環境

本研究では、フロリダマミズヨコエビと日本在来種ヨコエビとの形態と行動による識別点を明確にした。これにより多摩川水系を中心に関東各地（神奈川県、千葉県、埼玉県のさまざまな水系）におけるフロリダマミズヨコエビの分布調査が可能になり、各地での調査が進展し、現状が把握できた。これまで報告がなかった日本各地からの情報も集積された。 多摩川の二子橋（世田谷区）周辺では、フロリダマミズヨコエビの周年を通した定量サンプリングを行い繁殖時期や世代交代に関するデータを収集した。また同地点においてフロリダマミズヨコエビの環境選好性を明らかにするため、礫底河床において深度別のサンプリング、流速や底質の組み合わせによる微生息環境ごとの定量採集を行った。分散過程を推定する基礎情報を集積する目的で、塩分濃度に対する生理的耐性を飼育実験により明らかにした。また水鳥に付着しての拡散を確認するための予備的な実験観察と直接観察を行った。 フロリダマミズヨコエビの増加の著しい地点において、過去の群集構造との比較を行い、新たな外来動物によって群集構造にどのような変化が生じたかを解析し、フロリダマミズヨコエビという淡水小型甲殻類が生態系におよぼす影響を考察した。

This study clarified the keys for identifying Crangonyx floridanus Bousfield from the indigenous freshwater amphipod species based on morphology and behavioral characters. By means of these keys, it has become possible to research the distribution of Crangonyx floridanus in various areas in the Kanto Region (various water systems in Kanagawa Prefecture, Chiba Prefecture and Saitama Prefecture), focusing primarily on the Tama River system; studies were conducted in each area and the research team was able to gain an understanding of the current situation. This study also accumulated information from various regions of Japan, regarding which there had hitherto been no reports.
In the area around the Futago Bridge (in Setagaya-ku) over the Tama River, quantitative sampling of Crangonyx floridanus was carried out throughout the year, and data was gathered concerning the life cycle (breeding and growth periods) of these organisms. Moreover, in order to clarify the environmental preference of Crangonyx floridanus at this location, sampling was conducted at various depths on the gravel-base riverbed, and quantitative sampling was also conducted in relation to habitat variables, such as current velocity and bottom sediment characteristics.
With the aim of accumulating basic information for forecasting the spread of carngonycitd, the physiological resistance to saline concentrations was clarified in laboratory experiments. Moreover, preliminary experiments and direct observation were carried out in order to identify invasion pathways, such as “transportation” like attachment to waterfowl.
In areas where there has been a marked increase in Crangonyx floridanus, recent sampling data were compared with previous ones to analyze the change in community structures as a result of this new alien species, and the impact of the small freshwater crustacean Crangonyx floridanus on the ecosystem was assessed.

金田彰二（日本工学院専門学校）、石綿進一（神奈川県環境科学センター）、清水高男（淡水ベントス研究所）、平良裕之（千葉県立中央博物館）、佐竹　潔（独立行政法人　国立環境研究所）

Shoji Kanada (Nihon Kogakuin College)Shin’ichi Ishiwata (Kanagawa Environmental Research Center)Takao Shimizu (Freshwater Benthos Associates)Hiroyuki Taira (Natural History Museum and Institute, Chiba) Kiyoshi Satake (National Institute for Environmental Studies)