1. Electivity of M. leidyi Natural3x5x A. tonsa -0.098150.028882-0.13667 P. meadii 0.168221-0.39237-0.29547 T. turbinata 0.0882510.0904980.075988 Table 1. Average Electivity per each concentration. Electivity: -1 is selection against, 0 is no preference, and +1 is selection for a particular prey item (Rollwagen Bollens, 2003). Figure 4. Ingestion rate of M. leidyi at different plankton concentrations. A two-way ANOVA and Bonferroni posttest were used for statisical analysis. Variance in concentration (p-value 0.0007). Means significantly different (*) and non- significance (ns). Figure 3. Mean ± SD concentration of copepods present at each concentration. A 2-way ANVOA and a Bonferroni posttest were used for statistical analysis. Variance in concentration (p-value of <0.001) and copepods (p-value of 0.004). Means significantly different (A) and non-significance (ns). Sample were collected from Wallops Island, VA in Chincoteague Salt Marsh A plankton net was used to collect plankton and ctenophores Three phytoplankton concentrations were used (natural, 3x, and 5x). Three replicates were produced for each concentration. A subsample of each plankton sample was preserved in 5% formalin at the start (T 0 ) and end (T F ) of the experiment. In lab, from preserved samples, copepod were identified and counted for both T 0 and T F to determine the amount consumed for each concentration The Effects of Food Concentration on Feeding Habits of Mnemiopsis leidyi found in Chincoteague Bay, VA. Methods: Results: Ctenophores are gelatinous zooplankton characterized by their collablast cells (or “sticky” cells). Ctenophores, particularly Mnemiopsis leidyi (Figure 1), swim with their lobes spread open and their mouth forward (Reeve and Walter 1978) characterizing them as ambush predators (Waggett and Costello 1999). Strong swimming prey, such as the zooplankton Acartia tonsa, become easily attached to the extended lobes of the ctenophore (Waggett and Costello 1999). Bays and streams near farmland or urbanized areas are subjected to high levels of runoff (mostly from rainstorms). This increases the levels of nitrogen, phosphorus and other organic molecules within an ocean ecosystem, creating an eutrophic environment. Phytoplankton begin to grow in numbers or “bloom” due to a surplus in nutrients. This leads to an increase of other organisms within the food chain, mainly zooplankton (a natural predator of phytoplankton). Ctenophores also have the ability to increase in numbers under favorable conditions, Chincoteague Bay oysters and young flounders that feed on zooplankton. These commercially important species are then affected due to a reduction in zooplankton and predation on their larvae by ctenophores. By determining the ingestion rate of M. leidyi, it will be beneficial in determining the impact the ctenophores will have on other species present within the Chincoteague Bay. Introduction: Hypothesis: H 0 : By increasing the food availability given to M. leidyi, there will be no change in the feeding rate. H 1 : With increase in food concentration, M. leidyi will reach a maximal ingestion rate. Discussion: The most abundant food source at the beginning of the experiment was A. tonsa (Figure 3), significantly at the 5x concentration between P. meadii (p- value=<0.01) and T. turbinata (p-value=<0.001). The ingestion rate of M. leidyi increased at higher food concentrations on all species of copepods (Figure 4), but significantly from the natural concentration to the 5x concentration on A. tonsa (p-value=<0.01)and T. turbinata (p-value=<0.05). M. leidyi showed approximately neutral selectively for A. tonsa and T. turbinata, with a negative selectively for P. Meadii especially at higher food concentrations (Table 1). Acknowledgement: I would like to thank Dr. Nolan for all of her support and knowledge on ctenophores and copepods and Dr. Kliener for his statistical assistance. Citation: Figure 1. The feeding structures of M. leidyi. OL: oral lobe; M: mouth; T:tentillae; Au: auricle (Waggett and Costello 1999). Reeve, M.R. and Walter M.A. 1978 Nutritional Ecology of Ctenophore- A Review of Recent Research. Advances in Marine Biology. 15:249-287. Rollwagen Bollens, G. C. and Penry, D. L. 2003. Feeding dynamics of Acartia spp. Copepods in a large, temperate estuary. Marine Ecology Progress Series. 257:139-168. Waggett, R. and Costello, J.H. 1999 Capture mechanisms used by the lobate ctenophore, Mnemiopsis leidyi, preying on copepods Acartia tonsa. Journal of Plankton Research. 21:2037-2052. Figure 2. Map of Chincoteag ue Bay, VA A. tonsa was fed upon more often due to its higher abundance in all concentrations, not because of selectivity by M. leidyi. The slight negative electivity with P. meadii, is a possibly a result of the copepod’s swimming behavior because M. leidyi is a non-selective feeder. It is probably for ctenophores to increase in numbers through higher plankton abundance levels. Not only can ctenophores react positively to the greater number of plankton, but the electivity of M. leidyi illustrates consumption of any prey type available. Ultimately, the addition of nutrients to coastal areas aids this chain reaction. Loretta Pregartner Department of Biology, York College of PA