Individual- and Population-Level Effects of Temperature and Hypoxia on Two Demersal Fishes in Chesapeake Bay

摘要

Anthropogenically-induced climate change has resulted in increases in water temperature and the frequency and severity of hypoxic events in coastal areas worldwide. Temperature and hypoxia affect fishes' energetics which can, in turn, be reflected in changes in reproductive success and shifts in spatial distributions. In an effort to quantify these changes in Atlantic croaker (Micropogonias undulatus) and spot (Leiostomus xanthurus) in Chesapeake Bay. I: (1) estimated standard and maximum metabolic rates and hypoxia tolerances at five temperatures (10, 15, 20, 25 and 30°C) using intermittent-flow respirometry, (2) examined the effects of hypoxia exposure on metrics of reproductive potential and, (3) developed an individual-based, dynamic-seascape model of Atlantic croaker and spot based on data from the respirometry trials.;The first set of experiments showed that metabolic scope (i.e., the difference between standard and maximum metabolic rates, and within which all aerobic metabolic processes must operate) increased with increasing temperature in both species between 10 and 20°C, but plateaued above 25°C in Atlantic croaker and above 20°C in spot. Except at 10°C, the metabolic scope of Atlantic croaker was less than that of spot at all temperatures. In contrast to previous studies with Atlantic croaker from the Gulf of Mexico, the relative expression of hypoxia-inducible factors and metrics of reproduction (gonadosomatic index, most-advanced oocyte stage, and proportion of atretic oocytes) did not differ between Atlantic croaker captured under normoxic and hypoxic conditions in Chesapeake Bay. Simulations of the movements and distribution of Atlantic croaker and spot using individual-based models suggested that these species would occupy areas with warmer and better-oxygenated water than indicated by trawl survey observations from 1988-2014. Additionally, simulations indicated that a greater proportion of Atlantic croaker and spot in the Virginia waters of Chesapeake Bay would occupy the lower portion of Chesapeake Bay than indicated by capture rates from the trawl survey. My research suggests Atlantic croaker and spot are well-adapted to the environmental conditions of Chesapeake Bay during summer and are likely not affected by the frequent hypoxic episodes occurring in the subestuaries of the lower Chesapeake Bay. The apparent larger effect of elevated temperature on the metabolic scope of spot may provide them a greater capacity for movement, growth, and reproduction in warmer conditions and thus, a competitive advantage over Atlantic croaker as water temperatures continue to rise due to anthropogenically-induced climate change. My results indicate that intermittent exposure to hypoxic conditions is unlikely to negatively affect the reproductive potential of Atlantic croaker. Additional research, however, is necessary to better understand how this intermittent hypoxia exposure affects the endocrine pathways controlling reproduction. Finally, although climate-change science frequently focuses on the effects of rising coastal water temperature, and fisheries science and management on the effects on fish distributions, the results of my individual-based models suggest that predicting the effects of anthropogenically-induced climate change should not focus on temperature alone, as this may not be the most important driver of changes in fish distribution. More specifically, other factors such as time-area specific hypoxic events, prey availability, and predator avoidance likely contribute to the spatial distributions of these species in Chesapeake Bay.