The affect of introduced Bullfrogs, Rana catesbeiana, on nutrient dynamics and algae communities in a desert river

Authors: Robin Greene, John Sabo

Year: 2013 (xlv)

Abstract

Aquatic organisms such as fish, snails, and freshwater mussels affect nutrient dynamics and algae communities. They do this through nutrient excretion, grazing, and bioturbation of sediments. These processes are important because they influence the structure and function of aquatic ecosystems from the bottom, up. The Amercian Bullfrog, Rana catesbeiana, is originally from the eastern United States, but they have spread around the globe. They have altered many aquatic systems due to their abundance, voracious eating habits, and ability to transmit disease. However, little is known about how this introduced species affects nutrient dynamics and algae communities, and whether they are having a different impact than native amphibians. For my Masters research, I am studying the effect of Rana catesbeiana on nutrient dynamics and algae communities in the San Pedro River in southeastern Arizona. I will also compare the effect of introduced Rana catesbeiana tadpoles to native Woodhouse’s toads tadpoles, Anaxyrus woodhousii. Rana catesbeiana and Anaxyrus woodhousii both breed in the San Pedro River. Rana catesbeiana are reliant on permanent water and their large tadpoles (up to 35g) can remain in the river for 3 months-2 years before they metamorph. Anaxyrus woodhousii, however, only visit the river to breed and lay eggs. Their small tadpoles develop in the river shallows and metamorph within 5 weeks. Though both tadpole species feed on benthic algae and sediment, I predict their affect on nutrient dynamics and algae communities will differ. I will report my results from nutrient addition experiments and water sampling in areas with and without Rana catesbeiana. These observations will indicate how introduced Rana catesbeiana affect aquatic nutrient levels and whether this alters the limiting nutrients for algal growth.