest Monsoon. Deep-Sea Research (Part II, Topical Studies in Oceanography). 46:1745-1768.: Elsevier Science Ltd., Pergamon   10.1016/S0967-0645(99)00042-9   AbstractWebsite

Phytoplankton community structure is expected to shift to larger cells (e.g., diatoms) with monsoonal forcing in the Arabian Sea, but recent studies suggest that small primary producers remain active and important, even in areas strongly influenced by coastal upwelling. To better understand the role of smaller phytoplankton in such systems, we investigated growth and grazing rates of picophytoplankton populations and their contributions to phytoplankton community biomass and primary productivity during the 1995 Southwest Monsoon (AugustSeptember). Environmental conditions at six study stations varied broadly from open-ocean oligotrophic to coastal eutrophic, with mixed-layer nitrate and chlorophyll concentrations ranging from 0.01 to 11.5 mu M NO sub(3) and 0.16 to 1.5 mu g Chl a. Picophytoplankton comprised up to 92% of phytoplankton carbon at the oceanic stations, 35% in the diatom-dominated coastal zone, and 26% in a declining Phaeocystis bloom. Concurrent in situ dilution and super(14)C-uptake experiments gave comparable ranges of community growth rates (0.53-l.05/d and 0.44-1.17/d, to the 1% light level), but uncertainties in C:Chl a confounded agreement at individual stations.

Linacre, LP, Landry MR, Lara-Lara JR, Hernandez-Ayon JM, Bazan-Guzman C.  2010.  Picoplankton dynamics during contrasting seasonal oceanographic conditions at a coastal upwelling station off Northern Baja California, Mexico. Journal of Plankton Research. 32:539-557.   10.1093/plankt/fbp148   AbstractWebsite

The ecological dynamics of picoplankton were investigated at a coastal upwelling system of northern Baja California during six cruises (September 2007-November 2008). Populations of Prochlorococcus, Synechococcus, PicoEukaryotes and heterotrophic bacteria were assessed by flow cytometry (FCM). On each sampling date, we used an abbreviated three-treatment dilution technique and (14)C-uptake experiments to determine population (FCM) and community (TChl a) rates of growth, grazing and production from 24-h in situ incubations at three to four euphotic depths. Overall, picoplankton comprised an active and important component of the community, with biomass values (2.3-69.8 mu g C L(-1)) and production rates (0.8-68.4 mu g C L(-1) day(-1)) that varied positively with Chl a and community (14)C-production. The exception was an intense algal bloom (> 25 mu g Chl a L(-1)) during La Nina-intensified upwelling conditions in April 2008, during which biomass and production estimates of picophytoplankton were at their lowest levels, suggesting that the smallest primary producers were being replaced by larger cells. Thus, for most of the environmental circumstances encountered during our study, our results supported the recent "rising tide" hypothesis that improved growth (nutrient) conditions benefit all size classes, including picophytoplankton. Under extreme conditions of upwelling, however, the picophytoplankton declined abruptly, despite seemingly strong (average) growth rates. Future studies need to provide a better mechanistic understanding of the physical (advection), physiological (nutrient uptake and temperature) and ecological (food web) factors that result in this dramatic nonlinearity in picophytoplankton response to system forcing and richness.

Latasa, M, Landry MR, Schluter L, Bidigare RR.  1997.  Pigment-specific growth and grazing rates of phytoplankton in the central equatorial Pacific. Limnology and Oceanography. 42:289-298.   10.4319/lo.1997.42.2.0289   AbstractWebsite

Dilution experiments were performed during two transects across the central equatorial Pacific (3 degrees N-3 degrees S, 140 degrees W) to estimate growth and mortality rates of select phytoplankton groups distinguished by their characteristic pigments. The first transect was conducted in February-March 1992 during a moderate El Nino event; the second transect took place in August-September 1992, under normal upwelling conditions. Experiments with and without added nutrients (N, P, Fe, and Mn) indicated that growth rates were nutrient limited during El Nino conditions. Nevertheless, the enhanced growth rates with added nutrients during El Nino were less than rates without added nutrients during the normal upwelling period; therefore, nutrients alone did not account for all of the differences between cruises, Growth rates were different for the various algal groups. in August-September, diatoms grew at 1.7 d(-1), and prochlorophytes and prymnesiophytes at similar to 0.5 d(-1). Grazing by microzooplankton balanced growth for algal groups exhibiting the lowest growth rates (i.e. prymnesiophytes and prochlorophytes). Although microzooplankton grazing on diatoms and pelagophytes was also significant, a substantial fraction of their growth escaped consumption, accounting for most of the net chlorophyll production of the phytoplankton community.

