Presenter: Haila Schultz (University of Washington)

Description:
Over the past several decades, increased abundances of jellyfish have been reported globally. However, the role of jellyfish in marine food webs is not well understood. In Puget Sound, large aggregations of the moon jelly Aurelia labiata are seasonally abundant in protected embayments. These aggregations contain millions of individuals and can cover broad areas. Aurelia may compete with fish for zooplankton prey and alter the chemistry of the water column by releasing nitrogenous waste, but the extent of these interactions are still unknown. To address the question of how Aurelia aggregations affect zooplankton communities and water chemistry in the ecosystems they occupy, we conducted mesocosm experiments in the summers of 2019 and 2020 to evaluate their predation rates on natural zooplankton assemblages. We also conducted in-situ sampling of Aurelia, phytoplankton, and zooplankton inside and outside of dense aggregations in conjunction with water chemistry measurements. Experiments revealed that Aurelia were able to remove up to 75% of the available copepods from their environment in just two hours. In situ, we found that copepod density was up to 73% lower within aggregations than outside of aggregations located within the same embayments. Zooplankton comprise an important link in marine food webs, transferring energy from primary production up to higher trophic levels, so changes in their populations may impact fish and marine mammals in Puget Sound. Here, we demonstrate that Aurelia aggregations significantly alter zooplankton communities in their immediate environment, potentially limiting the prey availability for zooplanktivorous fish. In the future, results from this study will be used to model the impacts of jellyfish on fish populations in Puget Sound.