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Hassett, RP, Landry MR.  1990.  Seasonal changes in feeding rate, digestive enzyme activity, and assimilation efficiency of Calanus pacificus. Marine Ecology-Progress Series. 62:203-210.   10.3354/meps062203   AbstractWebsite

The feeding behavior of the marine calanoid copepod Calanus pacificus was investigated during the winter/spring transition in Puget Sound, Washington. USA. Maximum ingestion rate (Imax), maximum clearance rate (Fmax), and digestive enzyme activity were determined during spring and fall 1982, and the same measures plus assimilation efficiency were determined during spring 1984. Maximal feeding rates and digestive enzyme activity increasedconcurrently with the onset of the spring bloom in 1982. In 1984 feeding rates and digestive enzyme activity were already fully developed at the start of the sampling period, apparently due to an unusually early bloom in Puget Sound. Once developed, digestive enzyme activlty remained high even during periods when maxinlal feeding rates were declining. Assimilation efficiencies also were found to be relatively constant during the 1984 sampling.

Huntley, ME, Lopez MDG, Zhou M, Landry MR.  2006.  Seasonal dynamics and ecosystem impact of mesozooplankton at station ALOHA based on optical plankton counter measurements. Journal of Geophysical Research-Oceans. 111   10.1029/2005jc002892   AbstractWebsite

[1] Abundances of mesozooplankton-sized particles were measured at 45-m depth at station ALOHA (22.75 degrees N, 158 degrees W) during 18 cruises from February 1995 through December 1996 with an optical plankton counter (OPC). Mesozooplankton were also sampled with oblique net tows to 155 m depth. Vertical OPC profiles showed uniform total abundance in the upper mixed layer, usually > 45 m. OPC and net data agreed with respect to total abundance, size composition, abundance of individual size classes, and seasonal cycle of abundance. We found no evidence for significant contributions to OPC particle counts by diatom aggregates, Trichodesmium spp., or detritus. Variations in OPC estimates of abundance are well explained by diel behavior and seasonal cycles of species that dominate mesozooplankton abundance, of which 80% are copepods. The summer maximum in mesozooplankton abundance is due primarily to the increase of the six smallest OPC size classes (< 1.15 mm equivalent spherical diameter), dominated by 14 nonmigrating copepod species that account for more than 95% of average copepod abundance. Seasonal cycles of zooplankton egestion estimated from OPC measurements were highly correlated, and comparable in magnitude, with observed sinking flux measurements of both C and N. Sinking flux at the base of the euphotic zone was 0.67 and 0.77 mol C m(-2) yr(-1) and 81 and 87 mmol N m(-2) yr(-1), for 1995 and 1995, respectively. The potential contribution of mesozooplankton egestion in the mixed layer, based on OPC measurements, accounts for 95% and 90% of C and 86% and 81% of N, respectively.

Landry, MR, Selph KE, Brown SL, Abbott MR, Measures CI, Vink S, Allen CB, Calbet A, Christensen S, Nolla H.  2002.  Seasonal dynamics of phytoplankton in the Antarctic Polar Front region at 170 degrees W. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 49:1843-1865.   10.1016/s0967-0645(02)00015-2   AbstractWebsite

