Alex E. Parker, a doctoral candidate in oceanography at the University of Delaware’s Graduate College of Marine Studies, is the recipient of the sixth annual scholarship from the Delaware Mobile Surf Fishermen, a group of individuals dedicated to maintaining sport fisheries in Delaware. Parker will use the award to support his research on the role that marine bacteria play in the productivity of the estuary.
“The Delaware Estuary is one of the major estuaries of the United States and supports several important fisheries,” says Parker. “However, multiple stresses on the estuary including physical changes and the introduction of toxic materials, nutrients, and organic matter have changed its biogeochemistry. Many scientists believe that these changes, coupled with an overexploitation of important fish stocks, have resulted in the decline of at least one fishery — the American shad, for example.”
Estuaries are among the most productive marine ecosystems in the world; however, their ability to flourish is largely based on the amount of phytoplankton that is produced. These tiny one-celled marine algae provide the food for all other marine organisms, whether by being eaten themselves or by producing food for other organisms through photosynthesis. The growth of phytoplankton depends on photosynthesis, which uses sunlight to convert carbon dioxide into food, and on the availability of mineral nutrients such as nitrogen and phosphorus.
The Delaware Estuary has some of the highest mineral nutrient inputs of any estuary in the world, which suggests that its productivity should be relatively high. However, its productivity and biomass (the total mass of all living organisms in the estuary) is actually much lower than what is predicted by current biogeochemical models.
According to Parker, one potential explanation for this low productivity may be found in the role that marine bacteria play in the system. Traditionally, these microbes were thought only to function at the end of the food chain, acting to break down dead plants and other marine organisms.
“However, bacteria may step in immediately after photosynthesis,” says Parker. “They would then receive a significant fraction of the products of photosynthesis leaving less food for marine organisms higher in the food chain. This modification of the food chain is called the ‘microbial loop’ and lowers the overall productivity of the estuary.”
Parker is measuring the amount of carbon dioxide and mineral nutrients used by phytoplankton. In addition, he is determining how much of the food that phytoplankton produce is consumed by bacteria. His work will help clarify the effect, both seasonally and spatially, that bacteria have on the productivity of the estuary.
“I was very pleased to receive the scholarship,” says Parker. “I hope that my research will help address some of the ecological questions relevant to the mission and interests of the Delaware Mobile Surf Fishermen.”
“Alex Parker’s proposal was selected because it will contribute to assessment of the health of the Delaware Estuary,” says Dr. Ann Hastings, chair of the fishing group’s Subcommittee on Scholarships. “The results of his work will be incorporated into current biogeochemical models in an ongoing effort to improve predictions of microbial responses to nutrients in the estuary as well as to assess the effects of those nutrients on the food chain that sustains life in that environment.”