DENSITY-INDEPENDENT GROWTH OF HALIOTIS-IRIS MARTYN (MOLLUSCA, GASTROPODA)

The growth rate and nutritional status of abalone (Haliotis iris) exposed to low (similar to 0.3 m(-2)) and high densities of conspecifics (similar to 15 m(-2)) was measured in 5 x 5 m experimental enclosures. Over the duration of the experiment (15 months), estimates of the percent cover of macroalgae revealed no significant difference attributable to density except for crustose coralline algae which had significantly greater cover in high density enclosures. Drift seaweed, the preferred food of Haliotis iris was always present in low abundance (<5% cover). There was no significant effect of density on the relative gut fullness or growth of H. iris, but significant variation in the dry weight of pedal muscle was due to density. Measurements of the dry weight of gonad and the ash-free dry weight of pedal muscle or gonad were otherwise similar between low and high density treatments for H. iris. Shell growth was similar among high density and low density treatments but high in relation to other populations of H. iris. Density independent growth is consistent with the feeding biology of H. iris and may apply to other species of abalone.