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Sheridan, CC, Landry MR.  2004.  A 9-year increasing trend in mesozooplankton biomass at the Hawaii Ocean Time-Series Station ALOHA. Ices Journal of Marine Science. 61:457-463.   10.1016/j.icesjm.2004.03.023   AbstractWebsite

Mesozooplankton biomass in the North Pacific Subtropical Gyre (NPSG), as measured by the Hawaii Ocean Time-series pro-ram at Station ALOHA (22.45degreesN 158degreesW), increased significantly from 1994 to 2002. Tide changes occurred at a rate of 60 mg DW m(-2) yr(-1) for night-time collections and 45 mg DW m(-2) yr-1 for daytime collections. Principal components analysis indicates that the 9-year trend was driven by an increase in small (0.5-2.0 mm) zooplankton that do not migrate on a diel cycle. This plankton class is known to increase during the summer at Station ALOHA when the water column is most stratified, and a strong summertime response is also apparent within the long-term trend from 1998 through 2002. Both long-term and seasonal changes in zooplankton biomass at Station ALOHA can be linked to an enhanced role of nitrogen fixation in ecosystem productivity. Climate forcing from El Nino-Southern Oscillation (ENSO) events may have influenced nitrogen fixation, general ecosystem productivity, and thus zooplankton biomass in the NPSG. However. it is difficult to evaluate the effect of climate cycles in this region without the benefit of a longer time-series at Station ALOHA. Because biomass trends in higher-level consumers like mesozooplankton can have cascading influences on lower levels, understanding the relative roles of bottom-up climate influences and top-down trophic processes will be important in resolving long-term trends in community composition and structure in the subtropical North Pacific Ocean. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

Liu, H, Campbell L, Landry MR, Nolla HA, Brown SL, Constantinou J.  1998.  Prochlorococcus and Synechococcus growth rates and contributions to production in the Arabian Sea during the 1995 Southwest and Northeast Monsoons. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 45:2327-2352.   10.1016/s0967-0645(98)00073-3   AbstractWebsite

We investigated the growth rates of Prochlorococcus and Synechococcus spp. and their relative contributions to carbon production at five stations in the Arabian Sea during the late Southwest and early Northeast Monsoon seasons in 1995. Estimates of Prochlorococcus growth rates were based on diel cell cycle analysis. Accurate determination of the duration of the cell cycle terminal event, e.g., t(S +G2) was not possible for Synechococcus because of its highly variable cell cycle patterns (e.g., imperfect phasing, multiple DNA-replication peaks, and dark-arrested division). Consequently, growth and mortality rates of Synechococcus were estimated from diel variations in population abundance. The assumptions of this approach were validated by observations that Synechococcus cell division occurred only during the daytime as well as good agreement between growth rate estimates for Prochlorococcus compared to cell cycle analyses. Prochlorococcus growth rates were typically less than 1 doubling per day, although higher rates occurred in the surface waters at an offshore site (Stn. N7) during the SW Monsoon and at a coastal station (S2) during the NE Monsoon. For Synechococcus, maximum growth rates >2 d(-1) were observed at mesotrophic (nitrate concentration 0.1-3 mu m) onshore stations during both seasons. Synechococcus spp. grew much faster than Prochlorococcus in the upper water column at almost every station during both seasons, but the depth range of its maximum growth rate was shallower and its growth and abundance decreased sharply in deeper waters. In addition, growth rates of Synechococcus increased with nutrient availability whereas Prochlorococcus growth rates did not vary dramatically with nutrients. Although there was no significant difference in Synechococcus growth rates between the late SW and early NE Monsoon seasons, the estimated carbon production and relative contribution to primary production were greater during the early NE Monsoon due to the larger biomass of Synechococcus and lower total primary production. Maximum Prochlorococcus production was found only in the most oligotrophic regions, and Prochlorococcus was not a major contributor of primary production for the most part of the Arabian Sea during the SW and NE Monsoons. Overall, Prochlorococcus and Synechococcus were inversely related in terms of their relative contributions to primary production. (C) 1998 Elsevier Science Ltd. All rights reserved.

Liu, HB, Landry MR, Vaulot D, Campbell L.  1999.  Prochlorococcus growth rates in the central equatorial Pacific: An application of the f(max) approach. Journal of Geophysical Research-Oceans. 104:3391-3399.   10.1029/1998jc900011   AbstractWebsite

Minimum daily growth rates of Prochlorococcus were estimated for the central equatorial Pacific (12 degrees S-12 degrees N, 140 degrees W) during EI Nino (February-March 1992) and normal upwelling (August-September 1992) conditions. Growth rate estimates were based on the percentages of cells in the S and G(2) division phases at dawn (similar to 0700 LT) and dusk (similar to 1800 LT) as approximate values for f(min) and f(max) respectively. During both environmental conditions, depth-integrated growth rates of Prochlorococcus were higher in oligotrophic waters at the northern end of the transect (0.36-0.52 d(-1)) and decreased to a minimum at the equator. The lowest growth rates were found at the equator during El Nino and at 2 degrees N during normal upwelling, where a large biomass of buoyant diatoms had accumulated in the vicinity of a convergent front. Prochlorococcus growth rate reached a high of 0.64 d(-1) at 1 degrees S and maintained a moderate rate (0.36-0.49 d(-1)) throughout the southern end of the transect. An inverse relationship was found between the contribution of Prochlorococcus to the total primary production and nitrate concentration as well as total primary production measured by the C-14 method. While Prochlorococcus is a dominant primary producer in tropical and subtropical, open-ocean ecosystems generally, it is relatively more important in oligotrophic waters than in the nutrient rich equatorial upwelling zone.

