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2016
Goes, JI, Gomes HD, Selph KE, Landry MR.  2016.  Biological response of Costa Rica Dome phytoplankton to Light, Silicic acid and Trace metals. Journal of Plankton Research. 38:290-304.   10.1093/plankt/fbv108   AbstractWebsite

The Costa Rica Dome (CRD) is a unique open-ocean upwelling system, with picophytoplankton dominance of phytoplankton biomass and suppressed diatoms, yet paradoxically high export of biogenic silica. As a part of Flux and Zinc Experiments cruise in summer (June-July 2010), we conducted shipboard incubation experiments in the CRD to examine the potential roles of Si, Zn, Fe and light as regulating factors of phytoplankton biomass and community structure. Estimates of photosynthetic quantum yields revealed an extremely stressed phytoplankton population that responded positively to additions of silicic acid, iron and zinc and higher light conditions. Size-fractioned Chl a yielded the surprising result that picophytoplankton, as well as larger phytoplankton, responded most to treatments with added silicic acid incubated at high incident light (HL + Si). The combination of Si and HL also led to increases in cell sizes of picoplankton, notably in Synechococcus. Such a response, coupled with the recent discovery of significant intracellular accumulation of Si in some picophytoplankton, suggests that small phytoplankton could play a potentially important role in Si cycling in the CRD, which may help to explain its peculiar export characteristics.

Freibott, A, Taylor AG, Selph KE, Liu HB, Zhang WC, Landry MR.  2016.  Biomass and composition of protistan grazers and heterotrophic bacteria in the Costa Rica Dome during summer 2010. Journal of Plankton Research. 38:230-243.   10.1093/plankt/fbv107   AbstractWebsite

We investigated biomass and composition of heterotrophic microbes in the Costa Rica Dome during June-July 2010 as part of a broader study of plankton trophic dynamics. Because picophytoplankton (, 2 mm) are known to dominate in this unique upwelling region, we hypothesized tight biomass relationships between size-determined predator-prey pairs (i.e. picoplankton-nano-grazers, nanoplankton-micro-grazers) within the microbial community. Integrated biomass of heterotrophic bacteria ranged from 180 to 487 mg C m(-2) and was significantly correlated with total autotrophic carbon. Heterotrophic protist (H-protist) biomass ranged more narrowly from 488 to 545 mg C m(-2), and was comprised of 60% dinoflagellates, 30% other flagellates and 11% ciliates. Nano-sized (<20 mu m) protists accounted for the majority (57%) of grazer biomass and were positively correlated with picoplankton, partially supporting our hypothesis, but nanoplankton and micro-grazers (>20 mu m) were not significantly correlated. The relative constancy of H-protist biomass among locations despite clear changes in integrated autotrophic biomass, Chl a, and primary production suggests that mesozooplankton may exert a tight top-down control on micro-grazers. Biomass-specific consumption rates of phytoplankton by protistan grazers suggest an instantaneous growth rate of 0.52 day(-1) for H-protists, similar to the growth rate of phytoplankton and consistent with a trophically balanced ecosystem dominated by piconanoplankton interactions.

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.

Decima, M, Landry MR, Stukel MR, Lopez-Lopez L, Krause JW.  2016.  Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web. Journal of Plankton Research. 38:317-330.   10.1093/plankt/fbv091   AbstractWebsite

We investigated standing stocks and grazing rates of mesozooplankton assemblages in the Costa Rica Dome (CRD), an open-ocean upwelling ecosystem in the eastern tropical Pacific. While phytoplankton biomass in the CRD is dominated by picophytoplankton (<2-mu m cells) with especially high concentrations of Synechococcus spp., we found high mesozooplankton biomass (similar to 5 g dry weight m(-2)) and grazing impact (12-50% integrated water column chlorophyll a), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll a and mesozooplankton biomass, variability in herbivory was substantial, with lower rates in the central dome region and higher rates in areas offset from the dome center. While grazing rates were unrelated to total phytoplankton, correlations with cyanobacteria (negative) and biogenic SiO2 production (positive) suggest that partitioning of primary production among phytoplankton sizes contributes to the variability observed in mesozooplankton metrics. We propose that advection of upwelled waters away from the dome center is accompanied by changes in mesozooplankton composition and grazing rates, reflecting small changes within the primary producers. Small changes within the phytoplankton community resulting in large changes in the mesozooplankton suggest that the variability in lower trophic level dynamics was effectively amplified through the food web.

