Tolerance of Hyas araneus zoea I larvae to elevated seawater PCO2 despite elevated metabolic costs

Early life stages of marine crustaceans respond sensitively to elevated seawater PCO₂. However, the underlying physiological mechanisms have not been studied well. We therefore investigated the effects of elevated seawater PCO₂ on oxygen consumption, dry weight, elemental composition, median developmental time (MDT) and mortality in zoea I larvae of the spider crab Hyas araneus (Svalbard 79°N/11°E; collection, May 2009; hatch, December 2009). At the time of moulting, oxygen consumption rate had reached a steady state level under control conditions. In contrast, elevated seawater PCO₂ caused the metabolic rate to rise continuously leading to a maximum 1.5-fold increase beyond control level a few days before moulting into the second stage (zoea II), followed by a pronounced decrease. Dry weight of larvae reared under high CO₂ conditions was lower than in control larvae at the beginning of the moult cycle, yet this difference had disappeared at the time of moulting. MDT of zoea I varied between 45 ± 1 days under control conditions and 42 ± 2 days under the highest seawater CO₂ concentration. The present study indicates that larval development under elevated seawater PCO₂ levels results in higher metabolic costs during premoulting events in zoea I. However, H. araneus zoea I larvae seem to be able to compensate for higher metabolic costs as larval MDT and survival was not affected by elevated PCO₂ levels.     

Effects of ocean acidification, temperature and nutrient regimes on the appendicularian Oikopleura dioica: a mesocosm study

Increasing pCO₂ is hypothesized to induce shifts in plankton communities toward smaller cells, reduced carbon export rates and increased roles of gelatinous zooplankton. Appendicularians, among the most numerous pan-global “gelatinous” zooplankton, continuously produce filter-feeding houses, shortcutting marine food webs by ingesting submicron particles, and their discarded houses contribute significantly to carbon fluxes. We present a first mesocosm-scale study on the effects of temperature, pCO₂ and bloom structures on the appendicularian, Oikopleura dioica. There were effects of temperature and nutrients on phytoplankton communities. No shifts in functional phytoplankton groups, nor changes in particle sizes/morphotypes, known to impact appendicularian feeding, were observed under manipulated pCO₂ conditions. However, appendicularian abundance was positively correlated with increased pCO₂, temperature and nutrient levels, consistent with hypotheses concerning gelatinous zooplankton in future oceans. This suggests appendicularians will play more important roles in marine pelagic communities and vertical carbon transport under projected ocean acidification and elevated temperature scenarios.     

Territorial resource valuation deviates from habitat quality in an ecologically trapped,long-distance migratory bird

Preference measures are widely used in habitat selection studies to test an animal’s choice relative to particular habitat features, but most measures are subject to criticism as they fail to indicate the underlying behavioral motivation. Order of settlement on breeding sites has been proposed as an effective measure in migratory organisms, as it conceptually approaches a choice experiment. We tested the assumption that early red-backed shrikes (Lanius collurio) are more willing to defend their territorial resource than individuals arriving later. We earlier showed that shrikes arriving first settled in forest plantations that resulted in lower reproductive success compared to territories on farmland, suggesting an ecological trap. Therefore, individuals are expected to place higher value on the lower quality sites in forests. Within the context of resource valuation theory in animal contests, we used a simulated territorial intrusion experiment to measure territorial defense and to evaluate the perceived value of the territory during the settlement phase in both habitat types. Males arriving early were much more motivated to defend their territory than late birds. After correction for the disparity in the timing of arrival between habitat types, shrikes also more vigorously defended their territories in the forest habitat associated with the lowest reproductive returns. Although some resource valuation mechanisms remain unclear, our results show that early and late-arriving individuals strongly differ in behavioral motivation to hold their territorial resources. This study also demonstrates for the first time that organisms may exhibit a higher degree of territorial aggressiveness in a lower quality habitat.     

13C-labeling shows the effect of hierarchy on the carbon gain of individuals and functional groups in dense field stands

Measurements of resource capture by individuals, species, or functional groups coexisting in field stands improve our ability to investigate the ecophysiological basis of plant competition. But methodological and technical difficulties have limited the use of such measurements. Carbon capture, in particular, is difficult to asses in heterogeneous, dense field stands. Here we present a new approach to measure in situ daily gross carbon gain of individuals. It is based on measuring the 13C content of shoots after a few hours of continuous labeling of all assimilated CO2. The technique is simple and has few assumptions. A new, fully mobile facility was developed, capable of providing a labeling environment with a CO2 concentration close to atmospheric air and known, constant 13C-enrichment, while maintaining temperature and relative humidity within ambient values. This facility was used in seminatural grasslands of Germany and Argentina to explore the relationship between size and carbon gain of individuals of coexisting species growing in contrasting hierarchical positions, and to analyze the carbon gain of functional groups. In general, carbon gain per unit shoot mass increased with increasing size among small individuals, but it became independent of size among the largest ones. In consequence, competition appeared to be size asymmetric between subordinate individuals but size symmetric between dominant individuals. When comparing functional groups, the carbon gain per unit shoot mass of rosette dicots vs. grasses reflected not their relative contribution to stand biomass, but their hierarchical position: irrespectively of mass or growth form, being taller than neighbors was most important in determining carbon gain per unit shoot mass. We believe these results show that in situ measurements of carbon gain can provide valuable insight in field studies of plant competition.     

Convection under internal waves in an alpine lake

Environmental Fluid Mechanics - Turbulent mixing processes in deep alpine Lake Garda (I) have not extensively been observed. Knowledge about drivers of turbulent fluxes are important for insights...