Comparing the impacts of four ENSO events on giant kelp (Macrocystis pyrifera) in the northeast Pacific Ocean

Abstract

The 1982–83, 1986–87, 1991–92, and 1997–98 El Niño-Southern Oscillations (ENSOs) were compared with regards to their strength and timing in the tropical Pacific Ocean, changes in ocean temperature and wave intensity, and their impacts to giant kelp populations in the Northeast Pacific. The Multivariate ENSO Index, oceanographic data, and kelp abundance data all show that the 1982–83 and 1997–98 ENSOs were stronger and resulted in greater losses of giant kelp than the 1986–87 and 1991–92 ENSOs, but that the 1982–83 and 1997–98 ENSOs differed with regard to the arrival of destructive waves relative to when the ocean waters warmed and cooled. The 1982–83 ENSO was more destructive to the giant kelp populations in central California, USA than the 1997–98 ENSO, but the 1997–98 ENSO was more destructive to the giant kelp in southern California. These events appeared similarly destructive to the populations in Baja California, Mexico. Recovery of the kelp populations also varied among the two strong ENSOs due to the ocean conditions following each ENSO. In southern and Baja California, recovery was slow following the 1982–83 ENSO, while recovery was more rapid following the 1997–98 ENSO. Unfortunately, the monitoring programs used to evaluate the kelp populations stopped shortly after the 1997–98 ENSO, resulting in a lack of data for comparisons with the more recent weak ENSOs that occurred between 2002 and 2010, or with the strong ENSO that occurred in 2014–2016. This supports the need for continued long-term monitoring programs to better understand how climate anomalies impact coastal ecosystems. Key words: disturbance; ENSO; kelp forest; monitoring; ocean temperature; waves