隐秘螳臂相手蟹攀爬芦苇行为的昼夜变化

Plant-climbing Behavior of a Mudflat Crab, Chiromantes neglectum in 24 Hour Duration at Phragmites-dominated Tidal Marsh in Changjiang River Estuary

蟹类是潮滩沼泽（本文简称潮沼）湿地生态系统底栖动物重要组成之一。蟹类对潮沼植物活体的牧食以及对潮沼植物上筑巢繁殖鸟类的巢捕食表明,潮沼蟹类会攀爬上潮沼植物。然而对于潮沼中蟹类攀爬植物的行为了解甚少。隐秘螳臂相手蟹（Chiromantes neglectum）是长江口及邻近潮沼生态系统中的优势底栖动物之一。本研究在长江口芦苇（Phragmites australis）潮沼中通过野外直接观测计数估计潮沼地表、潮沼植物（芦苇）上隐秘螳臂相手蟹密度的昼夜变化,来分析其攀爬芦苇行为的时间变化规律。攀爬芦苇隐秘螳臂相手蟹密度和地表隐秘螳臂相手蟹密度均具有显著的昼夜差异（所有P〈0.05）,根据隐秘螳臂相手蟹攀爬密度、地表密度的昼夜变化结合野外行为观测发现,隐秘螳臂相手蟹一般在日落前后（17：00～19：00时）开始攀爬芦苇,在日出后（7：00时以后）大部分隐秘螳臂相手蟹都已经从芦苇上撤离回到潮沼表面。隐秘螳臂相手蟹攀爬比例也具有显著的昼夜变化（P〈0.05）,在夜间时段（19：00～5：00时）攀爬比例高于白天时段（5：00～19：00时）（P〈0.05）,夜间时段攀爬比例在0.16～0.34之间,白天时段攀爬比例在0.02～0.15之间。隐秘螳臂相手蟹相手蟹的总密度在各观测时间段间差异显著（P〈0.05）,夜间时段总密度要高于白天时段（P〈0.05）,表明隐秘螳臂相手蟹在白天时段会较多利用潮沼表面的洞穴,从而呈现出从潮沼植被、潮沼地表到潮沼表面洞穴间的昼夜移动。此外,不同观测日期之间隐秘螳臂相手蟹攀爬密度、地表密度、总密度和攀爬比例均存在显著差异（所有P〈0.05）,但是规律性不明显。隐秘螳臂相手蟹的植物攀爬行为似乎与取食芦苇叶片有关系,同时又受到光照强度昼夜变化的影响,具体影响隐秘螳臂相手蟹攀爬芦苇行为的因素以及隐秘螳臂相手蟹攀爬芦苇行为对潮沼湿地生态过程的影响有待进一步研究。

Crabs are important components of benthic fauna of tidal marsh ecosystem and they are recognized as the grazer to feed on living salt marsh plant leaves and bird eggs nested in tidal marsh plants. However, the plant-climbing behavior of tidal marsh crabs is poorly understood. Chiromantes neglectum, which was formerly identified as C. dehaani in Changjiang River estuary, actually they distributes in coastal wetlands of south China（see Komai et al. 2013 for details）, is a dominant zoobenthic species in tidal marshes of Changjiang River estuary. By direct observing on the density variation on both reed shoots and marsh surface during 24 hours, we studied the plant-climbing behavior of the mudflat crab, C. neglectum, at a Phragmites-dominated tidal marsh in Changjiang River estuary. We sample location, the hours and date of observation conduction, as well as the combination of those data with the total crab density（all the crabs on the leaves and march surface）, with crab density on the leaves and on the marsh surface. Bonferroni test was used to analysis the differences among observation times and also observation dates. We found significant variations in both crab density on the reed shoot and on marsh surface between daytime and night time（Fig. 1 and Table 1, all P〈0.05）. Most crabs began to climb on reed shoots after dusk（17：00﹣19：00） and come down to marsh surface from reed shoots before dawn（5：00﹣7：00）（Fig. 1）. There was a significant diel variation for the ratio of climbing crab density to total crab density（Fig. 1 and Table 1, P〈0.05）. The percent of climbing crabs was higher during the nighttime（from 0.16 to 0.34 during 19：00﹣5：00） than during the daytime（from 0.02 to 0.15 during 5：00﹣19：00）（P〈0.05）. The total crab density varied significantly among observing bouts（P〈0.05） with significantly higher total density during the nighttime than the daytime, indicating that C. neglectum individuals were prone to using burrows during the daytime, thus had a diel movement pattern among burrow, marsh surface and reed shoots. Furthermore, we found significant differences among observing dates for total crab density, climbing crab density, marsh surface crab density and percent of climbing crabs（Fig. 2 and Table 1, all P〈0.05）. It seems that plant-climbing behavior of C. neglectum was related to grazing on leaf blades of reed shoots and affected by the diel variation of light intensity. Further studies are needed to reveal what factors and how these factors affect plant-climbing behavior of C. neglectum and how plant-climbing behavior of C. neglectum relate to ecological processes of tidal marsh ecosystems.