Contribution of diatoms as food sources for post-larval abalone Haliotis discus hannai on a crustose coralline alga

Abstract

Survival and growth rates of post-larval abalone Haliotis discus hannai reared on a crustose (non-geniculate) coralline alga (CCA) Lithophyllum yessoense with diatoms (CCA + diatoms) and without diatoms (CCA − diatoms) were compared in the laboratory in order to determine the contribution of diatoms on CCA as food sources for post-larvae and the dietary value of CCA themselves. Experiments were performed for 5 weeks with two groups of different developmental stage, newly metamorphosed stage (younger postlarvae) and over 1 mm stage (older post-larvae). Both stages of post-larvae reared on CCA + diatoms grew well (53.4 ± 2.4 μm/day; mean ± SE and 85.0 ± 4.0 μm/day; mean ± SE, respectively). Younger post-larvae grew to over 2 mm in 5 weeks, and older ones reached over 4 mm in 5 weeks. There was no difference in shell length of younger post-larvae reared on CCA + diatom and CCA − diatom at the week 1. However, the mean growth rate of abalone on CCA − diatoms from the second to fifth week (24.4 ± 1.9 μm/day; mean ± SE) was significantly lower than that of individuals on CCA + diatoms and the younger post-larvae on CCA − diatoms reached only 1 mm shell length in 5 weeks. The older post-larvae also did not grow well (27.8 ± 3.3 μm/day; mean± SE) on CCA − diatoms and did not reach 3 mm by the end of the experiment. On CCA + diatoms, 74.6 ± 2.0 % (mean ± SE) of the younger post-larvae survived for the 5 weeks experiment. In contrast, the survival rate of the younger post-larvae reared on CCA − diatoms decreased rapidly until the second week, and 25.0 ± 12.6% (mean ± SE) of the individuals survived by the fifth week. The results of this study indicate that diatoms are essential for the rapid growth of post-larval abalone on the CCA. It is considered that the CCA L. yessoense itself is not principal food source for post-larval H. discus hannai from approximately 500 11m to at least 3 mm shell length.