Phytoplankton dynamics in the region of 55-70degreesS, 170degreesW were investigated using Sea-viewing Wide Field-of-View Sensor satellite imagery, shipboard sampling and experimental rate assessments during austral spring and summer, 1997-1998. We used image-analysis microscopy to characterize community biomass and composition, and dilution experiments to estimate growth and microzooplankton grazing rates. Iron concentrations were determined by flow-injection analysis. The phytoplankton increase began slowly with the onset of stratification at the Polar Front (PF) (60-61degreesS) in early November. Seasonally enhanced levels of chlorophyll were found as far north as 58degreesS, but mixed-layer phytoplankton standing stock was highest, approaching 200 mg C m(-3), in the region between the receding ice edge and a strong silicate gradient, which migrated from similar to62degreesS to 65degreesS during the study period. The most southern stations sampled on four cruises were characterized by small pennate diatoms and Phaeocystis. From the PF to the Southern Antarctic circumpolar current front (similar to65degreesS), this ice margin assemblage was seasonally replaced by a community dominated by large diatoms. The large diatom community developed only in waters where measured iron concentrations were initially high (greater than or equal to0.2 nM), and crashed when dissolved silicate was depleted to low levels. Phytoplankton growth rates were highest (0.5-0.6 d(-1)) between the PF and silicate front (60degreesS and 63degreesS) in December. In January, growth rates were lowest (0.1 d(-1)) near the PF, and the highest rates (0.34.4 d(-1)) were found in experiments between 64.8degreesS and 67.8degreesS. Phytoplankton production estimates were highest south of the PF through December and January, averaging 2.2-2.4 mmol C m(-3) d(-1) and reaching levels of 5 mmol cm(-3) d(-1) (64.8degreesS and 67.8degreesS in January). Microzooplankton grazers consumed 54-95% of production for experiments conducted on four AESOPS cruises. They were less efficient in balancing growth rates during the time of highest phytoplankton growth and increase in December, and most efficient in February-March, after the large diatom bloom had collapsed. The diatom bloom region in the present study is in an upwelling zone for Antarctic circumpolar deep water with high iron content. This may explain why this marginal ice zone differs from others where blooms have not been observed. (C) 2002 Published by Elsevier Science Ltd.

Landry, MR, Al-Mutairi H, Selph KE, Christensen S, Nunnery S.  2001.  Seasonal patterns of mesozooplankton abundance and biomass at Station ALOHA. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 48:2037-2061.   10.1016/s0967-0645(00)00172-7   AbstractWebsite

The zooplankton community of the central North Pacific has been sampled at Stn. ALOHA since 1994 as part of routine data collections for the Hawaii Ocean Time-series (HOT) Program. Typically, three day and three night tows are collected in the upper 150 m on each cruise with a l-m, 200-mum mesh net. Size-fractioned carbon and dry weight biomass have been determined for each sample, and one day and one night sample per cruise have been enumerated microscopically through 1996. The accumulated data show statistically significant seasonal signals, with peak biomass and abundance during the summer months for the total community and for smaller size fractions (0.2-0.5, 0.5-1, 1-2 mm). Interannual variability is seen as significantly higher nighttime biomass during summer 1996, which is also related to the enhancement of small size fractions. Comparisons of the present composition of the community to the results of classic studies at the CLIMAX site show remarkable similarities in the species sampled and their abundance ranges. Nonetheless, biomass estimates, corrected for relative capture efficiencies of the different net systems, suggest that there may have been an increase of about a factor of two in zooplankton standing stocks over the past two decades. This hypothesis raises issues about the comparability of the two sites, but the increase, if real, would be consistent with the observed decadal-scale increase in phytoplankton chlorophyll a. The small harpacticoid copepod, Macrosetella gracilis, demonstrates a strong summer maximum consistent with the increased abundance of nitrogen-fixing Trichodesmium spp. during mid-summer months, as described in recent studies at Stn. ALOHA. Accordingly, nitrogen fixation could provide the source of new nutrients to support higher productivity, larger phytoplankton, and enhanced zooplankton standing stocks in the summer, when the upper water column is most stratified and isolated from nutrient influxes from below. (C) 2001 Elsevier Science Ltd. All rights reserved.

Landry, MR.  1975.  Seasonal temperature effects and predicting development rates of marine copepod eggs. Limnology and Oceanography. 20:434-440. AbstractWebsite

Egg development rates of the marine copepod Acartia clausi are affected by the temperature history of the female parent. The eggs from animals collected during winter (8-10C) have significantly faster development rates under summer conditions (15-200C) than those collected during summer (18-200C). Adaptation of winter acclimated animals to summer conditions is a slow process requiring longer than one generation at 200C. Others have suggested that the egg development rates of different species of marine copepods from the arctic to the tropics are related to temperature by different functions: when the effects of metabolic depression at the low and high limits of a copepod's temperature range are considered, the data support the alternative proposal that the relative rates of egg development for nine species of arctic-temperate marine copepods follow a common temperature function.

