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 Marine Food Webs 

Dr. M.E. Frischer; Dr. R.F. Lee; Dr. J.R. Nelson; Dr. G.A. Paffenhofer; Dr. W. Savidge

While much of our biological research is aimed at developing our capacity to manage the coastal environment, a strong research emphasis is also placed on basic aspects of the marine food web.

Plankton play a fundamental role in the cycling of energy and materials in the oceans. Plant plankton (phytoplankton) are the base of the pelagic food webs and produce approximately one half of global oxygen, and remove an equivalent amount of carbon dioxide.

Three fates potentially consume primary production in the ocean: portions can be oxidized within the water column, portions can sediment to shelf/slope depots, and portions can be exported to the interior ocean. Bacteria and zooplankton mediate all three of these processes and thus can alter the pathway and residence time of particulate organic carbon. Drs. Frischer, and Paffenhofer focus their research on the roles that bacteria, metazoan, and protozoan zooplankton play in these processes, respectively.

It takes a talented team of scientists to address such issues because nature is complex and inherently non-linear.  Thus, the assembly of plankton communities and the functioning of pelagic ecosystems reflect the integrated effects of processes relating to resource availability and utilization, as well as losses due to grazing/predation, sinking, and advection.  These processes occur at a hierarchy of temporal and spatial scales, and are influenced by natural and anthropogenic activities.  Recognizable and repeated patterns occur as species adjust to rapid as well as longer-term changes in the balance of forces that cause birth/growth and losses to fluctuate.  Natural processes that influence birth/growth rates of plankton can be stochastic or repeated at annual intervals so that, given a dependable seeding source, annual patterns in species complexes and in ecosystem attributes may occur, albeit with highly variable abundances. 

Human activity can alter these processes at a variety of scales, and these can also interact with natural cycles in delivery systems, e.g. rainfall, runoff, drought/flooding, tropical storms, climate change).  Both bottom-up (resource availability such as nutrient loading) and top-down sequences (predator stocks through fishing/harvesting) can be affected by anthropogenic activities, and thus long-term patterns in planktonic ecosystem structure and function may result from and vary according to accelerated human occupation adjacent to estuaries and coastal waters.  Climate change in the coming decades is a foregone conclusion, and this process may accelerate or disguise human effects. Thus, cultural eutrophication and climate change are perhaps the two most important driving mechanisms of such patterns.  Various scientists at Skidaway are studying these processes and how ecosystems respond.

For example, Georgia estuaries are of tremendous importance in terms of their economic (tourism, seafood industry, recreational and commercial fisheries worth $100M/yr) and ecological significance.   However, coastal Georgia is reaching an environmental crossroads or “decision tree” regarding the future trajectory of its environmental quality and ecosystems.  A serious consequence of cultural eutrophication is development of hypoxia, which reduces habitat for fish and shellfish, forcing migration to waters with higher oxygen; for non-motile organisms, oxygen below metabolic or reproductive thresholds can be lethal or can impair recovery from other stresses such as harvesting, disease, and sedimentation.  Socioeconomic costs include losses to fisheries, seasonal tourism, and the seafood industry.  There are new species of harmful algae arriving almost every year, and a new invasive jellyfish appeared in 2007.  Absent corrective action, a new, less anthroponomic ecosystem can be expected.  One of the long-term goals is to provide research results and modeling tools that can be used to assess alternative management strategies for mitigating impacts of eutrophication, to maintain environmental quality, biodiversity, and healthy ecosystem function.

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