The importance of flow and settlement cues to larvae of the abalone, Haliotis rufescens Swainson

In now rank experiments, I tested the relative importance of active and passive processes to larvae settling on manufactured casts that were hydrodynamically rough at a small scale (mm to <1 cm). I predefined two distinct regions of small-scale flow that I used to manipulate larval settlement behaviour of the red abalone Haliotis rufescens Swainson. The larvae show a stringent settlement response associated with coralline red algae. Haliotis rufescens larvae settled preferentially to an inducer regardless of the flow conditions, as expected. However, the ability of H. rufescens larvae to show this stringent behaviour was altered by changing the small-scale Row. When the free-stream velocity was low, the larvae responded to a settlement cue regardless of the smalt-scale hydrodynamics. When free-stream velocity was higher, the larvae acted increasingly as passive particles in their deposition, but settled only in response to an inducer. The results were consistent in two now tanks, across 2 years and between different batches of larvae. (C) 2000 Elsevier Science B.V. All rights reserved.