Abundance estimation of Gigartina canaliculata Harvey, In San Quintin Bay, Baja California, Mexico

Abstract

Bimonthly samplings were carried out from March 1987 to January 1988 in San Quintín Bay, B.C., in order to determine the abundance of the alga Gigartina canaliculata Harvey (Bhodophyceae-Gigartinales). The highest biomass values obtained, expressed in dry weight, were 475 + 49 g/m² in May, 545 ±88 g/m² in July and 377 ± 47 g/m² in September. Extrapolated to the total area of 400,000 m², this represents 190 ± 19 tons, 218 ± 35 tons and 150 ± 19 tons, respectively. The lowest biomass value obtained was 120 ± 35 g/m² in January, which extrapolated to the 400,000 m², represents 48 ± 5.2 tons. The upwelling events that occur in San Quintín Bay at the end of spring and beginning of summer (Dawson, 1951; Alvarez-Borrego and Alvarez-Borrego, 1982) coincided with the highest biomass values recorded. The functional relation of wet weight versus dry weight had a regression coefficient r = 0.94 and was expressed by the equation y = 1.75 + 0.19 x. Sexual reproduction was maximum from September to January with 95% of the cystocarpic plants and minimum in May with 50%. The minimum reproduction in May and the highest percentage of sexually mature plants found during the autumn-winter season indicate a shift in the life cycle of G. canaliculata, caused in tum by a shift in seawater temperature which is controlled by upwelling events. The plants presented a quasi-homogeneous growth throughout the year (% proteins/% carbohydrates), with a growth index of 0.22-0.29 (0.29 corresponding to March).