Research

Biological Oceanography 

Benthic-pelagic coupling, Ecosystem dynamics, Marine habitat and ecosystems, Molecular ecology, Phytoplankton ecology, Plankton ecology, Polar processes, Zooplankton ecology. 

I am interested in, and worked in many different areas of phytoplankton, zooplankton, and fish ecology. Most recently I have focused on population dynamics of zooplankton in the ocean. Zooplankton provide the link between the primary producers (phytoplankton) and consumers at higher trophic levels (fish). Understanding these linkages is important for evaluating and modeling effects of climate change, eutrophication, overfishing, etc., on marine ecosystems. Important processes for zooplankton are birth, growth and mortality rates and I have studied all of these both in the field and in the laboratory.
Feeding behavior of zooplankton is an important factor determining growth rates. While this has been studied in the laboratory, determining actual in situ feeding behavior and feeding rates has been problematic. To overcome these difficulties I developed new molecular approaches to measuring in situ feeding behavior by zooplankton. This was initially bootlegged on another grant and then supported with a Small Grant for Exploratory Research (SGER) from NSF. We are now able to identify prey DNA sequences in the guts of zooplankton and to quantify the amounts of DNA of individual prey species. From this we are able to calculate in situ feeding rates on these individual prey species. This has been quite successful and we have been funded on two grants to use these techniques in the field.

In the first project, we were part of a larger study investigating the Bering Sea ecosystem. In our part we investigated feeding by the dominant Arctic copepod Calanus glacialis under extensive sea ice during early spring. We found high feeding and reproductive rates at this time despite extremely low phytoplankton levels in the water column. Using our molecular techniques we found that they were feeding on a dense layer of ice algae growing on the underside of the sea ice. We concluded that colder years, when ice cover is more extensive and persists longer, result in an extended period of higher food availability for C. glacialis compared with the brief ice-edge or water column phytoplankton bloom. This provides a longer period of growth for the population resulting in greater abundance of C. glacialis later during the spring compared with warmer years. Thus the success of this key Arctic copepod is dependent upon seasonal ice cover and its associated ice algae during spring. Any changes in the extent of this seasonal ice cover associated with climate change will adversely affect animals at higher trophic levels that feed upon this key species. The Bering Sea Shelf is a region of rapid climate change. Knowledge of how key species respond to this change will help predict overall ecosystem response and how important fisheries as well as endangered species may be affected.
In a second project, we are investigating feeding behavior by krill in the Antarctic. This is a key species in the ecosystem and has been the subject of many studies. While it has usually been considered to eat mainly phytoplankton in the water column, we hypothesize that, during periods of low food availability, krill may be eating organisms in the bottom sediments. Our molecular tools make it possible to investigate this question. Preliminary results from our initial cruise during austral winter this past May and June demonstrate that the krill are indeed ingesting sediments. This provides a new pathway for carbon flow: from the sediments to the water column. Our observations will mean that all of the ecosystem models for the Antarctic will have to be revised. Our observations will help understand how this ecosystem will respond to already ongoing climate changes.