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Landry, MR.  1975.  Dark inhibition of egg hatching of marine copepod Acartia clausi Giesbr. Journal of Experimental Marine Biology and Ecology. 20:43-47.   10.1016/0022-0981(75)90100-8   AbstractWebsite

Darkness completely and immediately suppresses hatching of the eggs of the marine copepod Acartia clausi Giesbr. When eggs are exposed to light after having been held in darkness past the time when they should have hatched, there is a semi-synchronous burst of hatching after a lag time of ≈ 15 min. This synchrony is carried through the first instar molt. Dark inhibition of hatching may possibly explain the large numbers of viable copepod eggs found in marine sediments.

Landry, MR, Selph KE, Yang EJ.  2011.  Decoupled phytoplankton growth and microzooplankton grazing in the deep euphotic zone of the eastern equatorial Pacific. Marine Ecology-Progress Series. 421:13-24.   10.3354/meps08792   AbstractWebsite

We conducted dilution depth-profile experiments in the eastern equatorial Pacific (EEP) to define regional characteristics of phytoplankton growth and microzooplankton grazing and to test the hypothesis that the process rates decouple in the deep euphotic zone where growth is negligible. We used an abbreviated 2-treatment dilution protocol to produce daily profiles at 8 depths of phytoplankton growth, microzooplankton grazing and cellular changes in chlorophyll a (chl a) content from surface waters to the 0.1% light depth. Experiments were conducted at 16 stations from 2 degrees N to 4 degrees S at 110 degrees W and from 110 degrees to 140 degrees W along the equator. Results were surprisingly robust and coherent over this broad spatial area and showed a euphotic zone essentially divided into 3 equal depth intervals. Mean (+/- SD) growth rates (0.83 +/- 0.16 d(-1)) exceeded grazing rates (0.42 +/- 0.15 d(-1)) in the light-saturated upper third of the water column. Growth, and to a lesser extent grazing, declined with light in the middle third. Effective cell growth was negligible (0.02 +/- 0.21 d(-1)) in the lower third (1 to 0.1% of surface irradiance), with grazing (0.18 +/- 0.17 d(-1)) exceeding growth in this layer. The deep euphotic zone accounted for 25.4 +/- 8.4% of the total euphotic zone chl a, 0.5 +/- 7.8% of depth-integrated phytoplankton growth and 12.7 +/- 7.2% of depth-integrated microzooplankton grazing on phytoplankton. The decoupling of growth and grazing processes under low light conditions at the base of the euphotic zone substantially affected our estimates of microzooplankton consumption of phytoplankton, which ranged from 51% of daily chlorophyll growth for experiments conducted in the upper euphotic zone to 69% for the depth-integrated euphotic zone. In addition, the excess of grazing over growth processes in the deepest stratum, which is typically overlooked in experimental studies, suggests that protistan grazers may have a much larger role in biogeochemical transformations of export fluxes than previously appreciated.

Schartau, M, Landry MR, Armstrong RA.  2010.  Density estimation of plankton size spectra: a reanalysis of IronEx II data. Journal of Plankton Research. 32:1167-1184.   10.1093/plankt/fbq072   AbstractWebsite

Many critical processes of ecosystem function, including trophic relationships between predators and prey and maximum rates of photosynthesis and growth, are size-dependent. Size spectral data are therefore precious to modellers because they can constrain model predictions of size-dependent processes. Here we illustrate a multi-step statistical approach to create size spectra based on a reanalysis of plankton size data from the IronEx II experiment, where iron was added to a marked patch of water and changes in productivity and community structure were followed. First, bootstrapping was applied to resample original size measurements and cell counts. Kernel density estimation was then used to provide nonparametric descriptions of density versus size. Finally, parametric distributions were used to obtain parameter estimates that can more easily be applied in models. A major advantage of this approach is that it provides confidence envelopes for the density distributions. Our analyses suggest three basic distributional patterns of cell concentration versus logarithm of equivalent spherical diameter for individual taxa. Composite size-densities of heterotrophs and photoautotrophs reveal important aspects of the coupling between protist grazing and the phytoplankton community

Landry, MR, Brown SL, Rii YM, Selph KE, Bidigare RR, Yang EJ, Simmons MP.  2008.  Depth-stratified phytoplankton dynamics in Cyclone Opal, a subtropical mesoscale eddy. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 55:1348-1359.   10.1016/j.dsr2.2008.02.001   AbstractWebsite

As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80-100m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0-40m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50-60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70-90 m showed little evidence of growth rate enhancement and was principally defined by a similar to 100-fold increase of large (> 20-mu m) diatoms and a shift from Prochlorococcus to diatom dominance (similar to 80%) of production. The intermediate layer of 50-60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal. (C) 2008 Elsevier Ltd. All rights reserved.

