Ecosystem and Fishery of Manila Clam (Ruditapes philippinarum) in Ise-Bay Related to Eco-Compatible Management of Its River Basin Complex

Abstract

Ise bay, Japan, is located at the river mouth of 10 class-A rivers, and its environment is closely related to management of their river basin complex (RBC). We developed a model to describe the ecosystem of RBC by developing three tool boxes: TB1 to describe the water/material flux network, TB2 to describe ecosystem mechanism in various categories of landscapes, and TB3 to standardize ecosystem services received at local sites and integrate them throughout RBC. Ecosystem has a function to change the fluxes, which is evaluated by TB2, and such flux change can be fed back to the flux networks in TB1. The outputs of the fluxes from the RBC are inputs for currents of water with various qualities to the bay, which can be computed by bay-dynamics modeling. Then it provides various fluxes from the bay interior to landscapes located along coastal zone, and it supports ecosystem there. Fishery is a kind of ecosystem service there. We focused on bivalve, Manila clam ( Ruditapes philippinarum ) because it uses various landscapes in a bay through its life cycle and it provides fishery activity as ecosystem service. We have developed TB1 and TB2 also in bay area successfully. Then, we evaluate the transition of quality of environments of RBC including Ise bay from the past to the present by using TB1-TB3 for river basin and bay area. Furthermore, we forecast the future situation and then we discuss how we can improve it through various combinations of measures and policies in the RBC as well as in the bay.