Bermuda Institute of Ocean Sciences
17 Biological Lane
St. George's GE 01
Bermuda
Tel: 441-297-1880
Fax: 441-297-8143
E-mail: fred.lipschultz@bios.edu

On this page are listed my current research activities along with a selection of my publications, as well as a description of my educational and administrative activities. 

Current Research Projects:
My research is centered on measuring the multifaceted movement of nitrogen in marine environments. These studies have taken place in an Alaskan River, the Delaware River, in the deep ocean off Peru and Mexico and the surface ocean of the North Pacific and Sargasso Sea measuring rates of bacterial and phytoplankton metabolism.  A recent review article summarized progress in the study of "new" production in the Sargasso Sea over the past 40 years.  In addition to Biological Oceanography, I have been pursuing studies of coral physiological processes, in particular the use of nutrients. These disparate measurements of nitrogen cycling are usually made using 15N, a stable isotope of the more common form of nitrogen, 14N, to measure the movement of nitrogen in the environment under study.  To measure these isotopes requires a mass spectrometer that also permits measurements of other light isotopes such as 13C and 12C for studies of photosynthesis.

Iron metabolism of Trichodesmium spp in the Sargasso Sea:
Trichodesmium is a colonial, nitrogen fixing cyanobacteria that is present in all of the world's oceans. This organism is the 'wild card' in all budgets of the upper ocean as nitrogen fixatiopuffn adds 'new' nitrogen to the ecosystem, thereby acting as a fertilizer. Trichodesium can form thick blooms on the surface or dwindle to only a few colonies per cubic meter. Although much research has been conducted on this organism, there are still major questions to be addressed.  Iron has been hypothesized to be a controlling factor for nitrogen fixation in the world's oceans, including the Sargasso Sea where calculations have suggested fixation is particularly intense.  However, the Fe:N ratio of Trichodesmium decreased dramatically prior to the highly seasonal input of iron on dust in the late summer (See Orcutt et al. 2001).  Individual colonies however continued to fix nitrogen as fast at high Fe:N as at low ratios, implying plasticity in metabolism and hence less control by iron.  A graduate student from Tom Church's lab at the University of Delaware, Kate Achilles, has measured Fe uptake from various ligands, as well as measurements of 15N & 13C fixation and Fe:N ratios.  Massive increases in colony abundance across the tropical-subtropical boundary at ~28o N were not matched by a change in the Fe:N ratio or the per colony fixation rate.  Along with little change in the [Fe], there was little evidence of iron limitation, adding to growing evidence that these organisms are likely limited by phosphorus rather than iron. 

Carbon isotopic composition of Trichodesmium spp.  One of the intriguing aspects of Trichodesmium is the high biomass of the colonial growth form which raises the possiblity of diffusion limitation of the cells in the interior of the colony.  Dan Tchernov at Rutgers University and I have found that there is a large change in the stable isotopic composition (d13C) of colonies in the Sargasso Sea with the biomass of the colony which can be regarded as a surrogate for the size.  In addition, there is a distinct seasonality to the average value of the colonies that does not correlate to the average colony biomass.  There are several possible explanations for these shifts, including CO2 diffusion limitation that leads larger colonies to increase their use of carbonic anhydrase to permit use of HCO3 -.   We have developed a model for the isotopic shifts due to the various metabolic pathways that incorporates recently developed "massive internal carbon cycling" paradigms.

Sources of atmospheric nitrate in rain.  Stable isotopes have many uses, including providing clues about the chemistry of atmospheric processes.  Meredith Galanter Hastings, a Ph.D. student of Danny Sigman at Princeton, has analyzed the d18O and d15N composition of NO3 - in rain collected in Bermuda.  There are dramatic shifts in both isotopes depending on the origin of the air mass bringing the rain to Bermuda.  In the summer, it appears that lightening is a significant source of nitrate and that high hydroxy radical (OH) concentrations at the higher temperatures causes the shift in the oxygen ratio.  Jump to the publication.