Landry, MR.  1980.  Detection of prey by Calanus pacificus - Implications of the first antennae. Limnology and Oceanography. 25:545-549. AbstractWebsite

Alanus pacificus, normally regarded as a passive filter-feeding copepod, displays active predatory behavior when fed with copepod nauplii. Larger nauplii are selectively preyed upon, even though they are better able to avoid capture than small nauplii. The involvement of the first antennae in the remote detection of motile prey is suggested by the experimental result that amputation of the antennae sharply reduces predatory feeding rates without affecting filter feeding.

Landry, MR.  1983.  The development of marine calanoid copepods with comment on the isochronal rule. Limnology and Oceanography. 28:614-624. AbstractWebsite

Development times of seven species of planktonic marine copepods were determined at 15C and excess food. Although details of instar durations varied among species, common trends were evident in relatively brief prefeeding stages and disproportionately long first- feeding and C5 stages. Males tended to mature before females. There was no relationship between generation time and species size; ecologically dominant species developed from egg to adult in roughly the same time, 19-21 days. Isochronal development was most closely approached by species of Acartia but was not strictly followed by any of the animals studied. In population dynamics studies, the assumption of isochronality can result in substantial errors in estimates of instar-specific mortality rates and, consequently, can seriously bias the interpretation of mortality patterns in nature and their possible causes.

Brown, SL, Landry MR, Selph KE, Yang EJ, Rii YM, Bidigare RR.  2008.  Diatoms in the desert: Plankton community response to a mesoscale eddy in the subtropical North Pacific. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 55:1321-1333.   10.1016/j.dsr2.2008.02.012   AbstractWebsite

As part of the E-Flux project, we documented spatial variability and temporal changes in plankton community structure in a cold-core cyclonic eddy in the lee of the Hawaiian Islands. Cyclone Opal spanned 200km in diameter, with sharply uplifted isopycnals (80-100m relative to surrounding waters) and a strongly expressed deep chlorophyll a maximum (DCM) in its central core region of 40 km diameter. Microscopic and flow cytometric analyses of samples from across the eddy revealed dramatic transitions in phytoplankton community structure, reflecting Opal's well-developed physical structure. Upper mixed-layer populations in the eddy resembled those outside the eddy and were dominated by picophytoplankton. In contrast, the DCM was composed of large chain-forming diatoms dominated by Chaetoceros and Rhizosolenia spp. Diatoms attained unprecedented levels of biomass (nearly 90 mu g Cl(-1)) in the center of the eddy, accounting for 85% of photosynthetic biomass. Protozoan grazers displayed two- to three-fold higher biomass levels in the eddy center as well. We also found a distinct and persistent layer of senescent diatom cells overlying healthy populations, often separated by less than 10 m, indicating that we were sampling a bloom in a state of decline. Time-series sampling over 8 days showed a successional shift in community structure within the central diatom bloom, from the unexpected large chain-forming species to smaller forms more typical of the subtropical North Pacific. The diatom bloom of Cyclone Opal was a unique, and possibly extreme, example of biological response to physical forcing in the North Pacific subtropical gyre, and its detailed study may therefore help to improve our predictive understanding of environmental controls on plankton community structure. (C) 2008 Elsevier Ltd. All rights reserved.

Neveux, J, Dupouy C, Blanchot J, Le Bouteiller A, Landry MR, Brown SL.  2003.  Diel dynamics of chlorophylls in high-nutrient, low-chlorophyll waters of the equatorial Pacific (180 degrees): Interactions of growth, grazing, physiological responses, and mixing. Journal of Geophysical Research-Oceans. 108   10.1029/2000jc000747   AbstractWebsite

