Hard clams of the genus Meretrix are known to excrete a long, thick cord of mucous from the base of their siphons, but few studies have examined the clams' use of this mucous cord as a means of passive locomotion, which may result as the cord is dragged about by water currents. In the present study of Meretrix lusoria, an inhabitant of intertidal sand flats, clam migration via the mucous cord was quantified over the course of a year in the intertidal zone of the Shirakawa River estuary in Kumamoto, Japan. After tidal emersion, many M. lusoria were found among cobbles flanking a roadway across the tidal flat, evidently having been stranded there while being dragged. Stranded clams were most abundant during spring tides from March to June. Most of them were of 25–40 mm in shell length (SL) whereas most clams in the nearby sandflat were under 15 mm in SL. Furthermore, the clams stranded among the cobbles were slightly lighter than those of the same SL found buried in the sand flat. In a laboratory study using clams of 20–60 mm SL, those of 25–30 mm SL secreted mucous actively under the influence of a strong flow of seawater. In a filed experiment, out-migration occurred more frequently in lighter clams than in heavier ones. Passive migration by means of the mucous cord might be an adaptive behavior of M. lusoria, providing a mean of escape from the poor food habitats.

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Habitat characteristics of the endemic Japanese crayfish, Cambaroides japonicus, were investigated with reference to riparian vegetation and macro-invertebrates. During April and October, 2002, 31 brooks and seven lakes were surveyed throughout the Shiribeshi Province of Hokkaido, Japan. Crayfish habitats were characterized by broadleaf (deciduous) trees dominated by Acer mono, in areas that were also the typical habitat of amphipods (Gammaridea). Crayfish did not occur in brooks covered by the coniferous tree Larix kaempferi. Such habitats were inhabited by haplotaxid oligochaetes, but not amphipods. In a laboratory experiment using the four potential diets, deciduous leaves (A. mono), conifer needles (L. kaempferi), dried amphipods (Gammaridea), and deciduous leaves of A. mono together with dried amphipods, juvenile crayfish grew and survived until Stage VI when offered amphipods only and deciduous leaves together with amphipods. In contrast, crayfish did not survive beyond Stage III when reared with only deciduous leaves or conifer needles. It is possible that the rich crude protein (over 34% in content) and fat (over 9%) in amphipods serve as important energy sources for the growth and survival of juvenile crayfish.

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The effects of a macroalgal mat (Ulva spp.) on the density, biomass, and composition of meiofauna were studied on intertidal sand flats at Zigozen beach in Hiroshima Bay. The density of nematodes and copepods in alga-covered sediment tended to be higher than that in unvegetated sediment. The biomass of meiofauna in sediment beneath the macroalgal mat was also higher than that in unvegetated sediment. A laboratory experiment demonstrated an increase in the density of copepods and nauplii in sand to which Ulva spp. was added, compared to control sand without algae. In addition, in the field the species composition of nematodes in alga-covered sediment was different from that in unvegetated sediment. In unvegetated sediment, the most dominant species of nematode was Desmodora sp. 1 (23%), but Dichromadora spp. were dominant in sediment covered by a macroalgal mat (27%). These results suggest that the macroalgal mat stimulates the population growth of some species of nematodes and copepods, which then contribute to the decomposition of the algae.

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