Landry, MR, Lorenzen CJ.  1989.  Abundance, distribution, and grazing impact of zooplankton on the Washington shelf. Coastal oceanography of Washington and Oregon. ( Landry MR, Hickey BM, Eds.).:175-210., Amsterdam ; New YorkNew York, NY, U.S.A.: Elsevier ;Distributor for U.S. and Canada, Elsevier Science Pub. Abstract
Landry, MR, Kirshtein J, Constantinou J.  1996.  Abundances and distributions of picoplankton populations in the central equatorial Pacific from 12 degrees N to 12 degrees S, 140 degrees W. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 43:871-890.   10.1016/0967-0645(96)00018-5   AbstractWebsite

Abundances and distributions of picoplankton were studied on two cross-equatorial transect cruises (12 degrees N, 140 degrees W-12 degrees S, 135 degrees W) during February-March (TT007) and August-September 1992 (TT011). Samples were collected in the upper 200 m from early-morning and late-afternoon hydrocasts at 15 stations on each cruise (60 depth profiles, 820 samples). Populations of heterotrophic bacteria, Prochlorococcus, Synechococcus and small autotrophic eukaryotes were enumerated by dual-beam how cytometry. At the northern end of the transect (7-12 degrees N), abundances and vertical distributions were similar to those reported for the oligotrophic North Pacific gyre, with Prochlorococcus and heterotrophic bacteria dominating in the upper euphotic zone, and Synechococccus and eukaryotes exhibiting peaks in cell abundance at depth. All populations were abundant throughout the euphotic zone close to the equator and at the southern end of the transect. Heterotrophic bacteria and Synechococcus were generally more abundant in late-afternoon hydrocasts. The diel enhancement followed the temporal pattern in beam c and suspended particulates, and was particularly strong in the equatorial upwelling region where it averaged 13.6% of the morning population for heterotrophic bacteria and 22.3% for Synechococcus. Conservative estimates of daily growth rates from these data are 0.25 and 0.40 day(-1), respectively, for the two populations. Near-surface maxima in heterotrophic bacteria were symmetrical around the equator, centered around 5 degrees S and 5 degrees N. Prochlorococcus was most abundant during local summer conditions at the respective ends of the transect. A minimum occurred in association with a dense aggregation of buoyant diatoms at the convergent front of a tropical instability wave (2 degrees N, TT011). The ratio of Prochlorococcus to total bacteria was generally in the range of 0.15-0.2 for the upper water column, but varied during TT011 from > 0.3 for the most northern stations to <0.1 at the 2 degrees N front. At higher latitudes, Synechococcus was more numerous during El Nino conditions (TT007) on both sides of the equator and at southern stations on both cruises. Autotrophic eukaryotes were more abundant during local winters at the ends of the transect and during the ''cold tongue'' conditions (TT011) at the equator. Picoplankton account for most of the chlorophyll biomass and primary production in the central equatorial Pacific. Nonetheless, their abundances and distributions are relatively stable and conservative while other populations, such as diatoms, respond more dramatically to environmental forcing. Copyright (C) 1996 Elsevier Science Ltd.

Al-Mutairi, H, Landry MR.  2001.  Active export of carbon and nitrogen at Station ALOHA by diel migrant zooplankton. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 48:2083-2103.   10.1016/s0967-0645(00)00174-0   AbstractWebsite

