Recruitment Dynamics of the Gulf of Riga Herring Stock: Density-Dependent and Environmental Effects

The Gulf of Riga and open-sea stocks of the Baltic herring have displayed remarkably consistent inverse recruitment and stock development patterns since the 1970s: the open-sea stocks steadily declined, whereas the Gulf stock increased rapidly in the early 1990s, reaching a peak abundance in the early 2000s and exceeding the level of the 1970s by a factor of 2¿3. The increase was accompanied by a decline in the mean weight-at-age and the condition factor. The estimated decline (by 30¿40%) in the average annual consumption rate per individual and changes observed in the zooplankton community suggest that density-dependent effects may have increased since the 1970s. The current period of high stock sizes is also characterized by greater recruitment variability. Historical fecundity investigations have established that the average egg production per individual has decreased in all age groups by 20¿ 50%, along with a decrease in mean weight and condition. Yet, the effect on recruitment has been low so far, because lower fecundity has been compensated by the greater abundance and population fecundity has been maintained at the original level. Recruitment appears to be more influenced by environmental conditions than by spawning-stock biomass.JRC.G.4-Maritime affair

EPOCA/EUR-OCEANS data compilation on the biological and biogeochemical responses to ocean acidification

The uptake of anthropogenic CO2 by the oceans has led to a rise in the oceanic partial pressure of CO2, and to a decrease in pH and carbonate ion concentration. This modification of the marine carbonate system is referred to as ocean acidification. Numerous papers report the effects of ocean acidification on marine organisms and communities but few have provided details concerning full carbonate chemistry and complementary observations. Additionally, carbonate system variables are often reported in different units, calculated using different sets of dissociation constants and on different pH scales. Hence the direct comparison of experimental results has been problematic and often misleading. The need was identified to (1) gather data on carbonate chemistry, biological and biogeochemical properties, and other ancillary data from published experimental data, (2) transform the information into common framework, and (3) make data freely available. The present paper is the outcome of an effort to integrate ocean carbonate chemistry data from the literature which has been supported by the European Network of Excellence for Ocean Ecosystems Analysis (EUR-OCEANS) and the European Project on Ocean Acidification (EPOCA). A total of 185 papers were identified, 100 contained enough information to readily compute carbonate chemistry variables, and 81 data sets were archived at PANGAEA – The Publishing Network for Geoscientific & Environmental Data. This data compilation is regularly updated as an ongoing mission of EPOCA.