Population Densities and Annual Activities of Mictyris Brevidactylus (Stimpson, 1858) in the Tanshui Mangrove Swamp of Northern Taiwan

淡水紅樹林短趾和尚蟹（Mictyris brevidactylus）之族群密度及年活動周期

史金燾(Jin-Taur Shih)

《Zoological Studies》 34卷2期 (1995/04) Pp. 96-105

摘要

This study reports on population densities, variations of population densities during the reproductive cycle, recruitment and growth of juveniles, and the egg-carrying period of Mictyris brevidactylus in the Tanshui mangrove swamp of northern Taiwan during 1988-1991. Peak population densities of crabs with carapace width (CW) ＞ 4.0 mm occurred during the reproductive (egg-carrying, January to April) and prereproductive (October to December) seasons and reached 110-226 crabs/m^2. Low crab densities of 62-85 crabs/m^2 were found during nonreproductive season (May to September), with a value about one-third of the other two seasons. Annual crab densities (110-133 crabs/m^2) remained stable during the entire study period (p= 0.6043). After release of their broods, some of the one- and two-year-old crabs were found dead in their nests. The surviving crabs molted from May to July and continued growing increasing their CW 30% by November. Crabs were first observed carrying eggs in late January and were still being observed in late April. However, no egg carrying crabs were found in May. The newly settled juveniles (1.2 mm CW) were first observed in April, attained 3.6 ± 0.4 mm CW, and comprised 70% of the total crab population density in June. At this time, the sexes of juveniles were identified. In December, most of juveniles reached＞ 5.5 mm CW and were almost sexually mature. The study of annual activities has helped understand the life history of M. brevidactylus.

關鍵字

族群密度的變異 ； 幼蟹 ； 幼蟹的補充 ； 抱卵期 ； 生殖周期

並列摘要

This study reports on population densities, variations of population densities during the reproductive cycle, recruitment and growth of juveniles, and the egg-carrying period of Mictyris brevidactylus in the Tanshui mangrove swamp of northern Taiwan during 1988-1991. Peak population densities of crabs with carapace width (CW) ＞ 4.0 mm occurred during the reproductive (egg-carrying, January to April) and prereproductive (October to December) seasons and reached 110-226 crabs/m^2. Low crab densities of 62-85 crabs/m^2 were found during nonreproductive season (May to September), with a value about one-third of the other two seasons. Annual crab densities (110-133 crabs/m^2) remained stable during the entire study period (p= 0.6043). After release of their broods, some of the one- and two-year-old crabs were found dead in their nests. The surviving crabs molted from May to July and continued growing increasing their CW 30% by November. Crabs were first observed carrying eggs in late January and were still being observed in late April. However, no egg carrying crabs were found in May. The newly settled juveniles (1.2 mm CW) were first observed in April, attained 3.6 ± 0.4 mm CW, and comprised 70% of the total crab population density in June. At this time, the sexes of juveniles were identified. In December, most of juveniles reached＞ 5.5 mm CW and were almost sexually mature. The study of annual activities has helped understand the life history of M. brevidactylus.

並列關鍵字

Variations of population densities ； Juvenile crabs ； Recruitment ； Egg-carrying period ； Reproductive cycle