Role of bioturbation and interspecific relationships in determining the distribution of three species of macrobenthos on an extensive intertidal saridflat in Ariake Sound

在日本九州西部有明海峡中部白川河口一个面积为4.1km^2的潮间沙洲上，三种大型底栖动物占优势。它们是两种双壳类（菲律宾蛤仔和四角蛤蜊）和生活在深达洞穴中的鬼虾（日本鬼虾）。菲律宾蛤仔和四角蛤仔分别分布在50%的滩涂的低潮带和中潮带，而日本蛤仔则分布在其余滩涂的潮带上部。作为产生这种异域分带格局的一种可能机制，种间竞争被假定为：（1）对食物的开发竞争和（2）鬼虾对沉积物的生物扰动对双壳类的ammensalistic干扰。为了证明上述机制（1），进行了碳和氮稳定同位素研究。实验测量的饮食组织同位素分馏为 ...更多信息 实验室中的三个物种给出了鬼虾中碳的2‰的值，这与目前接受的值（0-1‰）不同。应用分馏值的现场数据显示，食物来源的三个物种，仅限于河口浮游植物。双壳类和鬼虾的种群生物量估计分别为368吨和371吨。这些结果有力地表明存在着对食物的剥削竞争。关于上述机制（2），进行了田间试验，从2× 2 m的地块和对照地块（8个重复）中排除鬼虾。然而，六个月后，没有显着差异的青少年双壳贝类密度之间的两个地块检测。在自然条件下，菲律宾蛤仔幼鱼密度在低潮带最高，其次是双壳类。后来，成年双壳类一直分散到下部区域的上部。相比之下，无论是青少年和成年M.veneriformis的密度始终是最高的中间区。不同潮带沉积物表面的稳定性存在明显差异。这强烈表明，基质的稳定性将需要为菲律宾R.的生存和M.veneriformis将适应不稳定的基质。少

Three large-sized macrobenthos dominated the benthic community on an intertidal sandflat with an area of 4.1km^2 located at the mouth of the Shirakawa River in the central Ariake Sound, western Kyushu, Japan. They were the two bivalves (Ruditapes philippinarum and Mactra veneriformis) and the ghost shrimp (Nihonotrypaea japonica) that lives in a deep-reaching burrow. R.philippinarum and M.veneriformis were distributed separately in the lower and middle tidal zones of the 50% of the sandflat, while N.japonica was in the upper zone of the rest of the sandflat. As one possible mechanism that generated such allopatric zonation pattern, two kinds of interspecific competition were postulated ; (1)exploitation competition for food and (2)ammensalistic interference by the ghost shrimp bioturbation of sediments on the bivalves. To demonstrate the above mechanism (1), carbon and nitrogen stable isotope studies were conducted. The diet-tissue isotopic fractionation experimentally measured for the … More three species in the laboratory gave the value of 2‰ for carbon in the ghost shrimp, which was different from the currently accepted values (0-1‰). The application of the fractionation values to the field data has revealed that the food sources for the three species, was restricted to estuarine phytoplankton. The population biomass of the bivalves and the ghost shrimp was estimated at 368 ton and 371 ton, respectively. These results strongly suggest the existence of exploitation competition for food. Concerning the above mechanism (2), a field experiment was conducted, excluding the ghost shrimp from a 2×2m plot with a control plot (8 replicates). Six months later, however, no significant difference in the juvenile bivalve density between the two plots was detected. Under natural conditions, the density of juvenile R.philippinarum was highest in the lowest tidal zone, which was basically followed with bivalve growth for a while. Later adult bivalves had been dispersed as far as the upper part of the lower zone. By contrast, the density of both juvenile and adult M.veneriformis was consistently highest in the middle zone. The stability of the sediment surface was contrastingly different between these tidal zones. It was strongly suggested that substrate stability would be needed for the survival of R.philippinarum and that M.veneriformis would be adapted to unstable substrates. Less