Abstract:Rocky intertidal productivity is traditionally thought to be sustained almost solely by upwelled nitrate with remineralized forms of minor importance. Using tidepools as natural experimental mesocosms, we conducted 15 N-tracer experiments to test whether ammonium remineralized within the rocky intertidal is also a significant source of fixed N to localized ecosystem production. Comparison of tidepools with and without the dominant bivalve Mytilus californianus allowed consideration of its role in NH z 4 cyclin… Show more
“…Seawater frozen in an additional set of HDPE bottles was used to measure seawater d 15 NH 4 isotopes at University of Massachusetts, Dartmouth using methods reported previously (Pather et al 2014, Pfister et al 2014a. DOC was measured from approximately 25 mL of seawater filtered into 40-mL glass, carbon-free vials and immediately frozen.…”
Section: Measurements Of Particulate and Dissolved Organic Matter Andmentioning
Our research showed that kelp beds locally increased the pH, oxygen, and aragonite saturation state of the seawater, while seawater inorganic carbon content and total alkalinity were lowered. Kelp beds depleted nitrate and phosphorus concentrations, but enhanced ammonium and DOC concentrations. Kelp beds entrained distinct microbial communities, with higher taxonomic and phylogenetic diversity compared to seawater outside of the kelp bed, and kelp carbon fixation more than compensated for decreased phytoplankton production that occurred in their proximity. Thus, the diversity of pathways for carbon and nitrogen cycling is enhanced in proximity to kelp.Pfister, C. A., M. A.
“…Seawater frozen in an additional set of HDPE bottles was used to measure seawater d 15 NH 4 isotopes at University of Massachusetts, Dartmouth using methods reported previously (Pather et al 2014, Pfister et al 2014a. DOC was measured from approximately 25 mL of seawater filtered into 40-mL glass, carbon-free vials and immediately frozen.…”
Section: Measurements Of Particulate and Dissolved Organic Matter Andmentioning
Our research showed that kelp beds locally increased the pH, oxygen, and aragonite saturation state of the seawater, while seawater inorganic carbon content and total alkalinity were lowered. Kelp beds depleted nitrate and phosphorus concentrations, but enhanced ammonium and DOC concentrations. Kelp beds entrained distinct microbial communities, with higher taxonomic and phylogenetic diversity compared to seawater outside of the kelp bed, and kelp carbon fixation more than compensated for decreased phytoplankton production that occurred in their proximity. Thus, the diversity of pathways for carbon and nitrogen cycling is enhanced in proximity to kelp.Pfister, C. A., M. A.
“…For the final sample (T f ) after 3-5 hours of incubation, we filtered directly from the individual chamber. All nutrient concentrations were 190 analyzed at the University of Washington Marine Chemistry lab (methods from UNESCO, 1994), while isotope determinations were done at University of Massachusetts, Dartmouth using methodology for isotopic composition reported previously (Pather et al, 2014;Pfister et al, 2014Pfister et al, , 2016b. Briefly, nitrogen stable isotopes of ammonium were measured according to a modified version of the NH 4 oxidation method detailed in Zhang et al, (2007).…”
Section: Quantifying Enrichment Resultsmentioning
confidence: 99%
“…The mussels studied here also excrete ammonium and likely DON (Bayne and Scullard, 1977;Pather et al, 2014). Their filter feeding activities release DOC in many forms, and continually process organic matter that can be utilized by microbes (Jacobs et al, 2015).…”
Section: Microbial Metabolism and Dissolved Organic Carbonmentioning
confidence: 97%
“…The Second Beach site is described in Pather et al, (2014) and has tidepools at a height of 1.2 to 1.5 m above Mean Lower Low Water (MLLW), with a diversity of species (described in (Pfister, 2007;Pfister et al, 2016b). The chambers were 130 anchored into a number of these tidepools for 3-5 hours at a time during periods of low tides when the tidepools were emergent.…”
Section: Chambers For Assaying Microbial Metabolismsmentioning
confidence: 99%
“…Isotope dilution is important and indicates ammonium remineralization by species within the chamber. We quantified ammonium remineralization in chambers with 15 NH 4 tracer using the methods of (Pather et al, 2014 …”
Abstract. Microbial nitrogen processing in direct association with marine animals and seaweeds is poorly understood. Macrobiota supply a substrate for microbes to reside, and a source of excreted nitrogen and dissolved organic carbon (DOC). We tested the role of a mussel (Mytilus 15 californianus), a red alga (Prionitis sternbergii) and an inert substrate for microbial activity using enclosed chambers and enriched ammonium and nitrate. Chambers with seawater from the same environment served as a control. We found that mussels and Prionitis elevated ammonium oxidation and nitrate reduction two orders of magnitude over that of seawater, while the effect of simply an inert substrate had relatively little effect. Extrapolating to a square meter of shoreline, 20 microbial activity associated with mussels could oxidize 2.5 mmol of ammonium and reduce per 1.2 mmol of nitrate per day. A square meter of seaweed could produce even higher rates, at 135.2 and 320.5 mmol per day for nitrification and nitrate reduction, respectively. Seawater collected from the shore versus 2-5 km offshore showed no difference in ammonium oxidation or nitrate reduction. Microbial nitrogen metabolism associated with mussels did not change whether 25Biogeosciences Discuss., https://doi.org/10. 5194/bg-2018-198 Manuscript under review for journal Biogeosciences Discussion started: 17 May 2018 c Author(s) 2018. CC BY 4.0 License.
2we measured it at night or during the day. When we experimentally added DOC (glucose) as a carbon source, there was no change to nitrification rates. Added DOC did increase DIN and phosphorus uptake, indicating that elevating the concentration of DOC stimulated heterotrophic microbial activity, and suggests potential competition for DIN between heterotrophic and chemolithotrophic microbes and their seaweed hosts. Our results indicate that microbes in direct 30 association with coastal animals and seaweeds greatly enhance nitrogen processing, and likely provide a template for a diversity of ecological interactions.
In addition to their important effects on nitrogen (N) cycling via excretion and assimilation (by macrofauna and macroflora, respectively), many macrobiota also host or facilitate microbial taxa responsible for N transformations. Interest in this topic is expanding, especially as it applies to coastal marine systems where N is a limiting nutrient. Our understanding of the diversity of microbes associated with coastal marine macrofauna (invertebrate and vertebrate animals) and macrophytes (seaweeds and marine plants) is improving, and recent studies indicate that the collection of microbes living in direct association with macrobiota (the microbiome) may directly contribute to N cycling. Here, we review the roles that macrobiota play in coastal N cycling, review current knowledge of macrobial-microbial associations in terms of N processing, and suggest implications for coastal ecosystem function as animals are harvested and as foundational habitat is lost or degraded. Given the biodiversity of microbial associates of macrobiota, we advocate for more research into the functional consequences of these associations for the coastal N cycle.
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