The Influence of Ciliates on the Growth of Macrocystis pyrifera (Giant Kelp)

Andrea Munoz, Columbia University of New York, Ecology, Evolution and Environmental Biology, New York, NY, United States, Diane Y Kim, University of Southern California, Los Angeles, CA, United States and Adriane Clark Jones, Mount Saint Mary's University, Biology, Los Angeles, United States
The USC Wrigley Institute and Marine BioEnergy are investigating Macrocystis pyrifera (Giant Kelp) as a renewable source of carbon-neutral biofuel. The project rears juvenile sporophytes in a controlled nursery setting under sterile conditions before outplanting (a 45-day process). This project explored the potentially beneficial role of the microbial community that is eliminated in these early nursery efforts. We used an experimental Uronema ciliate (bacterivore) and a natural bacterial community to simulate microbial loop conditions in microcosms containing M. pyrifera apical meristem blades under two treatments: sterile seawater + f/2 medium; and sterile seawater + f/2 medium with ciliates. We asked the following questions: 1) Will the presence of ciliates enhance kelp growth?; 2) Does the presence of ciliates change the nutrient concentrations in the surrounding water?; 3) Do ciliates influence the microbial community on and surrounding M. pyrifera? Kelp blade size, number of ciliates, number of bacteria, nitrate concentration, and microbial DNA on and around the blades in each tank were measured/characterized over a 4-week experiment. The blades grown with ciliates exhibited an average increase of 5.00 cm while kelp in tanks without ciliates increased on average by 3.09 cm, though the difference was not significant in a two-tailed t-test. In 3 of 4 weeks, the tanks with ciliates had a greater decrease in nitrate compared to the tanks without ciliates-for example 180 μM decrease compared to 56 μM decrease in week 4. In all 4 weeks, the tanks with ciliates had smaller increases in bacterial abundance compared to the tanks without ciliates-for example 4.5 x 105 cells/ml increase compared to 5.64 x 105 cells/ml increase in week 4. In the future, researchers could utilize ciliates in a nursery setting to enhance kelp growth and reduce nursery time before outplanting, however, further studies are needed to define the impact of the microbial loop on kelp growth.