Taylor, AG, Goericke R, Landry MR, Selph KE, Wick DA, Roadman MJ.  2012.  Sharp gradients in phytoplankton community structure across a frontal zone in the California Current Ecosystem. Journal of Plankton Research. 34:778-789.   10.1093/plankt/fbs036   AbstractWebsite

Spatial variability of plankton biomass, community composition and size structure was investigated across a strong frontal transition (A-Front) in the southern California Current Ecosystem in October 2008. Depth profiles were taken across a 25-km transect of nine stations sampled semi-synoptically during one night and for 3 days following drifter arrays in the adjacent water masses. Community compositions are compared based on analyses by digital epifluorescence microscopy, flow cytometry and pigment composition by high-pressure liquid chromatography. Our results show three assemblages sharply delineated in space, with plankton at the front being compositionally distinct and biomass elevated relative to either of the adjacent water masses. Depth-averaged chlorophyll a (Chl a) varied by a factor of 2.3 (0.350.81 g Chl a L-1) and autotrophic carbon (AC) varied almost 3-fold (13.635.4 g C L-1) across the front. One of the most striking features was a sharp gradient in the distribution of Prochlorococcus (PRO) and Synechococcus (SYN), with PRO located in the warmer oligotrophic waters on the south side of the front and SYN located in the cooler mesotrophic waters to the north. Both PRO and SYN had local biomass minima directly at the front. The peak in phytoplankton biomass at the front was dominated by large (20 m) diatom cells, comprising 71 of the total community biomass. In contrast to previous studies of frontal features in the southern California Current, our study of the A-Front shows strong frontal enhancement of phytoplankton biomass and a shift of phytoplankton size structure towards larger cells.

Hassett, RP, Landry MR.  1988.  Short-term changes in feeding and digestion by the copepod Calanus pacificus. Marine Biology. 99:63-74.   10.1007/bf00644978   AbstractWebsite

The planktonic marine copepodCalanus pacificus exhibits an enhanced feeding rate, or hunger response, when exposed to food following short periods of starvation. In a scries of laboratory experiments with copepods collected from the main basin of Puget Sound, Washington, during 1982 and 1984, we measured maximum ingestion rate, assimilation efficiency, and digestive enzyme activity to determine the time scales over which the feeding behavior ofC. pacificus responds to increases in food. These laboratory results were then compared to field studies of diel fluctuations in digestive enzymes and gut fluorescence ofC. pacificus in Dabod Bay, a fjord of Puget Sound, during September, 1980, and the closely relatedC. marshallae off the Washington coast, in August, 1981. Laboratory experiments demonstrated that the hunger response ofC. pacificus lasts approximately 6 h before ingestion rate returns to a steady state level of about one-half maximum. On the order of 12h of starvation were required to induce the maximum ingestion rate of the hunger response. Digestive enzyme activities did not change over these time scales. Assimilation efficiency peaked within a few hours of the onset of feeding, with low initial rates possibly related to the period of starvation prior to feeding. These results were consistent with diel patterns observed in the field. The hunger response ofC. pacificus appears to be controlled by processes within the gut, and our results are discussed in relation to recent studies of the digestive processes of calanoid copepods.

Monger, BC, Landrey MR.  1992.  Size-selective grazing by heterotrophic nanoflagellates: An analysis using live-stained bacteria and dual-beam flow cytometry. Arch. Hydrobiol. Beih. Ergebn. Limnol.. 37( Bjoernsen PK, Riemann B, Monger BC, Eds.).:173-185.: SCHWEIZERBART'SCHE VERLAGSBUCHHANDLUNG, STUTTGART (FGR) AbstractWebsite

The effect of prey size on clearance rates of a direct-contact feeding chrysomonad (HNAN-1) was examined using dual-beam flow cytometry (FCM) and fluorescently-labelled prey prepared from living and heat-killed cultures. Over the range in prey sizes used in these experiments (0.7 to 1.4 mu m diameter, clearance rate increased approximately linearly with prey diameter. These results are consistent with model predictions based on the balance of hydrodynamic (repulsive) and van der Waals (attractive) forces. The high precision of FCM analysis allows unequivoval rejection of size-dependencies with exponents greater than 1.8. HNAN-1 does not discriminate between living Synechococcus cells or polystyrene micospheres of comparable size, or between living and heat-killed preparations of the heterotrophic bacteria Vibrio damsela and Pseudomonas diminuta . Significantly higher clearance rates were observed for HNAN-1 feeding on a small, living bacterial isolate from Kaneohe Bay, Hawaii, USA compared to heat-killed cells from the same culture or any of the larger prey used in our experiments.

