A physicochemically-constrained seawater culturing system for production of benthic foraminifera

Hintz, Christopher J., G. Thomas Chandler, Joan M. Bernhard, Daniel C. McCorkle, Suzanne M. Havach, Jessica K. Blanks,Timothy J. Shaw

Limnol. Oceanogr. Methods 2:160-170 (2004) | DOI: 10.4319/lom.2004.2.160

ABSTRACT: We present an apparatus and procedure for culturing deep-sea (i.e., bathyal) benthic foraminifera under physicochemically constrained conditions. A 1600-L recirculating culture system was constructed to contribute negligible trace metal contamination; the system was housed in an environmental room maintained near in situ temperatures but at atmospheric pressure. Peristaltic pumps continuously circulated 3 mL seawater min^–1 from the reservoir to 9 to 12 culture chambers. A 2-mm-thick layer of high-purity clay-sized silica substrate was used to minimize the impact of sedimentary microhabitats. Physicochemical parameters (salinity, alkalinity, pH, temperature) varied <2% throughout two culture experiments. Trace metal concentrations were initially set near open-ocean values and remained constant (i.e., within our analytical precision) during the experiments. Culture seawater was equilibrated with atmospheric CO₂, thus dissolved inorganic carbon δ¹³C varied ~1‰ over the course of each experiment, reflecting the seasonal atmospheric CO₂ isotopic variation. Culture seawater δ¹⁸O varied ~0.2‰. Each culture chamber was inoculated with as many as 100 foraminifers of single or multiple species. Pre-existing foraminiferal calcite was identified by fluorescent labeling prior to specimen introduction into culture. The cultures remained viable for >200 d in each experiment and produced up to 2,800 individuals per culture. The growth and reproduction of benthic foraminifera in a physicochemically constrained culture provide a new method for the experimentation and validation of geochemical proxies.