Effects of canopy removal on the understory algal community structure of coastal forests of Macrocystis pyrifera from southern South America

Abstract

Communities with similar physiognomy often have been expected to show similar ecological responses to experimental manipulations. This is the case in geographically disjunct communities of Macrocystis pyrifera, most of which have been described as showing notoriously similar patterns of vegetational stratification. Comparison of the ecological responses of the second and third vegetational strata to the removal of the floating canopy of M. pyrifera in forests in southern Chile point to differences with equivalent experiments performed in the northern Pacific. In southern Chile the second stratum which is formed by Lessonja flavicans decreases in biomass representation after removal of the floating M. pMfera canopy. The third stratum contains a number of fugitive species which are replaced by a numerically similar group of fugitive species after removal of the floating M. pyrifera canopy. The presence of perennial species in the third stratum seem unaffected by light changes resulting either from seasonal variation or from removal of the floating canopy. Total number of understory algal species in the forests from southern Chile is lower compared to giant kelp forests in California. Canopy removal does not significantly change the total number of species, although it changes the specific component in each experimental area. Thus, the ecological response of the understory algal community to the removal of the floating canopy of M. pyr'fera in southern Chile seems less dramatic than that which has been described for similar communities in the North Pacific Ocean.