Giant kelp (Macrocystis pyrifera) survival in deep water (25–40 m) during El Niño of 1997–1998 in Baja California, Mexico

Abstract

During the 1997-1998 El Nino, we examined seasonally a giant kelp population in deep water (25-40 m) off the coast of Northern Baja California. Though most popula- tions in the region completely disappeared, large fertile adults survived the entire warming event at depth. At 25 m, there was no significant change in density or num- ber of fronds per individual during the warming period from spring 1997 to spring 1998, though the surface can- opy sloughed off (died) down to 15 m depth. By summer 1998, recruitment occurred at all depths at the site. Adult survival at depth was most likely important in post-dis- turbance recovery in surrounding populations by occu- pying substratum, providing vegetative growth, and producing spores. Survival in deep water during this extreme El Nino may have been due to local hydrogra- phy, such as internal waves bringing cool nitrate-rich water into the deeper regions of the shelf from below the thermocline, providing a refugium against the warm tem- peratures, low nutrients, and heavy wave action associ- ated with warming events. Deep-water populations may regularly survive El Nino warming in this region due to internal wave activity, and go undetected due to the depth at which they occur and the sloughing of the shal- low (-15 m) biomass.