With a high proportion of diel migratory zooplankton and low particle fluxes, the oligotrophic subtropical Pacific is a region where migrant-mediated export of materials across the base of the euphotic zone should be particularly important for elemental budgets. To assess the magnitude of this export flux at Stn. ALOHA (22 degrees 45'N, 158 degreesW), we determined size-structured migrant biomass on 26 cruises (1994-1996) and used allometric equations to compute metabolic losses of respiratory carbon (DIC) and excreted ammonium (DIN) at the migrant's daytime depth (temperature). Depth-integrated (155m) migrant biomass varied interannually from 286 to 457 mg DW m(-2) and seasonally from 285 to 550 mg DW m(-2) (fall versus spring), with an overall average of 394 mg DWm(-2). The 2-5 mm size-fraction always dominated. Migrant fluxes varied from 0.22 to 0.37 mmol DIC m(-2) d(-1) and from 0.033 to 0.055 mmol DIN m(-2) d(-1) between years, with an overall average of 0.304 mmol C and 0.045 mmol N m(-2) d(-1) (15 and 20% of trap PC and PN fluxes). The fluxes were highest in the spring (0.405 mmol C and 0.060 mmol N m(-2) d(-1); 18 and 24% of trap PC and PN). Strong migratory taxa, defined as those that were virtually absent from the euphotic zone during the day, were dominated by Pleuromamma and Euphausia spp. and Aetideid copepods and accounted for 40% of the total biomass-derived estimates. Using mean cruise biomass structures and temperature information from Stn. ALOHA, migrant flux estimates with different literature-derived metabolic relationships and assumptions typically varied within 20% for carbon and 25% for nitrogen. When compared on the same basis, migrant flux estimates as % trap fluxes were higher for oligotrophic regions compared to the high-nutrient, low-chlorophyll equatorial Pacific. Long-term averages of migrant biomass were substantially (two- to three-fold) higher in the subtropical Pacific compared to the Atlantic, but migrant flux estimates were similar due to higher temperatures (18 versus 9 degreesC) at daytime depths in the Atlantic. Including the effects of undersampled micronekton, dissolved organic excretion, mortality losses at depth and inter-zonal fecal transport, mean flux estimates were about doubled for carbon (30% of trap PC) and approximately tripled for nitrogen (57% of trap PN) relative to those for DIC and DIN metabolic losses. (C) 2001 Elsevier Science Ltd. All rights reserved.

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.

Vedernikov, VI, Bondur VG, Vinogradov ME, Landry MR, Tsidilina MN.  2007.  Anthropogenic influence on the planktonic community in the basin of Mamala Bay (Oahu Island, Hawaii) based on field and satellite data. Oceanology. 47:221-237.   10.1134/s0001437007020099   AbstractWebsite

The anthropogenic impact on the biomass of coastal plankton communities caused by submerged disposal of urban sewage waters (dumping) was studied. The observations were carried out in August-September of 2002-2004 in Mamala Bay (Oahu Island, Hawaii) using satellite and sea truth methods. An analysis of the variability of the integral indicators of the water column determined on the basis of shipborne measurements allowed us to divide them into two groups: the elements most sensitive to the pollution (heterotrophic bacteria (H-Bact), the phototrophic cyanobacteria Synechococcus spp. (SYN), and chlorophyll a (CHLa)) and the elements that manifested episodic positive dependence on the inflow of the polluted waters (heterotrophic unicellular eukaryotes, small unicellular algae, the phototrophic green bacteria Prochlorococcus spp., as well as the total biomass of microplankton). It was shown that the submerged wastewater disposal in the region of the diffuser of the dumping device led to an insignificant (1.2-1.4 times, on the average) local increase in the integral biomass of H-Bact, SYN, and in the content of CHLa. A similar but sharper (1.5-2.1, on the average) increase in these parameters was found in the water layers with maximal biomasses. The possible pathways of disposed waters (under the pycnocline, at its upper boundary, and in the entire mixed layer) were analyzed on the basis of studying the vertical displacement of the biomasses of H-Bact, SYN, and prochlorophytes. The possibility of using the optical anomalies distinguished from satellite data as markers of anthropogenic eutrophication caused by dumping was confirmed. Application of such markers depends on the water transparency and on the shapes of the curves of the vertical distribution of autotrophic organisms.

Ohman, MD, Rudnick DL, Chekalyuk A, Davis RE, Feely RA, Kahru M, Kim HJ, Landry MR, Martz TR, Sabine CL, Send U.  2013.  Autonomous ocean measurements in the California Current ecosystem. Oceanography. 26:18-25. AbstractWebsite

Event-scale phenomena, of limited temporal duration or restricted spatial extent, often play a disproportionately large role in ecological processes occurring in the ocean water column. Nutrient and gas fluxes, upwelling and downwelling, transport of biogeochemically important elements, predator-prey interactions, and other processes may be markedly influenced by such events, which are inadequately resolved from infrequent ship surveys. The advent of autonomous instrumentation, including underwater gliders, profiling floats, surface drifters, enhanced moorings, coastal high-frequency radars, and satellite remote sensing, now provides the capability to resolve such phenomena and assess their role in structuring pelagic ecosystems. These methods are especially valuable when integrated together, and with shipboard calibration measurements and experimental programs.

Calbet, A, Landry MR, Nunnery S.  2001.  Bacteria-flagellate interactions in the microbial food web of the oligotrophic subtropical North Pacific. Aquatic Microbial Ecology. 23:283-292.   10.3354/ame023283   AbstractWebsite

The number and relative strengths of trophic linkages in the microbial community of the oligotrophic subtropical North Pacific were studied in 12 experiments from August 1998 to April 1999 at Stn ALOHA (100 km north of Oahu, Hawaii). Collected seawater was manipulated by sequential size-fractionation to truncate the food web at different organism sizes (1, 2, 5, 10 and 20 mum), and the response variable, net bacterial growth rate, was assessed from flow cytometric analyses of the changes in cell abundance (combined heterotrophic bacteria and Prochlorococcus) after 24 h incubations. The corresponding size structure of the protistan grazer assemblage was measured microscopically. With a coefficient of variability of 7 % and a 2-fold range overall, total bacterial abundance displayed relatively low temporal variability. Despite the relative constancy of standing stock, however, microbial community interactions varied markedly among the experiments. For experiments conducted at higher levels of bacterial biomass, the bacteria showed little growth response to the removal of predators and may have been resource limited. In contrast, the growth response was highest when conditions were defined by relatively low bacterial biomass and high heterotrophic flagellate biomass. Trophic cascades were evident only at intermediate to high levels of bacterial biomass, and may appear in transitions between high and low levels of bacterial biomass. These results suggest that resources and predators oscillate in importance in regulating open-ocean microbial populations. In such oscillations, the indirect influences of a protistan predatory chain may determine the balance between resource limitation and strong predatory control.

