半咸水介形虫Tanella opima Chen的种群动态研究

A STUDY ON POPULATION DYNAMICS OF THE BRACKISH-WATER OSTRACOD TANELLA OPIMA CHEN

上海芦潮港潮间带1982—1983年季节性沉积物样品中半咸水介形虫Tanella opima的种群动态调查表明,该种为多年生类型,其种群年龄和性比结构均具明显的季节性变化。繁殖活动受水温控制;4—10月产卵,水温不低于16℃;5—10月孵化,水温在20℃以上,种群在温暖季节(5—10月)由7个未成熟龄期的幼虫和成虫所组成,性比以雌性占优势;在寒冷季节(11—4月)则缺失前3个龄期的幼虫,性比以雄性为主。种群中最初2个龄期幼虫在母体壳内成长,这很可能是造成死种群和化石群中极少发现它们的原因。

The population dynamics of the brackish-water ostracod Tanella opima Chen is studied on the basisof seasonal sedimentary samples collected from a littoral location at Luchaogang,Shanghai during1982--1983. The population age and sex structures reveal that T. opima was a perennial species withconspicuous seasonal changes. Its reproduction was likely controlled by water temperature, withbreeding in the period from April to October,at a temperature of not lower than 16℃ and hatching inthe period from May to October,at a temperature above 20℃. The population consisted of adults andjuveniles of 7 immature instar stages in the warmer season (April to October)with a sex ratio in favourof females. In the cooler season(November to March)the juveniles were developed without the earliest3 instar stages and the adult sex ratio favoured males. Eggs and juveniles of the earliest 2 instars havebeen found to be retained in the carapace of the female,probably a reason of their rarity in both deadand fossil populations.