Taniguchi, DAA, Landry MR, Franks PJS, Selph KE.  2014.  Size-specific growth and grazing rates for picophytoplankton in coastal and oceanic regions of the eastern Pacific. Marine Ecology Progress Series. 509:87-101.   10.3354/meps10895   AbstractWebsite

Estimates of growth and grazing mortality rates for different size classes and taxa of natural picophytoplankton assemblages were measured in mixed-layer experiments conducted in 3 regions of the eastern Pacific: the California Current Ecosystem, Costa Rica Dome, and equatorial Pacific. Contrary to expectation, size-dependent rates for cells between 0.45 and 4.0 mu m in diameter showed no systematic trends with cell size both in and among regions. For all size classes, mean +/- SD growth rates ranged from -0.70 +/- 0.17 to 0.83 +/- 0.13 d(-1) and grazing rates between -0.07 +/- 0.13 and 1.17 +/- 0.10 d(-1). Taxon-specific growth rates for Prochlorococcus ranged from 0.17 +/- 0.12 to 0.59 +/- 0.01 d(-1), for Synechococcus from 0.68 +/- 0.03 to 0.97 +/- 0.04 d(-1), for picoeukaryotes from 0.46 +/- 0.13 to 1.03 +/- 0.06 d(-1), and for all cells combined between 0.45 +/- 0.03 and 0.65 +/- 0.02 d(-1). For grazing, Prochlorococcus rates ranged between 0.02 +/- 0.12 and 0.66 +/- 0.02 d(-1), Synechococcus rates between 0.24 +/- 0.08 and 0.92 +/- 0.05 d(-1), for picoeukaryotes between 0.19 +/- 0.10 and 0.78 +/- 0.09 d(-1), and for all cells between 0.16 +/- 0.05 and 0.75 +/- 0.02 d(-1). When comparing rates among taxa, only Prochlorococcus had consistently lower rates than Synechococcocus in all regions. No other trends were apparent. Temperature relationships based on the Metabolic Theory of Ecology were able to explain more of the variability among grazing rates than among growth rates for each taxon considered.

Freibott, A, Linacre L, Landry MR.  2014.  A slide preparation technique for light microscopy analysis of ciliates preserved in acid Lugol's fixative. Limnology and Oceanography-Methods. 12:54-62.   10.4319/lom.2014.12.54   AbstractWebsite

A slide preparation method for seawater samples preserved in acid Lugol's is presented here as an alternative to the traditional Utermohl settling chamber method for microplankton analysis. This preparation maintains the integrity of fragile cells, such as ciliates, resolves issues associated with the transience of samples prepared in settling chambers, and allows the use of automated image acquisition methods. Samples are filtered onto polycarbonate membranes and analyzed with transmitted light microscopy. The visibility of pore outlines is minimized by using mounting oil (Cargille Series A immersion oil, Certified Refractive Index, n(D)(25 degrees C) 1.5840 +/- 0.0002) with a refractive index matching that of the membrane material. We assessed the efficacy of this new method by comparing abundance and biomass estimates for ciliates in settled and filtered samples. Acceptable results were found for the most delicate of samples stored long-term in acid Lugol's. Some cell shrinkage occurred during the filtration and brief drying steps. Therefore, corrections for ciliate length and width measurements in filtered samples were determined to counteract this effect on total cell biovolume. Overall, the method provides a simple and stable alternative to settling chamber analysis for ciliates preserved in acid Lugol's.

