Food sources for Ruditapes philippinarum in a coastal lagoon determined by mass balance and stable isotope approaches.
The relationship between the food demand of a clam population (Ruditapes philippinarum (Adams & Reeve 1850)) and the isotopic contributions of potential food sources (phytoplankton, benthic diatoms, and organic matter derived from the sediment surface, seagrass, and seaweeds) to the clam diet were investigated. In particular, we investigated the manner in which dense patches of clams with high secondary productivity are sustained in a coastal lagoon ecosystem (Hichirippu Lagoon) in Hokkaido, Japan. Clam feeding behavior should affect material circulation in this lagoon owing to their high secondary productivity (ca. 130 g C m(-2) yr(-1)). Phytoplankton were initially found to constitute 14-77% of the clam diet, although phytoplankton nitrogen content (1.79-4.48 kmol N) and the food demand of the clam (16.2 kmol N d(-1)) suggest that phytoplankton can constitute only up to 28% of clam dietary demands. However, use of isotopic signatures alone may be misleading. For example, the contribution of microphytobenthos (MPB) were estimated to be 0-68% on the basis of isotopic signatures but was subsequently shown to be 35 ± 13% (mean ± S.D.) and 64 ± 4% (mean ± S.D.) on the basis of phytoplankton biomass and clam food demand respectively, suggesting that MPB are the primary food source for clams. Thus, in the present study, the abundant MPB in the subtidal area appear to be a key food source for clams, suggesting that these MPB may sustain the high secondary production of the clam.
Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan ; Faculty of Environmental and Symbiotic Science, Prefectural University of Kumamoto, Tsukide, Kumamoto, Japan.
Tomohiro
T
Komorita
Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
Rumiko
R
Kajihara
Faculty of Environmental and Symbiotic Science, Prefectural University of Kumamoto, Tsukide, Kumamoto, Japan.
Hiroaki
H
Tsutsumi
Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
Seiichiro
S
Shibanuma
Nishimuragumi Co. Ltd., Hokkaido, Japan.
Toshiro
T
Yamada
Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
Shigeru
S
Montani
D000818:Animals; D049872:Bivalvia / Q000254:growth & development / Q000502:physiology*; D002247:Carbon Isotopes; D004032:Diet; D017753:Ecosystem; D005502:Food; D020387:Food Chain; D005843:Geography; D007553:Isotope Labeling / Q000379:methods*; D007564:Japan; D009587:Nitrogen Isotopes; D010839:Phytoplankton / Q000502:physiology; D011157:Population Dynamics; D012621:Seasons; D012623:Seawater
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes