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Taylor, AG, Landry MR, Selph KE, Wokuluk JJ.  2015.  Temporal and spatial patterns of microbial community biomass and composition in the Southern California Current Ecosystem. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 112:117-128.   10.1016/j.dsr2.2014.02.006   AbstractWebsite

As part of the California Current Ecosystem Long Term Ecological Research (CCE-LTER) Program, samples for epifluorescence microscopy and flow cytometry (FCM) were collected at ten 'cardinal' stations on the California Cooperative Oceanic Fisheries Investigations (CalCOFI) grid during 25 quarterly cruises from 2004 to 2010 to investigate the biomass, composition and size-structure of microbial communities within the southern CCE. Based on our results, we divided the region into offshore, and inshore northern and southern zones. Mixed-layer phytoplankton communities in the offshore had lower biomass (16 +/- 2 mu g C L-1; all errors represent the 95% confidence interval), smaller size-class cells and biomass was more stable over seasonal cycles. Offshore phytoplankton biomass peaked during the winter months. Mixed-layer phytoplankton communities in the northern and southern inshore zones had higher biomass (78 +/- 22 and 32 +/- 9 mu g C L-1, respectively), larger size-class cells and stronger seasonal biomass patterns. Inshore communities were often dominated by micro-size (20-200 mu m) diatoms; however, autotrophic dinoflagellates dominated during late 2005 to early 2006, corresponding to a year of delayed upwelling in the northern CCE. Biomass trends in mid and deep euphoric zone samples were similar to those seen in the mixed-layer, but with declining biomass with depth, especially for larger size classes in the inshore regions. Mixed-layer ratios of autotrophic carbon to chlorophyll a (AC:Chl a) had a mean value of 51.5 +/- 53. Variability of nitracline depth, bin-averaged AC:Chl a in the mixed-layer ranged from 40 to 80 and from 22 to 35 for the deep euphotic zone, both with significant positive relationships to nitracline depth. Total living microbial carbon, including auto- and heterotrophs, consistently comprised about half of particulate organic carbon (POC). (C) 2014 Elsevier Ltd. All rights reserved.

Linacre, L, Landry MR, Cajal-Medrano R, Lara-Lara JR, Hernandez-Ayon JM, Mourino-Perez RR, Garcia-Mendoza E, Bazan-Guzman C.  2012.  Temporal dynamics of carbon flow through the microbial plankton community in a coastal upwelling system off northern Baja California, Mexico. Marine Ecology-Progress Series. 461:31-46.   10.3354/meps09782   AbstractWebsite

We investigated the temporal dynamics of carbon flow through the microbial food web of a coastal upwelling system (ENSENADA station) off northern Baja California during 6 cruises (September 2007 to November 2008). Carbon biomass assessments for major autotrophic size groups (pico- to micro-sized cells) and their microzooplankton grazers were based on analyses using flow cytometry, HPLC pigments and epifluorescence microscopy. Taxon-specific phytoplankton growth and microzooplankton grazing rates were determined from 24 h in situ incubations in the euphotic zone using an abbreviated 3-treatment dilution technique. Carbon biomass and instantaneous growth and grazing rate determinations were used to estimate daily rates of taxon-specific production and losses due to microzooplankton grazing. Overall, microbial biomass showed a close balance between autotrophic and heterotrophic components, except during a period of very strong upwelling (April 2008), which favored large phytoplankters and high primary production. Throughout a wide range of environmental conditions, the community primary production (PP) attributed both to small (mostly picophytoplankton and prasinophytes) and large (mostly diatoms and autotrophic dinoflagellates) autotrophs was significantly grazed (78 +/- 9% of PP) by small (< 20 mu m) and large (> 20 mu m) ciliates and flagellates (including mixotrophic dinoflagellates), respectively, showing complementary temporal shifts in protistan grazer types that matched the dominant phytoplankton. While large diatoms were strongly consumed by large ciliates during the 2 most productive periods (September 2007 and April 2008), pico- and nano-sized phytoplankton were grazed most by nanoflagellates and small ciliates from November 2007 to January 2008. Consequently, biogenic carbon production in this ecosystem is transferred through a multivorous food web.