Riemann, L, Steward GF, Fandino LB, Campbell L, Landry MR, Azam F.  1999.  Bacterial community composition during two consecutive NE Monsoon periods in the Arabian Sea studied by denaturing gradient gel electrophoresis (DGGE) of rRNA genes. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 46:1791-1811.   10.1016/s0967-0645(99)00044-2   AbstractWebsite

Horizontal and vertical variations in bacterial community composition were examined in samples collected during two Joint Global Ocean Flux Study (JGOFS) Arabian Sea cruises in 1995, The cruises, 11 months apart, took place during two consecutive NE Monsoon periods (January and December). Bacteria were harvested by filtration from samples collected in the mixed layer, mid-water, and deep sea at stations across the study area, Total bacterial community genomic DNA was analyzed by PCR amplification of 16S rRNA gene fragments, followed by denaturing gradient gel electrophoresis (DGGE). In total, 20 DGGE bands reflecting unique or varying phylotypes were excised, cloned and sequenced. Amplicons were dominated by bacterial groups commonly found in oceanic waters (e.g,, the SAR11 cluster of alpha-Proteobacteria and cyanobacteria), but surprisingly none of the sequenced amplicons were related to gamma-Proteobacteria or to members of the Cytophaga-Flavobacter-Bacteroides phylum, Amplicons related to magnetotactic bacteria were found for the first time in pelagic oceanic waters. The DGGE banding patterns revealed a dominance of approximate to 15 distinguishable amplicons in all samples. In the mixed layer the bacterial community was dominated by the same approximate to 15 phylotypes at all stations, but unique phylotypes were found with increasing depth. Except for cyanobacteria, comparison of the bacterial community composition in surface waters from January and December 1995 showed only minor differences, despite significant differences in environmental parameters. These data suggest a horizontal homogeneity and some degree of seasonal predictability of bacterial community composition in the Arabian Sea. (C) 1999 Elsevier Science Ltd. All rights reserved.

Chung, SP, Gardner WD, Richardson MJ, Walsh ID, Landry MR.  1996.  Beam attenuation and micro-organisms: Spatial and temporal variations in small particles along 140 degrees W during the 1992 JGOFS EqPac transects. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 43:1205-&.   10.1016/0967-0645(96)00030-6   AbstractWebsite

As part of the U.S. JGOFS EqPac program, transmissometer profiles were made from 12 degrees N to 12 degrees S at 140 degrees W during February-March (cruise TT007) and August-September (cruise TT011) 1992. Meridional sections of c(p) (beam attenuation due to particles) were prepared by selecting profiles made at a specific time during the day (similar to 18:00 h) to reduce the influence of diel variability and to facilitate point-to-point comparisons with other variables (e.g. T, nitrate, bioabundance, etc.). A tight correlation between beam c(p) and total scattering cross-section of micro-organisms was observed, suggesting that heterotrophic bacteria, prochlorophytes, cyanobacteria and small autotrophic eukaryotes (all < 3 mu m) were dominant contributors to beam c(p). Size-filtration experiments also confirmed that small particles (< 8 mu m) accounted for 41-89% of the c(p) signal in the equatorial Pacific. Contributions of the bacterial fraction and detrital material were assessed. Three biohydrographic regimes [northern (7 degrees-12 degrees N), equatorial (5 degrees N-5 degrees S) and southern (7 degrees-12 degrees S)] could be distinguished from characteristic profiles of c(p) and other variables. While the northern and southern regimes remained relatively constant in c(p) between El Nino (TT007) and cold surface water (TT001) conditions, the equatorial regime showed > 30% increase in surface beam c(p) and IBAC (integrated beam attenuation coefficient) during TT011 compared to TT007. This suggests that only the equatorial regime responds sensitively to the hydrodynamic factors (e.g. upwelling, currents, El Nino. tropical instability waves, etc.) regulating particle distributions. The c(p):chlorophyll a ratio, a proxy for the C:chlorophyll a ratio, also was calculated to obtain insight into biogeochemical cycles in the upper waters of the equatorial Pacific. Copyright (C) 1996 Elsevier Science Ltd.

