Effect of climatic variation on the relative abundance of the red alga Gelidium robustum in Baja California Sur, Mexico

The red alga Gelidium robustum is important, because of its commercial exploitation in Mexico as a raw material for the agar industry, providing 10% of the world production of agarophytes. In recent years, its annual harvest in Mexico has shown obvious, variations partly because of an increased harvesting effort, but also because of environmental changes. An analysis is presented of the effect that interannual variability of the sea surface temperature, wind speed, and upwelling index had on the relative abundance of this alga from 1980 to 1990. The results indicate a close relation between environmental fluctuations and the relative abundance of this species. The response of G. robustum to the different environmental conditions has not always been equal. During El Nino 1982-84, the sea surface temperature was the most important factor and there was a high negative correlation with the relative abundance. A lag period of three months showed a positive correlation with upwelling index and wind speed. Under normal conditions and during La Nina, the relative abundance of the alga showed a positive correlation with the sea surface temperature. For the upwelling index and wind speed, the relationship was similar to that during El Nino.