[1] In situ diel variations of extracted chlorophyllous pigments, beam attenuation by particles (c(p)), and in vivo chlorophyll fluorescence ( F-iv) were investigated during a 5-day time series in high-nutrient, low-chlorophyll waters of the equatorial Pacific ( date line = 180degrees). Samples were taken hourly at 10 depths in the upper 100 m during the first 48 hours, then sampling frequency decreased to 3 hours. In the 30 - 70 m layer the integrated chlorophyll concentrations, cp, and Fiv increased during the light period, but the minima and, especially, maxima were not fully synchronized. The lowest values of total chlorophyll a (Tchl a = chlorophyll a + divinyl-chlorophyll a) occurred around 5 - 6 hours, slightly ( 0 - 2 hours) before that of cp and Fiv. Tchl a reached a maximum around 1500 hours +/- 1 hour, clearly before c(p) (1700 hours) and F-iv (1900 hours). In the 0 - 30 m layer, diel variations of the integrated chlorophyll concentrations, cp, and Fiv were clearly out of phase. They showed a nocturnal increase in Tchl a, starting around midnight and peaking in early morning ( 0900 hours). In contrast, cp increased only during the light period in the upper 30 m, and variations of Fiv were largely opposite to those of extracted Tchl a. Specific phytoplankton growth (mu(0)) and grazing loss (g) rates were estimated from diel variations in the 30 - 70 m layer and compared to independent rate estimates from experimental incubations. These results are discussed in the context of physical processes and physiological responses of the cells to the daily photocycle.

Wheeler, PA, Kirchman DL, Landry MR, Kokkinakis SA.  1989.  Diel periodicity in ammonium uptake and regeneration in the oceanic subarctic Pacific: Implications for interactions in microbial food webs. Limnology and Oceanography. 34:1025-1033. AbstractWebsite

Diel periodicity in NH4+ uptake and regeneration in the nutrient-rich environment of the oceanic subarctic Pacific was examined. Surface water was incubated in large shipboard microcosms that allowed repeated sampling ofthe planktonic community for NH4+ cycling rates, bacterial production rates, and population densities of the dominant autotrophs and heterotrophs. Changes in NH4+ concentrations and isotopic enrichments indicated that regeneration took place exclusively at night. Nitrogen uptake rates and bacterial production were maximal during the day. Abundance of <2-µm autotrophic flagellates reached a maximum at the end of day or beginning of night, whereas abundance of zooflagellates in the <2-µm and 1-10-µm size classes showed a twofold variation with maximal abundances occurring at the beginning of day. These contrasting diel patterns suggest short-term, cyclic disequilibrium in production and grazing within the microbial food web. Hence, analysis of relationships among the various components of microbial populations in this type of environment will require sampling on much shorter time scales than has been attempted in past studies.

Hassett, RP, Landry MR.  1982.  Digestive carbohydrase activities in individual marine copepods. Marine Biology Letters. 3:211-221. AbstractWebsite

A digestive enzyme assay is presented that is applicable to small sample sizes, on the order of individual Calanus pacificus Brodsky. Responses to time and enzyme concentration were linear under the specified conditions. Assays of individual copepods revealed a high coefficient of variation for all three enzymes, indicating the potential for large variability in field samples. 90-95% of the variability was attributable to differences among animals. The digestive carbohydrases appear to be responding collectively, but it remains for controlled experiments to determine the extent of this relationship.

Landry, MR, Gifford DJ, Kirchman DL, Wheeler PA, Monger BC.  1993.  Direct and indirect effects of grazing by Neocalanus plumchrus on plankton community dynamics in the subarctic Pacific. Progress in Oceanography. 32:239-258.   10.1016/0079-6611(93)90016-7   AbstractWebsite

The effects of grazing of Neocalanus plumchrus C5 copepodids on plankton trophic coupling in the subarctic Pacific were examined in shipboard microcosm experiments during June 1987. Mixed-layer seawater was incubated for 5d in 601 containers under simulated in situ conditions and copepod densities ranging from 0 (control) to 0.75 copepods l-1. Direct grazing effects were determined from temporal changes in abundances of chlorophyll, diatoms, and ciliates. Indirect effects were evaluated from measured rates of primary production (C-14-bicarbonate uptake), bacterial secondary production (H-3-thymidine incorporation), and N-15-ammonium uptake and regeneration. Phytoplankton grew to higher than natural levels in all microcosms over the course of the incubations, but copepods reduced the rates of increase by factors suggesting time-averaged clearance rates of 120, 420, 450 and 170ml copepod-1d-1 for chlorophyll, Nitzschia spp., centric diatoms and ciliates, respectively. Of the rates measured, those largely attributable to phytoplankton growth (i.e. primary production and ammonium uptake) declined with increasing macrozooplankton grazing, in proportion to phytoplankton standing stock measured as chlorophyll a. In contrast, rates associated with microbial loop activity (thymidine incorporation and ammonium regeneration) were enhanced by macrozooplankton grazing. Consequently, increased copepod grazing resulted in a larger fraction of phytoplankton production being processed through the microbial loop.