Chung, SP, Gardner WD, Landry MR, Richardson MJ, Walsh ID.  1998.  Beam attenuation by microorganisms and detrital particles in the equatorial Pacific. Journal of Geophysical Research-Oceans. 103:12669-12681.   10.1029/98jc00608   AbstractWebsite

The transmissometer has been actively used to monitor the variability of particulate matter in the surface ocean. Attenuation due to water (c(w)) is constant at a given wavelength, so variability in the signal is due primarily to particles (beam c(p)) Most of the beam c signal appears to originate from particles < 20 mu m, which, in the euphotic zone, are most likely to be microorganisms. However, how much of the beam c(p) (lambda = 660 nm) is attributable to any given organism category or the detrital component is poorly known. To answer this question, at least numerical abundances and optical (scattering) cross sections of each category are needed. During the two transect cruises (TT007 and TT011) of the Joint Global Ocean Flux Study (JGOFS) Equatorial Pacific (EqPac) program (12 degrees N - 12 degrees S, 140 degrees W), particulate matter attenuation (beam c(p)) and abundances of four microorganism categories (heterotrophic bacteria, Prochlorococcus, Synechococcus, and small autotrophic eukaryotes) with their forward angle light scattering (FALS) information (flow cytometer) were simultaneously measured from the same water samples. The bulk scattering coefficients of each population and total scattering coefficients (b(p)) of these four picoplankton populations (b(p)(PICO)) were calculated and compared with beam c(p). In the equatorial Pacific, heterotrophic bacteria and Prochlorococcus were the most significant contributors to the beam c(p) (16 and 7% of beam c(p), respectively) via scattering, and autotrophic eukaryotes and Synechococcus were less important contributors (2 and 1%, respectively) in the equatorial Pacific. If absorption was also included, similar to 30% of the beam c(p) could be accounted for by these four populations in the euphotic zone, supporting the argument that a transmissometer at 660 nm is an effective tool in measuring the net biological processes in the open ocean. A rough estimate for the beam c(p) signal from nonliving detrital particles was also made in surface waters of the region.

Landry, MR, Fagerness VL.  1988.  Behavioral and morphological influences on predatory interactions among marine copepods. Bulletin of Marine Science. 43:509-529. AbstractWebsite

Relationships among predation rates, selection patterns, swimming speed and orientation, and morphology of prey sensory and capture appendages were examined for seven species of marine copepods—Calanus pacificus, Corycaeus anglicus, Euchaeta elongata, Labidocera trispinosa, Neocalanus cristatus, Oithona spinirostris, and Tortanus discaudatus. Among these species, the ratio of preferred prey size to predator size ranges over four orders of magnitude while length-scaled, maximum clearance rates vary 1,000-fold. Different degrees of adaptation to carnivory are evident from the morphologies of prey capture appendages. However, predatory superiority inferred from these adaptations is not necessarily reflected in predator-prey size relationships or clearance rates relative to more omnivorous species. Except for Neocalanus, optimal prey size is strongly correlated with size of the prey capture appendage. Similarly, major differences in the size, structure, and distribution of sensory hairs on the first antennae of these species suggest marked differences in their abilities to detect and respond to motile prey. However, most of the variability in maximum clearance rates is explained by differences in mean swimming speeds.

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.

Landry, MR, Ondrusek ME, Tanner SJ, Brown SL, Constantinou J, Bidigare RR, Coale KH, Fitzwater S.  2000.  Biological response to iron fertilization in the eastern equatorial Pacific (IronEx II). I. Microplankton community abundances and biomass. Marine Ecology-Progress Series. 201:27-42.   10.3354/meps201027   AbstractWebsite

During the IronEx II experiment in the eastern equatorial Pacific (May to June 1995), the response of the microplankton community to mesoscale iron fertilization was followed using a combination of marker-pigment, microscopical and flow cytometric techniques. Phytoplankton standing stock bloomed dramatically over a period of 6 d following 3 iron additions of 2 and 1 nM, respectively. Carbon biomass in the patch increased by a factor of 4, chlorophyll a by about a factor of 16 and diatoms by >70-fold relative to contemporaneous levels in the ambient community. The bloom then plateaued sharply and remained at a more or less constant level for 4 d, despite the addition of more iron (1 nM) and physiological indices (low C:chl. a ratio and elevated photochemical quantum efficiency) suggesting that the cells were healthy and growing rapidly. Relatively large pennate diatoms (Nitzschia spp., median length 20 to 24 mu m) dominated the patch bloom, with smaller pennate species and centric diatoms declining in relative importance. Heterotrophic bacteria increased at a slow rate (0.08 d(-1)) for >10 d during the experiment, as did heterotrophic nanoflagellates. There were also indications of enhanced cell size, cellular pigment content and possibly growth rates of small phytoplankton. Nonetheless, Little difference was observed between the ambient community and the peak patch bloom with respect to the size composition of auto- and heterotrophic populations <10 mu m in cell size. The relative constancy of the smaller size fractions, the sharp curtailment of net growth of the bloom after 6 d, and >3-fold increase in large heterotrophic dinoflagellates and ciliates suggest that protistan grazers may have played an active role in controlling the phytoplankton response to increased iron availability.

