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.