Coale, KH, Johnson KS, Chavez FP, Buesseler KO, Barber RT, Brzezinski MA, Cochlan WP, Millero FJ, Falkowski PG, Bauer JE, Wanninkhof RH, Kudela RM, Altabet MA, Hales BE, Takahashi T, Landry MR, Bidigare RR, Wang XJ, Chase Z, Strutton PG, Friederich GE, Gorbunov MY, Lance VP, Hilting AK, Hiscock MR, Demarest M, Hiscock WT, Sullivan KF, Tanner SJ, Gordon RM, Hunter CN, Elrod VA, Fitzwater SE, Jones JL, Tozzi S, Koblizek M, Roberts AE, Herndon J, Brewster J, Ladizinsky N, Smith G, Cooper D, Timothy D, Brown SL, Selph KE, Sheridan CC, Twining BS, Johnson ZI.  2004.  Southern ocean iron enrichment experiment: Carbon cycling in high- and low-Si waters. Science. 304:408-414.   10.1126/science.1089778   AbstractWebsite

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Twomesoscaleexperiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.

Landry, MR, Brown SL, Campbell L, Constantinou J, Liu HB.  1998.  Spatial patterns in phytoplankton growth and microzooplankton grazing in the Arabian Sea during monsoon forcing. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 45:2353-2368.   10.1016/s0967-0645(98)00074-5   AbstractWebsite

Spatial patterns in the rates of phytoplankton growth and microzooplankton grazing were investigated in the Arabian Sea during the Southwest Monsoon (August-September) and early Northeast Monsoon (December) seasons in 1995 using the seawater dilution technique. Nutrient-enhanced growth rates (mu(n)) averaged 1.2 d(-1) in the upper euphotic zone for both cruises and were similar between higher and lower nutrient stations, the former (>1.0 mu M NO(3)) being characteristic of the upwelling-influenced western coastal portion of the study region and the latter ( <0.5 mu M NOB) being typical of the central basin. Growth rates without added nutrients (mu(o)) were also comparable between cruises but strongly related to ambient nutrient conditions, averagong 1.1 d(-1) (91% of mu(n)) at the higher nutrient stations and 0.5 d(-1) (44% of mu(n)) at the lower nutrient stations. The rate estimates for phytoplankton losses to microzooplankton grazing (m) averaged 0.6 d(-1) for the upper euphotic zone and did not vary systematically between low- and high- nutrient stations. As a consequence, mu(o) and m were largely in balance for the more oligotrophic stations, while the eutrophic stations showed a growth differential over grazing of about 0.6 d(-1). These experimental results are consistent with observed differences in community structure, namely the dominance of picoplankton in oligotrophic offshore regions and the increased importance of the large diatom-mesozooplankton grazing pathway in the richer coastal areas. Overall, the spatial patterns, if not magnitudes, of the community responses to Southwest and Northeast Monsoon forcing were remarkably similar in this study, allowing for a relatively simple interpretation of the influence of enhanced nutrient supply on the rates and fates of phytoplankton production. (C) 1998 Elsevier Science Ltd. All rights reserved.

Parker, AE, Wilkerson FP, Dugdale RC, Marchi AM, Hogue VE, Landry MR, Taylor AG.  2011.  Spatial patterns of nitrogen uptake and phytoplankton in the equatorial upwelling zone (110 degrees W-140 degrees W) during 2004 and 2005. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:417-433.   10.1016/j.dsr2.2010.08.013   AbstractWebsite

