In the prawn Palaemon (Palaemon) paucidens DE HAAN which is widely distributed in inland fresh waters in Japan, affinity with environmental fresh and saline water was investigated for zoeal larvae. The larval survivorship was much better in diluted sea water (20∼60 % or 80 % concentrations of ordinary artificial sea water) than in fresh water under both conditions of starvation and feeding. Oxygen-consumption rate of newly hatched larvae (first-stage zoeae) was considerably greater in fresh water than in diluted or not diluted sea water, which is regarded to reflect the increment of energy cost for osmoregulation in freshwater medium. The cause of declined survivorship of P. paucidens larvae in fresh water was discussed in connection with their energy consumption and other physiological factors. Judging from larval physiological affinity with saline water, it is very likely that the infered evolutionary change of habitats from saline to fresh waters in this species has been accomplished without acquiring complete adaptation to external freshwater medium.
Growth of juveniles of the freshwater prawn Macrobrachium nipponense was investigated at the controlled water temperature 28±1°C in the laboratory. Among the individuals derived from a single brood, about a half of the females attained the body length 25 to 32 mm after ten weeks from the time of metamorphosis into postlarva, i. e., roughly estimated 15 weeks from the time of spawning by mother prawn. As the body size of such females was large enough to sexually mature in the field, it is probable that, under certain environmental conditions, females born at the beginning of a breeding season grow up and breed at the end of that breeding season which lasts three to four months. With this result, the data for growth and longevity of M. nipponense individuals in the field was critically reviewed.
Nicon sinica WU and SUN, 1979 (Nereididae, Polychaeta) is newly recorded from Japan. More than 50 specimens of the species were captured by one catch of a beam trawl, off Daio-zaki at a depth of 425 m. Their morphological variability and the sexual modification of parapodia are described. As a result of the examination on parapodial modification associated with the sexual stage, Sinonereis heteropoda WU and SUN, 1979 is thought to be possibly referred to Nicon sinica.
Survival rate at the settlement of a semelid bivalve Theoya lubrica was estimated from the change in the densities and size compositions of planktonic umboned larvae (shell length : 125-164 μm), metamorphosing larvae (132∼196 μm) and benthic juveniles (more than 164μm). They were simultaneously collected with plankton net, sediment traps set in the strata 0.4, 1 and 2 m above the bottom, and corer-type bottom sampler, in northern Bingo-Nada, the Inland Sea, from June to December. No significant difference was seen in the size composition of animals between the sediment traps and the bottom sampler. The density of metamorphosing larvae (2.9×102∼20.4×102 indiv./m2) was positively correlated to tidal range (210∼416 cm). From mid-June to mid-October, most of the metamorphosing larvae disappeared due to the oxygen-deficient bottom water, while planktonic larvae and benthic juveniles did not decrease markedly. At the settling period excluding the above-mentioned months, survival rate of the umboned larvae was estimated approximately 20 %, whose value was the same rate as that during the metamorphosing stage. This indicates that a large mortality hardly occurred in a transitional stage from planktonic to benthic lives.
Seasonal fluctuations of macrobenthic community structure were studied in Uranouchi Bay, Japan. In summer, there were no benthic animals in the middle and inner parts of the bay. Benthic animals were recolonized in winter. Dominant animal groups were polychaete worms and bivalves. Most of them were short-lived small animals and are the indicator species for organic pollution. This bay is enclosed, where culturing of yellowtails has been continued for more than 30 years. Therefore, the organic content in sediments is very high. It is also known that the oxygen depletion less than 10 % in saturation in bottom water occurs widely in summer. These facts on benthic community structure and bottom environmental conditions indicate that the organic pollution of this bay is very heavy. The improvement of the organic pollution in this bay will be performed only by the artificial topographic change to facilitate bay water mixing.
To clarify the effects of organic pollution on the macrobenthos, quantitative samples were obtained from the rivers and the harbor area in Osaka City between August 1984 and April 1987. The rivers were shown to be a polysaprobic zone by the predominance of oligochaetes. The densities and biomasses in the rivers were low, excepting in Neya River, where an extremely dense population of a tubificid oligochaete was found throughout the year. In the mouths of the rivers, i. e., the innermost part of the harbor, animals were scarce from spring to autumn owing to severe oxygen deficiency. In winter, however, Capitella capitata and several euryhaline species appeared in abundance by the rapid increment of the population. Then, clear faunal boundary was found to lie between the innermost part of the harbor and the area around the mouth of the horbor where Paraprionospio sp. (form A), Lumbrineris longifolia, Sigambra sp. and season-specific species such as Euchone sp. and Theora fragilis were distributed. Comparison of the dominant species in the present study with those in the previous studies suggests the change of environment during the past 30 years.
The vertical distribution pattern of rocky shore organisms was studied along two French coasts, at Marseille with no true intertidal and in Brittany with a large tidal amplitude of 9 -13m at spring tide. A marked zonation pattern was recognized on both shores and photographs of some of the common animals and plants are presented. At Marseille, the supralittoral zone was characterized by the periwinkle Melaraphe neritoides, which was also abundant in the upper mediolittoral zone characterized by the barnacle Chthamalus stellatus. Growths of the calcareous alga Lithophyllum tortuosum were conspicuous in the lower mediolittoral zone of exposed shores. Beds of the mussel Mytilus galloprovincialis developed around the upper fringe of the infralittoral zone and harbored many small animals, mainly amphipods, polychaetes and mollusks. Habitat segregation was recog-nized between closely related species, e.g. between Hyale spp. and between the nereids Perinereis cultrifera and Platynereis dumerilli. Along the coast of Brittany, the zonation pattern of the inter-tidal animals and plants as reported by Lewis (1964) was found. However, in the vicinity of Dinard, the chthamalid found in the higher eulittoral zone was not Chthamalus stellatus but C. montagui. The facilities of four marine stations, “Station Marine d'Endoume”, “Laboratoire Arago”, “Station Biologique de Roscoff” and “Laboratoire Maritime de Dinard”, are also presented.
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