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The feeding ecology of Sesarma plicata (Grapsidae: Sesarminae), the most abundant crab species in a mangrove forest dominated by Kandelia candel at Jiulongjiang Estuary, China, was investigated through field and laboratory experiments. Feeding preference and consumption rates were determined on mature, senescent and decomposed leaves of Kandelia candel, Bruguiera gymnorrhiza and Aegiceras corniculatum. In the laboratory, S. plicata preferred leaves of K. candel over those of B. gymnorrhiza and A. corniculatum, and consumed significantly more decomposed leaves than mature and senescent ones, irrespective of crab size. Field experiments with limited power failed to reveal detectable species preferences despite more consumption of K. candel, but decomposed leaves of each species were again preferred. Leaf characteristics associated with preference changed with plant species and leaf state. Low tannins and high water content characterized the preference for decomposed state of leaves. Species preference was significantly and negatively related to crude fibers and C:N ratios for mature leaves, and crude fiber for senescent leaves, but significantly and positively related to water content for decomposed leaves. Leaf consumption rates averaged for all leaf categories from laboratory no-choice feeding experiments were 0.101, 0.055 and 0.017 gDW ind−1 d−1 for large, medium and small crabs, respectively. In this forest, mean density of S. plicata was 20.5 ind m−2 as assessed by a manual catching method. Leaf litter removal rate during neap tides by sesarmid crabs was about 1.33 gDW m−2 d−1 in April 2006. The leaves removed by crabs were grazed on the sediment surface or taken into crab burrows, shredded and stored before being eaten. [ABSTRACT FROM AUTHOR]

The aim of the present study was to examine some general aspects of feeding in Tachypleus tridentatus juveniles and the possible strategies employed to survive on sand flats experiencing a fluctuating environment, in terms of temperature, salinity and tidal action. Activity of Tachypleus tridentatus juveniles in the field was studied on each visit between September 1997 and June 1998, during low tides when the animals were crawling at the sand surface in the intertidal zone at Shui Hau, Lantau Island, Hong Kong. The patterns of feeding trails produced by the juveniles in the field and their crawling rates were determined and compared. Juveniles began to crawl on the sand surface after the tide had receded and the substratum exposed for about 1 h. The numbers of animals observed increased and peaked after a further 1 h. The number of active individuals gradually declined as most re-burrowed when the tide returned. Juveniles generally crawled in pool areas on the sand surface. A seasonal pattern was also evident in the number of juveniles observed at the study site. Highest numbers were recorded in summer whilst only a few juveniles were seen in winter. Possible strategies adopted by the juveniles for successful survival on the sand flats are discussed. [ABSTRACT FROM AUTHOR]