WHAT SCALLOPS EAT? -STABLE ISOTOPE EXPERIMENT TO ASSESS FOOD RESOURCES FOR THE SCALLOPS WITH SUSPENDED AQUACULTURE IN LAKE SAROMA, JAPAN-

Kou Morita*, Emi Terasaki, Kimihiko Maekawa, Kouichi Sakaguchi, and Shigeru Montani
 
Graduate School of Environmental Science
Hokkaido University
Nl0W5 Kita-ku, Sapporo, Hokkaido, 060- 0810, Japan
kou-morita@ees.hokudai.ac.jp

Suspended shellfish aquaculture are carried on around the world, particularly oysters, scallops, and mussels are high proportion of all production of molluscs farming. Farming area and production of bivalve culture will increase greatly in the future, and this increased production may affect local aquatic ecosystems. Definition the carrying capacity which matches the local environment is necessary for realizing the sustainable development. To determine the carrying capacity, it is important that estimate available food resources for the suspended bivalves. Main food resources for them are suspended phytoplankton in the water column. Also they feed resuspended microphytobenthos in shallow area. Furthermore, it has been recently reported that resuspended epiphyte attached to many rope, cage, buoy and all in the culture is considerable amount of organisms for suspended bivalves. In this study, using stable isotope analysis, we estimated that available food organisms for the suspended scallop. Lake Saroma, northeastern Hokkaido in Japan, is this study site, which has the large scallop farming area of 79km2 (the total area of Lake Saroma is 150km2). The purpose of this study was to assess spatial and temporal variation of available food resources for suspended farmed scallop in Lake Saroma. Samples of stable isotope analysis were collected in three sampling stations monthly from April to November 2011. Besides, the experiment was carried out to establish the difference of δ13C and δ15N values and gut contents of scallops at three depths from May to October 2015.

The δ13C and δ15N values of scallops in Tokoro are significant different from others in 2011(FIG.1). This result showed that suspended scallops filter the different food organisms with different location. According to the result of experiment in 2015, we confirmed that there is the difference of stable isotope values of tissues with different layer. Additionally, microphytobenthos and epiphyte species appeared in gut contents. The above results suggest that epiphyte and microphytobenthos can be important food resources for the suspended scallops in culture.