IMPACT AND RECOVERY OF GELIDIUM-SESQUIPED ALE ALGAE-BIOMASS FOLLOWING2 EXPERIMENTAL HARVESTING METHODS IN THE BASQUE COUNTRY (SPAIN)

Two commercial harvests of Gelidium sesquipedale by plucking and cutti ng, were carried out in July 1989 and July 1990. The recovery rate was studied in order to obtain data to manage the exploitation. After the harvest, biomass reduction of ca. 80 % could be observed; the density of the fronds did not vary and the mean length of the population was reduced by 48 % by cutting and by 31 % by plucking. The most important period of biomass recovery extends over 3 to 4 months after the harve st. Therefore, in October there were no significant differences betwee n biomass mean values in the control and the harvest areas. During thi s period growth rates were very little in the control area, while in h arvest areas were approximately 1.3% day-1. From March to July growth rates were approximately 0.9% day-1 in both areas. Production was 1.4 times higher in harvested areas (ca. 1 100 g.m-2.yr-1) and the turnove r rate 2.5 times higher (ca. 6.8 yr-1). Epiphytes disappear after harv esting and recover their biomass along the next month, although never increasing significantly in relation to the control area.