Environmental changes and the dynamic response of biological community along the shore of Lake Biwa

目前琵琶湖有鱼类约70种。其中包括通过将栖息地扩展到湖泊深处和开阔的近海而在湖中形成物种的鱼类，以及像大口黑鲈和蓝鳃鱼这样的外来物种。还有大约50种软体动物，其中一半是该湖特有的。然而，这些鱼类和软体动物中的许多在其一生中或在其生命的一部分中利用湖泊的浅滩和内陆水域。湖岸人类活动的历史变迁调查大部分湖岸和内陆水域自古以来就被开发成水田，但在这二三十年里，这些地区的环境又发生了变化。这种环境变化可能引起湖岸浅水、内陆水域和稻田生物群落的变化。远离湖泊的土地开发也可能影响湖岸周围的淡水生物群落，特别是对河湖间洄游的鱼类。另一方面，利用水肺对湖岸底栖动物群落结构进行了水下直接观察，发现尽管大部分水生植物被外来物种占据，但许多底栖动物不仅依赖于湖底结构，还依赖于水生植物的状况。另一种情况是，虽然琵琶湖的水位主要取决于天气条件，但在很大程度上也取决于人类的管理，但由于湖泊水位的下降，导致鱼类种群因阻止其上游迁徙而分为河流种群和湖泊种群。

There are about 70 species of fishes in the present Lake Biwa. They include fishes which have been speciated in the lake by expanding their habitat into deep and open offshore of the lake, and also the exotic species like the largemouth bass the bluegill. There are also about 50 species of molluscs, a half of them are endemic to the lake.Many of these fishes and molluscs, however, utilize the shallow shore of the lake and inland waters through or during a part of their life. The survey on the historical changes in human activities along the lake shore revealed ; the most areas along lake shore and inland waters had been developed into paddy fields from old ages, however, the environment of these area has been changed again within this two or three decades. Such environmental changes might cause the changes in biological community in shallow waters along lake shore, inland waters and paddy fields. The land development far from the lake mightalso affect on the freshwater biological community around lake shore, especially on the fishes migrating between rivers and the lake.On the other hand, the underwater direct observation with the aid of SCUBA on the community structure of benthic animals along the lake shore revealed that many benthic animals depends on not only the lake bottom structure but also the condition of aquatic vegetation though the most of aquatic vegetation is occupied by exotic species. In another case, the decrease in lake water level causes the separation of fish population into riverine and lacstrine populations by blocking their upstream migration, though the water level of Lake Biwa is basically depends on the weather condition but also largely by human management.