Community assembly by limited recruitment in a hypoxia-stressed soft bottom: A case study of macrobenthos in Ariake Bay

抄録

Small species often dominate benthic communities in hypoxia-stressed sites, but the organizing process has rarely been investigated. Community assembly was investigated in northwestern Ariake Bay, which is exposed to hypoxia during summer. Sampling was performed 11 times between May 2010 and May 2012. The timing and duration of hypoxia differed between 2010 and 2011, which caused a different pattern of seasonal change in the community structure between the 2 years. The community was mainly composed of small species such as Theora fragilis, Veremolpa micra, and Sternaspis scutata at all times. The exception was the large arcid bivalve Scapharca kagoshimensis. This bivalve newly settled after hypoxia in 2010 and became a dominant species of the subsequent community, whereas its density decreased greatly after hypoxia in 2011. Interestingly, new settlement of arc shells did not occur in 2011 when hypoxia was relatively moderate compared with that in 2010. These results suggest that small species dominance at a hypoxia-stressed site cannot be attributable only to repeated hypoxic devastation and quick recovery of short-lived small species but also to the variability in natural recruitment of long-lived large species. Large species cannot easily recover if low recruitment years continue, even if hypoxic conditions are moderate. Therefore, the need for more attention to recruitment variability of large species is emphasized in striving to understand community assembly and efficiently restore coastal soft bottom communities that have deteriorated due to hypoxia.