Marine Biology (2006) 149: 1185–1197 DOI 10.1007/s00227-006-0298-0 RESEARCH ARTICLE Paolo Magni · Serena Como · Shigeru Montani Hiroaki Tsutsumi Interlinked temporal changes in environmental conditions, chemical characteristics of sediments and macrofaunal assemblages in an estuarine intertidal sandflat (Seto Inland Sea, Japan) Received: 11 November 2005 / Accepted: 20 January 2006 / Published online: 21 March 2006 © Springer-Verlag 2006 Abstract Five Weld surveys were conducted in an estu- sation of macrofauna, initiated by few opportunistic arine intertidal sandXat of the Seto Inland Sea (Japan) polychaetes (e.g., Cirriformia tentaculata and Polydora between April 1994 and April 1995. Chlorophyll a, sp.), apparently promoting a fast sediment recovery in pheopigments, total organic carbon and acid-volatile winter, and followed by new bivalve recruits in the next sulphides (AVS) of surface and subsurface sediments, spring. This study provides the Wrst evidence of signiWcant and macrofaunal assemblages were investigated in par- and interlinked within-year changes in chemical char- allel at 15 stations. Monthly hydrological data of low- acteristics of sediments and macrofaunal assemblages tide creek water adjacent to the Xat were used as a com- in an estuarine intertidal Xat at a small spatial scale (i.e., plementary environmental characterisation of the tens of meters). This demonstrates the high temporal study area. Strong temporal changes were found among variability of species–environment relations in these sampling dates, most remarkably in autumn with a systems and a close relationship in seasonally driven major increase of algal detritus and AVS, a sharp trophodynamic processes among primary producers reduction in macrofaunal abundances and species rich- and benthic consumers. We conclude that a thorough ness, and a massive mortality of the clam Ruditapes parallel evaluation of the temporal changes in chemical philippinarum. This dystrophic event was preceded by a characteristics of sediments should be taken into photoautotrophic and hypertrophic spring–summer account in assessing the year-round distribution and characterized by abundant fresh (i.e., living) algal mate- changes of intertidal macrofauna, particularly in eutro- rial, including microphytobenthos and macroalgae phic, estuarine intertidal Xats. (Ulva sp.). In summer, abundant macrofaunal assem- blages 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 Wlter-feeding bivalves Musculista Introduction senhousia and R. philippinarum. These are among the highest values reported in the literature for sedimentary Numerous studies on sandy beaches have recognized shores. From autumn, there was a progressive recoloni- physical forces (e.g., tidal level and beach morphody- namic states), environmental harshness (e.g., sediment instability) and sediment bulk properties (e.g., grain size) as major factors aVecting macrofaunal distribution Communicated by R. Cattaneo-Vietti, Genova (Dexter 1984; Allen and Moore 1987; Jaramillo et al. 1993; Brazeiro and Defeo 1996; James and Fairweather P. Magni (&) · S. Como IMC – International Marine Centre, Località Sa Mardini, 1996; McLachlan 1996; Defeo and McLachlan 2005). In Torregrande, 09072 Oristano, Italy tidally dominated estuarine Xats, benthic animals are E-mail: [email protected] also exposed to a highly dynamic environment, as related to tidal state and amplitude, current velocity and sedi- S. Montani Graduate School of Environmental Science, ment morphodynamics (Grant 1981; Renshun 1992; Hokkaido University, Kita 13 Nishi 8, Dyer et al. 2000; Magni and Montani 2005). Accord- Kita-ku, Sapporo, 060-0813 Hokkaido , Japan ingly, intertidal macrofauna possess a variety of capacity adaptations (sensu Gillmor 1982) to cope with the eVect H. Tsutsumi Faculty of Environmental & Symbiotic Sciences, of physical variables, including changes in mechanical Prefectural University of Kumamoto, activity (Tamaki 1987; Richardson et al. 1993) and feed- 3-1-100 Tsukide, 863-8502 Kumamoto , Japan ing behaviour (Miller et al. 1992; Hawkins et al. 1996; 1186 Karrh and Miller 1996). Along with species-speciWc extended studies on sediment characteristics and micro- adaptational strategies, estuarine macrofauna tend to phytobenthic assemblages (Magni and Montani 1997; associate in patchy assemblages (Reise 1979; Thrush Magni et al. 2000a; Montani et al. 2003), water chemistry 1991; Morrisey et al. 1992; Crooks 1998) and may (Montani et al. 1998; Magni and Montani 2000), and remain relatively stable in terms of their spatial distribu- benthic macrofauna (Magni and Montani 1998; Magni tion (McArdle and Blackwell 1989; Krager and Woodin et al. 2000b). Complete emersion of the study area occurs 1993), even