THE POPULATION BIOLOGY AND ECOSYSTEM EFFECTS OF THE SEA NETTLE, CHRYSAORA CHESAPEAKEI
Hood, Raleigh R
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Some of the longest population records of jellyfish are collected from visual shore-based surveys. As surface counting is inexpensive and simple, it is of interest to determine what can be learned from such records as well as the usefulness of the method. A 4-year time series of Chrysaora chesapeakei (formerly quinquecirrha) medusa counts collected using three sampling methods was analyzed. Medusa abundance was modeled by change points and was highly correlated between the sampling methods. The remaining signal was random, and indices indicated that medusae were aggregated. This study suggests more monitoring from visual shore-based surveys is an effective, low-cost method to increase information on jellyfish. Data from another long-term visual survey show that C. chesapeakei in the Cheasapeake Bay have declined since the 1960s. It is hypothesized that their loss results in a trophic cascade and increases in phytoplankton. However, due to confounding factors, it is not clear that C. chesapeakei drives the changes observed. A new 0-dimensional mechanistic model was formulated to include jellyfish. A data assimilation method, Approximate Bayesian Computation, was used to objectively calibrate the model and guide its development. The model fit to observations was improved by the addition of refractory non-living organic materials. Additionally, comments and suggestions related to the model development process are provided. Using the model, perturbation experiments were conducted to study the effect of changing modeled C. chesapeakei (CHRY). Then, sensitivity experiments of the environmental and ecological parameters were conducted to understand the conditions that are important in driving the response. The change in CHRY had the potential to affect every state variable and throughflow but the response did not always conform to the trophic cascade concept and was highly dependent on the parameters. The parameters that were most important in varying the response were related to the energetics of the zooplankton and parameters related to alternative pathways of loss or gains of the state variables. The resulting complexity highlights the far-reaching ecosystem effects of C. chesapeakei as well as the need for new frameworks to understand the response of ecosystems to perturbations.