Piontkovski, SA, Landry MR, Finenko ZZ, Kovalev AV, Williams R, Gallienne CP, Mishonov AV, Skryabin VA, Tokarev YN, Nikolsy VN.  2003.  Plankton communities of the South Atlantic anticyclonic gyre. Oceanologica Acta. 26:255-268.   10.1016/s0399-1784(03)00014-8   AbstractWebsite

Data collected during cruises of the Former Soviet Union (in 1963-1989) and the British Atlantic meridional transect program (in 1995-1999) were used to analyse macroscale patterns in phyto- and zooplankton biomass, size structure, species diversity, chlorophyll a, and plankton bioluminescence in the macroscale anticyclonic gyre of the South Atlantic Ocean. The spatial pattern of bioluminescence intensity was in good agreement with that of remotely sensed (CZCS) chlorophyll a, phosphate, salinity, and copepod species diversity index distributions especially in terms of geographic inclinations of the isolines, both associated with the north-westward pattern off the South equatorial current. Among the 416 copepod species recorded in samples, 51 species were noted throughout the whole gyre. On the other hand, there were a number of species found only in one of the currents. The mesozooplankton biomass size spectra (calculated in carbon units), exhibited a fairly stable slope of the curve from the eastern periphery of the gyre to its centre. The British Atlantic meridional transect program meridional transect through the western part of the gyre showed mesozooplankton size spectra in greater detail between the equator and 50degrees S. Although the spectra change slowly along the transect as far as 36degrees S, there is a general trend toward increasing slopes from the equatorial region to the oligotrophic central gyre. The calculated phyto-to-zooplankton ratio indicated that for the tropical anticyclonic gyres, the mesozooplankton carbon biomass could be represented as the exponential function of the phytoplankton carbon. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.

Landry, MR, de Verneil A, Goes JI, Moffett JW.  2016.  Plankton dynamics and biogeochemical fluxes in the Costa Rica Dome: introduction to the CRD Flux and Zinc Experiments. Journal of Plankton Research. 38:167-182.   10.1093/plankt/fbv103   AbstractWebsite

The Costa Rica Dome (CRD) is an open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone (OMZ). The region has unique characteristics, biomass dominance by picophytoplankton, suppressed diatoms, high biomass of higher consumers and presumptive trace metal limitation, but is poorly understood in terms of pelagic stock and process relationships, including productivity and production controls. Here, we describe the goals, project design, physical context and major findings of the Flux and Zinc Experiments cruise conducted in June-July 2010 to assess trophic flux relationships and elemental controls on phytoplankton in the CRD. Despite sampling during a year of suppressed summertime surface chlorophyll, cruise results show high productivity (similar to 1 g C m(-2) day(-1)), high new production relative to export, balanced production and grazing, disproportionate biomass-specific productivity of large phytoplankton and high zooplankton stocks. Zinc concentrations are low in surface waters relative to phosphorous and silicate in other regions, providing conditions conducive to picophytoplankton, like Synechococcus, with low Zn requirements. Experiments nonetheless highlight phytoplankton limitation or co-limitation by silicic acid, driven by a strong silica pump that is linked to low dissolution of biogenic silica in the cold shallow thermocline of the lower euphotic zone.

Landry, MR.  1978.  Population dynamics and production of a planktonic marine copepod, Acartia clausii, in a small temperate lagoon on San Juan Island, Washington. Internationale Revue Der Gesamten Hydrobiologie. 63:77-119.   10.1002/iroh.19780630106   AbstractWebsite

The population dynamics and production of Acartia clausii, a planktonic marine copepod, were studied during 1973 and 1974 in a small temperate lagoon. An approach which integrated laboratory and in situ experiments with time-series sampling of the field population was used to analyze seasonal changes in the parameters of population growth (development, growth, fecundity, and mortality) and to elucidate the processes which affect these changes. The objective of the study was to understand the factors which control the seasonal cycle of abundance.The cycles of abundance were similar in the two years of study and were not affected by differences in the cycles of tidal inflow, temperature, and food availability even though the latter two factors appreciably affected growth, development, and fecundity rates. The abundance cycle is controlled by an annually consistent pattern of copepodid and adult mortality believed to be due to predation by the three-spined stickleback, the dominant fish species in the lagoon. Cannibalism and periodic tidal stimulation of hatching of accumulated eggs in the sediment help to regulate population abundance within seasonal limits.Production by the lagoon population was 229 kg C for the entire study period; 84—88% of the annual production occurred from April through July. In the area of the lagoon greater than 3-m deep the mean daily productions during the peak months of each year were 70 and 55 mg C m(−2) for 1973 and 1974, respectively.

