Harmful Algae & Grazer Dynamics in a Changing Climate

Global climate change is expected to have profound impacts on biogeochemistry,
nutrient cycling and biological process in the ocean, and species inhabiting coastal ecosystems
are among the most vulnerable to these changes. Elevated temperature and/or CO2 alters toxicity for some harmful algal bloom (HAB) species, but the consequences of altered toxicity on community dynamics and trophic interactions have not been investigated. Likewise, growth, physiology and expression of enzymes involved in C and N metabolism for local HAB species show species and strain-specific responses to changes in temperature and/or CO2. Furthermore, some HAB species show substantial changes in nutrient quotas and partitioning of carbon biomass, even when no changes in growth rate are observed. Such shifts will likely alter the nutritional quality and mass transfer efficiency to grazers in a species-specific manner, possibly impacting zooplankton survival, growth and production rates.

The goals of this project are to investigate the effects of climate change on HAB species and the
consequences of altered toxicity and nutritional quality of HAB species on micro- and
mesozooplankton grazers. The interactive effects of temperature and CO2 on metabolism,
resource partitioning, and toxicity in two raphidophytes (Heterosigma akashiwo and Chattonella
) and a dinoflagellate species (Karlodinium veneficum) will be examined under nutrient replete or nutrient-limited conditions. Responses of the cultured micrograzers Oxyrrhis marina,
Favella sp., and Strombidinopsis acuminatum, and the model copepod, Acartia tonsa, to climate
change conditions will also be assessed. Once acclimated to CO2 and temperature levels
expected at the end of this century, their ability to graze the target HAB species compared to
non-harmful species cultured under the same conditions will be examined. The relative effects of
toxicity, starvation and possible changes in algal fatty acid content on micrograzers and copepod
grazing and egg production will be evaluated under both ambient and climate change-driven
growth conditions. Behavioral changes and other sub-lethal effects on zooplankton reproductive
output as a result of either toxicity or starvation will be evaluated. The possibility for direct and
indirect trophic interactions between a target alga, micro- and mesograzer exposed to the same
conditions will also be evaluated. Results of this project will lead to a better understanding of
how changes in growth, toxicity and nutritional quality of HAB species will impact competitive
interactions and trophic dynamics in coastal ecosystems of the future.

Featured Faculty

Jonathan Cohen

Jonathan Cohen picture

Associate Professor Marine Biosciences

Project Team


CEOE School & Departments

School of Marine Science & Policy

Advancing the understanding, stewardship, and conservation of estuarine, coastal, and ocean environments.

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Department of Geological Sciences

Discovering how geological processes have operated over various time scales to create and influence the planet’s surface environments.

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Department of Geography

Investigating the interactions between people and the environment and the processes that explain the location of human and natural phenomena.

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College of Earth, Ocean, and Environment • 111 Robinson Hall • Newark, DE 19716 • USA • Phone: 302-831-2841
Geography: 302-831-2294 • Geology: 302-831-2569 • Marine Science and Policy: 302-645-4212 • E-mail: ceoe-info@udel.edu

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