It's a Breve New World for Nitrogen Research at VIMS

10 The Crest It’s a Breve New World for Nitrogen Research at VIMS By David Malmquist help the plants extract or “fix” nitrogen it occurs in a dissolved organic form, thinking. They did so by adding a dose In recent years, blooms of harmful directly from the atmosphere. These within compounds such as urea and of heavy nitrogen isotopes to a sample algae have killed thousands of fish and plants play a key role in terrestrial amino acids. To date, researchers have of nitrogen gas, and then adding this raised public concern about the in- ecosystems by allowing vegetative mostly looked for forms of dissolved “labeled” nitrogen gas to seawater creasing number of such episodes growth in areas with nitrogen-poor inorganic nitrogen, such as ammonia containing colonies of Trichodesmium. along coastlines worldwide. soils. Farmers take advantage of this and nitrate, when trying to balance If specialized Trichodesmium cells do VIMS scientist Dr. Debbie Bronk ability when they alternate plantings of nitrogen budgets in the ocean. indeed fix nitrogen and share it with and colleagues are now working to corn, a heavy nitrogen feeder, with To test their hypothesis, Bronk and other cells, labeled nitrogen should better understand harmful algal blooms soybeans, a nitrogen-fixer that returns her colleagues have received a grant appear throughout the colony. by focusing on one of their key ingredi- nitrogen to the soil. from the National Science Foundation After sampling an unusually rich ents—the dissolved nitrogen that algae bloom of G. breve during their Septem- require for rampant growth. ber cruise, Bronk and Sanderson began Algal blooms are formed by investigating the relationship between aggregations of tiny marine plants that G. breve and Trichodesmium. They require nitrogen and other nutrients. added labeled nitrogen to a vial of Many scientists attribute the recent seawater containing a population of escalation in harmful algal blooms at Trichodesmium separated from a least in part to nutrient enrichment of surrounding population of G. breve by a coastal waters due to human activities semi-permeable membrane. The such as the application of nitrogen openings in this membrane are large fertilizers to fields and lawns. Rivers enough to allow passage of dissolved and the wind can transport nitrogen organic nitrogen, but too small for from these sources into shallow waters either organism. Thus any labeled offshore. nitrogen they detect in the tissues of G. But such thinking fails to fully breve will provide evidence that this explain the algal blooms that typically organism does indeed take up organic occur during fall in the eastern Gulf of nitrogen released by Trichodesmium. Mexico. The waters there are nitro- Early results from these tests confirm gen-poor, yet they frequently nurture their hypothesis. vast blooms of the toxic algae Bronk is also working with Craig Gymnodinium breve, or G. breve as Dr. Deborah Bronk (far right) collecting water samples aboard the R/V Walton Smith Tobias, a current post-doctoral student researchers call it. during a research cruise studying the fate of recently fixed nitrogen by Trichodesmium in at the Woods Hole Oceanographic These “red tides” threaten fishing the eastern Gulf of Mexico. Institution and VIMS graduate. Their and tourism along Florida’s west coast. goal is to further test the idea that The algae release a neurotoxin that can Trichodesmium is thought to play a to conduct a pair of research cruises dissolved organic nitrogen produced by kill fish, which then often float ashore similar role in nitrogen-poor tropical off Tampa Bay, Florida during each of the summertime Trichodesmium bloom and foul nearby beaches. Build-up of seas. Scientists suspect that specialized the next three years. The project is persists and is used by G. breve in the the toxin in shellfish such as oysters cells within a Trichodesmium colony part of the national ECOHAB (Ecol- fall. precludes their consumption by hu- extract atmospheric nitrogen dissolved ogy and Oceanography of Harmful The laboratory technique they use mans. There is also anecdotal evidence in seawater for their own growth and Algal Blooms) program, which was to test this link was developed by that the toxin can affect humans development. Then, scientists think, established by NSF and NOAA in Bronk. Applying this technique to directly. Swimmers exposed to the these cells release nitrogen-bearing response to the upward trend in measure the natural abundance of toxin have complained of itchy eyes compounds such as amino acids into harmful algal blooms along America’s organic nitrogen dissolved in seawater and scratchy throats, as have boaters, the surrounding water, to nurture other coasts. A July cruise is timed to collect has never been done before. It relies who could be exposed to the toxin if it cells in the colony. It is this dissolved samples of Trichodesmium during its on measuring the tell-tale ratio between enters the air when waves break. organic nitrogen, Bronk and her summer bloom. A September cruise is two naturally occurring nitrogen The luxuriant growth of nitrogen- colleagues believe, that leaks into the designed to sample G. breve. isotopes that results when loving algae in nitrogen-poor waters surrounding water and later stimulates This year the team took their first Trichodesmium fixes nitrogen. Detect- poses a fundamental question. Asks the growth of G. breve. pair of cruises. During the July cruise, ing nitrogen compounds within G. Bronk, “What’s fueling these guys?” The team’s hypothesis is based Bronk and her laboratory manager breve containing a similar ratio would The situation also provides a natural partly on the process of elimination, as Marta Sanderson began experiments to provide strong evidence of a link laboratory for studying the role that measurements show that inputs of test whether Trichodesmium colonies between the two organisms. nitrogen plays in marine food webs nitrogen from rivers and the air into fix nitrogen according to accepted elsewhere, including Chesapeake Bay. local waters fail to supply the quantities needed to support blooms of the extent Along with colleagues from the Environmental Education for observed. The team also points to the University of South Florida and Old Special People surrounding the YRSP Visitor’s Center timing of G. breve blooms along the Dominion University, Bronk is testing continued from page 9 is being produced and will be released the idea that the nitrogen required to west Florida coast. These occur in in September. An introductory guide to fuel G. breve in the Gulf of Mexico is early fall, shortly after Trichodesmium The project has been an overall developing environmental education supplied naturally by a colonial, nitro- undergoes its own annual summertime success. CBNERRVA plans to con- programs for the visually and hearing gen-fixing marine bacterium called bloom. tinue the field trips to YRSP this fall impaired is being completed to be Trichodesmium. Bronk suggests that previous and throughout the next year. For those distributed to the other National On land, bacteria within root research has overlooked the nitrogen who are visually impaired, an informa- Estuarine Research Reserves nodules on plants like peas and beans derived from Trichodesmium because tion audio tape of the trail immediately (NERRS) around the country.