Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • BCO-DMO Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

The mesocosm experiment was performed in August 2021 on the R/V Hugh Sharp, cruise HRS2110, at a station near the mouth of Chesapeake Bay. Surface water (2–5 m) was collected from the study site (37.27^o N, 76.09^o W), located near the mouth of the bay. Incubation medium was prepared by pumping surface water (~5 m) directly from the sample site through a series of nylon mesh and glass fiber filters, ending with a 0.3 μm filter, using a double diaphragm pump into three 24-L translucent polycarbonate (PC) carboys. Surface water inoculum was collected using a rosette system with 12–L Niskin bottles and a CTD profiler from 2–4 m depth and pre–filtered through 210 μm nylon mesh before being added to the mesocosms to produce a 10 % inoculation.

NaNO₃, NaH₂PO₄, and Na₂SiO₃ solutions were added to each carboy to achieve final concentrations of approximately 40 μM, 5 μM, and 50 μM, respectively. Carboys were incubated for eight days in an on–deck water bath, using a seawater flow–through system drawn from surface water and a plastic screen shade covering to keep incubation temperature and light similar to in situ conditions. Continuous light and temperature measurements were recorded using two Onset HOBO Pendant Temperature/Light data loggers suspended ~10 cm below the surface of the on–deck water bath.

Sub–incubations to measure nitrogen and carbon uptake rates using ¹⁵N–NO₃^- and ¹³C–HCO₃^- were carried out once per day. Sample water (150–200 mL) was aliquoted into PC bottles for triplicate sub–incubations for each carboy (9 sub–incubations per tracer per day). ¹⁵N–NaNO₃^- (1.5–2.67 mL of a 0.3 mM solution) and ¹³C–NaHCO₃^- (1–1.3 mL of a 30 mM solution) were added to each PC bottle to attain isotopic enrichments of ~8–93 % and ~10 %, respectively. Bottles were then placed into mesh bags to simulate surface water light intensities and incubated for 4 h (approximately 10:00 to 14:00 local time) in a similar water bath system as the carboys. Sub–incubations were terminated by filtration onto pre–combusted 0.3 μm 25 mm GF–75 filters. Filters were stored individually at -20^o C until analysis.

POM filters were fume acidified for 4–6 h in a desiccator with concentrated HCl, packed into tin capsules, and measured using a Sercon ANCA–SL Elemental Analyzer and a Europa 20/20 Isotope Ratio Mass Spectrometer (EA–IRMS). Transport rates (⍴) were calculated according to equations modified from Dugdale and Goering (1967).

- Imported "Mesocosm_CB2021_POMRates.xlsx" into BCO-DMO system
- Converted date to ISO format YYYY-MM-DD
- Created new UTC ISO formatted datetime field
- Renamed fields with number in front to comply with system requirements
- Exported file as "959935_v1_mesocosm_uptake_rates.csv"

NSF Award Abstract:
A recent global survey of surface ocean waters revealed that microbial parasites comprise half of the eukaryotic plankton diversity and suggested that biological interactions, including parasites, play an important role in the ecology of many types of microscopic algae, which are the base of the ocean food web, but not diatoms. Diatoms are among the most abundant microalgae, particularly in upwelling areas where nutrient-rich deep currents feed the ocean's surface and support the world's greatest fisheries. Yet this survey did not investigate high-productivity regions, leaving a significant knowledge gap. Diatoms may be successful in upwelling regions because they evade predators and parasites, but it seems more reasonable that they, like all other microalgae, also have biological enemies. In this study, the researchers use a large set of available samples from upwelling regions to investigate the effect of parasites on the proliferation of diatom communities and resulting primary production. The project supports a graduate student and provides hands-on research experiences for high school and undergraduate college students. The study data are also integrated into courses taught by the principal investigator.

The discovery that half of the eukaryotic diversity in the Tara Oceans sequence database belongs to putatively parasitic microbes implies a revolution in our understanding of biological control of primary production. Ecosystem models are only beginning to incorporate the effect of viruses on production and community composition, but eukaryotic parasites add yet another dimension with potentially vast biogeochemical implications. While viral predation is generally thought to divert material flux away from grazers and into the dissolved organic carbon pool, increasing community diversity and microbial biomass, phytoplankton biomass diverted into parasite biomass becomes available to grazers. Experimental determination of parasite activity is difficult in natural systems, so most of the evidence for diversity, abundance, and host interactions of eukaryotic parasites is based on DNA sequence data. The Tara Oceans database suggests that diatoms have very few biotic interactions, leading to a stronger dependence on bottom-up factors (e.g., nutrients). However, this database did not represent high productivity upwelling regions. This project addresses two hypotheses: 1) diatoms in highly productive episodic upwelling systems are involved in host-parasite interactions that can be identified in co-occurrence networks during blooms; and 2) the community composition and abundance of host-parasite pairs vary over the course of the bloom in a manner consistent with density dependence on the host. In this project, abundance, diversity, and dynamics of parasites in upwelling systems are investigated by tag sequencing, metagenomics, and targeted qPCR of diatom-parasite pairs identified from archived samples from diatom-dominated upwelling systems (California Current, Eastern Tropical Pacific), the North Atlantic Spring bloom, and from two mesocosm experiments of diatom blooms induced by inoculation of surface seawater into nitrate-rich Monterey Bay seawater. Biogeochemical parameters (nutrients, primary production, nitrate assimilation, etc.) for those samples are available. In addition, the research team is using the outputs of the bioinformatics analysis in network and time series analysis to discover links among hosts and parasites.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.