1. The impact of Climatic Changes on the Adaptation of Marine Fish in the Baltic Sea Evald Ojaveer Estonian Marine Institute of the University of Tartu Margers Kalejs Georga Apina 22-8, Valmiera 4201, Latvia

3. Structure Freshened Baltic water Halocline Modified saline water A chain of basins separated by topographic (coasts, islands, bottom relief), or hydrological (fronts) constraints SW and shallower parts -- boreal character NW and deeper parts -- arctic

5. Climate water masses inflows SW Atlantic saline frequent E Continental Typical Baltic strong,moderate NW Atlantic/arctic Freshened only very strong

6. Main environmental conditions AreaSalinity Ice (%) Temperature Spr.bloom Kattegat 12-30/32-34 2017/2II-III Belts,Sound 8-17/16-23 3017/2III Arkona 7.5-10/10-23517/2III-IV Bornholm 7-8.5/14-21017/2IV Gotland 8/11-1410 16.5/2 IV-V NW 7/9-124016.5/1 IV-V GofRiga 5-710018-19/0IV-V GofFinland4.5-7/6-1010016/0-0.5IV-V Bothn. Sea 6-710014-19/0IV-V Bothn. Bay 3-4.510013-17/0VI

7. SW E NW GoF GoR GOB Spr. herring + + + + + + Sandeel + + + + + + Stickleback + + + + + + Flounder + + + + + (+) Sprat + + + + (+) Cod + (+) (+) Rockling + (+) Plaice + (+)? Dab +

8. Adaptations Higher fecundity Earlier maturation Lower specific gravity of eggs Longer spawning period Survival of deviated individuals

9. Hydrographic conditions/year- class abundance

10. Influence of higher salinity and mild winters Increase in population abundance Extension of the area

11. Influence of stagnation,decrease of salinity in deeps, negative temperature anomaly in winter Weakening of immigration Strong natural selection for elimination of less adapted phenotypes

12. Anthropogenic impacts Increase of production in pelagic layers Oxygen depletion in deep layers Exploitation, especially overexploitation decreases abundance, possibly also genetic variation Introduction of alien species has controversial influence

13. Species of marine origin adapted in all regions of the Baltic Sea Clupea harengus membras -- 10-12 major populations Ammodytes tobianus -- probable several populations Pomatoschistus minutus Zoarces viviparus -- probably several populations Triglopsis quadricornis -- probably several populations Myoxocephalus scorpius

14. Species adapted in the Baltic Proper Platichthys flesus trachurus -- probably 6-7 local populations Gadus morhua callarias -- 2 populations Rhinonemus cimbrius Sprattus sprattus balticus Autumn spawning herring --several subpopulations

15. Species adapted in the SW part of the sea Pleuronectes platessa Limanda limanda -- probably 2 populations

16. Possible next important natural immigrant Mackerel Scomber scombrus