VUTURO, STEVEN A.; RATCLIFF, LANCE; VERDUGO, SHERRI A.; STURTEVANT, MARK A.*: The Distribution of the Gastropod, Theodoxus luteofasciatus, on a Mudflat in the Northern Gulf of California

The marine snail Theodoxus luteofasciatus (Neritidae) is a small but common intertidal gastropod that is striking due to its highly polymorphic and colorful shell pattern. In Cholla Bay (Sonora, Mexico) in the Northern Gulf of California, this snail is a member of a dense and complex community of animals on open mud flats. Organisms in this environment must cope with extreme changes in water level, salinity, temperature, and a variety of predators. We surveyed T. luteofasciatus populations in three distinct habitats within Cholla Bay: sandy areas adjacent to granite boulders, muddy areas near the margin of the bay, and flowing channels with coarse gravel near the middle of the bay. These habitats are distinct due to sediment type, presence of standing versus flowing water, and differences in invertebrate fauna. We find T. luteofasciatus utilizing all of these habitats. However, we also find differences in the relative abundance, size classes, and the frequency of certain color morphs in these areas as well. We present and discuss these results, and we also describe other parameters in this population including sex ratios, shell shape variations, and the presence of a large helmenthic parasite found in these snails. Human activity in the form of land development around Cholla Bay intensifies every year. Future plans include dredging the bay to build a marina. The data we present here will contribute to understanding how these events will impact upon the community of organisms in this ecosystem.