TEMPERATURE REQUIREMENTS OF SCYTOSIPHON LOMENTARIA (SCYTOSIPHONALES, PHAEOPHYTA) FROM THE GULF OF THESSALONIKI, GREECE, IN RELATION TO GEOGRAPHIC-DISTRIBUTION

Temperature requirements for growth, reproduction and formation of mac rothalli of a day-neutral strain of Scytosiphon lomentaria from the Gu lf of Thessaloniki were experimentally determined and correlated with the geographic distribution in the North Atlantic Ocean. The microthal lus grew in a wider temperature interval and better at higher temperat ures than did the macrothallus. Germlings acclimated to 5 or 15 degree s C grew sufficiently (>2% of maximum rate) and developed into macroth alli at 5-25 degrees C and 5-27 degrees C. Macrothalli acclimated to 1 0 or 15 degrees C grew sufficiently at 5-20 degrees C; Macrothalli acc limated to 15 degrees C survived at -1 degrees C and reproduced at 5 t o 23 degrees C. Regardless of the acclimation temperature, germlings a nd macrothalli grew optimally (>80% of maximum rate) at 15-25 degrees C and al 10-15 degrees C. The experimental data explain only the south ern distribution boundary of Scytosiphon in the North Atlantic. This b oundary is composite in nature: on the European coasts it is a growth boundary, whereas on the American coasts it is a lethal one.