Wirkungen von CO2 auf die Temperaturtoleranz und Fitnessindikatoren einer Crustaceenart aus verschiedenen Klimazonen

Abstract

Anthropogenic CO2 emissions threaten marine ecosystems by increasing water temperature and ocean acidification. In this study the impacts of climate change on the thermal tholerance of the spider crab Hyas araneus (L.) were investigated. Population comparisons were conducted on populations from Svalbard (79°N, habitat temperature 0 - 6 °C) and Helgoland (54°N, habitat temperature 3 - 18 °C), representing the species s northern and southern distribution range which is the temperate Northeast Atlantic to the Sub-Arctic region. The thermal tolerance window of H. araneus from Helgoland (54°N) was determined by measurements of the heart rate and hemolymph oxygen partial pressure upon temperatures ranging from 0 to 25 °C. Elevated CO2-concentrations induced a lowering of upper critical temperature from beyond 25 °C down to 23.5 °C (710 ppm). An increase of environmental CO2 concentrations to 3000 ppm caused a concomitant drop of the upper critical temperature to 21.1 °C. These results indicate, that the H. araneus population from Helgoland will knock on its physiological borders by synergistic effects of warming (up to 22.5 °C) and elevated CO2 concentrations. Additionally, studies on the impacts of climate change on early, potentially more sensitive life stages were conducted. Larvae of H. araneus of both populations were exposed to different temperatures and CO2 concentrations, revealing a temperature-dependent development. Larvae of Helgoland grew faster and had a higher fitness compared to those from Svalbard. Elevated CO2 concentration caused a disturbed development in all stages of both populations. Helgoland megalopae displayed the highest sensitivity against enhanced CO2 concentrations. In contrast, megalopae from Svalbard were more sensitive to warming. The negative effects of both, CO2 and temperature lead to the conclusion that the megalopae is a putative bottleneck stage during the species development. Moreover, the effect of climate change was investigated on the calcification capacity of the H. araneus larval stages. Elevated CO2 concentrations entailed population and temperature dependent reductions of the calcium contents of the larvae. In Helgoland larvae, reduction of calcium contents correlated positively with their body weight. In contrast, Svalbard larvae revealed a dramatic drop in calcium contents, with body weight remaining constant at cold temperatures (3 °C). Different to the Helgoland larvae, Svalbard larvae displayed increased calcification rates at warm temperatures (15 °C) under 3000 ppm CO2 exposure. Studies on Na /K -ATPase activity and expression identified additional differences in both H. araneus populations regarding thermal adaptation. Compared to Helgoland crabs, gill in vitro Na /K -ATPase activity of the Svalbard population showed a strong increment upon warming beyond their specific habitat temperature. This indicates a high thermal sensitivity of the Na /K -ATPase and a narrowed thermal window of the Svalbard population compared to the Helgoland population. Studying the effect of elevated CO2 concentrations on the thermal tolerance and fitness indicators of the spider crab Hyas araneus revealed different population specific physiological adaptations to their respective habitat temperatures. The synergistic effects of warming and ocean acidification will have negative effects on different processes of each population, related to various life stages due to physiological constraints. Furthermore, the progressing climate change will presumably lead to a nothward shift of the southern (Helgoland) distribution range of the species.