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Baines, SB, Chen X, Twining BS, Fisher NS, Landry MR.  2016.  Factors affecting Fe and Zn contents of mesozooplankton from the Costa Rica Dome. Journal of Plankton Research. 38:331-347.   10.1093/plankt/fbv098   AbstractWebsite

Mineral limitation of mesozooplankton production is possible in waters with low trace metal availability. As a step toward estimating mesozooplankton Fe and Zn requirements under such conditions, we measured tissue concentrations of major and trace nutrient elements within size-fractioned zooplankton samples collected in and around the Costa Rica Upwelling Dome, a region where phytoplankton growth may be co-limited by Zn and Fe. The geometric mean C, N, P contents were 27, 5.6 and 0.21 mmol gdw(-1), respectively. The values for Fe and Zn were 1230 and 498 nmol gdw(-1), respectively, which are low compared with previous measurements. Migrant zooplankton caused C and P contents of the 2-5 mm fraction to increase at night relative to the day while the Fe and Zn contents decreased. Fe content increased with size while Zn content decreased with size. Fe content was strongly correlated to concentrations of two lithogenic tracers, Al and Ti. We estimate minimum Fe: C ratios in large migrant and resident mixed layer zooplankton to be 15 and 60 mu mol mol(-1), respectively. The ratio of Zn: C ranged from 11 mu mol mol(-1) for the 0.2-0.5 mm size fraction to 33 mu mol mol(-1) for the 2-5 mm size fraction.

Frost, BW, Landry MR, Hassett RP.  1983.  Feeding behavior of large calanoid copepods Neocalanus cristatus and N. plumchrus from the subarctic Pacific Ocean . Deep-Sea Research Part A-Oceanographic Research Papers. 30:1-13.   10.1016/0198-0149(83)90029-8   AbstractWebsite

Oceanic waters of the subarctic Pacific exhibit a special ecological feature, a virtually seasonally invariant standing stock of phytoplankton (measured as chlorophyll a), that seems to reflect a balance, at least during spring and summer, between phytoplankton growth and zooplankton grazing. The grazers presumed to be responsible for the balance are the calanoid copepodsNeocalanus cristatus andN. plumchrus. Shipboard grazing experiments, utilizing both natural suspended particulate material and cultured phytoplankton as food for the copepods, showed that both species have at least three attributes of feeding behavior required to maintain steady standing stock of phytoplankton. That is, theNeocalanus species can feed at the low concentrations of phytoplankton that prevail in the open subarctic Pacific, they feed at similar rates on a broad range of particlessizes including the predominant particles, and they respond to small increases in phytoplankton concentration by proportionately larger increases in their feeding rate. Although both species ofNeocalanus attain larger body sizes than co-occurringCalanus pacificus andPseudocalanus sp., they have morphological specializations that seem to account for their unexpected ability to feed on very dilute suspensions of small phytoplankton cells. It appears that the perpetually low phytoplankton concentrations in the open subarctic Pacific do not permit maximum feeding effort by the species of Neocalanus.

Monger, BC, Landry MR, Brown SL.  1999.  Feeding selection of heterotrophic marine nanoflagellates based on the surface hydrophobicity of their picoplankton prey. Limnology and Oceanography. 44:1917-1927.   10.4319/lo.1999.44.8.1917   AbstractWebsite

Theory suggests that variation in the attractive solvation force associated with cell-surface hydrophobicity can significantly affect contact rates among small cells in aqueous environments and consequently may influence rates and selective impacts of marine nanoflagellate grazers feeding on picoplankton assemblages. To investigate this hypothesis, we assayed the natural range in hydrophobic characteristics of subtropical picoplankton from the oligotrophic subtropical Pacific (Station Aloha, 22 degrees 45'N, 158 degrees W) and mesotrophic Kaneohe Bay, Hawaii, using hydrophobic interaction chromatography (HIC) in conjunction with analytical flow cytometry. Variability in a relative index of cell-surface hydrophobicity (HIC index) for heterotrophic bacteria, Prochlorococcus and Synechococcus, exhibited some consistent spatial patterns. The HIC index for Prochlorococcus at Station Aloha varied about threefold, being consistently more hydrophobic in the upper 80 m of the water column and dropping abruptly below this depth. Heterotrophic bacteria were more hydrophobic near the surface and decreased slightly, but steadily, with increasing depth. The hydrophobicity of heterotrophic bacteria steadily increased along a Kaneohe Bay transect extending from oligotrophic to mesotrophic conditions. In experiments involving nanoflagellates grazing on laboratory cultures of Prochlorococcus, cell cultures exhibiting the highest HIC indices were grazed upon at the highest rates. An additional experiment involving mixtures of Prochlorococcus cells exhibiting high and low hydrophobicities showed that the average hydrophobicity of the uningested prey mixture was driven progressively toward lower hydrophobicity as the more hydrophobic cells were selectively removed through time. If these laboratory grazing results hold in nature, the rate at which picoplankton cells are cleared from suspension by nanoflagellates could vary by as much as twofold due solely to natural variation in cell surface hydrophobicity.

