Response of eastern Pacific giant kelp communities to ENSO-driven ocean changes

Large-scale climatic events such as the El Niño-Southern Oscillation (ENSO) have been associated with numerous impacts to aquatic ecosystem structure and population dynamics. In particular, giant kelp communities of the eastern Pacific Ocean have been affected to various degrees by storm-produced wave action and rises in ocean temperature often found during ENSO conditions. This presentation reviews the recent literature concerning the temporal and spatial dynamics of kelp forest damage, recruitment, and community structure both during and after ENSO events in the eastern Pacific Ocean. High waves may result in tearing of the kelp holdfast from the ocean floor and structural damage to the canopy. Superficial warming of ocean water limits nutrients available for kelp forest repair, growth, and recruitment. Both kelp storm mortality and recruitment density appear depth dependent. Height of the breaking waves determines the inner edge of the kelp forest while recruitment density declines with depth. Significant longshore mortality variability has been reported. Giant kelp on the longshore ends at a given depth suffered greater mortality than in the forest interior during some ENSO storm events, but fared better during the summer 1983 ENSO when greater exposure to nutrient-laden currents apparently favored survivorship. Some studies have reported alterations in community composition and trophic cascades due to modified regimes of sunlight, temperature, and food availability caused by changes in kelp abundance. However, other long-term research has found ENSO events have little effect on local-scale kelp community structure.