Re-thinking the “ecological envelope” of Eastern Baltic cod (Gadus morhua): conditions for productivity, reproduction, and feeding over time

Hypoxia is presently seen as the principal driver behind the decline of the former dominating Eastern Baltic cod stock (EBC; Gadus morhua). It has been proposed that both worsening conditions for reproduction and lower individual growth, condition, and survival are linked to hypoxia. Here, we elucidate the ecological envelope of EBC in terms of salinity stratification, oxygen content, and benthic animal biomasses, and how it has affected EBC productivity over time. The spawning conditions started deteriorating in the Gotland Deep in the 1950s due to oxygen depletion. In contrast, in the Bornholm Basin, hydrographic conditions have remained unchanged over the last 60 years. Indeed, the current extent of both well-oxygenated areas and the frequency of hypoxia events do not differ substantially from periods with high EBC productivity in the 1970s–1980s. Furthermore, oxygenated and therefore potentially suitable feeding areas are abundant in all parts of the Baltic Sea, and our novel analysis provides no evidence of a reduction in benthic food sources for EBC over the last 30 years. We find that while reproduction failure is intricately linked to hydrographic dynamics, a relationship between the spread of hypoxia and the decline in EBC productivity during the last decades cannot be substantiated.Peer reviewe

Recovery of the aquatic environment following the termination of fish farms [Andersö and Järsö

A study concerning the recovery of the water environment at two former fish farm sites, Andersö and Järsö, in the NW Aland archipelago, was performed in the summer 2003. The environmental effects of the two fish farms have been monitored during their active years (Andersö 1986-2002, Järsö 1981-2003),and now the recovery potential of the affected recipient areas were investigated. Diamond Fish Ab, Andersö is situated in the middle archipelago, in a narrow sound with a dominating north-south current. Alands Forell Kb, Järsö is located in a bay, where a threshold limits water exchange with the outer archipelago. The measured parameters in this study were hydrography, periphyton, zoobenthos and sediment. The warm weather in the summer 2003 resulted in high water temperatures. A stratification of the water column was observed, and it resulted in lower water temperatures in the bottom water especially at deeper stations. The safinity and secchi depth was higher in the Järsö- than in the Andersö-area and the oxygen content in the bottom water was genera/ly high throughout the summer. Measurements of nutrients in the water column showed medium high to high values of total phosphorus and nitrogen values in the two recipient areas. One deep station in the inner archipelago in the Andersö area, and two stations directly affected by the former fish farm in the Järsö area diverged from this pattern throughout the summer. At these stations very high nutrient values were obtained, and in the Järsö-area the content of oxygen in the bottom water was low. The content of chl a in the fotic zone was higher in the Andersö-area than in Järsö. Diverging values were obtained in the end of July, when an algal bloom in the Järsö area caused very high chl a -va/ues. The resu/ts from the periphyton incubation indicated a higher growth rate in the Järsö area. Effects of the fish farms could clearly bee seen in the organic, carbon and nitrogen contents of the sediment, which were higher at stations close to the recipients. The trend in the zoobenthos community is similar in the two recipient areas. At most stations, the abundance and biomass of the bottom fauna has diminished, although the diversity remained at the same level as last year. New opportunistic species have been found at the most affected sites, and the age distribution of Macoma balthica indicates that the recruitment has been successful in later years

Appendix A. Data included when assessing the baseline and prevailing conditions of open Baltic Sea macrofaunal diversity.

Data included when assessing the baseline and prevailing conditions of open Baltic Sea macrofaunal diversity

Shifting baselines in Antarctic ecosystems; ecophysiological response to warming in Lissarca miliaris at Signy Island, Antarctica

The Antarctic Peninsula has experienced a rapid increase in atmospheric temperature over the last 50 years. Whether or not marine organisms thriving in this cold stenothermal environment are able to cope with warming is of concern. Here, we present changes to the growth and shell characteristics of the ecologically important, small and short lived brooding bivalve Lissarca miliaris from Signy Island, Antarctica. Using material collected from the 1970’s to the present day, we show an increase in growth rate and adult shell deterioration accompanied by a decrease in offspring size, associated with an increase in annual average temperatures. Critical changes to the bivalve’s ecology seen today evidence the problem of a shift in baseline since the onset of warming recorded in Antarctica. These small bivalves are demonstrating ecophysiological responses to subtle warming that, provided warming continues, could soon surpass a physiological tipping point, adding to warming associated threats such as increased predatory pressure and ocean acidification