- Environmental stress can negatively affect the ability of organisms to reproduce. Energetic trade-offs exist in all organisms, and under stress, energy may be allocated away from reproduction and towards physiological defense and repair mechanisms. The rocky intertidal environment is ideal for investigating the influence of environmental stress, as organisms are exposed to both terrestrial and marine conditions due to tidal fluctuation. Aerial exposure at low tide can lead to high temperature, desiccation, and oxidative stress. Stress in the intertidal zone increases along a vertical gradient, as organisms in the high intertidal are exposed to air for longer periods of time than those in the low intertidal.
Mussels are typically the dominant space-occupiers on temperate rocky shores, and they span the vertical gradient by occupying the entire mid-zone, from the low intertidal, which is a relatively low-stress environment, to the high intertidal, which is a high-stress environment. In this dissertation, we compared growth, reproduction, physiological defenses, pigmentation, and survival of mussels from the low-stress and high-stress regimes. We also compared energy allocation towards reproduction in mussels across a gradient of food availability between sites on the central Oregon coast. Findings indicate that growth and energy allocation towards reproduction are reduced in the high edge of the mussel bed, and physiological defenses are increased. A pattern was revealed where mussels in the high edge of the mussel bed are accumulating high concentrations of carotenoid pigments into their gonadal tissues, which was previously thought to be a secondary sex characteristic of females. This suggests that mussels may be incorporating carotenoids into their gonads in an effort to protect their gametes from damage by oxygen free radicals generated during aerial exposure.
Results of this research have implications for intertidal systems under climate change scenarios, as extreme aerial temperature events are predicted to increase in frequency and severity, and changes in oceanic circulation may also occur. Based on the findings presented in this dissertation, increases in aerial temperature could potentially lead to decreased energy allocation towards reproduction, changes in spawning time, and reduced survival of adult mussels.