Food Web Consequences of a Seagrass Microparasite and a Crustacean Macroparasite
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Date
2021-11-23
Authors
Yoshioka, Reyn
Journal Title
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Publisher
University of Oregon
Abstract
Despite their ubiquity and known ecological impacts, parasites are still infrequently considered in studies of trophic ecology. Additionally, the most recognized effects of marine parasites on food webs are those caused by mass mortalities. In contrast to these density-mediated effects, trait-mediated indirect interactions (TMII), where host ecological function is altered through parasitism, are less conspicuous but not necessarily less important. In this dissertation, I present studies of potential TMIIs of two marine parasites. The protist Labyrinthula zosterae D. Porter & Muehlstein (Lz) infects the eelgrass Zostera marina L. First, in Chapter II, I ask whether Lz may increase the nutrition of eelgrass tissue by synthesizing DHA, a nutritious ω-3 fatty acid (FA), based on Lz’s relatives. By culturing Lz on various substrates, I found that Lz produces DHA as its primary FA and in detectable amounts in diseased tissue. This suggested that diseased tissue may be more nutritious for eelgrass consumers, which I tested in Chapter III using the detritivorous copepod Tisbe sp. Lilljeborg. Providing Tisbe either healthy or diseased eelgrass segments, I asked whether diseased eelgrass was functionally like detritus and fostered copepod population growth. Diseased eelgrass segments produced greater copepod numbers than healthy ones. Resulting copepods did not show clear differences in DHA, suggesting that FA changes were less important than eelgrass material becoming more labile via disease. Nonetheless, this showed that disease may foster secondary production.
In Chapter IV, I studied the effects of the rhizocephalan Sylon hippolytes M. Sars infecting the shrimp Pandalus danae Stimpson. Using a field survey, I found that Sylon increased rates of epibiosis on hosts, which may interfere with shrimp antipredator defenses. Infected shrimp also showed distinct FA profiles relative to uninfected ones, with changes substantial enough to alter dietary mixing model predictions. Thus, Sylon may affect marine trophic interactions and our understanding of them.
Altogether, this work shows that Lz and Sylon can substantially alter their hosts, producing unrecognized TMIIs in their ecosystems. The results encourage further research into these systems and a greater appreciation for marine parasites in food webs.
This dissertation includes both previously published and unpublished coauthored material.
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Keywords
eelgrass, fatty acid, Labyrinthula zosterae, marine trophic ecology, Pandalus danae, Sylon hippolytes