An environmental survey investigating the association between Labyrinthulomycetes and sea star wasting disease in Pisaster ochraceus of the Northeastern Pacific Ocean

A wasting disease has devastated sea star populations across the Northeast Pacific coastline. In 2016, three novel Labyrinthulomycetes – saprobic marine protists linked to other wasting diseases – were found living on diseased sea star tissue of Pisaster ochraceus. This raised the question of whether these Labyrinthulomycetes are a causal factor in sea star wasting disease (SSWD). I hypothesized that Labyrinthulomycetes are a causal factor in SSWD because most Labyrinthulomycetes isolated from living tissue are parasitic to their hosts. If Labyrinthulomycetes are a causal factor in the SSWD of P. ochraceus, they could be: H1) parasites – indicated by Labyrinthulomycetes found living specifically on the dermal tissue of P. ochraceus (host-specific); or H2) facultative parasites – indicated by Labyrinthulomycetes isolated from P. ochraceus and nearby decaying organisms (generalists). If Labyrinthulomycetes are not a causal factor in SSWD – simply taking advantage of already decaying organisms (H3) – then their isolation from diseased sea star tissue would be a result from these protists being at the right place at the right time. An environmental survey was conducted of the Labyrinthulomycetes of the Pacific coast of British Columbia to assess this association. I sampled diseased sea star tissue (P. ochraceus) and nearby decaying organisms from the intertidal zones to determine if these Labyrinthulomycetes are host-specific (H1) or generalists (H2 and H3). Identical Labyrinthulomycetes were isolated from a variety of decaying organisms. More specifically, Oblongichytrium porteri – one of the first Labyrinthulomycetes isolated from sea star tissue in 2016 – was found to have a wide abundance at all sampling locations on diseased sea star tissue and a variety of nearby decaying organisms. I conclude that the Labyrinthulomycetes associated with diseased P. ochraceus tissue are generalists, thereby rejecting H1. Further inoculation experiments are needed to determine whether Labyrinthulomycetes are facilitative parasites involved in SSWD (H2), or if they are just taking advantage of the readily available decaying matter (H3).Science, Faculty ofZoology, Department ofGraduat