The equatorial Pacific plays a central role in the global carbon cycle as the largest oceanic source of CO(2) to the atmosphere. The region has been described as a HNLC (High Nutrient, Low Chlorophyll) region with low chlorophyll being explained by either Fe limitation, Si(OH)(4) limitation, or a combination of the two. The autotrophic community in the equatorial upwelling zone (EUZ) is dominated numerically by small cell-sized picoplankton but also contains larger cells, including diatoms that require Si(OH)(4) and have been hypothesized to drive NO(3) uptake. The 1-D CoSiNE (Carbon, Silicon, Nitrogen Ecosystem) model was developed for the EUZ to evaluate the potential drivers of the HNLC condition. The model assumes two phytoplankton groups (small non Si(OH)(4) users and larger Si(OH)(4) requiring cells). Many of its predicted variables have not been measured in the field - specifically, uptake of NO(3), NH(4) and Si(OH)(4) by the larger cells versus the smaller picoplankton and biomass values (as particulate nitrogen, PN) of the two size classes. Two cruises to the EUZ were undertaken in December 2004 (EB04) and September 2005 (EB05) to collect these data, in part to test the conceptual basis and functioning of the CoSiNE model. These EUZ cruises were unique in having size-fractionated uptake rates and phytoplankton community composition at the same depths throughout the euphotic zone and at many stations representing a range of environmental conditions and community composition. Here, we report results pertaining to NO(3) and NH(4) uptake, PN, and f-ratio by different size fractions of the phytoplankton community collected during zonal (0 degrees Eq and 0.5 degrees N) and meridional surveys at 110 degrees W and 140 degrees W. Larger sized (> 5 mu m) phytoplankton contributed more to NO(3) uptake (up to 85%) than cells < 5 mu m and so had higher f-ratios. Several autotrophic functional groups were likely responsible for NO(3) uptake in the > 5-mu m size class, including both diatoms and dinoflagellates. The importance of diatoms in NO3 uptake appears to be variable, with biological "hotspots" around regions of locally enhanced upwelling associated with tropical instability waves (TIWs). In some cases. TIW activity favored diatoms, and Si(OH)(4) and NO(3) uptake were elevated strongly during TIW activity. Largely as a result of increased diatom productivity, integrated NO(3) uptake rates during the passage of these waves reached 6.74 mmol m(-2) d(-1), exceeding the mean values previously reported for the equator by > 2-fold. NH(4) concentrations and uptake were also dynamic, with lower values south of the equator and higher values to the north. The major contributors to NH(4) uptake were the smaller (< 5 mu m) phytoplankton that resulted in low total community f-ratios of 0.26 over both years. A > 2-fold increase in NH(4) uptake rates in 2005 was consistent with the observed roughly 2-fold increase in Prochlorococcus biomass. Our results highlight a potential area for improvement to the CoSiNE model, to include the role of autotrophic dinoflagellates. (C) 2010 Elsevier Ltd. All rights reserved.

Selph, KE, Landry MR, Taylor AG, Yang EJ, Measures CI, Yang JJ, Stukel MR, Christensen S, Bidigare RR.  2011.  Spatially-resolved taxon-specific phytoplankton production and grazing dynamics in relation to iron distributions in the Equatorial Pacific between 110 and 140 degrees W. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:358-377.   10.1016/j.dsr2.2010.08.014   AbstractWebsite

Phytoplankton dynamics were investigated in the eastern equatorial Pacific at 32 stations sampled during two cruises (December 2004 and September 2005). Based on standing stock analyses from HPLC pigments, flow cytometry and microscopy, we used a modified 2-treatment approach of the seawater dilution method to estimate taxon-specific phytoplankton growth and mortality rates in 8-depth per station profiles. These data were complemented by contemporaneous measurements of dissolved iron (Fe). The stations encompassed an equatorial zonal gradient (110 to 140 degrees W) of diminishing eastward Fe availability in the euphotic zone from upwelling of the Equatorial Undercurrent (EUC). Latitudinal variation was assessed by meridional transects at 110 and 140 degrees W. Overall, euphotic zone averaged growth rates were 0.53 +/- 0.17 d(-1) (total chlorophyll a), 0.34 +/- 0.15 d(-1) (divinyl chlorophyll a) and 0.86 +/- 0.32 d(-1) (fucoxanthin). Microzooplankton grazing accounted for 50-60% of daily production of eukaryotic algae, whereas essentially all growth of phototrophic prokaryotes was consumed daily. Fucoxanthin, representing diatoms, was a minor component of the accessory pigments, but diatom growth rates were both significantly higher than other taxonomically defined groups and dropped off more sharply with depth (low light level). Strikingly, no spatial or temporal trends were seen in the 256 growth rate measurements for each measured pigment. However, the diminishing eastward equatorial Fe gradient was associated with deepening subsurface pigment maxima and decreasing surface-layer pigment stocks (down to the 8% light level). In addition, integrated standing stocks of total chlorophyll a and Prochlorococcus (divinyl chlorophyll a) were strongly correlated with integrated iron at equatorial upwelling stations, yet no correlation with Fe was seen for any of the eukaryotic groups, including diatoms. This latter result is contrary to expectations from previous Fe addition experiments (in situ or in bottles), where diatom biomass increased relative to other phytoplankton. We hypothesize that the natural supply of Fe to the base of the euphotic zone from the EUC is less favorable for diatoms because of light limitation. Rather, new Fe is rapidly incorporated into a small phytoplankton-dominated community in the deep euphotic zone, and tightly coupled grazing control results in a system regulated by return of recycled Fe. (C) 2010 Elsevier Ltd. All rights reserved.

