J. E.Y~~. Mar. Bioi. EcoL, 1989, Vol. 134. pp. 89- 100 Elsevier 89 JEMBE 01307 Foraging on mangrove pneumatophores by ocypodid crabs Keiji Wada ’ and Daisy Wowor 2 ‘Srto Marine Biological Laboratory, Kyoto University,Shirahama, W akayama, Japun I’ ‘Division of Zoolog>‘. Research and De~elo~~lent Centre zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON for Biology, Bogor. Indonesia. (Received 28 July 1988; revision received 20 December 1988; accepted 23 June 1989) Abstraet: Seven species of ocypodid crabs living in mangrove swamps of Halmahera, Indonesia, were found to forage on pneumatophores of Sonneratia alba as well as on the substratum. The proportion of pneumatophore-foraging individuals among active crabs was highest in M acrophthalmus quadratus. The timetable of pneumatophore foraging by individuals of .U. quadratus exhibited no clear tendency in relation to low tide. When the bark of pneumatophores was scraped off together with growing macroalgae, M. quadratus foraged less frequently on it, compared with intact pneumatophores. When comparing M. quadratus foraging on pneumatophores and those on the substratum, the former had bark of pneumatophores and macroalgae in their stomachs more frequently and in larger quantities than the latter. These findings suggest that bark and macroalgae are important food items of M . quadratw in pneumatophore foraging. Key words: Foraging: Mangrove; Ocypodid crab; Plant-animal relationship; Pneumatophore INTRODUCTION Mangroves are well known for developing above-ground root systems, termed pneumatophores and prop roots. These roots provide attachment space for sessile animals such as barnacles and oysters (e.g., Berry, 1963; Macnae, 1966; Day, 1974). Some mobile animals climb up the roots (e.g., Warner, 1969; Day, 1974; von Hagen, 1977). Burrowing crabs and molluscs are found abundantly among the roots (Macnae, 1966, 1968; Macnae & Kalk, 1962). Furthermore, the prop root habitat is commonly utilized by fishes (Thayer et al., 1987). On the other hand, beneficial effects of animal activities on the roots have been pointed out. Simberloff et al. (1978) suggested that attacks of wood-boring isopods on the prop root initiates its branching which may aid the plant to survive wave action. Thus, it is assumed that there exist close relationships between animals and pneumatophores or prop roots. Ocypodid crabs are a common component of the macrobenthic fauna occurring among pneumatophores or prop roots in mangrove swamps. These crabs usually forage on the substratum surface during daytime exposure period. But one of the authors (K. Wada) found that some ocypodids often climbed the pn~umatophores of S~~~erffti~ Correspondence address: IS. Wada, Department of Biology, Faculty of Science, Nara Women’s University, Kitanoya-nishi-machi, Nara 630. Japan. 0022-0981.189603.50 0 1989 Elsevier Science Publishers B.V. (Biomedical Division)