Vertical Distribution of Larvae off the Coast of Assateague Island, Virginia Carlee Kaisen Department of Biological Sciences, York College of Pennsylvania Figure 1. Generalized life cycle of a crab. Introduction Several field experiments have shown that larvae tend to concentrate at specific depths in the water column. Beladade et. al (2006) found 27 taxa of fish larvae in their samples. Fifty-two percent of those larvae species were found at all depth intervals. However, the greatest larval abundance was found at the benthic interface. Larvae at the benthic interface were also smaller in size. Dittel and Epifanio (1982) found early zoeal stages of Ovalipes ocellatus, Cancer irroratus, and Callinectes sapidus at the surface, while later stages were found the benthic interface. Jones and Epifanio (2005) looked at Callinectes sapidus (blue crab) and Uca spp. (fiddler crab) and found that the density of megalopaes were lower at the surface than zoeal stages. Larvae may prefer to live at a given depth for a number of reasons. Living at the surface: Diet- Phytoplankton, the base of the food chain, photosynthesize at the surface. Thus, larvae may travel to the surface to eat. Many species are phototactic, giving them a way to locate their food items. Locomotion- The water flows at a faster rate at the surface then at the benthic interface allowing larvae to move to a new location. Living at the benthic interface: Safety- Larvae found at the benthic interface are provided with places to hide from predators. Maintain position- Since water flow is low at the benthic interface, larvae may move into this layer to maintain their position close to the shore. The vertical distribution of larvae off the coast of Assateague Island, VA has never been investigated. Hypothesis Ho:There is no difference in the larval assemblage at the benthic interface and in the surface in the waters off the coast of Assateague Island, VA. Conclusion Atlantic Herring were found to be larger at the surface perhaps as a means of predator avoidance. Large variance was seen between samples Different time of year Different substrate Large phytoplankton bloom in second year Strong variability indicates the need for additional samples to fully address this question. Acknowledgements : I would like to thank Dr. Nolan for all her time and effort helping me count and identify larvae. Her time and patience spending long hours in the microscope room is greatly appreciated. I would like to thank William Johnson from Goucher College for use of his benthic sled. I would like to thank NASA for their ship time and collecting my second sample. I would like to thank Sally Hoh for opening doors for me all the time. I would like to thank all my friends for their support. I would like to thank Adam for sitting in the microscope room with me for long hours and helping me clean up the large messes I made. Figure 2. Generalized life cycle of a fish. Methods EggFry JuvenileAdult Results Towed benthic sled and plankton net simultaneously for 5 minutes Preserved sample in 8% Formalin Filtered through 400 um mesh net to remove small organisms/debris Counted samples on Nikon SMZ-U dissecting microscope Counted species of zooplankton in 27ml Counted number of fish and crab larvae in entire sample Figure 9. Comparison of the average size of the Atlantic Herring found at the surface and benthic interface. A t- test resulted in significant difference with p= Therefore, the larger Atlantic Herring showed a preference for the surface. Figure 6. Average number of larvae from all three tows at the surface and benthic interface. After performing Welch’s correction test, the difference was not found to be significant. p= This, in a large part, can be attributed to the large number of blue crab megalopaes collected at the first benthic tow in September. Figure 5. Number of larvae found in each tow. Only one plankton tow captured larvae. Large variability was found between different sampling times and in different locations. Note the change in the y-axis scale. Figure 7. Average number of larvae found at the benthic interface. An ANOVA test indicated no significance between the samples. p= References Beladade, R., Borges, R., and Goncalves, E. J Depth Distribution of Nearshore Temperate Fish Larval Assemblages Near Rocky Substrate. Journal of Plankton Research, 28, Dittel, A. R. & Epifanio, C. E Seasonal Abundance and Vertical Distribution of Crab Larvae in Delaware Bay. Estuaries, 5, Jones, M. B. and Epifanio, C. E Patches of Crab Megalopae in the Mouth of Delaware Bay-An analysis of Spatial Scales. Journal of Shellfish Research, 24, Figure 8. Average number of copepods found in samples from the surface and benthic interface. An unpaired t-test resulted in no significance. p= This indicates that food availability was similar at the surface and benthic interface. Figure 4. Benthic Sled used for benthic interface tows. Figure 3. Plankton net used for surface tows. Found at: