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

摘要

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#x2009;+#x2009;diatoms) and without diatoms (CCA#x2009;#x2212;#x2009;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#x2009;+#x2009;diatoms grew well (53.4 #xB1; 2.4 #x3BC;m/day; mean #xB1; SE and 85.0 #xB1; 4.0 #x3BC;m/day; mean #xB1; 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 #x2212; diatom at the week 1. However, the mean growth rate of abalone on CCA #x2212; diatoms from the second to fifth week (24.4 #xB1; 1.9 #x3BC;m/day; mean #xB1; SE) was significantly lower than that of individuals on CCA + diatoms and the younger post-larvae on CCA #x2212; diatoms reached only 1 mm shell length in 5 weeks. The older post-larvae also did not grow well (27.8 #xB1; 3.3 #x3BC;m/day; mean#xB1; SE) on CCA #x2212; diatoms and did not reach 3 mm by the end of the experiment. On CCA + diatoms, 74.6 #xB1; 2.0 (mean #xB1; 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 #x2212; diatoms decreased rapidly until the second week, and 25.0 #xB1; 12.6 (mean #xB1; 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.