The flora and ecological distributions of tropical seagrasses were investigated in Nagura Bay, Ishigaki Island, okinawa. Seagrass meadows in the Bay are developed along the coast, their areal extensions wide at the inner part and narrow at the outer part of the bay. Six genera, eight species of seagrasses, Zostera japonica, Halodule uninervis, H. pinifolia, Syringodium isoetifolium, Cymodocea rotundata, C. serrulata, Thalassia hemprichii, and Halophila ovalis are found there. Ecological distribution of seagrasses are analyzed for their habitat utilization, mainly from the view point of vertical range, horizontal situation in the bay, areal extent of distribution and dominance in biomass. Thalassia hemprichii is the most common species in upper sublittoral zone and becomes dominant at various habitat situations. Though there are some degree of overlap, species pairs of Halodule and Cymodocea exhibit considerable difference in habitat utilization within each congeneric species pair. Zostera japonica, Syringodium isoetifolium and Halophila ovalis grow at limited habitat conditions, respectively. Several species jointly appeard in most sampling localities, three types of associations such as Halodule pinifolia-Halophila ovalis association, T.hemprichii-C. rotundata association and T.hemp-richii-C. serrulata association, are recognized.

View full abstract

In a small cove, Odawa Bay, at the Pacific coast of central Japan, the modes of life of starfishes collected by a small Danish seine were surveyed. On Astropeeten scoparius, A. polyacanthus and Luidia quinaria of five species of starfish collected, theri foods were examined by gut contents analysis. Food of both species of Astropecten was resemble with each other, but it was different with it of L. quinaria which feeds mainly on ophiurans. Distributions of asteroids in the bay were revealed; A. scoparius and Asterias amurensis were found in bay-head area having muddy sediment, A. polyacanthus is found in the same area on rocks or pbbles, and L. quinaria in extensive areas with soft bottom over the bay. The breeding seasons of starfishes were estimated that both species of Astropecten were May-June, L. quinaria around August, A. amurensis February-April, and A. pectinifera April-May. From the results above, it would be considered that the five asteroids having the modes of life resemble each others coexist in Odawa Bay shifting mutually their food habit, habitat, breeding season and so on.

View full abstract

A bird's-eye view was given of a trend of the studies on soft-bottom benthic communities in the last ten years, which stress biological interactions for their structuring mechanism.In these works three major tendencies could be recognized: 1. Descriptions about the historical and regional diversification of different functional groups based on feeding-and mobility modes. 2. Efforts to elucidate the role of dynamic interactions between species or species groups in the same trophic level for the cause of segregation of several species assemblages. These interactions have been considered to operate between adults or between adults and larvae, indirectly through bioturbation and/or directly through interference with one another and ingestion of larvae by established adults. 3. Attempts to evaluate the influences of predators as a modifier of the species composition of the benthic communities. Fundamental and methodological problems we often encounter in the field and the laboratory were examined, when we are to observe and carry out experiments to quantify the contribution of each of those biological factors separated from that of physical ones.

View full abstract

Sandy bottom caprellids samples from off Kochi, South Shikoku, was examined. A new species Orthoprotella hamata n. sp. is described, and two other rare species, Pseudoproto fallax and Protogeton inflatus are illustrated.

View full abstract