HABITATS AND DISTRIBUTION PATTERNS OF MARINE LUMINOUS BACTERIA IN THEWESTERN BALTIC-SEA

Numbers of luminous bacteria were counted at three stations of the bra ckish water ecosystem of the western Baltic Sea from July 1985 to July 1986. Additional samples were taken during three cruises from station s at the North Atlantic Ocean, the Norwegian Sea and adjacent marine a reas. - In Kiel Eight (western Baltic) values varied between 0 and 68, 000 luminous cfu l(-1). With exception of the - coastal station a dist inct seasonal distribution pattern was shown in a water depth of 20 m: high numbers found in summer were opposed to low numbers in winter, t he peaks being rather high in comparison to those of other areas. Stat istical analysis showed that the results of 20 m were significantly di fferent from those of 0 and 10 m depth; however, there was no correlat ion with temperature and salinity. Taxonomic studies revealed that the population consisted primarily of the genus Photobacterium. - The opt imum of salinity was not a brackish but a marine one and was about 30 parts per thousand for the majority of the strains tested. A smaller n umber of strains grew best at a salinity between 10 and 15 parts per t housand. Optima of temperature ranged from 15 to 20 degrees C for most of the test strains. - Taxonomic analysis was also performed with lum inous strains from marine areas adjacent to the western Baltic Sea, Ph otobacterium being the dominant genus here, too. Luminous bacteria wer e also enriched from the external surface and the gut contents of whit ings (Merlangius merlangus) and cods (Gadus morhua). A model is propos ed which explains the distribution pattern found. According to this, t he gut-dwelling luminous bacteria are transported by their hosts from the North Sea into the western Baltic Sea. Here they are released into the environment, thus inhabiting another niche.