1. Introduction Aureococcus anophagefferens, which was first observed blooming in Narragansett Bay, Rhode Island in 1985, is a toxic phytoplankton. For the past 20 years, it has been affecting mussels and clams in the northern part of the Atlantic Ocean with its unknown toxin. This toxin appears to be slowing their cilia down preventing them from feeding as efficiently. Since its discovery, this phytoplankton has traveled down the coastline and, in the late1990’s, it was detected off the coast of Virginia. Oysters, Crassostrea virginica, the main shellfish grown in the south, also feed by filtration by using cilia to move the food. It is unknown if A. anophagefferens could potentially have an effect on oyster cilia as well. The objective of this experiment is to compare the response of oysters to the toxic phytoplankton Aureococcus anophagefferens and Pelagomonas calceolata, a nontoxic phytoplankton from the same class. Null Hypothesis: There is no difference in feeding and growth rates in Crassostrea virginica when fed Aureococcus anophagefferens and Pelagomonas calceolata. Abstract: Aureococcus anophagefferens is a toxic phytoplankton that has been killing mussels and clams for the past twenty years with its unknown toxin. This experiment tests the hypothesis that there is no difference in feeding and growth rates in oysters when fed A. anophagefferens and Pelagomonas calceolata. For four weeks two groups of oysters were fed the two types of phytoplankton, while their feeding rates and weights were measured. The results showed that there was no difference in the oysters’ weights after four weeks. However there was a significant decrease in the amount of food that the A. anophagefferens oysters were eating in comparison to the P. calceolata oysters. Although it has not yet been demonstrated, this could be because of the toxin buildup within the oysters, causing their cilia rate to slow and prevent the oysters from eating as efficiently. Methods: *The phytoplankton was ordered from The Provasoli- Guillard National Center for Culture of Marine Phytoplankton *Oysters were purchased from Aquaculture Genetics and Breeding Technology Center, Virginia Institute of Marine Science *The oysters were divided into two groups, one set of beakers was fed Aureococcus anophagefferens while the other set was fed Pelagomonas calceolata (about 100,000-400,000 cells/ml) *The oysters were fed twice a week for four weeks *Control beakers were also kept to monitor the phytoplankton’s actual growth rate in 24 hours *By taking the fluorescence, the amount of food the oysters ate was calculated (Limnology and Oceanography Vol XVII, B.W. Frost, 1972. ) *Wet weights were also measured Results: Difference in Oysters Weights from Start to Week 4 When Fed P. calceolata and A. anophagefferens Figure 1. Wet oyster weights from week 0 to week 4. A paired t-test indicated that there was no significant difference. Comparison of Oyster Ingestion Rates Feeding on P. calceolata and A. anophagefferens Figure 2. Oyster ingestion rates for those fed P. calceolata and A. anophagefferens. Oysters fed P. calceolata consistently ate approximately 1% of the food available to them per hour, while the oysters fed A. anophagefferens actually ingested less and less as time went on. An ANOVA test showed that there was a significant difference in the ingestion rate A. anophagefferens fed oysters over the course of the experiment. Conclusion: There was a significant difference in the oysters feeding rates between the beakers fed P. calceolata and the beakers fed A. anophagefferens. The weights of the A. anophagefferens fed oysters did decrease as the experiment continued while the weights of the P. calceolata fed oysters increased. Although this was not a statistically significant difference, maybe if the experiment had run longer the analysis data would show otherwise. Additionally, perhaps it would have made a difference if more replicates had been used. This could indicate the cilia in the A. anophagefferens fed oysters were interrupted by this unknown toxin and became incapable of functioning as efficiently, as previously seen with mussels and clams. The Effects of Aureococcus anophagefferens in Comparison to Pelagomonas calceolata on the feeding and growth rates of Crassostrea virginica Shannon Lynne Dozier, Department of Biological Sciences, York College of Pennsylvania Dr. Nolan, Mentor Acknowledgements Especially Dr. Nolan, and the rest of the YCP Biology Department. Kristen Mace and Carlee Kaisen for always showing me love and support. My family for believing in me and not letting me change my major. Sally Hoh for being the best BFF there ever was (next to God of course). http://ccmp.bigelow.org/ Greenfield, D., Lonsdale, D., Cerrato, R., and Lopez, G. 2004. Effects of Background Concentrations of Auroecoccus Anophagefferens on growth and feeding in the bivalve Mercenaria Mercenaria. Marine Ecology Progress Series. 274:171-181.