Monger, BC, Landry MR.  1990.  Direct interception feeding by marine zooflagellates: the importance of surface and hydrodynamic forces. Marine Ecology-Progress Series. 65:123-140.   10.3354/meps065123   AbstractWebsite

We present a theory of direct-interception feeding by marine zooflagellates based upon fundamental principles of hydrodynamics and physical chemistry. Analysis shows that in the absence of confounding behaviors the balance between fluid drag and a complex set of surface-forces uniquely determines prey trajectories about zooflagellate grazers and consequently, clearance rate (volume cleared flag.-1 h-1) and specific clearance rate (volume cleared [volume flag.]-1 h-'). As a first approximation to this general 'Force-Balance' approach, we utilize a model taken from the filtration literature (Spielman & Goren 1970 [Envlron. Sci., Tech. 4: 135-140]) in which wall-corrected fluid drag is balanced with the London-van der Waals force (FLondon). Using literature estimates of FLondon, and a standard grazer swimming speed (Ug) of 200 pm S -', clearance rates (ClrFR) and specific clearance rates (SpClrFB) are predicted to range respectively from 0.13 to 1.8 nl flag.-1 h-1 and from 0.09 to 7.6 X 104 h-1for grazer (Rg) and prey (Rp) radii typical of zooflagellate-picoplankton interactions. Analysis shows that ClrFB is roughly proportional to Rp0.8which strongly contrasts with the RP2.0 proportionality predicted by a model based on geometric considerahons (Fenchel 1982a [Mar. Ecol Prog. Ser 8: 211-2231, 1984 [in: 'Flows of energy and materials in marine ecosystems', Plenum Press]). For given zooflagellate and prey size, ClrFB can be up to 10 times greater than Geometric model predictions with the greatest disparity between models occurring for relatively large grazers feeding on small prey. ClrFB is generally within a factor of 2 of empirical values in the literature, but in some instances underpredicts by an order of magnitude. The remaining discrepancies may be explained by uncertainties in grazer size, swimming speeds and London-van der Waals force. Attempts to incorporate nonspherical shapes, flagellar hydrodynamics, and hydrophobic and steric forces remain viable areas for fine-tuning the model's predictive capabilities.

Landry, MR, Lehnerfournier JM, Sundstrom JA, Fagerness VL, Selph KE.  1991.  Discrimination between living and heat-killed prey by a marine zooflagellate, Paraphysomonas vestita (Stokes). Journal of Experimental Marine Biology and Ecology. 146:139-151.   10.1016/0022-0981(91)90021-n   AbstractWebsite

A recombination-deficient strain (EM1035) of Escherichia coli (Migula) was used to test the ability of the marine zooflagellate Paraphysomonas vestita (Stokes) to discriminate between living and heat-killed prey of similar size and morphology. Cell division of EM1035 was prevented by relatively short exposure to UV-irradiation. Fluorescent staining with rhodamine isothiocyanate did not affect the viability of the bacterial cells or the growth and feeding rates of the zooflagellate. P. vestita fed preferentially on living cells when presented with an equal density mixture of heat-killed and UV-irradiated (nondividing) cells. The flagellate discriminated between living and dead cells with a preference ratio of about 20 suggesting that chemosensory cues may be important in the feeding selectivity of some marine protozoans.

Stukel, MR, Landry MR, Ohman MD, Goericke R, Samo T, Benitez-Nelson CR.  2012.  Do inverse ecosystem models accurately reconstruct plankton trophic flows? Comparing two solution methods using field data from the California Current Journal of Marine Systems. 91:20-33.   10.1016/j.jmarsys.2011.09.004   AbstractWebsite