Gutierrez-Rodriguez, A, Slack G, Daniels EF, Selph KE, Palenik B, Landry MR.  2014.  Fine spatial structure of genetically distinct picocyanobacterial populations across environmental gradients in the Costa Rica Dome. Limnology and Oceanography. 59:705-723.   10.4319/lo.2014.59.3.0705   AbstractWebsite

We investigated the spatial variability of picocyanobacterial community structure across the Costa Rica Dome (CRD), an offshore upwelling system characterized by high seasonal abundance of Synechococcus spp. We constructed clone libraries of the rpoC1 gene to survey picocyanobacterial diversity and developed specific real-time quantitative polymerase chain reaction assays to assess the distribution of genetically distinct Synechococcus (SYN) and Prochlorococcus (PRO) populations across vertical and horizontal physicochemical gradients. Flow cytometry data showed that cell abundances for both SYN and PRO were highest near the dome center. Phylogenetic analysis of rpoC1 sequences revealed a remarkably high and distinctive picocyanobacterial diversity (FLU1-3, CRD1, Clade II, XV, XVI) that included "novel'' SYN and PRO genotypes. Furthermore, genetically different populations exhibited vertical and horizontal spatial partitioning. Abundances of distinct SYN genotypes peaked at subsequent depth horizons, leading to a fine vertical structure with at least three populations stacked within the upper 30-40 m at the dome. Clade II and FLU1A peaked in surface waters, while maximum concentrations of CRD1, FLU1B, and Clade XVI occurred in the upper and lower thermocline, respectively. Horizontally, Clade II abundance in surface waters remained high across the entire region, while SYN genotypes CRD1 and FLU1A increased with shoaling of the thermo- and nutricline toward the center of the dome to become the dominant genotypes of the SYN assemblage in the dome. Below the mixed layer, Clade XVI and PRO genotype FLU2, virtually absent outside the dome, became abundant components of the picocyanobacterial assemblage. Despite their phylogenetic relatedness, FLU1A and FLU1B subclades followed different distributional patterns, suggesting ecological significance of the microdiversity within the clade. The unprecedented fine vertical structure demonstrated for SYN genotypes is driven by sharp physicochemical gradients (e.g., density, nutrient, oxygen, and trace metals) created by the dome and the presence of a shallow oxycline that enhances habitat diversification.

Monger, BC, Landry MR.  1993.  Flow cytometric analysis of marine bacteria with Hoechst 33342. Applied and Environmental Microbiology. 59:905-911. AbstractWebsite

We investigated the accuracy and precision of flow cytometric (FCM) estimates of bacterial abundances using 4',6-diamidino-2-phenylindole (DAPI) and Hoechst 33342 (110342, a bisbenzamide derivative) on paraformaldehyde-fixed seawater samples collected from two stations near Oahu, Hawaii. The accuracy of FCM estimates was assessed against direct counts by using epifluorescence microscopy. DAPI and HO342 differ in two aspects of their chemistry that make HO342 better suited for staining marine heterotrophic bacteria for FCM analysis. These differences are most important in studies of open-ocean ecosystems that require dual-beam FCM analysis to clearly separate heterotrophic bacterial populations from populations of photosynthetic Prochlorococcus spp. Bacterial populations were easier to distinguish from background fluorescence when stained with 110342 than when stained with DAPI, because HO342 has a higher relative fluorescence quantum yield. A substantially higher coefficient of variation of blue fluorescence, which was probably due to fluorescent complexes formed by DAPI with double-stranded RNA, was observed for DAPI-stained populations. FCM estimates averaged 2.0 and 12% higher than corresponding epifluorescence microscopy direct counts for HO342 and DAPI-stained samples, respectively. A paired-sample t test between FCM estimates and direct counts found no significant difference for HO342-stained samples but a significant difference for DAPI-stained samples. Coefficients of variation of replicate FCM abundance estimates ranged from 0.63 to 2.9% (average, 1.5%) for natural bacterial concentrations of 6 x 10(5) to 15 x 10(5) cells ml-1.

