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

摘要

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 populations 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 number of fronds per individual during the warming period from spring 1997 to spring 1998, though the surface canopy 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-disturbance recovery in surrounding populations by occupying substratum, providing vegetative growth, and producing spores. Survival in deep water during this extreme El Nino may have been due to local hydrography, 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 temperatures, low nutrients, and heavy wave action associated 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 shallow (15 m) biomass.