Dolan, JR, Landry MR, Ritchie ME.  2013.  The species-rich assemblages of tintinnids (marine planktonic protists) are structured by mouth size. Isme Journal. 7:1237-1243.   10.1038/ismej.2013.23   AbstractWebsite

Many microbial taxa in the marine plankton appear super-saturated in species richness. Here, we provide a partial explanation by analyzing how species are organized, species packing, in terms of both taxonomy and morphology. We focused on a well-studied group, tintinnid ciliates of the microzooplankton, in which feeding ecology is closely linked to morphology. Populations in three distinct systems were examined: an Eastern Mediterranean Gyre, a Western Mediterranean Gyre and the California Current. We found that species abundance distributions exhibited the long-tailed, log distributions typical of most natural assemblages of microbial and other organisms. In contrast, grouping in oral size-classes, which corresponds with prey-size exploited, revealed a geometric distribution consistent with a dominant role of a single resource in structuring an assemblage. The number of species found in a particular oral size-class increases with the numerical importance of the size-class in the overall population. We suggest that high species diversity reflects the fact that accompanying each dominant species are many ecologically similar species, presumably able to replace the dominant species, at least with regard to the size of prey exploited. Such redundancy suggests that species diversity greatly exceeds ecological diversity in the plankton.

Landry, MR.  1976.  Structure of marine ecosystems: an alternative. Marine Biology. 35:1-7.   10.1007/bf00386669   AbstractWebsite

In “The Structure of Marine Ecosystems” (1974), Steele developed a simulation model which suggested that the stability of planktonic communities was dependent on a threshold response allowing phytoplankton a refuge in concentration below which herbivorous zooplankton did not feed. Observations from the North Sea were presented to support this hypothesis. In order to more realistically represent the simulated herbivores, Calanus spp., several of Steele's assumptions have been modified. The results of the revised model indicate that feeding thresholds are not essential for the long-term realism and stability of the simulated system and suggest an alternative, ecosystem control through predation.

Eppley, RW, Swift E, Redalje DG, Landry MR, Haas LW.  1988.  Subsurface chlorophyll maximum in August-September 1985 in the CLIMAX area of the North Pacific. Marine Ecology-Progress Series. 42:289-301.   10.3354/meps042289   AbstractWebsite

The deep chlorophyll maxlmum (DCM) IS a widespread feature In the subtropical gyre of the North Paclflc In mid-August 1985 chlorophyll concentration increased In the DCM, then declined over time at 95 to 110 m depth near 28"N 155"W During the higher chlorophyll perlod the DCM lay within the top of the nitracline. Later, as the chlorophyll concentratlon decllned and the DCM deepened, following the 24.9 slgma-t surface, the maxlmum was above the nitracllne. The DCM was also a maxlmum in abundance of autotrophlc flagellates. Particulate nitrogen was retained over time in the euphotic zone relative to particulate carbon and chlorophyll. Phytoplankton growth rate at 90 to 110 m depth averaged 0 11 d-1 and phytoplankton carbon was about 10 µg I-1, about 50% of the total particulate carbon.