Huh, CA, Ku TL, Luo SD, Landry MR, Williams PM.  1993.  Fluxes of thorium isotopes in the Santa Monica Basin, offshore California. Earth and Planetary Science Letters. 116:155-164.   10.1016/0012-821x(93)90051-a   AbstractWebsite

Fluxes of Th-234, Th-232, Th-230 and Th-228 increase with depth in the water column of Santa Monica Basin, following the flux of particulate inorganic matter. Temporal variability in flux is generally low for the shorter lived and predominantly radiogenic Th-234 and Th-228, but high for Th-230 and the nonradiogenic Th-232. The flux profiles are largely controlled by lateral advection of detrital material resuspended from the basin slope. Most of the shorter lived Th-234 and Th-228 scavenged from the water column are produced in situ or locally, whereas most of the authigenic Th-230 is transported from elsewhere. From the concentration (in dissolved and particulate forms) and flux profiles of these isotopes, the residence time estimate of dissolved Th is 1-2 months in the upper 50 m and 1-2 years in the entire water column. The corresponding residence times for particulate Th are 4 days and approximately 40 days, respectively. The average rate at which suspended particles work their way downward via aggregation and settling is estimated at 6-10 m/day. In the context of the documented circulation pattern in the region, these results suggest that most pollutants introduced to the Santa Monica Basin will be exported out of it.

Greene, CH, Landry MR, Monger BC.  1986.  Foraging behavior and prey selection by the ambush entangling predator Pleurobrachia bachei. Ecology. 67:1493-1501.   10.2307/1939080   AbstractWebsite

Ctenophores and other gelatinous predators in the ocean are ephemeral in their spatial and temporal distributions, but often have a dramatic impact on the dynamics of their prey populations. Considerable information is currently available on the functional and numerical responses of several nearshore ctenophore species; however, an understanding of their potential for shaping the structure of natural zooplankton assemblages requires further information on the selective nature of their predation. Prey selection by the tentaculate ctenophore Pleurobrachia bachei was examined in the laboratory with predation experiments and videotaped observations of predator and prey behavior. Prey types offered to the ctenophore included each of the developmental stages of Calanus pacificus, adult Acartia clausii, and adult Pseudocalanus sp. Pleurobrachia exhibited an unusual, bimodal pattern of prey selection on the different developmental stages of Calanus. Calanus' vulnerability increased through the naupliar stages, dropped at the first copepodid stage, and then rose again throughout the subsequent copepodid stages prior to another decline at the adult stage. Adult Acartia and Pseudocalanus were found to be among the most vulnerable of the prey types offered to Pleurobrachia. We conclude that Pleurobrachia's diet is determined by the relative availability and vulnerability of prey, and that vulnerability to the ctenophore can be predicted from prey swimming speeds and the susceptibility of prey after encounter.

Bathmann, U, Bundy MH, Clarke ME, Cowles TJ, Daly K, Dam HG, Dekshenieks MM, Donaghay PL, Gibson DM, Gifford DJ, Hansen BW, Hartline DK, Head EJH, Hofmann EE, Hopcroft RR, Jahnke RA, Jonasdottir SH, Kiorboe T, Kleppel GS, Klinck JM, Kremer PM, Landry MR, Lee RF, Lenz PH, Madin LP, Manahan DT, Mazzocchi MG, McGillicuddy DJ, Miller CB, Nelson JR, Osborn TR, Paffenhofer GA, Pieper RE, Prusova I, Roman MR, Schiel S, Seim HE, Smith SL, Torres JJ, Verity PG, Wakeham SG, Wishner KF, Marine Zooplankton C.  2001.  Future marine zooplankton research - a perspective - Marine Zooplankton Colloquium 2. Marine Ecology-Progress Series. 222:297-308.   10.3354/meps222297   AbstractWebsite

During the Second Marine Zooplankton Colloquium (MZC2) 3 issues were added to those developed 11 yr ago during the First Marine Zooplankton Colloquium (MZC1). First, we focused on hot spots, i.e., locations where zooplankton occur in higher than regular abundance and/or operate at higher rates, We should be able to determine the processes leading to such aggregations and rates, and quantify their persistence. Second, information on the level of individual species, even of highly abundant ones, is limited, Concerted efforts should be undertaken with highly abundant to dominant species or genera (e.g., Oithona spp,, Calanus spp., Oikopleura spp., Euphausia superba) to determine what governs their abundance and its variability. Third, zooplankton clearly influence biogeochemical cycling in the ocean, but our knowledge of the underlying processes remains fragmentary. Therefore a thorough assessment of variables that still need to be quantified is required to obtain an understanding of zooplankton contributions to biogeochemical cycling. Combining studies on the 7 issues from MZC1 with the 3 from MZC2 should eventually lead to a comprehensive understanding of (1) the mechanisms governing the abundance and existence of dominant zooplankton taxa, and (2) the control of biodiversity and biocomplexity, for example, in the tropical ocean where diversity is high. These recommendations come from an assemblage of chemical, physical and biological oceanographers with experience in major interdisciplinary studies, including modeling. These recommendations are intended to stimulate efforts within the oceanographic community to facilitate the development of predictive capabilities for major biological processes in the ocean.