Abstract: Intertidal ocypodid crabs of the two genera Dotilla and Scopimera have unique membranous windows(‘tympana’)on their legs for aerial gas exchange, and the former also has them on its thoracic sterna. The osmoregulatory capabilities of Dotilla myctiroides and Scopimera pilura in dilute external media were compared, and microstructure of their tympana was examined to clarify whether they have an osmoregulatory function as well as a respiratory one, because respiratory surfaces are probablc sitcs for osmoregulation or of water/ion loss. Although both D. myctiroides and S. pilura were hyperosmoregulators, the former species was much the weaker in this respect. Histological results showed that the tympana have simple, thin respiratory epithelia in both of these species as well as S. proxima, which indicates that the tympana are probably sites of water/ion loss. The thicker cuticle in Scopimera species than in D. myctiroides may be an adaptive characteristic for maintaining blood osmolality in dilute media, and this was confirmed by silver staining, which indicated that the loss of Cl^-through tympana was smaller in Scopimera than in Dotilla. However, at the same time, the longer blood/gas diffusion distance due to the thickened cuticle must result in lower efficiency of gas exchange. Hence, a trade-off between respiratory efficiency and water/ion retention is involved in the development of tympana. From this viewpoint, the presence/absence of tympana among species of the subfamily Dotillinae, which includes Dotilla and Scopimera, is reviewed with reference to some taxonomic and phylogenetic considerations.

View full abstract

Abstract: The first record of an entocytherid ostracod from Japan is reported. Uncinocythere occidentalis(Kozloff and Whitman, 1954)was found living commensally on the crayfish Pacifastacus leniusculus trowbridgii in Hokkaido, Japan. This is also the first record of U. occidentalis outside the western United States and it is postulated that it is an invasive species in Japan, unwittingly imported with this North American crayfish.

View full abstract

Abstract: I examined the diversity and abundance of benthic animal communities in an intertidal seagrass bed at Haad Chao Mai National Park, Thailand, in relation to small-scale spatial heterogeneity of the seagrass vegetation. In this seagrass bed, two dominant seagrasses, Halophila ovalis and Thalassia hemprichii, coexist in a mosaic of monospecific vegetation. I collected benthic animals at the center, edge and outside of the H. ovalis vegetation at one site that bordered an unvegetated sand flat and at another site surrounded by T. hemprichii vegetation. A total of 3146 benthic animals from 61 taxa were collected. The most numerious species was the lucinid bivalve Pillucina sp., composing more than 60% of the individuals. Although the species composition of benthic animals did not differ largely among the three positions at each site, taxa richness(the number of taxa)was higher in the center of the H. ovalis vegetation than the edge of and outside the vegetation. Among the four dominant taxa, Pillucina sp. and a sabellid polychaete were generally more abundant in the center of the vegetation than at the edge of and outside the vegetation, whereas significant variation among positions was not detected in the densities of capitellid and spionid polychaetes. Significant among-position variation was also detected in the relative abundance of some taxa. The patterns of among-position variation in taxa richness and abundance did not differ between the two sites. These findings suggest that small-scale spatial heterogeneity of seagrass vegetation has a great impact on the diversity and abundance of benthic communities in intertidal seagrass beds, and that the responses of benthic animals to habitat heterogeneity are species specific.

View full abstract

Abstract: Stable carbon and nitrogen isotopes were analyzed for 3 mangrove crabs, Uca vocans, Sesarma mederi, and Scylla serrata, and their food resources in a mangrove-fringed estuary in Thailand. Isotope compositions of mangrove biota ranged from -14.9 to -31.1‰ for δ¹³C, and from 2.9 to 12.5‰ for δ¹⁵N. The isotopic composition showed that U. vocans was a herbivore, feeding mainly on epiphytic algae and macroalgae, while S. mederi was a herbivore and/or detritivore, feeding heavily on mangrove leaves and detritus. The diet compositions of U. vocans and of S. mederi did not change as each species grew. On the other hand, the diet composition of S. serrata changed as it grew; small sizes were omnivorous, feeding probably on small crabs and plant materials, while medium and large sizes were predominantly carnivores, feeding on a variety of slow moving invertebrates such as worms, crabs and mollusks. Our results show that stable isotope analysis can be used as an alternative to conventional food web analysis approaches. The δ¹³C and δ¹⁵N values were useful source and trophic indicators, respectively.

View full abstract

Abstract: It was recently reported that oocytes have no cortical crypts even in the pre-maturation and mature stages in the small penaeid shrimp Metapenaeopsis dalei. To determine whether this is a general feature in the oogenesis of the species of Metapenaeopsis, the morphologies of the oocytes of M. aegyptia, M. barbata, and M. sinica were observed histologically in the present study. Fairly developed yolk-granule stage and pre-maturation stage oocytes(Stages V and VI)were observed from early summer to autumn when the gonad somatic index was high, but mature oocytes were never observed throughout the year. No cortical crypts were observed in the late phase of the pre-maturation stage oocytes(Stage VI). Oocytes at the yolk-granule stage and the early phase of the pre-maturation Stage V were simultaneously observed with Stage VI oocytes in the same histological sections. These results seem to indicate the absence of cortical crypts through oogenesis and the occurrence of multiple spawning at short intervals in all three species, similarly to M. dalei. Such features might thus be general for the genus Metapenaeopsis.

View full abstract

Abstract: To evaluate the adaptive significance of shell preference, we investigated the functional roles of gastropod shell species in the intertidal hermit crab Pagurus filholi in terms of tolerance to desiccation stress at high temperature, fecundity and growth rate. Tolerance to desiccation stress(6h at 37°C) did not differ among the shell species occupied and between sexes, and survival rate reached 70-80%. The number of eggs females brooded significantly differed depending on shell size and shell species. Although we did not detect any significant effects of shell size and species on crab growth rate, males tended to grow faster than females, and crabs in large shells tended to grow faster than crabs in small shells. It is suggested that shell preference of P.fiholi has been shaped by the crabs' attempt to maximize growth or fecundity. Sexual differences in shell preference are discussed in terms of the difference in relative importance of rapid growth for the fitness of each sex.

View full abstract