ALBERT

Beschreibung: Dates of Cruise: 16.05. – 28.05.2016 Areas of Research: Physical, chemical, biological and fishery oceanography Port Calls: Klaipeda, Lithuania, 21.05. – 23.05.2016

Beschreibung: Dates of Cruise: 13.05. – 29.05.2017 Areas of Research: Physical, chemical, biological and fishery oceanography Port Calls: Visby, Sweden, 19.05. – 21.05.2016

Beschreibung: The disappearance of larger individuals and the decrease in individual body condition suffered by Atlantic cod Gadus morhua in the eastern Baltic during the past two decades can be expected to affect the stock reproductive output. To investigate this, female G. morhua were collected during the spawning and pre-spawning period in 2015-2016. The current individual potential fecundity (FP) of eastern Baltic G. morhua was estimated and analysed in relation to total length (LT) and indices of nutritional status such as body condition (K) and hepato-somatic index (IH) using generalized linear models. In addition, the current prevalence of atresia and its potential relation to K were investigated. Moreover, a calibration curve to estimate FP from oocyte diameter, based on the autodiametric oocyte counting method, was established for the first time for eastern Baltic G. morhua and can be used for future fecundity studies on this stock. The results showed that FP was mainly positively related to fish length, but K and IH also contributed significantly to the variation in FP. The model predicted that fish with K=1·2 have a FP 51% higher than fish of the same LT with K=0·8. The prevalence of fecundity regulation by atresia was 5·8%, but it was found only in fish in the pre-spawning maturity stage and with low K. Temporal changes in biological features such as the length composition and individual body condition of eastern Baltic G. morhua, should be accounted for when estimating stock reproductive potential.

Beschreibung: Wochenbericht der Forschungsreise mit R.V. „Alkor“ AL 493 13.05.2017 – 20.05.2017

Beschreibung: 16.05.2015 - 30.05.2015 Physical, chemical, biological research and fishery oceanography This multidisciplinary cruise extended a long-term data series on (eco-)system composition and functioning of the Baltic Sea, with a focus on the deeper basins. The series has been collected in similar form since 1986. A key characteristic of the cruise is the integration of oceanographic and biological information to enhance understanding of environmental and (fish) population fluctuations, and evolutionary processes in this system. The resulting datasets and samples are an essential component of the international EU project BONUS BIO-C3 coordinated by GEOMAR. The spatial focus lay on the Bornholm Basin (the most important spawning area of Baltic cod), but also included the Western Baltic Sea, Arkona and Gotland Basin, Gdansk Deep, and Stolpe Trench. Specific investigations included a detailed hydrographic survey (oxygen, salinity, temperature) of the Bornholm Basin, plankton surveys (zoo- and ichthyplankton, with the goal to determine the composition and the abundance and vertical and horizontal distribution of species, and to take samples for later measurements of nutritional condition), and pelagic fishery hauls for clupeid and gadoid fish. The latter served to determine stock structure, gonadal maturation, stomach contents, and egg production of sprat and cod, and to sample tissue for later genetic analyses and otoliths for age estimatation of individual cod. The abundance and distribution of fish species in the investigated area was also assessed with hydroacoustic methods. Additional cruise components were: (i) cod gonad and liver sampling for the determination of lipid content and histological studies; (ii) vertically resolved phytoplankton and zooplankton sampling for studies of plankton phenology.

Beschreibung: R.V. ALKOR Cruise No.: AL 457 Dates of Cruise: 16.05. – 30.05.2014 Areas of Research: Physical, chemical, biological and fishery oceanography Port Calls: Gdynia, Poland, 22.05. – 24.05.2014

Beschreibung: 12.05. – 27.05.2014 Port Calls: Karlskrona, Sweden, 18.05. – 20.05.2014; Rönne, Danmark, 24.05. – 25.05.2014

Beschreibung: The Baltic Sea is a dynamic environment responding to various drivers operating at different temporal and spatial scales. In response to climate change, the Baltic Sea is warming and the frequency of extreme climatic events is increasing (Lima & Wethey 2012, BACC 2008, Poloczanska et al. 2007). Coastal development, human population growth and globalization intensify stressors associated with human activities, such as nutrient loading, fisheries and proliferation of invasive and bloom-forming species. Such abrupt changes have unforeseen consequences for the biodiversity and the function of food webs and may result in loss of ecological key species, alteration and fragmentation of habitats. To mitigate undesired effects on the Baltic ecosystem, an efficient marine management will depend on the understanding of historical and current drivers, i.e. physical and chemical environmental conditions and human activities that precipitate pressures on the natural environment. This task examined a set of key interactions of selected natural and anthropogenic drivers in space and time, identified in Task 3.1 as well as WP1 and WP2 (e.g. physico-chemical features vs climate forcing; eutrophication vs oxygen deficiency vs bio-invasions; fisheries vs climate change impacts) by using overlay-mapping and sensitivity analyses. The benthic ecosystem models developed under Task 2.1 were used to investigate interactions between sea temperature and eutrophication for various depth strata in coastal (P9) and offshore areas (P1) of the Baltic Sea. This also included investigation on how the frequency and magnitude of deep-water inflow events determines volume and variance of salinity and temperature under the halocline, deep-water oxygen levels and sediment fluxes of nutrients, using observations and model results from 1850 to present (P1, P2, P6, P9, P12). The resulting synthesis on the nature and magnitude of different driver interactions will feed into all other tasks of this WP3 and WP2/WP4. Moreover, the results presented in this report improve the process-based and mechanistic understanding of environmental change in the Baltic Sea ecosystem, thereby fostering the implementation of the Marine Strategy Framework Directive.