Coastal shallow water, particularly tidal flats, provide essential ecosystem services, with bivalves playing a key role in material cycling. This study assesses the impact of bivalves on material cycling processes in the Hichirippu Lagoon, Hokkaido, and the Midorikawa River tidal flats, the Ariake Bay, Kyusyu, Japan, to clarify the systems supporting their populations. Carbon and nitrogen stable isotope analyses of the Hichirippu Lagoon revealed that the dense clam (Ruditapes philippinarum) population mainly feeds on microphytobenthos, with daily feeding rates comparable to the standing stocks of primary producers such as microphytobenthos and phytoplankton. Long-term observations indicated that during summer, clam excretions support microphytobenthos productivity, thereby sustaining an internal nutrient cycle. Conversely, during winter, oceanic nitrate supports system productivity. In the Midorikawa River tidal flats, the maintenance of Asian mussel (Arcuatula senhousia) populations necessitates external food inputs, given that their feeding rate can reach ≤ 22-fold the primary production. The accumulation of mussel feces in sediments corresponded with the secondary production scale, highlighting feces, alongside feeding and the secondary production, as integral to material cycling. This study explores bivalve population dynamics by examining nutrient cycling, primary production, and organic matter flows, aiming to illuminate the broader ecological roles bivalves play within these ecosystems.
Tomohiro KOMORITA (Thu,) studied this question.