Abstract
Fisheries activities can play an important role in the uptake of nutrients flowing from land to the sea. An example that illustrates such uptake is the role of Nori (Porphyra) culture in nutrient dynamics. However, nutrient supply may influence the quality of the fishery product, and frequent discoloration of cultured Nori has been a serious problem in recent years, in Japan. This study focused on Bisan-Seto, located in the eastern part of the Seto Inland Sea, as a production area of Nori. Areas prone to damage were identified and the relationship between Nori production density and nutrient supply to the culture farms were analyzed. In Okayama prefecture there was no variation in Nori production through time as the crop aged. In 2002, there was a significant decrease in Nori production in the eastern part of Bisan-Seto, which is an area of large-scale production. The average nutrient distribution from February 1995 to February 2006 was below 3μg-at L-1. At these values, Nori discoloration is inevitable. Thus, Bisan-Seto seems to be an area of the sea where Nori culture is prone to damage. Furthermore, in the Tosan area located in the eastern part of Bisan-Seto, the tidal current was weak, with an average velocity of less than 10 cm sec-1. Such a weak current may result in an insufficient supply of nutrients. Damage to Nori culture occurred in eastern Bisan-Seto, where Nori production per unit area was high given the nutrient fluxes experienced there. These results suggest that the balance between nutrient supply and culture density is a factor influencing damage to Nori culture.
