Interlinked temporal changes in environmental conditions, chemical characteristics of sediments and macrofaunal assemblages in an estuarine intertidal sandflat (Seto Inland Sea, Japan) |
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Authors: | Paolo Magni Serena Como Shigeru Montani Hiroaki Tsutsumi |
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Affiliation: | (1) IMC – International Marine Centre, Località Sa Mardini, Torregrande, 09072 Oristano, Italy;(2) Graduate School of Environmental Science, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, 060-0813 Hokkaido , Japan;(3) Faculty of Environmental & Symbiotic Sciences, Prefectural University of Kumamoto, 3-1-100 Tsukide, 863-8502 Kumamoto , Japan |
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Abstract: | Five field surveys were conducted in an estuarine intertidal sandflat of the Seto Inland Sea (Japan) between April 1994 and April 1995. Chlorophyll a, pheopigments, total organic carbon and acid-volatile sulphides (AVS) of surface and subsurface sediments, and macrofaunal assemblages were investigated in parallel at 15 stations. Monthly hydrological data of low-tide creek water adjacent to the flat were used as a complementary environmental characterisation of the study area. Strong temporal changes were found among sampling dates, most remarkably in autumn with a major increase of algal detritus and AVS, a sharp reduction in macrofaunal abundances and species richness, and a massive mortality of the clam Ruditapes philippinarum. This dystrophic event was preceded by a photoautotrophic and hypertrophic spring–summer characterized by abundant fresh (i.e., living) algal material, including microphytobenthos and macroalgae (Ulva sp.). In summer, abundant macrofaunal assemblages reached the highest biomass values (455 g wet weight m−2 or 60.6 g ash free dry weight m−2), with a major contribution of filter-feeding bivalves Musculista senhousia and R. philippinarum. These are among the highest values reported in the literature for sedimentary shores. From autumn, there was a progressive recolonisation of macrofauna, initiated by few opportunistic polychaetes (e.g., Cirriformia tentaculata and Polydora sp.), apparently promoting a fast sediment recovery in winter, and followed by new bivalve recruits in the next spring. This study provides the first evidence of significant and interlinked within-year changes in chemical characteristics of sediments and macrofaunal assemblages in an estuarine intertidal flat at a small spatial scale (i.e., tens of meters). This demonstrates the high temporal variability of species–environment relations in these systems and a close relationship in seasonally driven trophodynamic processes among primary producers and benthic consumers. We conclude that a thorough parallel evaluation of the temporal changes in chemical characteristics of sediments should be taken into account in assessing the year-round distribution and changes of intertidal macrofauna, particularly in eutrophic, estuarine intertidal flats.An erratum to this article can be found at |
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