Isotopic evidence for phytoplankton as a major food source for macrobenthos on an intertidal sandflat in Ariake Sound, Japan

• Published in: Marine ecology. Progress series (Halstenbek) 2005-01, Vol.304, p.101-116
• Main Authors: Yokoyama, Hisashi, Tamaki, Akio, Koyama, Kazuki, Ishihi, Yuka, Shimoda, Katsumasa, Harada, Kazuyuki
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Diet; Estuaries; Food; Fractionation; Fundamental and applied biological sciences. Psychology; Mactra veneriformis; Marine; Microalgae; Nihonotrypaea japonica; Nitrogen; Phytoplankton; Plants; Ruditapes philippinarum; Sea water ecosystems; Sediments; Synecology; Upogebia major
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps304101

To delineate a soft-shore trophic structure, macrobenthos was collected from an intertidal sandflat at the mouth of the Shirakawa River in the central part of Ariake Sound, Kyushu, Japan, on 3 occasions in 2003 (January, March, and June to July during the rainy season), and the isotopic compositions of animals and their potential food sources were analyzed. Food sources of animals were assessed based on the diet – tissue isotopic fractionation (δ13C = 0.6 to 2.0‰, δ15N = 3.4 to 3.9‰) of 3 main constituent species (the bivalvesMactra veneriformisandRuditapes philippinarumand the ghost shrimpNihonotrypaea japonica), which had been determined by an earlier laboratory experiment. The results revealed that (1) consumers were classified into 3 groups; a group consisting of 51 species including 4 main species (the above-mentioned species and the mud shrimpUpogebia major) that derived nutrition mainly from coastal phytoplankton, one consisting of 7 species that incorporated more13C-enriched material (e.g. benthic microalgae) and a group consisting of 4 species that incorporated more13C-reduced material (e.g. riverine organic matter); (2) the phytoplankton-based trophic structure was composed of 3 trophic levels; (3)M. veneriformisjuveniles collected during the rainy season appeared to incorporate riverine organic matter; and (4) reeds from the flood plain, detrital terrestrial plant material, sewage effluents and seaweeds were not food sources for most consumers. We concluded that the high phytoplankton biomass and scarcity of benthic microalgae on this sandflat account for its phytoplankton-based trophic structure.