Survival, growth, and radula morphology of Haliotis kamtschatkana postlarvae fed six species of benthic diatoms

Haliotis kamtschatkana is the only abalone native to the Pacific Northwest of North America. Haliotis kamtschatkana populations are in decline, and current restoration efforts in Washington State rely on out-planting hatchery-produced juveniles. Hatchery personnel report highest mortalities in the postlarval stage of H. kamtschatkana, mainly during the first 3 to 6 months. Postlarvae feed on films of benthic diatoms, and the purpose of this study was to test six diatom species (Achnanthes brevipes, Amphora sauna, Amphiprora paludosa, Cylindrotheca closterium, Navicula incerta, and Nitzschia laevis) as suitable diets for H. kamtschatkana. Diatom diet suitability might rely on several factors, including diatom characteristics as well as the postlarva's ability to ingest the diatoms. The radula is a crucial feeding structure for gastropods and may display morphological plasticity, but this has never been characterized in H. kamtschatkana. We investigated survival, growth, and radula morphology of H. kamtschatkana postlarvae when fed one of six benthic diatom species for 61 days post-settlement. Amphora sauna yielded the highest survival, in a statistically homogenous subgroup with N. incerta, A. paludosa, and C. closterium. Achnanthes brevipes yielded exceptionally low survival, on par with a starvation control. Cylindrotheca closterium yielded significantly better growth than all other diets except A. sauna. Radula development was similar to that of other abalone species. The shape and size of the radula did not explain success or failure of any of the diatom diets since the radula morphology of H. kamtschatkana was comparable to other abalone that have succeeded when fed these same diets. We found no relationship between diatom diet and radula morphology. We recommend A. sauna as a suitable diet for newly settled H. kamtschatkana postlarvae, and that a combination of A. sauna and C. closterium be used to supplement feeding on naturally occurring biofilms.

Automated summary

Haliotis kamtschatkana, the only abalone species native to the Pacific Northwest of North America, is facing population decline. This study examined the suitability of six diatom species as diets for H. kamtschatkana postlarvae. Among the diatom species tested, Amphora sauna was found to be the most suitable diet for newly settled postlarvae, with Cylindrotheca closterium as a suggested supplement. Radula morphology did not appear to be related to the success or failure of the diatom diets.