The Structure and Regulation of Some South American Kelp Communities

• Published in: Ecological Monographs
• Main Author: Dayton, Paul K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1985
• Subjects: Pacific; Antarc*; Antarctica; Tierra del Fuego
• Online Access: http://dx.doi.org/10.2307/2937131; http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F2937131; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F2937131; https://onlinelibrary.wiley.com/doi/pdf/10.2307/2937131; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.2307/2937131

The main objective of this study was to evaluate how physical stress and herbivores influence the distribution, abundance, size frequency, and mortality of the giant kelp, Macrocystis pyrifera, in the southeast Pacific. These factors were studied for the kelp and the echinoid herbivore Loxechinus albus over a wide latitudinal range (56°—42° S) of South America on RV Hero cruises in 1972 and 1973. There were large kelp forests with many large plants in the southern Isla de los Estados and Tierra del Fuego sites. Sources of kelp mortality in these sites include entanglement with drift plants and heavy encrustation of bivalves. This resulted in a considerable amount of drifting kelp, and the sea urchins appeared to have abundant food and did not attack living kelp plants. Nevertheless, the urchin densities usually were relatively low and the Loxechinus size frequencies skewed to larger size classes, suggesting that their populations may be limited by larval availability in the Westwind Drift. There were also some large kelp forests in the northern Golfo Corcovado and Isla Chiloe areas, but here the kelp forests seemed relatively ephemeral and Loxechinus appeared to be harvested by humans. The intermediate latitudes (54°—46° S) in areas semiexposed to oceanic waves were characterized by situations in which Loxechinus overexploit the kelps and maintain urchin—coralline algae "barren grounds." In these areas kelps occur only where urchin access is restricted by wave exposure, ephemeral clumps of Desmarestia ligulata, and rarely, by a predator, the asteroid Meyenaster gelatinosus. In many areas the shallow distribution of Macrocystis was restricted by competition with the large fucoid Durvillaea antarctica. These relationships were evaluated by removal and addition experiments. Much more important than latitudinal relationships to both kelp and urchin distribution and abundance patterns were exposure gradients, from shores subject to strong oceanic swells to protected fjords. Transect data suggest that Loxechinus ...