Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Long chain n-3 polyunsaturated fatty acids (LCn-3 PUFAs) such as EPA and DHA are important biomolecules regulating production in marine ecosystems. This study examined how the interaction at the phytoplankton-zooplankton interface affected the transfer of LCn-3 PUFAs to higher trophic levels. Heterotrophic dinoflagellates contained higher levels of EPA and DHA than their algal prey, suggesting heterotrophic dinoflagellates enhanced the nutritional value of poor quality algae and subsequent transfer to the next trophic level. Formation of EPA and DHA in the dinoflagellates appears to be achieved by the elongation and desaturation of shorter fatty acid chains rather than through de novo synthesis.

Fatty acid content in the copepod Acartia tonsa resembled the fatty acid signature of its prey, further supporting the idea that heterotrophs depend on their diet to obtain these nutrients, and their nutritional value is subject to the type of food consumed. Transfer of DHA to A. tonsa, was improved by feeding on a heterotrophic dinoflagellate grown on a poor quality algae, versus feeding on the algae itself. Thus omnivorous copepods may compensate dietary deficiencies by feeding on a variety of prey items.

The presence of EPA and DHA can be used as a proxy for the nutritional value of copepods. A. tonsa fed nutritiously poor algae also affected the fatty acid content of its predator. Pseudopleuronectes americanus fed low quality copepods, had lower levels of EPA and DHA than those fed copepods with higher levels of these fatty acids. However, content of these fatty acids did not have a direct effect on the growth rate of the fish. The finding herein does not support consumption of LCn-3 PUFAs as important factors regulating growth in juvenile fish. These results, albeit discouraging, are by no means comprehensive in elucidating the role of n-3 PUFAs for fish health. It is possible that due to food limitation, the effect of food quality was confounded.

Field collected data in a nursery ground for juvenile P. americanus showed that the quantity of EPA and DHA in the prey for the fish at the time of sampling was low. The low availability of these fatty acids in the plankton suggests this estuary is at times suboptimal for the growth and development of P. americanus. EPA and DHA are critical for P. americanus growth; however, the low availability of LCn-3 PUFAs does not by itself explain differences in growth rates. It is clear that further field studies should combine physical, biological and chemical factors in order to evaluate the nutritional status of the nursery ground.



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