Abstract

The Jugyo intertidal zone, located in Boryeong of Chungcheongnam-do Province on the west coast of Korea, is a well-known for natural seed production of the Manila clam Ruditapes philippinarum. In the present study, to understand the spatial distribution and density of natural seeds of wild Manila clams inhabiting this tidal flat, sediments were collected from 48 sites during mid-March in 2017 and 2018, and the density and size of the clams were measured. The collected clams were divided into five size groups (< 5mm, 5-10 mm, 10-20 mm, 20-30 mm, and > 30 mm). In addition, the clams were various ages, from spats measuring < 5 mm in length to those longer than 30 mm. In particular, during the 2017 survey, the densities of the five groups were comparable however, during the 2018 survey, over 90% of the individuals were spats of < 5 mm, whereas large individuals over 40 mm were not observed. Taken together, these results indicate that in the studied tidal flat, annual production fluctuates greatly, thus stable seed production should be induced through the continuous inhabitation of large individuals that serve as brood stock, as well as maintaining suitable sediment type.