Latitudinal variations of the yield and quality of agar from Gelidium robustum (Gelidiales, Rhodophyta) from the main commercial harvest beds along the western coast of the Baja California Peninsula, Mexico

The yield and quality of agar from Gelidium robustum from the main commercial harvest beds along the western coast of the Baja California Peninsula (Mexico) were evaluated within a latitudinal range of about 800 km (31A degrees 47'N to 27A degrees 05'N). Samples from six locations, Bahia Todos Santos, El Rosario, Isla de Cedros, Islas San Benito, Punta Eugenia, and Bahia Asuncin, were analyzed. Bryozoan, protein, and agar content in the seaweed were estimated. The agar quality was determined by the content of 3,6-anhydrogalactose, sulfate, gel strength, and gelling and melting temperature. All the values of these variables were correlated and then with the satellite-derived data of the sea surface temperature (SST), net primary production (NPP), and photosynthetic active radiation (PAR) measured at each harvest bed during the summer months (June, July, and August) of 2000. In the northern and central region, the agar yield was 35% to 37% (Bahia Todos Santos, El Rosario, Isla de Cedros, and Islas San Benito), whereas lower yields were obtained from the southern beds (Punta Eugenia and Bahia Asuncin). In contrast, the agar quality increased from the northern to the southern beds. A lower gel strength was obtained from Bahia Todos Santos and El Rosario (268 A +/- 16 and 205 A +/- 5 gcm(-2)) with a higher gel strength obtained from Isla de Cedros, Islas San Benito, and Bahia Asuncin (384 to 444 A +/- 25 gcm(-2)). Yield was not correlated with the bryozoan content but was inversely correlated with the protein content in the seaweed. The sulfate content in the agar was inversely correlated with the gel strength and with the melting temperature. The 3,6-anhydrogalactose content showed slight variations among harvested beds. Analysis of satellite-derived data showed an equatorward increase of the SST, NPP, and PAR. The agar content correlated inversely with the equatorward increase of the NPP, whereas agar quality, i.e., gel strength, correlated positively with the NPP and PAR. No significant effects were observed on the yield and quality of agar with the latitudinal change of the SST.