Effects on the Animal Community of Dislodgment of Holdfasts of Macrocystis pyrifera

Effects ofnatural dislodgment ofholdfasts ofM acrocystispyrifera (L.) C. Agardh on the associated holdfast community were studied during a 110-day period. Six holdfasts were collected at the beginning of the study and analyzed to determine the abundance of major taxa at time O. Forty-four holdfasts were detached from the rocky substrate and suspended on three midwater buoys to simulate natural dislodgment and drift in the kelp forest. The most abundant taxa associated with attached and drift holdfasts were decapod crustaceans, mollusks, polychaetes, ophiuroids, echinoids, asteroids, isopods, and amphipods. Only amphipods and isopods increased significantly in density in drift holdfasts during the experimental period. All other invertebrate taxa showed a decrease in abundance during the 3-month experiment. A RICH AND DIVERSE community of macronursery areas (Andrews 1945, Bayne 1964, and micro-invertebrates is associated with Jones 1971, 1972, Moore 1972, 1973b,c, 1974, holdfasts of brown macroalgae. Most of the 1978, Cancino and Santelices 1981, Ojeda and studies related to the invertebrate fauna assoSantelices 1984, Vasquez and Santelices 1984, ciated with holdfasts have a taxonomic emSnider 1985). phasis (e.g., Colman 1940, Ghelardi 1971, Storms can have a considerable effect on Moore 1971, 1973a, Quast 1971). Ghelardi M. pyrifera kelp plants by "uprooting" and (1971) identified over 150 species of invertedetaching the plants. Holdfasts are also disbrates inhabiting the holdfasts of Macrocystis lodged as the plants age, and, ind~ed, many of pyrifera (L.) C. Agardh off La Jolla, Calithe animals that burrow and feed upon the fornia, representing nine different groups of holdfasts can eventually disrupt their own organisms (Nematoda, Polychaeta, Isopoda, "homes." According to Dayton et at. (1984), Gammaridae, Caprellidae, Pelecypoda, Gasthe most important cause of mortality of tropoda, Ophiuroidea, and Chelifera). Snider established M. pyrifera plants is entanglement (1985), studying the patterns of emergence with drifting plants. The drifters, with their of demersal zooplankton associated with heavy holdfasts suspended in the water colM. pyrifera holdfasts off Point Lorna, Caliumn, slowly meander through the kelp forest, fornia, reported 22 gammarid amphipod entangling additional plants, resulting in a species. Other authors have described the "snowball effect." Dislodged plants with atecological interactions of the invertebrate tached holdfasts may drift through an estabcommunities occurring in the holdfasts. lished kelp forest for up to 18 months and Holdfasts of brown algae are important to cause 50% yearly mortality of the adult Mair-fauna-because--they-pretvide-meehanical -crocystis-population-1n-the-outer-Petint--b0ma-shelter from wave impact and bottom surge, kelp forest (Dayton et at. 1984). refuge from predators, food supply, and Processes related to the rate of change of fauna associated with drifting holdfasts may be influenced by predation, competition, abandonment, and reproduction. Vasquez and Santelices (1984) documented such processes in holdfasts of Lessonia nigrescens Bory in central Chile, and Ojeda and Santelices