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 Baja California for industrial production is affected by seasonof collection and epiphyte loading. The alga is epiphytized to various extents by the bryozoan Membraniphora tuberculata ('conchilla') and the resulting calcareous crust on the alga diminishes the price of the seaweed biomass. Classification of the algal biomass quality by the agar industry is based on the apparent 'conchilla' content from visual examination. The different quality classes can be categorized quantitatively into premium class (30-40% w/w of 'conchilla' load), 2ndclass (? 50% w/w) and 3rd class (> 60% w/w). For samples collected at two exploited beds, the biomass obtained from Bahia de Tortugas hada lower epiphytic coverage than that from Bahia Asuncion. The agar yield from different quality classes of G. robustum was strongly affected by the bryozoan epiph ytic 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 and 44.2% with two maximum values observed, one in summerand the other in winter. Gel strength ranged between 515 and 665 g cm^-2, reaching a maximum during autumn. [ABSTRACT FROM AUTHOR]