Graduate Thesis Or Dissertation
 

An Integrated Approach to the Investigation of Age, Growth and Population Dynamics of Burrowing Thalassinidean Shrimps in a U.S. West Coast Estuary

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/r781wj64j

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  • Two indigenous species of burrowing shrimp inhabit and often dominate the intertidal zone of estuaries along the US West Coast, the ghost shrimp, Neotrypaea californiensis, and the blue mud shrimp, Upogebia pugettensis. Both species are considered ecosystem engineers and play a role in maintaining estuarine health and ecosystem function. They also have a negative interaction with oyster production in Pacific Northwest (PNW) estuaries, which has necessitated a better understanding of their ecology and population dynamics in order to try to manage their impacts. Development of population models requires detailed information regarding an animal’s age and growth. Because crustaceans do not retain calcified structures over a lifespan, estimates of age are typically based on body size which can vary significantly over environmental gradients. A series of field and laboratory studies were conducted to understand factors controlling growth of burrowing shrimps in the Yaquina River estuary and validate an alternative, biochemically-based (lipofuscin) aging technique as a method to overcome the challenges of determining age in crustaceans. Analysis of shrimp diets along an estuarine gradient using fatty acid and stable isotope biomarkers revealed spatial patterns in diets between species and showed condition to be associated with availability of high-quality foods. Laboratory investigations of temperature on shrimp growth rates indicated temperature to be less important in controlling growth than food but may influence the accumulation of lipofuscin at environmental extremes for N. californiensis. Field growth experiments showed that lipofuscin accumulation rate in N. californiensis was consistent between sites but growth varied significantly. Size was a better predictor of age for U. pugettensis than lipofuscin concentration but growth was shown to correlate with thermal history. Finally, mortality rate was estimated for N. californiensis using the lipofuscin aging method and a cohort-based approach with data from 4 years of broad-scale population surveys in Yaquina Bay, Oregon. Mortality rate for adult N. californiensis was estimated to be 0.719 (95% CI; 0.633-0.793 yr⁻¹) and did not vary significantly across cohorts. Population simulations were also conducted to understand current and future patterns in shrimp density. Simulations revealed that spatial patterns in burrowing shrimp density could be explained by variation in mortality and recruitment rates. Results from these studies provide information needed to incorporate population ecology into management plans for burrowing shrimp in PNW estuaries. Methodologies developed in this project could also be applied to improve understanding of growth and population dynamics of other hard-to-age crustacean species on the US west coast and worldwide.
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