Bidigare, RR, Chai F, Landry MR, Lukas R, Hannides CCS, Christensen SJ, Karl DM, Shi L, Chao Y.  2009.  Subtropical ocean ecosystem structure changes forced by North Pacific climate variations. Journal of Plankton Research. 31:1131-1139.   10.1093/plankt/fbp064   AbstractWebsite

Biological responses to basin-scale climate forcing in the subtropical North Pacific Ocean are assessed based on temporal variations in plankton community structure observed at Station. ALOHA and results of a coupled plysical-biogeochemical model. Observational data and model simulations for the period 1990-2004 reveal distinct temporal patterns, with significant increases in net primary productivity, modeled nitrate flux into the euphotic zone and the measured downward of particulate nitrogen during 1999-2004. Concurrent increases in microalgae, cyanobacteria and modeled and measured zooplankton biomass were also observed during this period. We provide evidence that these responses were a consequence of climate forcing that destratified the upper ocean, making it more susceptible to mixing events and nutrient entrainment. These findigs underscore the importance of nitrate flux and plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time scales.

Landry, MR.  1981.  Switching between herbivory and carnivory by the planktonic marine copepod Calanus pacificus. Marine Biology. 65:77-82.   10.1007/bf00397070   AbstractWebsite

Adult females of the omnivorous copepod Calanus pacificus, collected from the plankton off La Jolla, California, USA (June, 1978), fed disproportionately on the prey in greatest relative abundance when given mixtures of diatoms (Thalassiosira fluviatilis) and copepod (C. pacificus) nauplii as food. This switch from herbivorous to carnivorous behavior may be significant in nature during the decline of phytoplankton blooms. More generally, the widespread omnivorous habit among pelagic animals suggests a responsive and flexible trophic organization which contributes to the resiliency of planktonic communities in a dynamic physical environment.

de Baar, HJW, Boyd PW, Coale KH, Landry MR, Tsuda A, Assmy P, Bakker DCE, Bozec Y, Barber RT, Brzezinski MA, Buesseler KO, Boye M, Croot PL, Gervais F, Gorbunov MY, Harrison PJ, Hiscock WT, Laan P, Lancelot C, Law CS, Levasseur M, Marchetti A, Millero FJ, Nishioka J, Nojiri Y, van Oijen T, Riebesell U, Rijkenberg MJA, Saito H, Takeda S, Timmermans KR, Veldhuis MJW, Waite AM, Wong CS.  2005.  Synthesis of iron fertilization experiments: From the iron age in the age of enlightenment. Journal of Geophysical Research-Oceans. 110   10.1029/2004jc002601   AbstractWebsite

[1] Comparison of eight iron experiments shows that maximum Chl a, the maximum DIC removal, and the overall DIC/ Fe efficiency all scale inversely with depth of the wind mixed layer (WML) defining the light environment. Moreover, lateral patch dilution, sea surface irradiance, temperature, and grazing play additional roles. The Southern Ocean experiments were most influenced by very deep WMLs. In contrast, light conditions were most favorable during SEEDS and SERIES as well as during IronEx-2. The two extreme experiments, EisenEx and SEEDS, can be linked via EisenEx bottle incubations with shallower simulated WML depth. Large diatoms always benefit the most from Fe addition, where a remarkably small group of thriving diatom species is dominated by universal response of Pseudo-nitzschia spp. Significant response of these moderate ( 10 - 30 mu m), medium ( 30 - 60 mu m), and large (> 60 mu m) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of "dissolved'' Fe ( filtrate < 0.2 mu m) maintained during an experiment determines the dominant diatom size class. However, this is further complicated by continuous transfer of original truly dissolved reduced Fe(II) into the colloidal pool, which may constitute some 75% of the "dissolved'' pool. Depth integration of carbon inventory changes partly compensates the adverse effects of a deep WML due to its greater integration depths, decreasing the differences in responses between the eight experiments. About half of depth-integrated overall primary productivity is reflected in a decrease of DIC. The overall C/Fe efficiency of DIC uptake is DIC/Fe similar to 5600 for all eight experiments. The increase of particulate organic carbon is about a quarter of the primary production, suggesting food web losses for the other three quarters. Replenishment of DIC by air/sea exchange tends to be a minor few percent of primary CO(2) fixation but will continue well after observations have stopped. Export of carbon into deeper waters is difficult to assess and is until now firmly proven and quite modest in only two experiments.