HETEROTROPHIC EUKARYOTIC PLANKTON COMMUNITY DIVERSITY IN AN INDIGENOUS HAWAIIAN MARICULTURE SYSTEM

Abstract

Marine microorganisms are the engine that drive the global cycling of carbon, nitrogen, and many other elements by carrying out key ecosystem functions and are exquisitely responsive to environmental changes and perturbations of the food web. Subtropical coastal ecosystems are ecologically dynamic systems and susceptible to environmental perturbations caused by human activities such as pollution, development and changes in land usage; yet, microbial dynamics within coastal ecosystems in Hawaiʻi are understudied. Loko iʻa (Indigenous Hawaiian mariculture) practices use the ambient dynamic environment of estuaries to facilitate the growth of phytoplankton and macroalgae for the husbandry of herbivorous fish. The long term operation of loko iʻa are reliant on healthy and well described microbial food web systems. The Heʻeia Fishpond is situated at the ocean terminus of the Heʻeia watershed valley. This constructed tidal estuary provides an opportune place to describe fundamental ecological aspects of heterotrophic plankton communities such as mesozooplankton and the ecologically important yet understudied choanoflagellates. My research utilized microscopic identification and amplicon sequencing to describe fundamental ecological aspects of the mesozooplankton and choanoflagellate communities residing in Heʻeia Fishpond. With our community partners at Paepae o Heʻeia, we found that zooplankton abundance varied spatially and tidally. During high tides when salinity is at its relative peak, zooplankton at mākāhā (sluice gates) correlate with tidal amplitude and potential summer spawning events. I also developed and evaluated molecular primers specific to the choanoflagellate 18S rRNA gene to describe the overall diversity of choanoflagellates in Heʻeia Fishpond and inferred environmental drivers that influence choanoflagellate diversity. We found that choanoflagellate diversity within the fishpond is higher than initial descriptions and influenced primarily by tidal forcing. These results are the first ecological studies to specifically quantify choanoflagellate amplicon sequence abundance from environmental samples. My thesis demonstrates the importance of conducting microbial community surveys of the heterotrophic plankton community as they are critical to fishpond stability and productivity. Our results also highlight the need for additional research on estuarine zooplankton communities, choanoflagellate community ecology and further research on potential diseases that can destabilize the trophic structure of this extensive coastal habitat.