Kelp patty neuston community structure and variation

The neuston community structure of drifting patties of the large, structurally complex brown algae Macrocystis pyrifera and adjacent open water were studied in southern California. Neuston samples were collected in Santa Monica Bay between November 1996 and January 2001. There was high overlap in the taxonomic composition of the kelp patty and open water community, but the abundances of common species were different. The density and composition of numerically dominant taxa was more variable in the kelp patty than in the open water. The inter annual variation in the kelp patty community structure appears to be related to anomalously warm water temperatures during the strong El Niño conditions that occurred in 1997. The intra annual variation in kelp patty neuston was probably the result of a combination of physical and biological processes. The densities of open water zooplankton in kelp patties increased with increasing wind speed and the magnitude of change appears to be species specific. The kelp patty density of the small pelagic harpacticoid Euterpina acutifrons was less than that of the open water at winds less than 5 m/s but more than four times greater than that of the open water during winds of 5–10m/s. Species-specific behavior within Langmuir circulation in the open water and in the wind-driven surface current within the kelp patty during winds of at least 3 m/s results in zooplankton aggregations in kelp patties.