A restoration project of the Kumamoto oyster habitats in Haimen County, Jiangsu Province, China

Summary

The Kumamoto oyster (Crassostrea sikamea), the sole reef-building species among three oyster species coexisting on China's Liyashan intertidal reef in Jiangsu Province, had seen its reef area shrink by 38.8% over a decade due to sedimentation, habitat loss and overfishing, threatening a habitat that also serves as the primary spawning ground for the protected roughskin sculpin. Researchers from the Chinese Academy of Fishery Science tested two restoration approaches, substrate supplementation and remote oyster-spat setting, finding through 2013 surveys that substrate scarcity was the main limiting factor and that a candidate remote-setting source population had higher disease prevalence and lower genetic diversity than natural Liyashan stock, leading them to pursue substrate addition using recycled oyster shell, found more cost-effective than clam shell, brick or granite. In July 2013, about 1,000 kg of recycled shell was packed into 16,000 mesh bags and used to build 53 single- and two-layer artificial reef structures across five sites. Monitoring through May 2014 found oyster abundance on restored reefs ranging from 147 to 564 individuals per bag, with resident faunal communities reaching densities comparable to the adjacent natural reef, though most single-layer reefs were partially or fully buried by silt while taller two-layer reefs performed better, and only two of five sites showed strong results. Difficulties included unpredictable natural recruitment, persistent sedimentation, low phytoplankton availability slowing growth, and disturbance from ongoing fishing. The project rates itself successful, crediting the superior vertical structure of multi-layer shell-bag reefs for promoting larval settlement, while acknowledging silt burial undermined much of the single-layer reef effort.