| Summary: | The pelagic ecosystem is facing a number of changes due to anthropogenic forcing; in particular global warming, ocean acidification and expanding hypoxia all may strongly affect marine organisms. The consequences for pelagic ecology likely involve altered organismal physiology and shifts in species geographic and vertical distributions. Here I address these questions with an understudied but ecologically important group of zooplankton, the pteropod mollusks. A multi-season study of the Ross Sea of the Southern Ocean investigated the metabolic rate of Limacina helicina antarctica and Clione limacina antarctica in comparison with mean chlorophyll a concentrations. Laboratory experiments demonstrated a pronounced suppression of metabolism for Limacina helicina antarctica during food deprivation, which mirrored that of freshly caught specimens in seasons differing in regional primary productivity. Carbon dioxide, elevated to levels expected in the next century, had a pronounced effect on the oxygen consumption of Limacina helicina antarctica; however, this effect was only apparent when animals were well-fed. Distributional studies in the eastern tropical Pacific region examined the patterns of pteropods in association with variations in oxygen concentration, temperature, depth and pH at two sites in the eastern tropical Pacific during 2007 and 2008. There were three distinct patterns of pteropod distribution, each with differing exposure to temperature, oxygen and carbon dioxide. Energetics experiments revealed that pteropods which are naturally exposed to high levels of carbon dioxide in oxygen minimum zones are not affected by hypercapnia, whereas those which never experience elevated carbon dioxide levels respond with a reduction in oxygen consumption. Generally pteropods had a suppression of metabolic rate under conditions of both low temperature and low dissolved oxygen with implications for biogeochemical cycling in oxygen minimum zones. My results demonstrate that pteropods will respond in a species specific fashion to the predicted changes in the physical and chemical parameters of the pelagic ecosystem. While some organisms may acclimate to climate change, others face habitat compression, reduced fitness, and changes in biogeography. My work also indicates that predicting organismal response to ocean acidification is dependent on achieving a more complex understanding of the immediate physiological state of an individual animal, the duration of exposure, and local hydrography.
|
|---|