A large fraction of the carbon dioxide added to the atmosphere by human activity enters the sea, causing ocean acidification. We show that otoliths (aragonite ear bones) of young fish grown under high CO2 (low pH) conditions are larger than normal, contrary to expectation. We hypothesize that CO2 moves freely through the epithelium around the otoliths in young fish, accelerating otolith growth while the local pH is controlled. This is the converse of the effect commonly reported for structural biominerals.

No abstract

No abstract

Larvae, juveniles, and adults of Japanese anchovy, Engraulis japonicus, were distributed throughout the Kuroshio‐Oyashio transition region off northern Japan as far offshore as 170°E in 1996 and 1997. The growth trajectories of individual larvae and early juveniles were backcalculated using the biological intercept method based on the allometric relationship between otolith radius and somatic length. Mean larval growth rates ranged from 0.49 to 0.71 mm day–1 in the transition region, and were comparable to those reported from the Pacific coastal waters of central Japan, which is the principal distribution range of E. japonicus. In terms of growth, the Kuroshio‐Oyashio transition region seemed to be a favourable nursery area for larval E. japonicus. Larval growth tended to decline from the inshore to the offshore waters in the transition region. Thermal conditions did not show an inshore–offshore trend in the survey area and did not explain the longitudinal trend in growth rates.

No abstract

Growth trajectories during larval to early juvenile stages in Japanese sardine ( Sardinops melanostictus ) were backcalculated based on the widths of otolith daily increments from 1996 to 2003 in the nursery grounds, Kuroshio–Oyashio transitional waters. Planktonic larvae hatched near Kuroshio have been transported northeastward from the Kuroshio waters to the transitional waters. We show that the somatic growth rates sharply increased after metamorphosis to the early juvenile stage, whereas previously, others showed that growth rate decreases during the larval stage. Otolith growth rates were more variable during the juvenile stage than the larval stage. Interannual variations in the otolith growth rate after metamorphosis explained more than 80% of variation in abundances of recruits (ca. 8–10 months old) in the Pacific coastal waters, whereas no correlation was found between the growth rate during the early larval stage and abundance. Our result was consistent with the hypothesis of growth rate-dependent recruitment success in the Kuroshio–Oyashio transitional waters.

No abstract

During periods when the population size of Japanese anchovy Engraulis japonicus is large, the abundance of 1-yr olds has been considered to be dependent on the growth and survival processes in the late larval and early juvenile stages in the Kuroshio-Oyashio transition region off northern Japan. Recent growth rates for 10 days before capture of larval and early juvenile E. japonicus were estimated and examined in relation to the surface water temperature and the available copepod density in 1997, 1998 and 1999. Late larval and early juvenile E. japonicus were distributed in the waters with temperature from 15 to 19°C and available prey density from 10 to 1000 mg dry weight (DW) m )2 in the transition region. The late larval growth rates were found to be regulated more strongly by water temperature than by copepod density in the waters <16°C, and more strongly by copepod density than water temperature in the waters <100 mg DW m )2 in the Kuroshio-Oyashio transition region. The recent growth rates decreased from the western waters to the eastern waters in the survey area 140-170°E in 1998, correlating with decreases of food availability to 50-100 mg DW m )2 . While in 1999, the recent growth rates were faster in the waters east of 150°E, resulting from eastward expansion of warm water ranges and high available prey density 100-400 mg DW m )2 .The key environmental factors regulating late larval growth rate of E. japonicus in the transition region seem to be spatially different between years.