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Travel Report: Rachel Munger
Rachel Munger, a master's student in the Department of Biological Sciences, received a Graduate International Research Travel Award (GIRTA) to further her research in The Bahamas.
After receiving a Graduate International Research and Travel Award (GIRTA) from SFU, I travelled to The Bahamas to conduct my Master's project as a visiting researcher based out of the Cape Eleuthera Institute (CEI) on Eleuthera Island. There, I was able to carry out a four month field experiment to assess the functional roles of two sea cucumber species in shallow seagrass habitats. I conducted my fieldwork from a CEI research vessel, where my team and I carried out approximately 400 hours of scientific dives over 70 field days. I spent the remainder of my time using the CEI facilities to conduct lab experiments and process samples in preparation for shipment back to SFU.
My Master’s thesis aims to understand the functional interchangeability of two sea cucumber species, and the effect their removal (e.g., through fishing) may have on the growth of turtle seagrass beds and sediment health. Sea cucumbers play an important role in tropical seagrass meadows as bioturbators and consumers of detritus, which can enhance seagrass meadow productivity. Additionally, their pee can act as a fertilizer thereby enhancing seagrass growth.
Small-scale Bahamian export fisheries have led to local depletions of sea cucumbers, as they are highly sought in Asian markets for their dried form known as bêche-de-mer, the demand for which has already collapsed and endangered many populations worldwide due to poor management. Given that the functional contributions of sea cucumbers in tropical ecosystems are poorly understood, I investigated the ecosystem-level consequences of sea cucumber removal under two scenarios of species loss. If the two species differ in their nitrogen excretion and bioturbation rates, then they may differ in their overall effect on turtle seagrass productivity and sediment health.
We surveyed 35 patch reef sites in Rock Sound where the five-toothed and the donkey dung sea cucumber are found. My experiment contained three density-controlled manipulations: (1) only five-toothed sea cucumbers, (2) only donkey dung sea cucumbers, and (3) a sea cucumber removal treatment. Rock Sound provided the perfect setting to conduct a large scale manipulative experiment in an area where sea cucumbers have not yet been exploited, to better inform sustainable fisheries management and planning.
We visited these sites at three time points: once before the manipulations, and twice throughout the summer. During each visit, we measured seagrass growth rate, shoot density, and blade height. We also took cores from the seagrass bed to quantify above- and below-ground biomass, and used smaller cores to sample the surface sediment layer to obtain measures of organic matter and chlorophyll content. Lastly, we collected seagrass shoots to quantify nitrogen content of the blades.
We also measured nitrogen excretion rates of both sea cucumber species collected from the wild, briefly kept in water-filled containers, and returned to reefs. By taking length, weight, and girth measurements, we were able to relate nitrogen excretion rate (e.g pee) of cucumbers to body size, which allowed us to convert any biomass measurements of sea cucumbers at field sites to nitrogen excretion equivalent.
I am grateful to have been welcomed into the scientific community at CEI, and was struck by how genuinely interested other international researchers were in my research. During my field season, we collected an invaluable amount of data which will shed light on the ecological roles two sea cucumber species, and the overall ecosystem response if either species is fished. I feel fortunate to have spent substantial time diving as a marine ecologist in the Caribbean Sea, and to have become so acutely familiar with my study system. I could not have completed this field season without my fellow research partner and research assistant who supported me through countless long field and lab days. I experienced first hand how to collaborate with a small field team; it was a rigorous and long process, but it was extremely rewarding. I am sincerely grateful to my supervisor Isabelle Côté for the opportunity, and for the learning experiences the GIRTA granted me.