Survival, moulting and reproduction of the mangrove crab, Sesarma messa from north eastern Australia

Adults of the mangrove crab, Sesarma messa were captured using pit traps in a mid-intertidal Ceriops tagal stand located at Cape Ferguson, near Townsville. The crabs and sediment from the capture site were transferred to 9 plastic aquaria after sieving the sediments to remove macroinvertebrates. Three randomly selected males and females were assigned to each aquaria after being measured across the carapace, weighed and marked with a plastic tag. The aquaria were maintained under ambient conditions in an outside shadehouse. Seawater was connected to each aquarium and the supply was regulated to simulate a one hour tide every day, which covered the sediment surface with about 10 cm of water.The first rearing experiment was designed to test the effects of litter quantity, using senescent Ceriops tagal leaves. Three replicate aquaria were subjected to one of three treatments: no leaf litter added, limited leaf litter added and excess leaf litter added. At the end of each week leaf litter remaining in each aquaria were removed and new leaves added. The aquaria were checked every 2-3 days for ovigerous and moulting individuals over a period of 10 weeks. Ovigerous females were removed at the end of the incubation period and placed in jars containing seawater until hatching occurred. Three subsamples of 200 larvae were collected from each female and the subsamples, as well as the remaining larvae were dried at 65 °C for 3 days and the total number of larvae calculated.In order to assess the availability of microbial organisms on the mud surface as an alternative food source, bacterial densities were determined from three replicate 3.14 ml samples of sediment collected with a syringe from each aquaria and from the forest where the sediment was collected. The second rearing experiment, using the same aquaria as above, was designed to test the effects of leaf species on the performance of Sesarma messa. Crabs were given excess amounts of senescent leaves from one of three species: Ceriops tagal; Rhizophora stylosa and Bruguiera exaristata. Three replicate aquaria were assigned to each treatment. Leaves were removed weekly and new leaves provided. In this experiment, only two males and two females were assigned to each aquaria to reduce the possibility of overcrowding. The number of live, moulting and ovigerous individuals was recorded weekly for 9 weeks.The absorption efficiency of Sesarma messa was assessed by placing each of 10 crabs in individual bowls for one week and then adding to each container half a senescent leaf of Ceriops tagal, Rhizophora stylosa, Bruguiera exaristata and Avicennia marina. The other half of each leaf was placed in a separate container as a control for leaf weigh loss not due to crab feeding. Leaves were weighed at the beginning of the experiment and wet weights converted to dry weights. After 24 hours, leaf remains and control leaves were collected, oven dried at 65°C for 5 days and reweighed. Leaves were then ashed at 500°C for 24 hours to determine ash free dry weight. The total amount of organic matter ingested by each crab was calculated by summing the ingestion rate for each leaf species. After a further 24 hours, crabs were removed from each container and all faecal matter collected on GFC filters. The filters were oven dried to a constant weight at 65°C. Faecal material was then weighed to the nearest 0.001g, ashed at 500°C for 24 hours and reweighed. This research was undertaken to investigate the link between the quality and availability of mangrove litter and the secondary production of sesarmid crabs in mangrove forests.

研究人员于汤斯维尔附近的弗格森角的中潮带角果木（Ceriops tagal）林分内，使用陷捕器（pit traps）捕获了墨萨相手蟹（Sesarma messa）的成体。将捕获的螃蟹及采集位点的沉积物过筛去除大型无脊椎动物后，转移至9个塑料水族箱中。随后对每只螃蟹测量头胸甲尺寸、称重并用塑料标签标记，之后随机选取3只雄性与3只雌性螃蟹放入每个水族箱。水族箱置于室外遮阴棚的自然环境中养护，每个水族箱均连接海水供应系统，通过调控供水模拟每日一次时长1小时的潮汐，使沉积物表面被约10 cm深的海水覆盖。
首个饲养实验旨在探究枯落物数量对墨萨相手蟹的影响，实验材料为衰老的角果木（Ceriops tagal）叶片。设置3组处理，每组设置3个重复水族箱：不添加叶片枯落物、添加少量叶片枯落物、添加过量叶片枯落物。每周末移除各水族箱内剩余的叶片枯落物并更换新鲜叶片。在为期10周的实验周期内，每2-3天检查一次水族箱，记录抱卵与蜕皮个体的情况。抱卵雌蟹在抱卵孵化期结束后被移出，放入盛有海水的容器中直至幼体孵化。从每只雌蟹处采集3个各含200只幼体的子样本，剩余幼体与子样本均置于65℃下烘干3天，以此计算幼体总数量。
为评估泥表微生物作为替代食物的可获得性，研究人员使用注射器从每个水族箱及原始红树林采集位点采集3个重复的3.14 ml沉积物样本，测定其中的细菌密度。
第二个饲养实验沿用上述水族箱，旨在探究叶片种类对墨萨相手蟹生存状态的影响。为每组水族箱提供过量的衰老叶片，叶片选自3个树种：角果木（Ceriops tagal）、红海榄（Rhizophora stylosa）与无刺木榄（Bruguiera exaristata），每个处理设置3个重复水族箱。为避免过度拥挤，每个水族箱仅投放2只雄性与2只雌性螃蟹。每周移除旧叶并更换新鲜叶片，实验周期为9周，每周记录存活、蜕皮与抱卵个体的数量。
为评估墨萨相手蟹的吸收效率，研究人员将10只螃蟹分别置于单独的容器中饲养一周，随后向每个容器内投放半片衰老的角果木、红海榄、无刺木榄与白骨壤（Avicennia marina）叶片，另一半叶片放入单独容器作为对照，用以校正非螃蟹取食导致的叶片重量损失。实验开始时称量叶片重量，并将湿重换算为干重。24小时后收集剩余叶片与对照叶片，置于65℃下烘干5天后再次称重；随后将叶片置于500℃下灰化24小时，测定其无灰干重。通过汇总各叶片物种的取食速率，计算每只螃蟹摄入的总有机质含量。再过24小时后，从各容器中取出螃蟹，使用GFC滤膜收集所有粪便。将滤膜置于65℃下烘干至恒重，称量粪便重量（精确至0.001 g），随后将粪便置于500℃下灰化24小时后再次称重。
本研究旨在探究红树林枯落物的质量与可获得性，与红树林内相手蟹科螃蟹次级生产力之间的关联。