Survival and growth rates of post-larval abalone Haliotis discus hannai fed conspecific trail mucus and/or benthic diatom Cocconeis scutellum var. parva

Abstract

The settlement rate and growth rate of post-larval Haliotis discus hannai were compared in the laboratory when raised on the following three experimental substrata. (1) Mucus: trail mucus of juvenile H. discus hannai (3 cm in shell length); (2) diatom: monoculture of the benthic diatom Cocconeis scutellum var. parva; (3) diatom and mucus: C. scutellum var. parva coated with trail mucus of juvenile abalone. The mean percentage of larvae that settled were 48.7 on mucus, 98.0 on diatom, and 97.3% on diatom and mucus substrata. All post-larval abalone that settled on the mucus substratum died by the end of the third week, with a mean shell length during the third week of 711.9 μm. Individuals on the diatom substratum died by the end of the second week, with a mean shell length during the second week of 481.6 μm. Post-larvae on the diatom substratum and on the mucus substratum did not reach 800 μm in shell length; the size at which they are able to utilize the cell contents of C. scutellum var. parva. In contrast, on the diatom and mucus substratum, 70.0% of the individuals survived to the end of the experimental period (4 weeks). Individuals on the diatom and mucus substratum grew well over the entire experimental period and reached approximately 1.4 mm in shell length 4 weeks after settlement. Post-larvae reared on the diatom and mucus substratum grew to more than 800 μm by feeding initially on the trail mucus of conspecific juveniles, which was probably supplemented with extracellular diatom mucus and decomposed cells of the diatom. Once they reached about 800 μm, they were able to access diatom cell contents.