Landry, MR, Selph KE, Decima M, Gutierrez-Rodriguez A, Stukel MR, Taylor AG, Pasulka AL.  2016.  Phytoplankton production and grazing balances in the Costa Rica Dome. Journal of Plankton Research. 38:366-379.   10.1093/plankt/fbv089   AbstractWebsite

We investigated phytoplankton production rates and grazing fates in the Costa Rica Dome (CRD) during summer 2010 based on dilution depth profiles analyzed by flow cytometry and pigments and mesozooplankton grazing assessed by gut fluorescence. Three community production estimates, from C-14 uptake (1025+/-113 mg C m(-2) day(-1)) and from dilution experiments analyzed for total Chla (990+/-106 mg C m(-2) day(-1)) and flow cytometry populations (862+/-71 mg C m(-2) day(-1)), exceeded regional ship-based values by 2-3-fold. Picophytoplankton accounted for 56% of community biomass and 39% of production. Production profiles extended deeper for Prochlorococcus (PRO) and picoeukaryotes than for Synechococcus (SYN) and larger eukaryotes, but 93% of total production occurred above 40 m. Microzooplankton consumed all PRO and SYN growth and two-third of total production. Positive net growth of larger eukaryotes in the upper 40 m was balanced by independently measured consumption by mesozooplankton. Among larger eukaryotes, diatoms contributed similar to 3% to production. On the basis of this analysis, the CRD region is characterized by high production and grazing turnover, comparable with or higher than estimates for the eastern equatorial Pacific. The region nonetheless displays characteristics atypical of high productivity, such as picophytoplankton dominance and suppressed diatom roles.

Selph, KE, Landry MR, Taylor AG, Gutierrez-Rodriguez A, Stukel MR, Wokuluk J, Pasulka A.  2016.  Phytoplankton production and taxon-specific growth rates in the Costa Rica Dome. Journal of Plankton Research. 38:199-215.   10.1093/plankt/fbv063   AbstractWebsite

During summer 2010, we investigated phytoplankton production and growth rates at 19 stations in the eastern tropical Pacific, where winds and strong opposing currents generate the Costa Rica Dome (CRD), an open-ocean upwelling feature. Primary production (C-14-incorporation) and group-specific growth and net growth rates (two-treatment sea-water dilution method) were estimated from samples incubated in situ at eight depths. Our cruise coincided with a mild El Nino event, and only weak upwelling was observed in the CRD. Nevertheless, the highest phytoplankton abundances were found near the dome center. However, mixed-layer growth rates were lowest in the dome center (similar to 0.5-0.9 day(-1)), but higher on the edge of the dome (similar to 0.9-1.0 day(-1)) and in adjacent coastal waters (0.9-1.3 day(-1)). We found good agreement between independent methods to estimate growth rates. Mixed-layer growth rates of Prochlorococcus and Synechococcus were largely balanced by mortality, whereas eukaryotic phytoplankton showed positive net growth (similar to 0.5-0.6 day(-1)), that is, growth available to support larger (mesozooplankton) consumer biomass. These are the first group-specific phytoplankton rate estimates in this region, and they demonstrate that integrated primary production is high, exceeding 1 g C m(-2) day(-1) on average, even during a period of reduced upwelling.

Landry, MR, de Verneil A, Goes JI, Moffett JW.  2016.  Plankton dynamics and biogeochemical fluxes in the Costa Rica Dome: introduction to the CRD Flux and Zinc Experiments. Journal of Plankton Research. 38:167-182.   10.1093/plankt/fbv103   AbstractWebsite

The Costa Rica Dome (CRD) is an open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone (OMZ). The region has unique characteristics, biomass dominance by picophytoplankton, suppressed diatoms, high biomass of higher consumers and presumptive trace metal limitation, but is poorly understood in terms of pelagic stock and process relationships, including productivity and production controls. Here, we describe the goals, project design, physical context and major findings of the Flux and Zinc Experiments cruise conducted in June-July 2010 to assess trophic flux relationships and elemental controls on phytoplankton in the CRD. Despite sampling during a year of suppressed summertime surface chlorophyll, cruise results show high productivity (similar to 1 g C m(-2) day(-1)), high new production relative to export, balanced production and grazing, disproportionate biomass-specific productivity of large phytoplankton and high zooplankton stocks. Zinc concentrations are low in surface waters relative to phosphorous and silicate in other regions, providing conditions conducive to picophytoplankton, like Synechococcus, with low Zn requirements. Experiments nonetheless highlight phytoplankton limitation or co-limitation by silicic acid, driven by a strong silica pump that is linked to low dissolution of biogenic silica in the cold shallow thermocline of the lower euphotic zone.