Increasing pressure on freshwater resources due to terrestrial feed ingredients for aquaculture production.

As aquaculture becomes more important for feeding the growing world population, so too do the required natural resources needed to produce aquaculture feed. While there is potential to replace fish meal and fish oil with terrestrial feed ingredients, it is important to understand both the positive and negative implications of such a development. The use of feed with a large proportion of terrestrial feed may reduce the pressure on fisheries to provide feed for fish, but at the same time it may significantly increase the pressure on freshwater resources, due to water consumption and pollution in crop production for aquafeed. Here the green, blue and gray water footprint of cultured fish and crustaceans related to the production of commercial feed for the year 2008 has been determined for the major farmed species, representing 88% of total fed production. The green, blue and gray production-weighted average feed water footprints of fish and crustaceans fed commercial aquafeed are estimated at 1629 m3/t, 179 m3/t and 166 m3/t, respectively. The estimated global total water footprint of commercial aquafeed was 31-35 km3 in 2008. The top five contributors to the total water footprint of commercial feed are Nile tilapia, Grass carp, Whiteleg shrimp, Common carp and Atlantic salmon, which together have a water footprint of 18.2 km3. An analysis of alternative diets revealed that the replacement of fish meal and fish oil with terrestrial feed ingredients may further increase pressure on freshwater resources. At the same time economic consumptive water productivity may be reduced, especially for carnivorous species. The results of the present study show that, for the aquaculture sector to grow sustainably, freshwater consumption and pollution due to aquafeed need to be taken into account.

Model of the carbon concentrating mechanism in chloroplasts of eukaryotic algae.

A generic chloroplast-based model for the carbon concentrating mechanism (CCM) in eukaryotic algae is presented. The fine structure of chloroplasts is represented by separate compartments: marginal and bulk stroma, pyrenoid, girdle lamella, bulk thylakoids, and central lamella traversing the pyrenoid. The roles of the individual structural elements of the chloroplast with respect to the CCM and the effect of carbonic anhydrase activity in various compartments are analysed. Hypothetical HCO(-)(3)transport into the acidic thylakoid lumen is adjusted by imposing an optimization principle: a given [CO(2)] at the site of RuBisCO is achieved with minimum energy costs for the CCM. Our model is highly efficient in terms of saturation of RuBisCO carboxylase activity and the affinity of the chloroplast for CO(2), if either a girdle lamella or a pyrenoid is present. The highest efficiency is achieved with a pyrenoid. A eukaryotic CCM is not necessarily associated with accumulation of dissolved inorganic carbon (DIC) as in cyanobacteria. Chloroplasts are categorized into four types corresponding to morphological characteristics of all major algal classes with regard to the presence of pyrenoids, girdle lamellae, and the distribution of CA activity.

Temporal trends in deep ocean Redfield ratios.

The Redfield ratio [carbon:nitrogen:phosphorus (C:N:P)] of particle flux to the deep ocean is a key factor in marine biogeochemical cycling. Changes in oceanic carbon sequestration have been linked to variations in the Redfield ratio on geological time scales, but this ratio generally is assumed to be constant with time in the modern ocean. However, deep-water Redfield ratios in the northern hemisphere show evidence for temporal trends over the past five decades. The North Atlantic Ocean exhibits a rising N:P ratio, which may be related to increased deposition of atmospheric nitrous oxides from anthropogenic N emissions. In the North Pacific Ocean, increasing C:N and C:P ratios are accompanied by rising remineralization rates, which suggests intensified export production. Stronger export of carbon in this region may be due to enhanced bioavailability of aeolian iron. These findings imply that the biological part of the marine carbon cycle currently is not in steady state.