Impacts of organic waste from a yellowtail cage farm on surface sediment and bottom water in Shido Bay (the Seto Inland Sea, Japan)

Abstract

The environmental impacts of a yellowtail (Seriola quinqueradiata) culture on sediment and water qualities were investigated at an intensive cage farm located in a coastal ecosystem (Shido Bay, the Seto Inland Sea, Japan) during low and high feeding times. The experimental design involved the establishment of surrounding sites (10m from the cages) and a transect extending away from the cage at 0, 10, 50, and 100m. The organic matter depositions were measured using sediment traps. Surface sediments and bottom water characteristics were also described. The organic depositions of the yellowtail cage farm in Shido Bay on the sediment were quite significant compared to the control site (100m from the cage) and extended to 10m around the fish farms. Due to the high organic deposition under the cage, the surface sediment showed an elevated level of organic-enriched sediments, and led to an increase in the production of sulfides. Oxygen depletion of the bottom water was accompanied by organic-enriched sediments and production of high-acid volatile sulfide (AVS) contents in the surface sediments, and caused a significant increase in ammonium (NH4+) and phosphate (PO43−) concentrations in the bottom water. As a result, impacts of organic waste from a yellowtail cage on surface sediments and bottom water quality were clearly found in Shido Bay. Statement of relevancePresent study, the organic waste impacts of a yellowtail (Seriola quinqueradiata) culture on sediment and water qualities were investigated at an intensive cage farm located in a coastal ecosystem (Shido Bay, the Seto Inland Sea, Japan) during low and high feeding times. The results indicated that dramatic impacts of organic waste from a yellowtail cage on surface sediments and bottom water differences in Shido Bay.