Detecting changes in whelk abundance using hermit crab shell utilization in Oregon's rocky marine intertidal Public Deposited

http://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/41687j772

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  • Utilization and preference of whelk shells by the hairy hermit crab are examined in the following to further define the ecology of Oregon’s mid to low intertidal ecosystems. The study was conducted at Tokatee Kloochman State Natural Area (TK) where I made observations before collecting data. My observations were of two whelk species, the channeled dogwinkle (Nucella canaliculata), and the northern striped dogwinkle (Nucella ostrina). Observing an apparent decreased abundance of the channeled dogwinkle and an unchanging abundance of the northern striped dogwinkle initiated the preliminary research of this study. Cause for such a shift in species abundance is a topic of interest, however we must first establish that this shift has indeed occurred and discover how it may be influencing the current ecosystem at TK. The goal of this study is to determine if channeled dogwinkle survival had changed in the early spring of 2016 at the TK site. Searching for empty shells of the two species, as evidence that many individuals from one species have died in recent months, was largely unsuccessful. There were not enough empty shells at TK to determine if channeled shells are more abundant than striped. Investigating why there would be so few empty whelk shells I found a potential explanation. Hermit crabs use vacant snail shells and there are many hermit crabs at the TK site. I shifted my focus and proposed that if there was a decrease in channeled dogwinkle abundance it may be observed in the shell utilization by hermit crabs. The hairy hermit crab (Pagurus hirsutiusculus) uses empty snail and whelk shells, but has expressed a preference for shells of certain species in similar ecosystems. I have observed these hermit crabs at TK using shells from both species so I needed to determine whether a shell preference could account for differential utilization of shells by the hermit crabs. I also needed to assess whelk abundances for the same reason. If the hermit crab does not have a shell preference between the channeled and the striped species then a higher utilization of shells from one whelk species would be evidence for greater numbers of vacant shells from this species available to the hermit crabs. The shell preference experiments did not show a significant shell preference between the two species of whelk. Also, I found no statistical evidence that the channeled species and the striped species are at different abundances. Finally, I could confidently use the shell utilization of hairy hermit crab at TK to determine whether more channeled dogwinkle shells were recently available than northern striped dogwinkle. The shell utilization study did reveal a statistically higher number of channeled dogwinkle shells being used by the hairy hermit crab than the northern striped dogwinkle.
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