Temporal variation of Laminaria ochroleuca Bachelot de la Pylaie (Laminariales, Phaeophyceae) biomass on the Moroccan Atlantic coast: Implication for commercial harvesting

Abstract

For sustainable harvesting of wild stocks of economically important seaweed species, knowledge on the temporal variation of the standing stock biomass of the target species is an important prerequisite before any commercial harvesting concession can be granted. In this regard, a monthly in situ monitoring of the standing stock biomass of Laminaria ochroleuca (Bachelot de la Pylaie, 1824) was conducted during a two-year cycle at Sidi Bouzid located on the Moroccan Atlantic coast in the south of the city of El Jadida. Development of morphological parameters as proxy for growth i.e. blade length (L; cm), stipe length (S; cm) and dry biomass (kg.m-2) were monitored and measured. The shortest blade length was recorded in January 2004 and 2005 respectively (51.1 and 60 cm), the maximum was recorded in June 2004 and 2005 respectively (103.2 and 121.6 cm). Minimum biomasses are recorded in January of the two cycles of growth, it is about 0.60 kg.m-2 in 2004 and 0.98 kg.m-2 in 2005, the highest biomasses are recorded in May–June 2004 (1.9 kg.m-2) and in August for the year 2005 
(3.9 kg.m-2). Individuals found in June 2005 have shorter stipe (8.21 cm) while maximum stipe length was recorded on October 2005 (22.8 cm). Mean yearly densities of L. ochroleuca were 34 and 32 plants/m² in 2004 and 2005 respectively. Therefore, the exploitation of this species should be carried out from June with harvest period reduced to a maximum of 2 months to allow the algae to grow in autumn.