Landry, MR.  1978.  Predatory feeding behavior of a marine copepod, Labidocera trispinosa. Limnology and Oceanography. 23:1103-1113. AbstractWebsite

The behavior of Labidocera feeding on early developmental stages of five common species of planktonic calanoid copepods was investigated to determine its species-specific impact on a mixed copepod community. Feeding rates on individual prey were not affected by prey density or the availability of alternate prey; threshold feeding behavior was not observed. Capture rates of naupliar prey of all species increase as a function of their size even though larger nauplii appear better able to avoid capture. In general, the ability of Labidocera to capture individuals of a prey species decreases abruptly after the prey develop to the cope-podid stages. As a consequence of the limited susceptibility of copepodid stages to capture by Labidocera and higher feeding rates on larger nauplii, the predatory impact of Labidocera is greatest on the largest of the prey species.

Landry, MR, Lehnerfournier JM, Fagerness VL.  1985.  Predatory feeding behavior of the marine cyclopoid copepod Corycaeus anglicus. Marine Biology. 85:163-169.   10.1007/bf00397435   AbstractWebsite

Feeding rates, patterns of prey selection, and starvation tolerance were investigated for adult males and females of the cyclopoid copepod Corycaeus anglicus collected from the waters of Friday Harbor, Washington, USA. Selection by C. anglicus was determined largely by prey body-size, but was also affected by species and developmental stage. Small developmental stages of all prey species were fed upon at relatively low rates. The small calanoid species Acartia clausii was increasingly vulnerable to predation by C. anglicus as it progressed through successive developmental stages. Larger prey species, Pseudocalanus sp. and Calanus pacificus, were more vulnerable in intermediate stages, the C3 and N6 stages, respectively. Larger and smaller prey were characteristically attacked at different sites on their bodies; however, attack sites fell within a similar range of body widths, 130 to 170 μm. Males of Corycaeus anglicus killed a maximum of 1.4 prey d-1 when feeding on the optimally-sized adult females of Acartia clausii, which are approximately equivalent to its own body length. Males fed at approximately double the rates of females. Despite its small size and apparent lack of metabolic stores, this cyclopoid is highly tolerant of starvation conditions. Median survival time without food is at least 2 wk for both males and females. In its predatory behavior, C. anglicus employs an ambush-type strategy and seems to be adapted for infrequent encounters with relatively large prey.

Chappell, PD, Vedmati J, Selph KE, Cyr HA, Jenkins BD, Landry MR, Moffett JW.  2016.  Preferential depletion of zinc within Costa Rica upwelling dome creates conditions for zinc co-limitation of primary production. Journal of Plankton Research. 38:244-255.   10.1093/plankt/fbw018   AbstractWebsite

The Costa Rica Dome (CRD) is a wind-driven feature characterized by high primary production and an unusual cyanobacterial bloom in surface waters. It is not clear whether this bloom arises from top-down or bottom-up processes. Several studies have argued that trace metal geochemistry within the CRD contributes to the composition of the phytoplankton assemblages, since cyanobacteria and eukaryotic phytoplankton have different transition metal requirements. Here, we report that total dissolved zinc (Zn) is significantly depleted relative to phosphate (P) and silicate (Si) within the upper water column of the CRD compared with other oceanic systems, and this may create conditions favorable for cyanobacteria, which have lower Zn requirements than their eukaryotic competitors. Shipboard grow-out experiments revealed that while Si was a limiting factor under our experimental conditions, additions of Si and either iron (Fe) or Zn led to higher biomass than Si additions alone. The addition of Fe and Zn alone did not lead to significant enhancements. Our results suggest that the depletion of Zn relative to P in upwelled waters may create conditions in the near-surface waters that favor phytoplankton with low Zn requirements, including cyanobacteria.

Monger, BC, Landry MR.  1991.  Prey size dependency of grazing by free-living marine flagellates. Marine Ecology-Progress Series. 74:239-248.   10.3354/meps074239   AbstractWebsite

Currently, there are 3 distinct and conflicting predictions of the dependency on prey size of the clearance rates [(volume cleared of prey) flag.-1 time-1) of flagellates that feed by the mechanism of direct-interception. Clearance rates for this group of organisms have been predicted to be proportional roughly to either the first, second or third powers of prey radius indicating either weakly, moderately or strongly size-selective grazing behaviors, respectively. These predicted relationships were tested experimentally for cultured and natural flagellate populations fed mixtures of large and small fluorescently labelled prey (either heat-killed bacteria or latex microspheres). Evidence from 7 experiments indicated that flagellate feeding is only weakly size-selective; that is, clearance rate varies, roughly, in direct proportion to prey radius. These results provide preliminary support of a prey capture model that is based entirely on the interaction of hydrodynamic forces and surface forces arising between free-living marine flagellates and picoplankton-size prey. The extent to which small size provides a refuge from grazing mortality among the picoplankton, and the potential for a significant population of dormant bacteria, is probably less than previously believed; consequently the role of the most minute bacteria in pelagic food webs may require reexamination.