Model-to-data comparisons reveal influence of jellyfish interactions on plankton community dynamics

Taxonomic shifts can alter predator feeding preference and modify ecosystem dynamics through top-down control. In Barnegat Bay-Little Egg Harbor Estuary (New Jersey, USA), sea nettle Chrysaora quinquecirrha abundances have increased in the northern portions of the estuary. We evaluated the geographical variation in top-down influence of C. quinquecirrha on plankton community dynamics. We simulated a range of jellyfish- to copepod-dominated ecosystems using a size-resolved nutrient-phytoplankton-zooplankton (NPZ) model. Zooplankton feeding was parameterized as a community average based on predator-prey size ratios and breadth of prey sizes of dominant species. We compared model outputs to data collected in the estuary during 2 summer months of high C. quinquecirrha abundance. We predicted that data from the northern region would be more similar to the jellyfish-dominated model outputs, because C. quinquecirrha abundance is higher in the north. Contrary to expectations, all northern sites had observational data more similar to the copepod-dominated model outputs, and the site that was most similar to the jellyfish-dominated model outputs was in the C. quinquecirrha-free southern region. These results may indicate complex interactions between C. quinquecirrha and the ctenophore Mnemiopsis leidyi, a voracious copepod predator that is nearly absent in the northern region despite having wide environmental tolerances. Predation by C. quinquecirrha may limit the distribution of M. leidyi and indirectly strengthen copepod dominance in the northern region of the estuary. These results suggest that top-down control by jellyfish can be strongly influenced by competition among gelatinous taxa.