Effects of ocean acidification on growth and physiology of Ulva lactuca (Chlorophyta) in a rockpool-scenario, link to supplementary data

Rising atmospheric CO2-concentrations will have severe consequences for a variety of biological processes. We investigated the responses of the green alga Ulva lactuca (Linnaeus) to rising CO2-concentrations in a rockpool scenario. U. lactuca was cultured under aeraton with air containing either preindustrial pCO2 (280µatm) or for the end of the 21st century predicted (700µatm) pCO2 for 31 days. We addressed the following question: Will elevated CO2-concentrations affect photosynthesis (net photosynthesis, rETR(max), Fv/Fm, pigment composition) and growth of U. lactuca in rockpools with limited water exchange? Two phases of the experiment were distinguished: In the initial phase (day 1-4) the Seawater Carbonate System (SWCS) of the culture medium could be adjusted to the selected atmospheric pCO2 condition by continuous aeration with target pCO2 values. In the second phase (day 4-31) the SWCS was largely determined by the metabolism of the growing U. lactuca biomass. In the initial phase, Fv/Fm and rETR(max) were only slightly elevated at high CO2-concentrations whereas growth was significantly enhanced. After 31 days the Chl a content of the thalli was significantly lower under future conditions and the photosynthesis of thalli grown under preindustrial conditions was not dependent on external carbonic anhydrase. Biomass increased significantly at high CO2-concentrations. At low CO2-concentrations most adult thalli disintegrated between day 14 and 21, whereas at high CO2-concentrations most thalli remained integer until day 31. Thallus disintegration at low CO2-concentrations was mirrored in a drastic decline in seawater DIC and HCO3-. Accordingly, the SWCS differed significantly between the treatments. Our results indicated a slight enhancement of photosynthetic performance and significantly elevated growth of U. lactuca at future CO2-concentrations. The accelerated thallus disintegration at high CO2-concentrations under conditions of limited water exchange indicates additional CO2 effects on the life cycle of U. lactuca when living in rockpools.

Data on the biogeochemical cycle of methane in the ocean

Geological, mineralogical and microbiological aspects of the methane cycle in water and sediments of different areas in the oceans are under consideration in the monograph. Original and published estimations of formation- and oxidation rates of methane with use of radioisotope and isotopic methods are given. The role of aerobic and anaerobic microbial oxidation of methane in production of organic matter and in formation of authigenic carbonates is considered. Particular attention is paid to processes of methane transformation in areas of its intensive input to the water column from deep-sea hydrothermal sources, mud volcanoes, and cold methane seeps.

Bacteriological investigations in the Persian Gulf

While the R.V. "Meteor" was in the eastern Persian Gulf, during the time between March 31 and April 14, 1965, bacteriological investigations of the water and sediment were performed. The content of saprophytic bacteria in the water decreases from the coasts outward to the middle of the gulf. This shows a good correlation with the turbidity values. In a sediment core from the southern part of the gulf, the bacterial counts in all the horizonts were much higher than those from the northern part of the Persian Gulf. This agrees with the findings of the geologists, according to which the proportion of carbon compounds in the sediments decreases from south to north. Luminous bacteria were found in many samples of water. Their proportion of the saprophytic flora becomes less from south to north. Most of the water samples also contained pigmented bacteria. On freshwater medium, relatively few bacteria were able to develop. The proportion of these non-halophilic forms amounted up to 7 % (average about 1 %) of the total saprophytic count, in 22 samples examined. In this group the pigmented forms played a very large role. A comparison of the distribution of saprophytic bacteria in the eastern Persian Gulf with that in other inland seas such as the North Sea and the Baltic Sea shows, that the saprophytic counts in the subtropical Persian Gulf (arid region) lie clearly below those in corresponding sea areas of the temperate zones (humid region). This is to be attributed above all to the greater flow of organic nutrients into the latter.