Salinity-temperature effects on growth and reproduction of Scytosiphon lomentaria (Fucophyceae) along the salinity gradient in Danish waters

Four day-neutral strains of Scytosiphon lomentaria (Lyngbye) Link were collected along the salinity gradient from the North Sea (32% salinity) to the Baltic around Bornholm (8%) and grown under long-day conditions at temperatures from 5 to 30°C combined with salinities of 30, 20, 10 and 5%.The North Sea strain grew best at 3% salinity and a temperature interval of 7.2–23.5°C, the Baltic strain at 10–20% and a temperature range of 4.6–26. 7°C. The strains from Roskilde Fjord (18%) and the Sound (13%) grew equally well in 30 and 20% and at a wide temperature range.Fertile microthalli with unilocular sporangia and macrothalli with plurilocular sporangia were observed at all salinities in strains from Roskilde Fjord and the Sound but at different temperature intervals. The Baltic strain lacked the ability to produce fertile microthalli; formation of plurilocular sporangia was delayed, and sporangia developed only in a very narrow temperature interval.These results indicate the existence of salinity-temperature ecotypes of Scytosiphon. The inner Danish waters serve as an interface between the seaweed populations of the North Sea and the Baltic.