Settlement of abalone larvae (Haliotis laevigata Donovan) in response to non-geniculate coralline red algae (Corallinales, Rhodophyta)

Settlement trials with larvae of the abalone Haliotis laevigata and three s pecies of nongeniculate coralline red algae (NCA) revealed a species-specif ic response. The number of settled larvae was significantly greater on Spor olithon durum than on two other species of NCA (Mesophyllum engelhartii and Hydrolithon rupestre) co-occurring in the habitat. Settlement on Sporolith on durum commenced immediately after competent larvae were added. When offe red a choice between two growth-forms of S. durum, larvae initially preferr ed the more complex lumpy growth-form to the encrusting growth-form, but th is result was not significant after 48 h. This indicates that surface chara cteristics of the species influence settlement of Haliotis laevigata, but a re not the main factors. When the algal thallus was damaged, the number of settled larvae was greater on damaged than on undamaged pieces of Sporolith on durum and Mesophyllum engelhartii, but less on damaged pieces than on un damaged pieces of Hydrolithon rupestre. Settlement on Sporolithon durum was also significantly greater when the photosynthetic pigments in the outermo st cells of the thallus were present. These results indicate that inducers of settlement are highly variable and dependent on both the NCA species and species-specific characteristics. No larvae settled on the bottom or sides of the jars, suggesting that the inducers of settlement may not be soluble in water after their release from the algal thalli. Alternatively, inducer s an not released in a large enough concentration, even when the algal thal lus has been damaged. We conclude that the inducers are algal in origin. La rvae of the abalone Haliotis laevigata do not settle gregariously in respon se to recently-settled conspecific larvae. Gregarious settlement behaviour was, however, observed with 7-day-old conspecifics. (C) 1999 Elsevier Scien ce B.V. All rights reserved.