Assessing Ecosystem Dynamics Amongst Zooplankton, Phytoplankton and Jellyfish (Mastigias) in Meromictic Marine Lakes

Abstract

Meromictic lakes, due to solute density, contain permanently stratified water and a floating bacterial plate–a chemocline. Marine lakes usually contain small, unique ecosystems. Meromictic marine lakes have not been researched as greatly as other aquatic systems, and therefore interactions between organisms within meromictic marine lakes have not been extensively documented.The most prevalent organisms dwelling in Jellyfish Lake, a meromictic marine lake, are three phytoplankton species of Ceratium (Protozoa: Dinophyta: Dinophyceae: Peridiniales: Ceratiaceae), the two zooplankton species Oithona and Acrocalanus (Crustacea: Macillopoda: Copepoda), and Mastigias (Scyphozoa: Rhizostomeae: Mastigiidae). This study was conducted to explore the relationships between the Mastigias, zooplankton, and phytoplankton in Jellyfish Lake and to try to project if top-down control or intraguild competition is influencing ecosystem dynamics in Jellyfish Lake. For eighteen plankton samples, copepods in different life stages (Oithona, Acrocalanus, nauplii, eggs and carapaces) were counted, and the total abundance of copepod organisms was calculated for Jellyfish Lake. Mastigias were not exerting top-down control on the zooplankton population. Top-down control was not exerted by the zooplankton on the phytoplankton population. Jellyfish Lake could be sensitive to El Nino-Southern Oscillation, which occurs around the Palauan Islands and can substantially alter ecosystem dynamics. Human recreational disturbances have been noted to influence the abundance of organisms. Further research could be performed on Mastigias’ feeding habits to help elucidate how Mastigias consume prey and if this could be affecting ecosystem dynamics.