Gelidium robustum agar: quality characteristics from exploited beds and seasonality from an unexploited bed at Southern Baja California, Mexico

The yield and gel properties of agar from Gelidium robustum, harvested in B aja California for industrial production is affected by season of collectio n and epiphyte loading. The alga is epiphytized to various extents by the b ryozoan Membraniphora tuberculata ('conchilla') and the resulting calcareou s crust on the alga diminishes the price of the seaweed biomass. Classifica tion of the algal biomass quality by the agar industry is based on the appa rent 'conchilla' content from visual examination. The different quality cla sses can be categorized quantitatively into premium class (30-40% w/w of 'c onchilla' load), 2nd class (similar to 50% w/w) and 3rd class (> 60% w/w). For samples collected at two exploited beds, the biomass obtained from Bahi a de Tortugas had a lower epiphytic coverage than that from Bahia Asuncion. The agar yield from different quality classes of G. robustum was strongly affected by the bryozoan epiphytic coverage, while its gel characteristics were not. Algae collected at Punta Prieta, an unexploited bed not affected by 'conchilla', showed seasonality in agar yield. It ranged between 17.5 an d 44.2% with two maximum values observed, one in summer and the other in wi nter. Gel strength ranged between 515 and 665 g cm(-2), reaching a maximum during autumn.