First Advisor

Bradley Buckley

Term of Graduation

January 2023

Date of Publication

1-1-2023

Document Type

Thesis

Language

English

Subjects

aerial exposure, bivalves, cell cycle, climate change, intertidal, temperature

Physical Description

1 online resource ( pages)

Abstract

The intertidal zone is a place of rapid and frequent change that is home to a variety of creatures who are essential to the integrity of the habitat. Mussels are robust sessile bivalves that anchor to the rocks of the intertidal. The prominent species on the Oregon Coast, the Common Bay Mussel (Mytilus trossulus), plays an essential role as a coastal food source, water column filter, and barrier to prevent erosion due to wave action. Mytilus trossulus withstands daily shifts in temperature, salinity, and tide, as well as seasonal changes. Global climate change due to excess carbon emissions is expected to increase temperature, decrease salinity, and cause shifts in sea level beyond what intertidal organisms such as M. trossulus experience. Observing the response of M. trossulus to these changing conditions can reveal the limits of essential intertidal invertebrates leading to its potential as a biological indicator for climate change. To gain a comprehensive understanding of the impacts of climate change, we must understand seasonal impacts and navigate various ways of testing impacts on this species. The aim of this work was to: 1) characterize seasonal weight variability in the gametes, gills, and adductor muscles of M. trossulus, 2) use protein assay and flow cytometry to further understand the impact of seasonal and climate changes, and 3) understand the influence of tidal fluctuation on a mussels survivability in response to short-term changes in temperature and salinity. Approximately 190 mussels were collected from the Boiler Bay Intertidal Research Reserve in the Fall (November 15, 2020), Winter (February 26, 2021), and Spring (May 15, 2021). Mussel body size varied greatly (5-30 g), but during the Spring individuals could reach 45 g (Figure 2.4). Fulton’s Body Condition Index (K) was calculated to assess nutritional condition between the seasons. The average seasonal weight of adductor muscles (Fall= 0.177 g, Winter= 0.153 g, Spring= 0.259 g), gametes (Fall= 0.14 g, Winter= 0.206 g, Spring= 0.655 g), and gills (Fall= 0.345 g, Winter= 0.314 g, Spring= 0.576 g) were measured and revealed an increase in gamete weight in the Winter and Spring and gill weight in the Spring. Mussels (n= 15 from each season) were placed in a treatment group that was based on temperature (12.8C, 15.5C, and 18.3C) and salinity (0 ppt, 15 ppt, and 35 ppt). Following those treatments, n= 5 mussels were measured and dissected, leading to the performance of a Bradford Protein Assay to assess protein concentration in adductor muscles and flow cytometry to assess the cell cycle within gills. A decrease in the protein concentration of adductor muscles in response to increases in temperature and decreases in salinity could impact muscle contraction resulting in a decreased ability to protect internal organs. There was no significant impact on the concentration of protein within the adductor muscles in response to these treatments. In this study, flow cytometry was used to understand the impact of seasonal changes and climate changes on distribution of gill cells in the cell cycle. Changes in the cell cycle of gill tissue could lead to cellular arrest or death (apoptosis). Flow cytometry revealed over 50 % of cells were in G1 phase in the Fall and Winter, while in the Spring 46.9 % percent of cells were in G1 phase. This led to an increase in potentially apoptotic/non-phase content and an increased sensitivity to increases in temperature and decreases in salinity during the Spring. Following the temperature and salinity treatments, n= 5 mussels were placed in an aerial exposure at a specified temperature (12.8C, 15.5C, and 18.3C) and n= 5 mussels were placed underwater at 12.8C and 35 ppt. These exposures revealed that the mussels collected and treated during the Spring experienced mortality more frequently and rapidly than mussels from other seasons. Additionally, nearly all mussels that were submerged post treatment survived past 300 hours while during the aerial exposures mortality occurred more rapidly as temperatures were increased and salinities decreased. Efforts to understand seasonal impacts create a more accurate and comprehensive understanding of how environmental stressors are impacting an organism. This study demonstrates the impact of seasonality on the health of an organism, revealing that sensitivity to environmental stressors increased during the Spring which is spawning season. Temperature increases and salinity decreases were shown to have an impact on mussel survivability, but only after being pushed to the worst of conditions. Mytilus trossulus is a robust species, tough enough to withstand high wave action, solar radiation, and frequent environmental fluctuation. As changes to the environment increase, this species may experience a reduction in overall fitness and protective abilities. Comprehensive and long-term climate change policy will need to be implemented to prevent even the toughest of organisms from stress and mortality.

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