Drift macroalgae as a potential dispersal mechanism for the white abalone Haliotis sorenseni

The endangered white abalone Haliotis sorenseni, Bartsch 1940 is distributed throughout the Southern California Bight and northern Baja California, a range of 900 km, despite a short 5 d larval dispersal stage. Casual observation of 1 to 3 yr old white abalone during routine monitoring of hatchery-raised individuals revealed behavior that may provide an alternative long-range dispersal mechanism. Two new behaviors were observed during this study. Juvenile and young adult white abalone assume a 'standing' position in response to the presence of a drifting substrate. Many then 'climb' onto fragments of drifting kelp Macrocystis pyrifera, other benthic macroalgae, and drifting substrates in flumes. Such behavior has not previously been described for any abalone species. To test the frequency and duration of the behavior, fragments of macroalgae typically found in white abalone habitat were passed down a flume stocked with juvenile and young adult white abalone. An average of more than 6% of the abalone climbed onto M. pyrifera during the short 20 s transit time of the algae down the flume. Significantly more abalone (p < 0.01) climbed onto M. pyrifera than any other test substrate, including 2 other macroalgae species and a rubber test substrate. Trials with red abalone resulted in no instances of standing or climbing behavior. Duration of white abalone attachment on kelp suspended in the water column in the laboratory was prolonged (up to 51 d in tests). Such behavior in the wild could result in transport distance of 100s of km. The movement of the drift algae may bring it and the rafting abalone to isolated rock outcrops that are adult habitat. Algal rafting could potentially transport individual or groups of juvenile and early adult abalone far beyond the range of larval dispersal.