Einfluss von Ozeanversauerung und Temperatur auf Chloridzellen der Embryonen und Larven des Atlantischen Herings (Clupea harengus) - Effects of ocean acidification and temperature on chloride cells in Atlantic herring (Clupea harengus) embryos and larvae

Abstract

With climate change carbon dioxide and temperature is predicted to increase in the ocean surfaces. The oceans have the ability to slow down global warming by taking up CO₂ which hydrates in water producing carbonic acid and lowering the pH. This reaction is called ocean acidification and the research of its impacts on marine organisms is of global interest in science. Additional to this problem is the speed of the climate change, since industrial revolution pH has already decreased by 0.1 to a current value of about 8.1 in the surface ocean and calculations estimate a decrease in pH in the upper water layers of between 0.14 and 0.35 units until the end of this century. The aim of this study is to investigate the consequences according to ocean acidification on the early life stage of the Atlantic herring (Clupea harengus), since these stages are predicted to be highly vulnerable due to predation and environmental changes. Additionally the development of organs and physiological pathways is not yet completed which will gradually be functional in the weeks after hatching. Organs important for acidbase regulation are absent in embryos and larvae and thus challenging the larvae to cope with acidified waters. Specialized cells in the skin of fish larvae called chloride cells are identified to take over the function of ion regulatory organs until formation of gills is completed. In laboratory based experiments the effects of ocean acidification and temperature on the distribution, size and number of chloride cells as well as on the early ontogeny of embryos and larvae were investigated. Therefore two experiments were conducted firstly using four treatments of elevated pCO₂ concentrations (380, 1120, 2400, 4000 ppm) at constant temperature and secondly examining the synergistic effects of three temperatures a cold (6.5°C), a median (8.6°C) and a warm (12.3°C) treatment combined with three pCO₂ concentrations (380, 1120, 4000 ppm). CO₂ levels were chosen according to today´s value of 380 ppm as a control and to the predicted value until the end of this century. For the Baltic Sea even higher values are calculated due to areas with unmixed water bodies and oxygen minimum zones. Temperatures were chosen according to natural spawning behaviour of herring starting at 4°C as a control and to predicted warming of the oceans. Results showed a negative impact of ocean acidification on the survival of herring larvae with decreased fertilization (2nd experiment) and increased mortality rates at hatch (1st and 2nd experiment). Furthermore decreased length at higher CO₂ levels were detected in embryos. The effects on chloride cells were variable, showing no significant change in cell number. There was found one effect in higher cell sizes on the trunk and one in the pericardial region with increasing CO₂ levels. First appearance of chloride cells of herring embryos was visible at 20-somite stage on the epidermis of the yolk sac at 3dpf