Atmospheric inputs of nitrogen to the Sargasso Sea.  Although it has been suggested based on geochemical evidence that rates of nitrogen fixation are quite high in the Sargasso Sea, and specifically also near Bermuda, direct field measurements do not support such high rates.  Recent work by Angela Knapp, also a Ph.D. student at Princeton with Danny Sigman, revealed that one line of evidence supporting high rates could be explained by atmospheric input of nitrate rather than nitrogen fixation.  Although low values of d15 N in nitrate in the surface ocean have been attributed to nitrogen fixation, Angie has found that the low values could be explained by measured inputs of "light" d15NO3- in rain at Bermuda, along with other sources of isotopically light nitrogen such as ammonium and DON. 

YELLOWNEW  A recent grant to Mike Lomas, Nick Bates, Dave Nelson and I will permit us to study "new" production in the Sargasso Sea in response to the strong atmospheric forcing that occurs during the winter.  Prior research in the Sargasso has been limited winter weather so that most of knowledge is based on the period after and before the classic "spring bloom".  Use of a sufficiently large ship will permit us to measure new production using 15N, net community production with measurements of the carbon system, and the silica cycle with radioactive silica.  We suggest that  intermittant deep mixing and stratification events during the winter greatly enhances new production by organisms such as diatoms and this component of annual production has been seriously undersampled in past.

Coral Reef Interests:
One of the most important attributes of corals that account for their success in colonizing the tropical waters is the tight recycling of nutrients between the host animal and dinoflagellate symbiont. Interestingly there is little direct evidence of recycling: the hypothesis is based largely on circumstantial evidence!  Along with several students, I have been studying what happens to nutrients such as ammonium, food nitrogen and phosphorus as they enter the symbiotic association.  These projects are conducted by graduate students who are participating in BIOS's Graduate Intern Program. This program provides inexpensive housing, boats and lab space as well as some financial support.

Inorganic nutrient physiology of symbioses clearpixelInitial work used 15N labelled ammonium to trace the movement of nitrogen from the environment into the symbiotic association and then its redistribution within the association. There does not appear to be rapid recycling of newly assimilated nitrogen from the plant to the animal as we expected. Another unexpected result is the large amount of assimilation by the animal itself as evidenced by appearance of the labeled nitrogen in animals with no symbionts and in animal tissues remote from the tentacles where the plants are located.  Jump to the citation .

Inorganic nutrient uptake by corals has typically been studied at far higher concentrations than normally experienced on reefs and under uncontrolled flow conditions.   A graduate student from University of Maryland, Tom Shyka, determined the response of Madracis mirabili s, a common hard coral, to realistic concentrations of ammonium and flow regimes. flume. Tom used a novel method for determining ammonium that permitted measurements of concentrations as low as 5nM and he used a flume (at right) to control the flow regime. He has found that Madracis has a Km of about 40 nM but more importantly, there appears to be a threshold of 10-15 nM below which the coral cannot utilize ammonium. Since concentrations measured on Bermuda's reef during the fall are about 5 nM, ammonium is not available for growth unless concentrations are temporarily increased due to excretion by animals for instance. There was also a strong affect of flow on the ability of the corals to take up ammonium.  Jump to the citation.

A similar set of findings was recently been collected by another student from UMD, Brian Badgely, who used nitrate (NO3-) rather than ammonium.  Using a similar protocol, he has found that Madracis mirabilis is not capable of net uptake of nitrate whereas all other corals tested can utilize this nutrient.  Even after an entire month exposed to high concentrations, this one coral still didn't show any interest whereas other corals removed from the reef were immediately capable of rapid uptake. Brian further characterized the effects of light, flow and preconditioning on several corals, finding that uptake rates increased with flow unless sufficiently high concentrations (e.g. 6 uM) were used where uptake was flow independent.   Jump to the citation.

