Giant kelp (Macrocystis pyrifera, Phaeophyceae) recruitment near its southern limit in Baja California after mass disappearance during ENSO 1997-1998

During the ENSO event of 1997-1998, density and population structure were e valuated in a Macrocystis pyrifera forest located in Bahia Tortugas, Baja C alifornia, Mexico, near the southern limit of the species' distribution in the Northern Hemisphere. Observations in Bahia Tortugas were made quarterly from January 1997 to September 1998 using SCUBA diving surveys, No macrosc opic plants were found in the Bahia Tortugas area from October 1997 to Apri l 1998, a local absence of at least 7 months. Aerial surveys further sugges t regional disappearance along most of the Baja California coast during the event. Unexpectedly, plants were found in Bahia Tortugas again in July 199 8, in spite of the widespread disappearance of the species less than a year earlier. Long-distance spore dispersal was an unlikely cause of the recrui tment because: 1) the nearest spore source was more than 100 km away; 2) re cruitment appeared to be simultaneous at many sites and occurred rapidly af ter the cessation of the ENSO event; and 3) the recruits occurred in the sa me areas as before disappearance. We suggest that a microscopic stage that was not visible during dive surveys survived the stressful conditions of EN SO and caused the recruitment event, supporting the hypothesis that a bank of microscopic forms can survive conditions stressful to macroscopic algae.