where the sediment and organisms are twice a month, during a spring low tide, at about +50 cm mobile (Hewitt et al. 1997). Ysebaert and Herman (2002) the local (Takamatsu port) mean sea level (Magni and assessed the inXuence of environmental variables (e.g., Montani 1998). Duration of sediment emersion varies mud content, chlorophyll a (chl a), bed-level height, between few hours per cycle in December–January to salinity, tidal current velocity) on the interannual vari- less than 1–2 h/cycle in September–October (Magni and ability of estuarine intertidal macrofauna at various spa- Montani 1998). At low tide, a creek of the river Shin con- tial scales, varying from kilometres to metres. They nects the upper estuary to the rear to the adjacent sub- showed that on larger (104–103 m) spatial scales “assem- tidal zone (Fig. 1). blages and individual-species abundances correlate sig- niWcantly with the environmental variables that are Field sampling inXuenced by geomorphological changes” (Ysebaert and Herman 2002). Samplings were conducted at low tide at 15 stations In addition to physical variables, especially in estua- randomly chosen within a surface area of about rine tidal Xats, re-suspension and deposition of organic 50£100 m and were repeated on Wve diVerent dates matter from the overlying water, in situ processes of between spring 1994 and spring 1995: 25 April (spring micro- and macroalgal production and decompositon 94, Sp94), 22 July (summer, Su), 25 October (autumn, A) tend to be high and strongly Xuctuating throughout the and 20 January (winter, W) 1994, and 15 April 1995 year (Heip et al. 1995; Magni and Montani 2000; (spring 95, Sp95). At each sampling station, emerged Montani et al. 2003). These processes suggest that the sediment samples were collected for geochemical analy- chemical characteristics of sediments may also have sis at seven to eight locations using an acrylic core tube major implications on the composition and temporal (3 cm i.d.) gently pushed by hand into the sediment. The changes of macrofaunal assemblages. On the other hand, surface (0–0.5 cm) and subsurface (0.5–2 cm) layers few Weld studies are available in this regard (Castel et al. were carefully sliced oV the sediment. Sediment samples 1989), especially on a year-round basis in estuarine from the same layer were pooled together and brought intertidal sandXats. to the laboratory within 2 h for further treatment and This work is a follow-up of a multi-year study on the chemical analysis. Duplicate sediment samples for mac- cycling of biophilic elements (C, N, P, Si) conducted in a rofauna were collected at each station using a 100-cm2 tidal estuary of the Seto Inland Sea, Japan (e.g., Magni stainless steel core (10 cm in depth) and sieved on a 1998; Montani et al. 1998; Magni and Montani 2000). In mesh size of 1 mm. The residue of each replicate was the present work, we investigated the year-round distri- separately Wxed in a 10% buVered formaldehyde solu- bution of hydrological features of low-tide creek water, tion, stained with rose Bengal. chemical characteristics of sediments and macrofaunal Low-tide ebbing water near the emerged Xat was assemblages in the lower part of the sandXat. We aimed monitored at two creek stations monthly between 1994 to evaluate the temporal changes in both environmental and 1996, as extensively reported in Magni and Montani variables, including sediment chl a, pheopigments, total (2000). We present here the mean values of major hydro- organic carbon (TOC) and acid-volatile sulphide (AVS), logical variables most relevant to this study [i.e., temper- + and macrofauna, and to assess their relationships. This ature, salinity, dissolved oxygen (DO), NH4-N, chl a, work is intended to assess temporal patterns, links and pheopigments, particulate organic carbon (POC) and trophodynamic processes among primary producers and total suspended matter (TSM)] and redirect for details benthic consumers of an estuarine intertidal sandXat on water sample treatment and analysis to our compan- occurring on a year-round basis at a small spatial scale ion paper (Magni and Montani 2000). (i.e., tens of meters). Sediment sample treatment and analysis In the laboratory, chl a and phyto-pigment degradation Materials and methods products (pheopigments) were extracted from duplicate subsamples of wet sediment (about 1 g) using 90% ace- Study area tone. After 24 h of darkness at 4°C, the samples were sonicated for 5 min, centrifuged at 3,000 rpm (1000 g) We conducted the investigations on a sandXat of the for 10 min, and extracts were spectrophotometrically Seto Inland Sea, southwestern Japan (Fig. 1). The Xat is analysed (Jasco, Uvidec¡320). Chl a and pheopigment located in a mixed-semidiurnal