MSI Technical Seminars

Edna Granéli
Marine Sciences Dept., Kalmar University, Sweden

Monday, February 12, 2007, 9:00 AM
This seminar has been moved to the Video Classroom

"Top-down bottom-up control of Harmful Algal Blooms (HABs)"

The systematic overexploitation of marine resources through fishing has lead to changes at the top level of food chains. These changes have cascaded down through the food chains. From lakes it has been known since around 1980 that a reduction in the number and size of larger, piscivores (predators on smaller fishes) leads to an increase in the biomass of smaller, planktivorous fishes. This, in turn, leads to higher predation pressure on larger zooplankton and as a consequence, the grazing pressure on phytoplankton will decrease. This mechanism is especially strong in nutrient-rich waters. Thus, over-fishing and eutrophication may work synergistically to increase phytoplankton biomass. HAB species, in addition, have the advantage over other phytoplankton groups in that they are to a variable extent grazing resistant by being un-palatable (through the production of toxins and/ or through body shape/size). Diminished grazing in combination with a higher availability of inorganic nutrients; the capability to use nutrients in dissolved and organic form; an increase in toxicity, allelopathy and grazer deterrence when growing under N and P unbalanced conditions; is certainly a scenario that gives the upper-hand allowing HA-species to grow and develop blooms at the cost of grazer sensitive non-HAB phytoplankton species.

For more information about Dr. Granéli, visit her website at: http://www.bom.hik.se/ngred/