We used an up-to-date, a high accuracy CO 2 manipulation system to investigate the sensitivity of organisms to CO 2 acidification, rearing marine calcifiers under elevated CO 2 in running water. We evaluated the effects of elevated partial pressures of carbon dioxide (pCO 2 ) in seawater on larvae of the commercially important marine gastropod Ezo abalone Haliotis discus hannai. In larval Ezo abalone, no effect of exposure to <1100 latm pCO 2 seawater was observed in fertilization, malformation, or mortality rates until 15 h after fertilization. However, compared to control larvae in seawater (450 or 500 latm pCO 2 ), the fertilization rate and the hatching rate (15 h after fertilization) decreased with increased pCO 2 exposure (1650 and 2150 latm pCO 2 ) and the malformation rate increased significantly, with the larval shell length being smaller 75 h after hatching. These results suggest that ocean acidification will potentially impact the marine population of Ezo abalone as a human food source in the future.

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To elucidate the external cues triggering spawning of Haliotis diversicolor, changes in the gonads of adults and the occurrence of newly settled post-larvae were monitored from 2001 to 2004 in Sagami Bay, Japan. The gonad index (GI) and gonad somatic index (GSI) of both sexes began to increase between April and June 2002, peaked in September, and then decreased significantly by early October. In other years, GI and GSI were significantly lower in autumn. Between June and September in each year, almost all females had a mature ovary and most were capable of spawning, but the occurrence of newly settled post-larvae (< 500 µm in shell length) was strictly limited to the periods just after typhoons passed through the study area. The GI and GSI of both sexes also decreased significantly only after typhoon events. Although mature adults experienced various changes in seawater temperature, tidal height and lunar phase during the survey periods, evidence of spawning was observed only after typhoon events. There were no specific trends in seawater temperature and lunar phase before newly settled post-larvae were collected. Our results suggest that spawning of H. diversicolor is strongly associated with typhoon events. Most individuals had an immature ovary just after the passage of a typhoon. However, 1 mo after spawning, most individuals had a mature ovary with a high GI, suggesting that H. diversicolor requires an interval of about 1 mo between successive spawning events.

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The feeding behavior and growth of post-larval Haliotis diversicolor with initial shell lengths (SL) of approximately 500 mm (Exp. 1-1 and 1-2), 800 mm (Exp. 2), and 1200 mm (Exp. 3) were studied in a laboratory setting while they fed on four species of benthic diatom Achnanthes longipes, Cocconeis sublittoralis, Cylindrotheca closterium, and Navicula ramosissima. Exp. 1-1 and 1-2 revealed no marked differences in post-larval growth rates (mean 24-39 mm SL/day) among the diatom species. However, marked differences in growth rates among the species were revealed in Exp. 2 and 3. Three species, A. longipes, Co. sublittoralis, and Cy. closterium, produced faster growth (Exp. 2 mean 29-51 mm/day, Exp. 3 mean 36-44 mm/day) than N. ramosissima (Exp. 2 mean 18 mm/day, Exp. 3 mean 23 mm/day). Post-larvae fed N. ramosissima had lower digestion efficiency (42.8%) than those fed other diatom species (90.7-100%). Diatom extracellular substances appeared to be principally used from post-settlement to 800 mm SL, and diatom cell contents were required to produce rapid growth of larger post-larvae (>800 mm SL). It is likely that the availability of each diatom for post-larvae was affected by diatom morphology, attachment strength, frustule strength, and post-larval size.