TEMPERATURE RESPONSES AND DISTRIBUTION OF SEVERAL MEDITERRANEAN MACROALGAE BELONGING TO DIFFERENT DISTRIBUTION GROUPS

The temperature responses of six macroalgae, isolated from the Mediter ranean Sea, were experimentally determined and correlated with their g eographic boundaries in the North Atlantic Ocean. The algae fall withi n three phytogeographic groups: (1) the warm-temperate Mediterranean-A tlantic group (Carpomitra costata), (2) the Amphiatlantic temperate gr oup (Colpomenia peregrina and Stictyosiphon soriferus) and (3) the Amp hiatlantic tropical to warm-temperate group (Gigartina teedii). One sp ecies from the genus Gracilaria i.e. G. verrucosa, has also been inves tigated. Gametophytes of Carpomitra costata survived at 1 - 23-degrees -C and grew sufficiently (> 20% of maximum rate) at 10 - 20-degrees-C. The temperature responses of this phase did not explain the distribut ion boundaries of this species. Sufficient growth, reproduction and fo rmation of macro-thalli of Colpomenia peregrina proceeded at 10 to 25- degrees-C. Germlings of this species grew better at higher temperature s than the macrothalli, but tolerated a similar temperature range (4 - 30-degrees-C). Its geographic distribution cannot be entirely explain ed on the basis of the experimental data. Styctiosiphon soriferus surv ived at -1 to 28-degrees-C and grew sufficiently between 5 and 25-degr ees-C. Reproduction occurred at 5 to 20-degrees-C; at 25-degrees-C spo rulation was inhibited and the germlings did not form upright thalli. The experimental evidence is in agreement with the distribution in eas tern America, the Mediterranean and the Black Sea, but not on the open European Atlantic coasts. Thalli of Gigartina teedii pre-incubated at 5 and 30-degrees-C, and at 15-degrees-C grew sufficiently at 15 - 30- degrees-C and at 10 - 30-degrees-C, respectively. Thalli cultivated at 15-degrees-C survived at 4 - 31-degrees-C. The northern geographical boundary of this species in eastern Atlantic is a growth and reproduct ion limit and the southern boundary a lethal one. Gracilaria verrucosa survived a wide temperature range (2 - 34-degrees-C) and grew suffici ently at 15 - 30-degrees-C confirming the warm-loving character of the genus.