Despite the increasing use of linear inverse modeling techniques to elucidate fluxes in undersampled marine ecosystems, the accuracy with which they estimate food web flows has not been resolved. New Markov Chain Monte Carlo (MCMC) solution methods have also called into question the biases of the commonly used L(2) minimum norm (L(2)MN) solution technique. Here, we test the abilities of MCMC and L(2)MN methods to recover field-measured ecosystem rates that are sequentially excluded from the model input. For data, we use experimental measurements from process cruises of the California Current Ecosystem (CCE-LTER) Program that include rate estimates of phytoplankton and bacterial production, micro- and mesozooplankton grazing, and carbon export from eight study sites varying from rich coastal upwelling to offshore oligotrophic conditions. Both the MCMC and L(2)MN methods predicted well-constrained rates of protozoan and mesozooplankton grazing with reasonable accuracy, but the MCMC method overestimated primary production. The MCMC method more accurately predicted the poorly constrained rate of vertical carbon export than the L(2)MN method, which consistently overestimated export. Results involving DOC and bacterial production were equivocal. Overall, when primary production is provided as model input, the MCMC method gives a robust depiction of ecosystem processes. Uncertainty in inverse ecosystem models is large and arises primarily from solution under-determinacy. We thus suggest that experimental programs focusing on food web fluxes expand the range of experimental measurements to include the nature and fate of detrital pools, which play large roles in the model. (C) 2011 Elsevier B.V. All rights reserved.

Chen, BZ, Landry MR, Huang BQ, Liu HB.  2012.  Does warming enhance the effect of microzooplankton grazing on marine phytoplankton in the ocean? Limnology and Oceanography. 57:519-526.   10.4319/lo.2012.57.2.0519   AbstractWebsite

We evaluated a hypothesis derived from the metabolic theory of ecology (MTE) that the ratio of microzooplankton herbivory (m) to phytoplankton growth (mu) will arise in a warming ocean because of the different temperature dependencies of autotrophic and heterotrophic organisms. Using community-level growth and grazing data from dilution experiments, generalized additive models (GAMs) were constructed to describe the effects of temperature and chlorophyll on m: mu. At low chlorophyll levels, m: mu decreases with increasing temperature, whereas at high chlorophyll levels, m: mu increases initially with temperature before reaching a peak and then declines. These complex responses of m: mu result from mixed effects of temperature and chlorophyll on microzooplankton biomass (B-z), biomass-specific microzooplankton grazing rate (m: B-z), and phytoplankton growth rate (mu). B-z decreases with rising temperature and increases with rising chlorophyll. m: B-z increases with temperature and decreases with chlorophyll. Nutrient-enriched growth rate of phytoplankton (mu(n)) and mu increase with increasing temperature and chlorophyll. Holding chlorophyll constant, the calculated activation energies of m: B-z and mu(n) are 0.67 +/- 0.05 and 0.36 +/- 0.05 eV, respectively, both consistent with previous MTE estimates for heterotrophs and autotrophs. Our study indicates that warming may enhance phytoplankton losses to microzooplankton herbivory in eutrophic but not in oligotrophic waters. The GAM analysis also provides important insights into underlying system relationships and reasons why community-level responses in natural systems may depart from theory based on laboratory data and individual species.

Landry, MR, Haas LW, Fagerness VL.  1984.  Dynamics of microbial plankton communities: experiments in Kaneohe Bay, Hawaii. Marine Ecology Progress Series. 16:127-133.   10.3354/meps016127   AbstractWebsite

The dynamics of the microbial plankton community of Kaneohe Bay, Hawaii were investigated in September 1982 using in situ diffusion chambers and dilution manipulations. Total community carbon at the time of the experiments was estimated at 86 pg C 1-' of which Chlorella sp. accounted for 47 %, autotrophic microflagellates 14 %, chroococcoid cyanobacteria 11 %, and heterotrophic microflagellates and bacteria each 9 %. Instantaneous growth rates ranged from 1.2 to 1.9 d-' and 1.4 to 2.0 d-l, and mortality rates varied from 0.5 to 1.1 d-' and 0.1 to 0.4 d-' for heterotrophic bacteria and cyanobacteria, respectively, yielding net population growth rates of 1.0 to 1.3 and 1.5 to 2.7 doublings d-' for the 2 populations. Chlorella sp., on the other hand, experienced only slight net growth (0.1 to 0.3 doublings d-l) despite a growth coefficient of about 0.9 d-'. Phagotrophic microflagellates, presumed to be the dominant microbial grazers, consumed about 4.7 times their body carbon d-' and grew at net populationrates of 1.4 to 1.9 doublings d-l. However, microflagellates were food limited and did not control bacterial populations. From these data it appears that recent arguments for rapid material cycling within microbial communities of oligotrophic oceans may be overstated