Preference and availability of food resource explains contrasiting life-history traits of sympatric unionoid mussels(Unio douglasiae and Lanceolaria grayana)

For better management of biodiversity, it is imperative to understand process that allows sympatric occurrence of related species. Sympatric species can differ in various life-history traits which have presumably been selected under surrounding environmental constraints. We examined the preference and availability of food resource for two sympatric species of unionoid mussels, U. douglasiae and L. grayana, in relation to their mobility and growth characteristics (i.e., growth rates and longevity). Field survey was conducted in floodplain water bodies (FWB) of Kiso River, Japan. Mobility was determined by mark-recaptures of individuals. Growth characteristics were determined by repeated measures of bagged individuals. Bagged individuals were eventually sacrificed and measured for C/N stable isotope ratio together with potential food resources. Unio douglasiae grew faster, and was shorter-lived and more mobile, compared with L. grayana; the former selectively fed on seston (largely phytoplankton) whereas the latter showed broader food selection. Primary productivity gradient explained the FWB-scale habitat distribution of two species. Observed life-history traits matched beneficial surviving strategies in respective habitat, suggesting the role of specialization of trophic position for their sympatric occurrence.

Effects of turbid water on periphyton vary with velocity

Various methods which discharge sediments in dam reservoirs have recently been implemented. Highly turbid water is run off to downstream regardless of any methods, but the effects on stream ecosystem are poorly understood. Experimental studies have shown that turbid water has negative effects on benthic periphyton. However, many of the studies have examined at slower velocity than at that actually observed in effluent floods. Thus, we examined effects of velocity and turbid water (suspended solids) on benthic periphyton, using experimental channels which can provide high velocity (0.5 ? 4.0 m/s). Inorganic matter in periphyton increased with suspended solids. On the other hand, effects of suspended solids on chlorophyll a depended on velocity. Although chl. a did not vary with suspended solids in low velocity (0.5 m/s), that increased with suspended solids in high velocity (4.0 m/s), suggesting that inorganic layer formed on the surface of periphyton may prevent abrasion of algae. This study indicates that effects of sediment discharge on benthic periphyton vary with contents of suspended solids and velocity.

Effects of bed load on primary production in streams

Bed load would be a factor to decrease primary production of epilithic algae in gravel bed streams through the disturbance of stream bed, the processes of the decrease, however, have not been recognized well. In this research, we examined how bed load decreased primary production based on large scale experiments and a numerical model. An experimental stream with bed load supply consisting of sand indicated lower primary production, same level of standing crops of epilithic algae (chl-a) and higher areal cover ratio of sand, compared with a experimental stream without bed load supply. Algal standing crop had been expected to be lowered by “abrasion effect”, this result, however, showed that the increase of areal cover ratio of sand was thought to be a dominant process (cover effect) because instable materials were not suitable for epilithic algae. A numerical model to predict algal standing crop, in which primary production, abrasion and cover effect were incorporated into, showed that cover effect increased as the accrual of bed load, but abrasion effect could be weakened if resources for algal growth are abundant.

Restoration strategies of floodplain water bodies for conservation of endangered deepbody bitterling fish

<em>A. longipinnis</em> is endemic to Japan and designated as natural monument while its distribution is rather patchy and population viability is in serious doubt. Bitterling fish spawn in live unionoid mussels, remains, and hatch inside mussels during their development periods till emerging as larvae (i.e., parasitism or commensalism). Floodplain water bodies (FWBs), which are either connected to or isolated from the main channel, provide one of major habitat for bitterling fish. Deteriorations of floodplain habitat are manifested after 1970s as a result of riverbed degradation and concurrent floodplain terrestrialization. Thus, there is an urgent need to understand habitat requirements of <em>A. longipinnis</em>, including host mussel distribution, and habitat stability, to develop effective habitat restoration strategies. We examined distribution of <em>A. longipinnis</em> and measured physical habitat environment in 104 FWBs. Occurrence of <em>A. longipinnis</em> were predicted in FWBs having large surface area, abundant mussels, high connectivity to neighboring FWBs, and being sheltered from flood shear stress. With habitat and species distribution relationships, restoration strategies for <em>A. longipinnis</em> are discussed with some sites being planned for or already manipulated with experimental treatments.