Vertical distribution of Limacina helicina larvae in the Pacific sector of the Arctic Ocean during autumn

Abstract

Limacina helicina, a species of Pteropoda (Cuvier, 1804), plays an important role in the food web and carbon cycle in subpolar and polar regions. The presence of aragonite unsaturated water in the Pacific sector of the Arctic Ocean necessitates the need to examine damage caused by ocean acidification on species with aragonite shells. According to previous studies that examined the impact of acidification on shell-bearing species by employing incubation experiments, young stages (veligers and juveniles) are more vulnerable than adults. In the present study, vertical distribution of the young stages of L. helicina in the Arctic Ocean during autumn was observed to evaluate the effects of environmental factors on their distribution. Veligers and juveniles showed high abundances from the surface to 30 m depth in the basin regions around the Chukchi Plateau (Stations 39, 45, and 49) but were restricted to a depth of 20–30 m, overlying a strong halocline formed by the inflow of less saline water. Veligers were predominant in the basin regions, indicating that active reproduction occurred in September. Since adult females involved in reproduction were abundant in the shelf regions, their reproduction patterns varied with different periods and regions. Unsaturated aragonite waters and damaged shells were not observed in the study area, possibly due to dilution by sea ice melt water inflowing from the shelf regions. This study showed that the distribution of the young stages of L. helicina was predominantly concentrated in the upper 30 m of the basin due to stratification with a strong halocline in the shallow layers caused by the inflow of sea ice melt water.