Date of Award

Fall 12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Chair

Dr. Chet Rakocinski

Committee Chair Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 2

Dr. Mark Peterson

Committee Member 2 Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 3

Dr. Robert Griffitt

Committee Member 3 Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 4

Dr. Andrew Evans

Committee Member 4 Department

Coastal Sciences, Gulf Coast Research Laboratory

Abstract

While the scientific community is in consensus that coastal systems are threatened by climate change, few climate change studies test the effects of more than one variable directly related to climate change. The dissolved oxygen (DO) levels of the ocean are currently subject to both global warming and eutrophication; 94% of all hypoxia zones are expected to experience >2°C increase by 2035. This dissertation aims to examine how a model organism responds to simultaneous thermal and DO stress involving four levels of DO (100%, 70%, 50%, and 20%) saturation and three temperatures (15°C, 20°C, and 25°C).

The polychaete, Capitella teleta, maintained aerobic respiration at low DO levels under natural temperatures, 15°C and 20°C, but reduced its respiration by 40% at 25°C under hypoxia (20% saturation). The main anaerobic pathway of C. teleta was mediated by strombine dehydrogenase, in addition to weak activity by three additional pyruvate oxidoreductases. Anaerobic respiration at 25°C under normoxia was symptomatic of functional anaerobiosis, suggesting this species may be near its critical limit. Total energy production based on combined aerobic and anaerobic respiration suggests that large individuals (range from 0.003-0.012 g) may be limited under low DO and high temperatures.

Specific growth rates under starvation ranged from -2.34 to -69.31% d and were significantly influenced by temperature. Weight loss was significantly greater during the first 24 h and declined over 72 h. Weight losses were unrelated to body size. Under fed conditions, specific growth rates varied from -50.58 to 30.76%; a significant interaction occurred between DO level and body size. Small individuals lost less weight with increasing DO, whereas large individuals consistently exhibited negative growth rates across DO levels. There was a significant interaction between DO level and time, in that during the first 48 h growth was negative at lower DO levels, but positive at high DO levels.

Egestion rates were significantly influenced by temperature, DO, and time. Egestion rates at low DO respond strongly to increasing temperature and decrease over time. Overall, C. teleta was capable of surviving low DO and high temperatures; however, the species was near its critical thermal limit at 25°C.

ORCID ID

orcid.org/0000-0002-7068-4837