Pasulka, AL, Landry MR, Taniguchi DAA, Taylor AG, Church MJ.  2013.  Temporal dynamics of phytoplankton and heterotrophic protists at station ALOHA. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 93:44-57.   10.1016/j.dsr2.2013.01.007   AbstractWebsite

Pico- and nano-sized autotrophic and heterotrophic unicellular eukaryotes (protists) are an important component of open-ocean food webs. To date, however, no direct measurements of cell abundance and biomass of these organisms have been incorporated into our understanding of temporal variability in the North Pacific Subtropical Gyre (NPSG). Based primarily on epifluoresence microscopy augmented with flow cytometry, we assessed the abundance and biomass of autotrophs and heterotrophic protists at Station ALOHA between June 2004 and January 2009. Autotrophic eukaryotes (A-EUKS) were more abundant in both the upper euphotic zone and deep chlorophyll maximum layer (DCML) during winter months, driven mostly by small flagellates. A higher ratio of A-EUKS to heterotrophic protists (A:H ratio) and a structural shift in A-EUKS to smaller cells during the winter suggests a seasonal minimum in grazing pressure. Although Prochlococcus spp. comprised between 30% and 50% of autotrophic biomass in both the upper and lower euphotic zone for most of the year, the community structure and seasonality of nano-and micro-phytoplanlcon differed between the two layers. In the upper layer, Trichodesmium spp. was an important contributor to total biomass (20-50%) in the late summer and early fall. Among A-EUKS, prymnesiophytes and other small flagellates were the dominant contributors to total biomass in both layers regardless of season (10-20% and 13-39%, respectively). Based on our biomass estimates, community composition was less seasonally variable in the DCML relative to the upper euphotic zone. In surface waters, mean estimates of C:Chl a varied with season highest in the summer and lowest in the winter (means=156 +/- 157 and 89 +/- 32, respectively); however, there was little seasonal variability of C:Chl a in the DCML (100 m mean=29.9 +/- 9.8). Biomass of heterotrophic protists peaked in the summer and generally declined monotonically with depth without a deep maximum. Anomalous patterns of A:H variability during summer 2006 (low mesozooplankton, high A-EUKS and H-dinoflagellates) suggest that top-down forcing is strong enough to impact lower trophic levels in the NPSG. Continued studies of community abundance and biomass relationships are needed for adequate representations of plankton dynamics in ecosystem models and for developing a predictive understanding of both intra-and inter-lower trophic level responses to climate variability in the NPSG. (c) 2013 Elsevier Ltd. All rights reserved.

Baker, ET, Feely RA, Landry MR, Lamb M.  1985.  Temporal variations in the concentration and settling flux of carbon and phytoplankton pigments in a deep fjord-like estuary. Estuarine Coastal and Shelf Science. 21:859-877.   10.1016/0272-7714(85)90079-4   AbstractWebsite

The weekly mass flux of C and phytoplankton pigments at five depths in the main basin of Puget Sound, a deep (∼200 m) fjordlike estuary, was sampled for a year with moored sequentially-sampling sediment traps. Flux measurements were compared with weekly samples of suspended pigments in the euphotic zone and bi-monthly samples of total suspended matter and particulate C throughout the water column at the mooring site.Seasonal changes in the total mass flux at all depths were small; instead, physical (river runoff, bottom resuspension) and biological (phytoplankton blooms) events caused occasional sharp increases on a weekly scale. The dry weight concentration of pigments in the trap samples mirrored the concentration of pigments in the euphotic zone suspended matter, increasing from 0·01% in winter to a maximum of 0·65% in late summer. Bloom-induced changes in the pigment concentration were observed almost simultaneously in the euphotic zone and in the traps to a depth of 160 m, indicating a rapid vertical transfer of surface-originating particles by organic aggregates. In contrast to the strong seasonal signal in the pigment concentration, C concentration varied by only a factor of three during the year.The seasonal trend of C/pigment ratios in the C flux arises from at least two sources: (1) a balance between terrestrial sources of C during the high-runoff winter season and in-situ primary production in spring and summer, and (2) cycling of C through the zooplankton population. Budget calculations suggest that the loss of primary-produced C and pigment from the euphotic zone by settling is ∼5% regardless of season. On an annual basis, this C flux (16 g m−2) is sufficient to support previously measured values of benthic aerobic respiration at the mooring site. To account for other C sinks such as burial, predation and chemical oxidation, however, terrestrial C sources and alternate transport pathways, such as vertical advection and sediment movement down the steep basin walls, are necessary.

Landry, MR, Hassett RP.  1985.  Time scales in behavioral, biochemical, and energetic adaptations to food-limiting conditions by a marine copepod. Food limitation and the structure of zooplankton communities : proceedings of an international symposium held at Plön, W. Germany, July 9-13, 1984. ( Lampert W, Ed.)., Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung Abstract

The copepod Calanus pacificus Brodsky adapts behaviorally, biochemically, and energetically to food-limiting conditions; however, the direction and extent of these adaptations vary on different temporal scales. Seasonally, Calanus enters a diapause state characterized by reduced metabolism, digestive enzyme activity and feeding. On the scale of daily migrations, only feeding rate responds to food level. However, on the time scale of phytoplankton bloom events (days to weeks), feeding potential, digestive enzyme activity, and assimilation efficiency all increase in response to chronically low food. Both the seasonal and shorter term adaptations are important in the context of the seasonal, high-energy coastal environments in which the copepod predominates. The seasonal response minimizes the rates of energy utilization allowing the species to survive extended periods of low food during the winters.

