Assessing ecosystem dynamics amongst zooplankton, phytoplankton and jellyfish ( Mastigias) in meromictic marine lakes
Schimon, Ann K.
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Interactions between trophic levels can create a complex network of population dynamics, such as higher trophic levels regulating lower trophic levels (top-down control), lower trophic levels regulating higher trophic levels (bottom-up control) or organisms within a trophic level competing for resources (intraguild predation). These interactions have been greatly studied in many ecosystems but not as thoroughly in some aquatic environments, such as meromictic marine lakes. In this particular lake type, water does not mix between the top and bottom due to a chemocline. Therefore, I conducted this study to better understand if dynamics between trophic levels, such as top-down control or intraguild predation, were influencing organism abundance within meromictic marine lakes. Jellyfish Mastigias (Scyphozoa), zooplankton and phytoplankton samples were collected for approximately 10 yr from a meromictic marine lake, Jellyfish Lake. I calculated the abundance of the different organisms in the lake. Eighteen samples were selected, and I hand-counted the total amount of copepods: Oithona, Acrocalanus, nauplii, eggs and carapaces. Top-down control and intraguild competition were not observed to be influencing the ecosystem dynamics. Possible strongly influential abiotic factors, like El Nino-Southern Oscillation (ENSO), or other organisms, like human recreationalists, could have been disturbing trophic level dynamics. Other possible suggestions for the observed results were that the diel vertical migration (DVM) of zooplankton and the presences of symbiotic zooxanthellae on Mastigias could have diminished the ability or need for Mastigias to capture zooplankton.