Organic Nitrogen Sources:
anemone_gutCorals also acquire nutrients from feeding on a wide variety of zooplankton.  Greg Pinak, a PhD condidate from Duke University, labelled brine shrimp with 15N and then fed the live shrimp to the sea anemone, Aiptasia pallida (left), to study how the nitrogen is partitioned or divided between the zooxanthellae and the host animal.  He has found that the animal retains the bulk of the nitrogen over periods as long as 2 weeks however, the zooxanthellae symbiont receive their "share" very, very quickly.  Within 2 hours of the host feeding on a shrimp, the zooxanthellae have all they will receive which implies that the host's digestion process releases nitrogen into the coelenteron that is rapidly assimilated by the zooxanthellae.  This was a surprise as the received wisdom was that the host would initially retain all of the nitrogen and then slowly release it to the symbiont from catabolic processes rather than directly during digestion.  Jump to Greg's publications

In addition to the traditional food souce of zooplankton for corals, another student has demonstrated that corals can acquire nitrogen from sediment that lands on their surface.  Matt Mills, who received his PhD from Ken Seben's lab at the University of Maryland, labeled fine and coarse natural sediment by exposing the natural bacterial population to 15N.  Most corals exposed to the sediment were able to remove and retain nitrogen from either sediment type, but Madracis mirabilis was entirely unable to process the nitrogen. mmirabilis_lo In addition, Matt found that the zooplankton did not receive any of the nitrogen over the time frame of the experiment, in marked contrast to Greg's results with zooplankton.  Matt's results will be published soon.

Production of DOC & DON by corals.  Jon Sharp at University of Delaware has had a longstanding interest in dissolved organic carbon and nitrogen and we have collaborated through the efforts of Ph.D. student Allison Beauregard to measure the production of these compounds and compare rates to 13CO2 and 15NO3- uptake rates as well loss of inorganic carbon (DIC).  She found that Diploria strigosa consistently released pulses of DOC & DON at predictable times of the day along with a steady release of both organic classes.  These pulses have also been observed by Christine Ferrier-Pages group in Monaco for a different coral.  Interestingly, the high concentrations from the pulses disappear within the incubation chamber, indicating  reabsorption by the coral.  However, since both the steady release and the pulse would be swept away under conditions on the reef, corals could be a significant source of organic matter to other reef organisms.

Education:

• Ph.D. 1984, Harvard University in Environmental Engineering
• M.S. 1976, University of Maryland in Botany
• B.S. 1973, University of Maryland in Biochemistry

Representative Publications: 

