The Assimilation of Elements Ingested by Marine Copepods

Reinfelder, John R.; Fisher, Nicholas S.

doi:10.1126/science.251.4995.794

Cited by 370 publications

(352 citation statements)

References 16 publications

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“…The similarities between Fe and Th behavior suggest that changing the particle size spectrum and chemistry is the dominant net effect of grazing, and this process may be important for other hydrolyzed particle reactive metals, like aluminum. In studies of metazoan grazers (Reinfelder & Fisher 1991, Hutchins et al 1995, strong correlations have been found between grazer assimilation efficiency and prey subcellular partitioning of trace elements. In this study the assimilation efficiencies of protists for Fe and Th were not measured.…”

Section: Discussionmentioning

confidence: 99%

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Barbeau¹,

Kujawinski²,

Moffett³

2001

Aquat. Microb. Ecol.

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To characterize trace metal cycling in marine systems as mediated by heterotrophic protists, we conducted a series of laboratory experiments in 2-organism model systems consisting of bacteria and protistan grazers. Trace metal isotopes ( 59 Fe and 234 Th), 14 C, and bulk organic carbon measurements were used to follow the chemical transformation of bacterial carbon and associated trace metals by several different grazer species. Results indicate that grazers were able to cause repartitioning of Th and regeneration of Fe from bacterial prey into the dissolved phase (< 0.2 µm), even in particle-rich laboratory cultures. For both Th and Fe, protist grazing led to the formation of relatively stable dissolved and colloidal metal-organic species. Metal/carbon ratios of the particle pool in some model systems with grazers were significantly altered, indicating a decoupling of trace metal and organic carbon cycling through the grazing process. Different protist species exhibited substantial variation (up to a factor of 10) in their ability to quantitatively remobilize trace metals from bacterial prey. The implications of these findings for trace metal cycling in marine systems are discussed. KEY WORDS: Marine protists · Iron · Thorium · Organic carbon · RecyclingResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 24: 69-81, 2001 suggests that the effect of protist grazing on trace metals in the oceans is both geochemically and ecologically significant.This study presents some of the first data on the regeneration and recycling of cell-associated Fe and Th isotopes in conjunction with cellular organic carbon by heterotrophic protists in laboratory culture. Despite the widespread use of naturally occurring Th isotopes as analogues for particle-reactive species (Clegg & Whitfield 1991, Gustafsson et al. 1997) and as tracers of particulate organic carbon (POC) export from the upper ocean (e.g. Buesseler et al. 1992, Murray et al. 1996, almost nothing is known about the actual mechanism of Th cycling via protists and associated organisms of the 'microbial loop'. Very few model system studies have examined the mechanism of Fe recycling in seawater via protistan grazing (Hutchins & Bruland 1994, Chase & Price 1997. Both of these studies employed the grazer Paraphysomonas sp. In the present study several different grazer species (including Paraphysomonas) were examined in terms of Fe, Th and organic carbon remineralization.In the first experiment, a model system study, the size fractionation of Fe and Th isotopes and organic carbon was followed as a heterotrophic nanoflagellate (Cafeteria sp., a free-living flagellate 3-5 µm diameter) consumed bacterial prey. Next a sequence of experiments was conducted in order to determine the relative abilities of 3 different kinds of protists to remobilize cell-associated Fe and Th (Cafeteria sp.; Uronema sp., a benthic scuticociliate 7-15 µm in length; and Paraphysomonas imperforata, a free-living flagellate 5-7 µm in diameter, whic...

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Section: Discussionmentioning

confidence: 99%

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Barbeau¹,

Kujawinski²,

Moffett³

2001

Aquat. Microb. Ecol.

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“…Given the reported influence of factors such as ingestion rate (this study; Munger and Hare unpubl. data), food quality (Reinfelder and Fisher 1991;Wang and Fisher 1996), and temperature (M.-N. Croteau, INRS-Eau, unpubl. data) on metal assimilation efficiency, such differences among studies are to be expected.…”

Section: Discussionmentioning

confidence: 99%

Cadmium sources and exchange rates for Chaoborus larvae in nature

Munger

Hare

Tessier

1999

Limnology & Oceanography

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Although freshwater insects are known to accumulate trace metals in the laboratory from both water and food, the relative importance of metal sources for these animals, as well as the rate at which they take up and eliminate their metal, has not been measured in nature. We describe a novel in situ approach that allowed us to determine that trophic transfer is the main source of cadmium for larvae of a common lake-dwelling animal, the phantom midge Chaoborus punctipennis. We transferred C. punctipennis larvae from a low-cadmium to a high-cadmium lake, where they were exposed in 64-m-mesh mesocosms to the prevailing high-Cd concentrations in water and to various quantities of prey collected from the Cd-rich lake. Our experimental design ensured exposure of C. punctipennis larvae to realistic Cd concentrations in water and in a natural mixture of prey types. Our results indicate that larvae take up their Cd mainly from prey. Thus models of metal dynamics and effects on these invertebrates are likely to be more realistic if they include food as a metal source. Using the same mesh mesocosm design, we also determined that C. punctipennis larvae transferred from a high-Cd to a low-Cd lake lost their Cd slowly. Combining our information on Cd uptake and loss from C. punctipennis allowed us to model Cd exchange between this insect and its surroundings.

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“…In waters with relatively large zooplankton populations, the flux of fecal pellets would contribute more significantly to POC flux. C assimilation rates for ingestion and preferential loss of C from fecal pellets, result in lower C / 234 Th in larger pellets (Fisher et al, 1987;Reinfelder and Fisher, 1991;Lee and Fisher, 1992). Thus a shift from a region where flux is dominated by phytodetritus to one with higher zooplankton grazing and C export as fecal pellet material would result in a shift to lower C / 234 Th ratios.…”

Section: Regional Variations In C / 234 Thmentioning

confidence: 99%

An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy

et al. 2006

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Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the 234 Th activity distribution (in order to calculate 234 Th fluxes) and an estimate of the C / 234 Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / 234 Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / 234 Th either increases or is relatively invariant with increasing particle size (size classes N 1 to 100s Am). Observations also suggest that C / 234 Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from 234 Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2-3). We recommend sampling for C / 234 Th from a standard depth of 100 m, or at least one depth below www.elsevier.com/locate/marchem the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple 234 Th profiles and C / 234 Th samples during the course of longer observation periods to better sample temporal variations in both 234 Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column. D

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The Assimilation of Elements Ingested by Marine Copepods

Cited by 370 publications

References 16 publications

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Cadmium sources and exchange rates for Chaoborus larvae in nature

An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy

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