Landry, MR, Monger BC, Selph KE.  1993.  Time-dependency of microzooplankton grazing and phytoplankton growth in the subarctic Pacific. Progress in Oceanography. 32:205-222.   10.1016/0079-6611(93)90014-5   AbstractWebsite

Dilution experiments were conducted on SUPER Program cruises in June 1987 and May and August 1988 to assess the role of microzooplankton in controlling phytoplankton stocks in the subarctic Pacific. Net growth rates of chlorophyll a varied in individual experiments from -0.4 to +0.7d-1. Experiments incubated for 48h gave higher net estimates than 24h incubations (0.01 to 0.22 d-1 for different cruises), ''aggerating the imbalance between growth and grazing. Specific growth rates (mu) and grazing mortality (m) for 24h incubations were approximately balanced for the June and May cruises, and net growth estimates from the dilution experiments predicted changes in chlorophyll concentrations for May that closely matched those observed in the field, A major decline in phytoplankton abundance in the middle of May coincided with a high abundance of ciliates. Cell counts indicated that Synechococcus and small autotrophic nonflagellates were always kept in check by microzooplankton grazing, even when chlorophyll indicated uncontrolled phytoplankton growth in August 1988 experiments. Diatoms showed high growth potential in most incubations and dominated among the cells that bloomed in August. Our results support the hypotheses that micrograzers are major consumers of phytoplankton in the subarctic Pacific and that their grazing can control some elements of the phytoplankton community. However, growth limitation, presumably from iron deficiency, remains essential to the explanation of phytoplankton control in mid to late summer.

Price, NM, Harrison PJ, Landry MR, Azam F, Hall KJF.  1986.  Toxic effects of latex and Tygon tubing on marine phytoplankton, zooplankton and bacteria. Marine Ecology Progress Series. 34:41-49.   10.3354/meps034041   AbstractWebsite

Natural plankton assemblages were incubated with a small piece of silicone. Tygon or latex rubber tubing in 200 m1 of culture to determine potential long-term toxic effects of the tubing. Drastic decreases in cell numbers and chlorophyll fluorescence indicated that over 95% of the phytoplankton were killed by the latex rubber tubing in 4 d. Even a 1 mm piece of latex tubing lulled -90 % of the phytoplankton. The most resistant specles were Thalassjosira spp. and pennate diatoms. Growth of heterotrophic bodonid flagellates was unaffected by small amounts of latex tubing (1 mm) and larger pieces decreased growth only marginally. Bacterial numbers decreased initially, but resistant forms began to grow at the end of the experiment. New unwashed Tygon tubing significantly decreased phytoplankton growth rates, but much less than latex tubing. Washing Tygon tubing, by pouring as little as 200 ml of seawater through a 1 m piece of 0.6 cm diameter tubing, removed this toxlc effect. No inhibitory effects were found with silicone tubing. Short-term effects of the presence of tubing in the culture medium were documented by measuring phytoplankton photosynthetic rates (14C uptake) and 3H-thymidine incorporation into bacteria. Latex and unwashed Tygon tubing significantly decreased these metabolic rate processes. Tubing effects on zooplankton survival, fecundity and egg viability were tested for the copepod Acartia clausii. Latex tubing had the largest effect on these parameters followed by Tygon tubing. Silicone tubing exerted no significant effect.

Stukel, MR, Landry MR, Benitez-Nelson CR, Goericke R.  2011.  Trophic cycling and carbon export relationships in the California Current Ecosystem. Limnology and Oceanography. 56:1866-1878.   10.4319/lo.2011.56.5.1866   AbstractWebsite

We constructed a simple non-steady-state model of trophic cycling relationships in the California Current Ecosystem and tested its predictions of mesozooplankton fecal-pellet export against vertical carbon-flux measurements by the (234)Th method taken during Lagrangian experiments. To assess trophic relationships, we simultaneously measured (14)C-primary production and chlorophyll-based rate estimates of phytoplankton growth, microzooplankton grazing, mesozooplankton grazing, and net phytoplankton growth. Study locations ranged from coastal upwelling to offshore oligotrophic conditions. E-ratios (carbon export : (14)C-primary production) predicted by the model ranged from 0.08 to 0.14, in good agreement with both the magnitude and the variability found in contemporaneous measurements of (234)Th export and C: (234)Th-ratios of sinking particles. E-ratios were strongly decoupled from new production estimates. The lowest measured and predicted e-ratios were associated with higher nutrient chlorophyll parcels with net accumulating phytoplankton in the inshore region. For our study sites, variability in export efficiency was determined by the local net balance of growth and grazing and the relative strengths of grazing pathways to microzooplankton and mesozooplankton. Despite very different plankton assemblages studied, the consistently good agreement between independently measured production-grazing processes and biogeochemical rates suggest that zooplankton are the major drivers of vertical carbon-flux in this system during springtime.