• Lipschultz, F., J.J. Cunningham and J.C. Stevenson. 1980. Nitrogen fixation associated with four species of submerged angiosperms in the central Chesapeake Bay. Estuar. Coast. Mar. Sci. 9: 813-818.
• Lipschultz, F. and G. Krantz. 1980. Production optimization and economic analysis of an oyster (Crassostrea virginica) hatchery on the Chesapeake Bay, Maryland, U.S.A. Proc. World Mariculture Assoc. 7: 15-18.
• Lipschultz, F., O.C. Zafiriou, S.C. Wofsy, M.B. McElroy, F.W. Valois and S.W. Watson. 1981. Production of NO and N2O by soil nitrifying bacteria. Nature 294: 641-643.
• Lipschultz, F., S.C. Wofsy and L.E. Fox. 1986. Nitrogen metabolism of the eutrophic Delaware River ecosystem. Limnol. Oceanogr. 31: 701-716.
• Lipschultz, F., S.C. Wofsy, B.B. Ward, L.A. Codispoti, G. Friederich and J.W. Elkins. 1991. Bacterial transformations of inorganic nitrogen in the oxygen deficient waters of the eastern tropical South Pacific Ocean. Deep-Sea Res. 37: 1513-1541.
• Lipschultz, F. 1995 Nitrogen specific growth rates of marine phytoplankton isolated from natural populations of particles by flow cytometry. Mar. Ecol. Prog. Ser. 123: 245-258
• Villareal, T. and F. Lipschultz. Single cell, internal nitrate concentrations of large oceanic phytoplankton from the Sargasso Sea. J. Plankton Res. 31: 689-696
• Lipschultz, F., O.C. Zafiriou and LA. Ball. 1996. Seasonal fluctuations of nitrite concentrations in the deep oligotrophic ocean. Deep-Sea Res. 43:403-419
• Lipschultz, F. and N.J. Owens. 1996. An assessment of nitrogen fixation as a source of nitrogen to the North Atlantic Ocean. Biogeochemistry 35:261-274
• Bester, C., F. Lipschultz, R. Ream, D. Tomasino and H. Trapido-Rosenthal (1997) Effects of exposure to exogenous amino acids on the cellular physiology of cultured zooxanthellae. Proceedings of the 8th International Coral Reef Symposium, 2, 1287-1290.
• Brzezinski, M., T. Villareal, F. Lipschultz. (1998) Silica production and the contribution of diatoms to new and primary production in the central North Pacific Gyre.  Marine Ecology Progress Series 167:89-104.
• Branton, M.A., T.H. McRae, F. Lipschultz, P.G. Wells (1999) Production of a small, heat shock a-crystallin protein by Madracis mirabilis after exposure to heat stress.  Can. J. Zoology 77:675-682.
• Villareal, T.A., L. Joseph, M.A. Brzezinski, R.F. Shipe, F. Lipschultz and M.A. Altabet, 1999. Biological and Chemical Characteristics of the Giant Diatom Ethmodiscus (Bacillariophyceae) in the central north Pacific Gyre. J. Phycol. 35: 896-902.
• Orcutt, K.M., F. Lipschultz, K. Gundersen, R. Arimoto, J.R. Gallon, A.F. Michaels, A.H. Knap (2001) Seasonal pattern and significance of N fixation by Trichodesmium at the Bermuda Atlantic Time-series Study (BATS) site.   Deep-Sea Research, 48:1683-1608.
• Lipschultz, F. (2001) A time series assessment of the nitrogen cycle in the Sargasso Sea.  Deep-Sea Research, 48: 1897-1924.
• Lipschultz, F and C. Cook. 2002.  Uptake and assimilation of 15N-ammonium by the sea anemones, Aiptasia pallida and Bartholomea annulata: interaction of host and zooxanthellae.  Mar. Biol. 140:489-502.
• Lipschultz, F., N. Bates, C. Carlson and D. Hansell. 2002 . New production in the Sargasso Sea: History and current status.  Global Biogeochem. Cycles 16: 1-16
• Piniak, G. A. and F. Lipschultz, 2003. Role of host feeding and inorganic nitrogen in the partitioning of prey nitrogen between host and zooxanthellae in the anemone Aiptasia pallida. Proc. 9th Intl. Coral Reef Symp., Bali, Indonesia, Indonesian Institute of Sciences, p.527-532.
• Karl, D., A. Michaels, B. Bergman, D. Capone, E. Carpenter, R. Letelier, F. Lipschultz, H. Paerl, D. Sigmon and L. Stal, 2002.  Dinitrogen fixation in the world's oceans.  Biogeochem  57: 47-98.
• Kelty, R. and F. Lipschultz, 2003. Phosphorus allocation by zooxanthellae isolated from Aiptasia pallida. Proc. 9th Intl. Coral Reef Symp., Bali, Indonesia, Indonesian Institute of Sciences, p.155-158.
• Mills, M. , F. Lipschultz and K.P Sebens.  Uptake of suspended and deposited particulate matter nitrogen by scleractinian corals.  Accepted in Coral Reefs.
• Piniak, G. A., F. Lipschultz and J. McClelland.  Assimilation and partitioning of prey nitrogen within two anthozoans and their endosymbiotic zooxanthellae.  Accepted in Mar. Ecol. Prog. Series
• Hastings, M.G., D.M. Sigman, F. Lipschultz. Isotopic evidence for sources changes in nitrate in rain at Bermuda.  Accepted in J. Geophys Res. Atmos
• Shyka, T., F. Lipschultz, K. Sebens. Effect of water flow on uptake of nanomolar concentrations of ammonium by the scleractinian coral, Madracis mirabilis.  Submitted to Mar. Ecol. Prog. Series.
• Badgley, B., F. Lipschultz and K. Sebens.  Nitrate uptake by Diploria strigosa and the effects of concentration, water flow, and other environmental variables. Submitted to Mar. Biol.