Abstract
The distribution and the seasonal periodicity of the marine algae from 7 different biotopes of Thermaikos Gulf [Greece] were investigated. The marine algal flora consists of 19.8% Chlorophyceae, 24.7% Phaeophyceae and 55.5% Rhodophyceae with a R/P Quotient [respiration/productivity] of 2.25 of boreal floristic character. Maximum vegetative growth occurred in winter for the Chlorophyceae, in summer for the Phaeophyceae, whereas the Rhodophyceae show a peculiarity. Their reproductive growth occurred in winter and summer and it is independent of the vegetative growth. An increase of pollution in the Gulf might be responsible for the alteration in the composition of the flora.