Interaction Between Water-Column Structure and Reproduction in Jellyfish Populations of Mobile Bay
William M. Graham
Dauphin Island Sea Lab, Dauphin Island AL 36528
Current theories of regional jellyfish increases include overall system production due to coastal eutrophication, and relaxation of competition for food resources by increased fishing activity on planktivorous fishes. Though these theories are not exclusive of each other, they do not account for life-history characteristics such as reproduction and how the environment may regulate jellies by directly influencing fertilization success. Over the past year, we have made observations of medusae and their vertical distribution in the coastal plume and estuarine waters of Mobile Bay using an in situ video profiler. Analysis of these data reveals that medusae are most abundant at strong density discontinuities (i.e., pycnoclines and convergent fronts). We believe that the concentration of medusae in these regions is an active behavioral response to environmental stimuli that serves to increase feeding due to locally concentrated prey, and to increase reproductive success by minimizing the effects of gamete dilution. This two-year SGER study will investigate the latter. Using in situ observations of the vertical distribution of spawning males, we will first determine if density discontinuities serve as centers of gamete release for male medusae. This information will then be combined with in situ observations of the male to female ratio throughout the water column, dye cloud diffusion within the pycnocline, and the physical properties of the water column in a simple model that will predict horizontal and vertical dispersion rate of sperm as well as the probability of released sperm being intercepted by a female. Aurelia aurita is abundant in the coastal waters of Alabama, and has the potential to significantly impact human life as well as the flow of energy and nutrients in the ecosystem.  This study will thus address two of the issues identified by ACES as the most important issues affecting coastal environments: species composition and diversity, and ecosystem services to humans.