Bollens, GCR, Landry MR.  2000.  Biological response to iron fertilization in the eastern equatorial Pacific (IronEx II). II. Mesozooplankton abundance, biomass, depth distribution and grazing. Marine Ecology-Progress Series. 201:43-56.   10.3354/meps201043   AbstractWebsite

Mesozooplankton (202 to 2000 mu m) biomass, abundance, taxonomic composition, depth distributions and gut pigment contents were measured inside and outside of an iron-enriched patch during the IronEx II study in the eastern equatorial Pacific. Mean carbon biomass remained nearly constant in the ambient community, but increased 2- to 3-fold during early stages of the phytoplankton bloom. The increases were due primarily to small calanoid and cyclopoid copepods and copepod nauplii in the mixed layer and appeared to be the result of 2 processes. First, significantly higher abundances of nauplii in the patch indicated that adult copepods responded reproductively, at least initially, to the increased food. Second, changes in copepod vertical migratory behaviors in response to reduced light penetration and increased food abundance in the patch apparently resulted in an upward displacement of copepods from the lower euphotic zone into the mixed-layer. Mesozooplankton gut pigment content also increased significantly inside the patch, largely in proportion to the increased concentration of phytoplankton chlorophyll a, and estimates of carbon consumed suggest that mesozooplankton standing stock was growing at maximal, or near maximal, temperature-dependent rates (1.0 d(-1)) at the peak of the patch bloom. Nonetheless, zooplankton abundance and biomass declined, rather than increased, during this period. The premature decline of mesozooplankton in the patch suggests that they might have been cropped by their predators in a tightly coupled trophic network or that their reproductive output may have failed to produce viable young when the food resources were dominated by diatoms.

Landry, MR, Constantinou J, Latasa M, Brown SL, Bidigare RR, Ondrusek ME.  2000.  Biological response to iron fertilization in the eastern equatorial Pacific (IronEx II). III. Dynamics of phytoplankton growth and microzooplankton grazing. Marine Ecology-Progress Series. 201:57-72.   10.3354/meps201057   AbstractWebsite

Phytoplankton growth and microzooplankton grazing were investigated during the IronEx II mesoscale enrichment experiment using the seawater dilution technique combined with group-specific pigment markers. Growth rate estimates for the phytoplankton community increased greater than or equal to 2-fold, from 0.6 d(-1) in the ambient environment to 1.2-1.6 d(-1) in the iron-enhanced bloom. Grazing lagged growth, allowing phytoplankton biomass to accumulate at a high rate (similar to 0.8 d(-1)) initially. However, grazing mortality ultimately increased 3- to 4-fold to 1.2-1.4 d(-1), largely balancing growth by Day 6 of the experiment. Increased rates were broadly distributed among phytoplankton taxa, but they differed in timing. Whereas picophytoplankton showed more of a steady balance between growth and grazing, increasing grazing pressure on diatoms followed a 3-5-fold increase in larger (>20 mu m) heterotrophic dinoflagellates and ciliates, which grew in response to enhanced diatom biomass. In the ambient environment, phytoplankton production was 15 to 20 mu g C l(-1) d(-1), with diatoms accounting for 17 % of growth and 7 % of grazing losses. Total phytoplankton production increased to 150-200 mu g C l(-1) d(-1) at the peak of the patch bloom, where 79 % of growth and 55 % of microzooplankton grazing involved diatoms. Phytoplankton grazing mortality was significantly correlated with grazer biovolume, and high carbon-specific grazing estimates at the bloom peak indicated growth rates similar to 1.0 d(-1) for the heterotrophic community and up to 1.4 d(-1) for >20 mu m heterotrophs. During several days when high phytoplankton biomass was relatively constant in the patch bloom, the pennate diatom dominated the community and remained physiologically healthy and growing at a fast rate, even though nutrient conditions were suboptimal. Efficient cropping of diatoms by large protistan grazers and rapid remineralization of iron and biogenic silica were required to maintain this dynamic balance. Contrary to expectations, the carbon export ratio did not increase with the iron-induced diatom bloom. Thus, mesoscale iron-enrichment of high-nutrient, low chlorophyll waters in the eastern equatorial Pacific clearly demonstrated that phytoplankton growth rates and standing stocks were iron-limited. However, the food web also demonstrated a remarkable resiliency to environmental perturbation by establishing a new balance in which the essential features of a microzooplankton-dominated, low export system were maintained.

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.

Gaudy, R, Le Borgne R, Landry MR, Champalbert G.  2004.  Biomass, feeding and metabolism of mesozooplankton in the equatorial Pacific along 180 degrees. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 51:629-645.   10.1016/j.dsr2.2004.05.004   AbstractWebsite

Mesozooplankton biomasses, grazing rates, and metabolism (respiration, ammonium and phosphate excretion) were measured in the central Pacific (180; 8degreesS-8degreesN) during the EBENE cruise, in October-November 1996. In the HNLC zone, the highest mesozooplankton biomass occurred between 6degreesS and the equator. The decrease of biomass at the northern part of the HNLC zone was accounted to the passage of a tropical instability wave, carrying poorer zooplankton concentrations from the north. Within the HNLC zone, most of the biomass (60-96%) was found above 100 m in accordance with the upper distribution of phytoplankton and heterotrophic protists. No significant day-night differences were observed in mesozooplankton biomass. These results suggest a strong and permanent coupling between mesozooplankton and the first links of the food chain. Respiration and phosphate excretion rates were steady at the different latitudes, but at the equator, grazing rates were the lowest, and ammonium excretion the highest. These variations were accounted to latitudinal differences in microzooplankton density and in particles C/N ratios, suggesting that more nitrogen was available for food at the equator. Moreover, among the dominant copepod species, higher proportions of carnivorous were found at the equator. Higher particle grazing and ammonium excretion rates occurred at the equator during the day, while the chlorophyll gut content of copepods did not show any significant diel cycle. These results suggest a strong trophic link between mesozooplankton feeding activity, on the one hand, and cyclic variations of phytoplankton production and of of their main predators (microzooplankton protists), on the other hand. From biomass estimations of phytoplankton and protists in the euphotic layer and results of dilution experiments, the production and grazing mortality of the main autotrophic taxa (from picoplankton to microplankton) were computed at the equator. Mesozooplankton, which was mainly involved in the catch of the largest (>8 mum) food particles, such as diatoms or dinoflagellates, accounted for only a minor part (22%) in total phytoplankton grazing, compared to microzooplankton. As the chlorophyll ration was insufficient to balance its metabolism expenditures, mesozooplankton had to to complete its diet with other sources of food such as microzooplankton. The low level of zooplankton metabolic O:N ratios, suggesting the use of a food with a large protein content, supports of this hypothesis. (C) 2004 Elsevier Ltd. All rights reserved.

Taylor, AG, Landry MR, Selph KE, Yang EJ.  2011.  Biomass, size structure and depth distributions of the microbial community in the eastern equatorial Pacific. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:342-357.   10.1016/j.dsr2.2010.08.017   AbstractWebsite

We investigated the biomass, size structure and composition of microbial communities over a broad area of the eastern equatorial Pacific (4 degrees N-4 degrees S, 110-140 degrees W) during cruises in December 2004 (EB04) and September 2005 (EB05). Vertical-profile samples were collected at 30 stations at depths extending from the surface to the 0.1% light level, and each sample was analyzed quantitatively by flow cytometry and epifluorescence microscopy. Autotrophic biomass averaged 14.8 +/- 4.2 (1 s.d.) mu g CL(-1) for the euphotic zone, with dinoflagellates comprising 39%, Prochlorococcus 28%, other flagellates 18%, Synechococcus 7.5%, and diatoms 6.3%. Nanoplankton accounted for 46% of autotroph biomass, while pico- and microphytoplankton comprised 39 and 16%, respectively. C:Chl averaged 64 +/- 14 for the euphotic zone, with a mean mixed-layer value of 78 +/- 20 and a minimum of 36 +/- 15 at the 1% light level. Heterotrophic biomass averaged 7.0 +/- 1.2 mu g C L(-1) for prokaryotes, 1.6 +/- 0.9 mu g CL(-1) for dinoflagellates, 1.5 +/- 1.1 mu g C L(-1) for other flagellates, and 2.1 +/- 0.4 mu g C L(-1) for ciliates. Euphotic zone integrated biomass varied 2-fold, 1.2 to 2.5 g C m(-2), among stations, decreasing west to east with the gradient in euphotic zone concentrations of dissolved iron. Overall, community biomass and the contributions of functional groups displayed remarkable constancy over our study area, but some patterns were evident, such as the enhancement of picophytoplankton in the leading (upwelling) edges of tropical instability waves and larger diatoms in the trailing (downwelling) edges. Prochlorococcus, in particular, exhibited more variability than expected, given its generally assumed role as a stable background species in the tropical oceans, and was positively associated with the areas of enhanced autotrophic carbon and Chl a. With corrections for different methodological assumptions taken into account, our EB05 estimates of mixed-layer community biomass are 27-35% higher than values for JGOFS studies in 1992. (C) 2010 Elsevier Ltd. All rights reserved.

Decima, M, Landry MR, Rykaczewski RR.  2011.  Broad scale patterns in mesozooplankton biomass and grazing in the eastern equatorial Pacific. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:387-399.   10.1016/j.dsr2.2010.08.006   AbstractWebsite

