My research interests are in phytoplankton and bacterial ecology. Phytoplankton are the base of the food chain and animal productivity depends on the available phytoplankton biomass. Some species of phytoplankton are toxic and when they occur in high densitities (e.g. red tides) can cause massive fish kills as well as human death from the consumption of contaminated shellfish. Bacteria are the major decomposers of organic matter and consumers of dissolved oxygen. In areas where the inputs of organic matter are high, due to urban activities for example, bacterial respiration can reduce the dissolved oxygen to levels that are deleterious to other organisms. Bacteria also constitute a large biomass which is a source of food for specialized predators and many bacterial species are pathogens of higher organisms.

My research is focussed on assesing the role of bacteria in trophic dynamics and in the biogeochemical cycling of carbon. Planktonic heterotrophic bacteria (bacterioplankton) are a large and metabolically active group in aquatic systems that contribute significantly to the total biomass and to the flow of carbon. Bacterial cell densities often exceed 1 X 10⁹ cells liter^-1. Bacterial biomass in marine systems is generally greater than that of zooplankton and can be 20 % of phytoplankton biomass. Estimates of bacterial biomass and growth rate show that bacterial biomass turns over rapidly (hours). Comparison of bacterial biomass production rates with corresponding rates of phytoplankton production and biomass indicate that bacteria consume a substantial fraction (20 to 40 %) of the carbon fixed by phytoplankton. Bacteria are now considered major secondary producers as they convert dissolved organic matter (DOM) derived from primary producers into an abundant biomass. The consumption of bacterial biomass by specialized predators (ciliates and flagellates) may be an important pathway for the transfer of DOM to metazoan food webs. I have performed studies in various marine and freshwater systems and I am currently working in south Puget Sound (Eld, Budd Inlets).

Diatoms and dinoflagellates are 2 major groups of marine phytoplankton. Diatoms account for most of the marine primary production. They are non-motile and are characterized by the yellow-brown pigment fucoxanthin and the presence of a silicious frustrule (skeleton). Their shapes are geometric and exhibit various symmetries (radial, bilateral). Dinoflagellates are characterized by the pigment peridinin which gives them a distinctive reddish-brown color. They can grow in large densities (>10,000 per ml), discolor the water and form what is referred to as red tides. Some species contain toxins which can accumulate in shellfish, and can also cause massive fish kills. Dinoflagellates can be armored (cellulose plates) or naked. They normally have two flagella (trailing and transverse) and swim in a spiral trajectory. Dinoflagellates account for most of the bioluminescence observed in surface waters. They are very unusual organisms in that they have characteristics of both prokaryotes (condensed chromosomes) and eukaryotes (organelles). In addition, some dinoflagellate species are both photosynthetic and heterotrophic (utilize dissolved organic matter or eat other plankton).

I have been documenting the seasonal changes in phytoplankton species in a local estuary (Budd Inlet). Generally, diatoms species dominate the phytoplankton assemblage during fall and winter. Dinoflagellates become abundant during the spring and summer.

These are examples of diatoms found in south Puget Sound. On the left is the solitary diatom, Ditylum brightwellii (total length = 100 um). On the right is the colonial diatom Chaetocerus curvisetus (bar = 10 um).

These are examples of dinoflagellates found in south Puget Sound. Ceratium fusus (left, bar = 100 um) and a Protoperidium species (righ, bar - 10 um).

Publications in Refereed Journals

Chin-Leo, G., D.L. Kirchman. (1988). Estimating bacterial production in marine waters from the simultaneous incorporation of thymidine and leucine. Appl. Env. Microb. 54:1934-1939.

Chin-Leo, G., D.L. Kirchman. (1990). Unbalanced growth in natural assemblages of marine bacterioplankton. Mar. Ecol. Prog. Ser. 63:1-8.

Chin-Leo, G., R. Benner. (1991). Dynamics of bacterioplankton abundance and production in seagrass communities of a hypersaline lagoon. Mar. Ecol. Prog. Ser. 73:219-230

Chin-Leo, G., R. Benner. (1992). Enhanced bacterioplankton production and respiration at intermediate salinities in the Mississippi River plume. Mar. Ecol. Prog. Ser. 82: 87-103

Gardner, W.S., R. Benner, Chin-Leo, G., J.B. Cotner, B.J. Eadie, J.F. Cavaletto, M.B. Lansing. (1994). Mineralization of organic material and bacterial dynamics in Mississippi River Plume water. Estuaries. 17:816-828

Benner, R., Opsahl, S., Chin-Leo, G., Richey, J.E. (1995). Respiration and bacterial carbon metabolism in the Amazon River system. Limnol. Oceanogr. 40:7-1262-1270

Published Abstracts

Chin-Leo, G., D.L. Kirchman. (1986). Abundance and production of free and attached bacteria associated with the seasonal pycnocline in Chesapeake Bay. EOS 67 (16):982

Chin-Leo, G., D.L. Kirchman and R.B. Biggs. (1987). Diel variations of leucine and thymidine incorporation: Implications for the estimation of bacterial production in a dynamic environment. EOS 68 (16):330.

Chin-Leo, G., R.B. Biggs, and D.L. Kirchman. (1987). Changes in relative rates of protein and DNA synthesis in natural assemblages of bacteria as a response to fluctuating DOM concentrations. EOS 68 (50):1729.

Chin-Leo, G., R. Benner (1990). Utilization of dissolved organic matter by bacteria in the Laguna Madre Estuary, Texas. EOS 71 (2):186

Gardner, W., B. Eadie, R. Benner, D. Pakulski, J. Cotner, G. Chin-Leo (1993). Organic matter mineralization and bacterial dynamics in the Mississippi River Plume. Estuaries (12th Biennial International Estuarine Research Conference, Hilton Head, S.C., Nov 1993).

Technical Reports

Benner, R., Chin-Leo, G., Gardner, W., Eadie, B., Cotner, J. (1991). The fates and effects of riverine and shelf-derived DOM on Mississippi River Plume/Gulf Shelf Processes. Proceedings of the NECOP (Nutrient Enhanced Coastal Ocean Productivity) Workshop, October 2-4, 1991, Chauvin, LA. Sponsored by NOAA and LUMCON. TAMU-SG-92-109

Book Chapters

Chin-Leo, G. Bacterial secondary productivity. (1997). Chapter 3 in Manual of Environmental Microbiology, 1st edition. American Society for Microbiology. Washington, D.C.

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