Densitometric analyses and airborne infrared photographs obtained from year to year, together with field observations, were employed to quantify the extent of fluctuations in the previously identified algal populations on various sites. Besides, spectroradiometric records of similar algal populations were also obtained. This study confirms the possibility to collect automatic and repetitive data with SPOT, satellite that will permit a control and management of intertidal seaweeds at a very large scale.