Physiological and behavioral responses to temperature and flow in the barnacle Balanus glandula Darwin (1854)

Abstract

Given the scale and pace of anthropogenic change in marine environments, it is important to understand the manner in which organisms respond to environmental uncertainty. For many aquatic species, fundamental processes such respiration and feeding are potentially limited by the exchange of materials to and from their fluid environment. As a consequence, environmental factors such as water temperature and flow can profoundly impact the ecology and physiology of marine organisms. This dissertation evaluates the role of water temperature and velocity on respiration, feeding and ultimately growth in the barnacle, <italic>Balanus glandula</italic>. By conducting respiration experiments over a wide range of thermal (5 to 25°C) and fluid conditions (1 to 150 cm s<super>-1</super>), I demonstrate the importance of approaches that evaluate the combined effects of multiple environmental factors when examining physiological and behavioral performance. Model analysis of the data suggests that respiration is limited by the delivery of oxygen at low velocity (< 7.5 cm s<super>-1</super>) and high temperature (20 to 25°C). In contrast, respiration is limited by the capacity of barnacles to absorb oxygen at high flows (40 to 150 cm s<super>-1</super>) and low temperatures (5 to 15°C). Moreover, there are many intermediate flow-temperature conditions where both mass transfer and kinetic limitation are important. When oxygen delivery was limited (in low flow-high temperature treatments), barnacles displayed distinct "pumping" behaviors of their cirral appendages, a strategy that may serve to increase ventilation. Cirral beating behavior was also important in predicting patterns of feeding. The delivery of food particles (brine shrimp cysts) to the cirral net peaked at intermediate water velocities (7.5 to 20 cm s<super>-1</super>) and temperatures (15°C) likely due to short, abbreviated beating strokes at high velocities and high temperature, low cyst delivery rates at low velocities and slow beating rates at low temperatures. Capture efficiency, or the ratio of cysts captured to cysts encountered, was highest under the slowest flow (1 cm s<super>-1</super>). Model analysis of these observations demonstrated that detailed characterization of cirral beating behavior (i.e., whether they are employ fully extended versus abbreviated beating behavior) are required to accurately predict patterns of cyst capture. Model predictions of barnacle growth were generated using these respiration and feeding data. Peak growth rates are predicted at moderate water temperatures (15°C) and velocities (20 to 30 cm s<super>-1</super>). Barnacles at slow velocities should experience lower growth, due to lower encounter rates with suspended food particles, whereas at high velocities, barnacles experience lower feeding efficiencies, which also reduces their potential for growth. At low temperatures, cirral beating behavior slows, reducing feeding capacity and in turn growth, whereas at high temperatures, high metabolic can impose limits on growth. These predictions were consistent with growth rates measured in two experiments - one that manipulated water temperature and velocity and a second that measured growth under field conditions at different temperatures and velocities. Moreover, these results underscore the importance of considering the interaction between multiple environmental factors and provide evidence that they shape responses in physiology, behavior and growth