We investigated biomass distributions and grazing rates of mesozooplankton in the eastern equatorial Pacific between 110 degrees-140 degrees W and 4 degrees S-4 degrees N during cruises in December 2004 (EB04) and September 2005 (EB05). Median (+/- SE) euphotic zone estimates of zooplankton biomass, collected with a 200-mu m mesh net, varied from 2.27 +/- 0.24 g dry weight m(-2) during EB04 to 3.13 +/- 0.22 g dry weight m(-2) for EB05 (however, when stations from overlapping regions were compared, no significant differences were found between years). Trends in gut fluorescence estimates of mesozooplankton grazing followed biomass, with significantly higher median rate estimates during EB05 (3.39 +/- 0.32 mg pigment m(-2) d(-1)) than during EB04 (2.31 +/- 0.34 mg pigment m(-2) d(-1)). Spatial gradients in mesozooplankton biomass and grazing on meridional transects sampled at 110 degrees W in 2004 and 140 degrees W in 2005 could be interpreted as either in situ growth/grazing responses or downstream advective flows relative to spatial patterns in phytoplankton. The present zooplankton biomass estimates for the equatorial Pacific are 80-90% higher than those from similar measurements made by the US Joint Global Ocean Flux Studies EqPac Program in 1992. Our grazing rates similarly exceed EqPac estimates by a factor of 2 or 3, in absolute terms and as percent of phytoplankton biomass consumed daily (11% - EB04; 14% - EB05). Although the equatorial region has not been regularly sampled between EqPac and the present study, both the magnitude and the direction of the observed changes are consistent with the documented decadal increase in mesozooplankton biomass in the adjacent North Pacific Subtropical Gyre based on monthly sampling at Stn. ALOHA, as well as an increase in the strength of the trade winds. These results may be indicative of a general shift up in productivity or community size structure and role of mesozooplankton in the open-ocean tropical/subtropical Pacific, and they provide important time points for validating the performance of ecosystem models of the region. (C) 2010 Elsevier Ltd. All rights reserved.

Landry, MR, Postel J, Newman J, Peterson WK.  1989.  Broad-scale distributional patterns of hydrographic variables on the Washington/Oregon shelf. Coastal oceanography of Washington and Oregon. ( Landry MR, Hickey BM, Eds.).:1-40., Amsterdam ; New YorkNew York, NY, U.S.A.: Elsevier ;Distributors for the U.S. and Canada, Elsevier Science Pub. Co., Abstract

The Washington-Oregon coastal zone is a classical Eastern Boundary Current region. The area is extremely productive, the productivity dependent on near-shore infusions of nutrients into surface layers during wind-driven coastal upwelling. The Washington-Oregon coastline is much more regular than areas off California or off the East Coast, where large capes lend complexity to both the physical environment and the ecosystem response. The relatively straight coastline and broad, deep shelf greatly simplify the physical environment, so that processes responsible for much of the variance are more easily identified. The system response from mid-Oregon northward, although not strictly two-dimensional, is more so than many other coastal areas. Consequently, the system is amenable to the testing of relatively simple models integrating wind forcing with physical, chemical and biological responses in the upper water column. This book is an integrated synthesis of physical, chemical, geological and biological research in a dynamic shelf ecosystem characterized by seasonal, wind-driven upwelling, major river influences, extensive silt deposits, productive pelagic and demersal fisheries, and unique surf-zone communities. The broad scope of the book includes: detailed analyses of physical circulation and sediment transport; production and utilization of organic matter in the marine food web; river influences on regional hydrology and sediment deposition; inputs and inventories of anthropogenic chemicals in the water column and sedimentary deposits. Much of the book is based on primary analyses of previously unpublished data sets. Interdisciplinary approaches are emphasized in models and discussions of coastal upwelling dynamics, hydrographic patterns and anomalies, benthic boundary-layer processes and larval transport, oceanographic influences on commercial stocks, mechanics of chemical cycling and accumulation, and surf-zone production. An extensive index and references complete the book. The book is intended both to document and explain specific regional features of the Washington/Oregon shelf system and, more generally, to illustrate the complexities of interactive influences on the dynamics of coastal ecosystems. Oceanographers, both researchers and students, will be very interested in this book, and it can also be used by governmental agencies and industries dealing with coastal zone management and planning.

Laws, EA, Landry MR, Barber RT, Campbell L, Dickson ML, Marra J.  2000.  Carbon cycling in primary production bottle incubations: inferences from grazing experiments and photosynthetic studies using (14)C and (18)O in the Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:1339-1352.   10.1016/s0967-0645(99)00146-0   AbstractWebsite

Estimates of photosynthesis based on the incorporation of (14)C-labeled inorganic carbon into particulate carbon were compared to estimates of gross photosynthesis based on net O(2) production and the production of (18)O(2) from H(2)(18)O during the US Joint Global Ocean Flux Study (US JGOFS) Arabian Sea process cruises. For samples incubated below the surface and at optical depths < 3, the (14)C uptake : gross photosynthesis ratio averaged 0.45 +/- 0.1. This result is in accord with theoretical considerations of the combined effects of the Mehler reaction, photorespiration, dark respiration, excretion, and grazing effects on the two estimates of photosynthesis. The (14)C uptake:gross photosynthesis ratio was distinctly higher (0.62) for samples incubated at the surface. This result is likely due to UV light effects, since the O(2) and (14)C incubations were done in quartz and polysulfone bottles, respectively. The (14)C uptake:gross photosynthesis ratio was lower (0.31) for bottles incubated at optical depths > 3. This result probably reflects an increase in the ratio of dark respiration to net photosynthesis in the vicinity of the compensation light level. (C) 2000 Elsevier Science Ltd. All rights reserved.