The role of circadian rhythm and environmental factors in the regulation of sea urchin spawning.

Simultaneous video recording of the sea urchin spawning behavior and recording of environmental factors enabled us to found synergism of the effects of circadian rhythm and phytoplankton on the spawning activity of the sea urchin Strongylocentrotus intermedius (Agassiz, 1864).

Reproduction-related effects of green alga Coccomyxa sp. infestation in the horse mussel Modiolus modiolus.

The effects of Coccomyxa sp. infestation on the reproductive characteristics of the horse mussel Modiolus modiolus from the north-western Pacific (Peter the Great Bay, Sea of Japan) are demonstrated in this study. The mussels were collected monthly from May to September of 2009, and the prevalence of females and males with green tissues was 39% and 47%, respectively. Overall, the green alga infection caused a mild effect on gametogenesis in the horse mussel. The dynamics of gonad development in the healthy and infected mussels during the study period was generally similar, with the spawning being partial and occurring from the beginning of June to the first half of September; total spawning was recorded at the end of this period. However, several negative reproduction-related effects of the green alga infestation were observed, i.e., general gonadal underdevelopment, which was apparent from significant decrease in the acinus areas of the ovaries and testes and an increase in the connective tissue layer between the acini, a delay in some stages of the reproductive cycle and production of decreased number of spermatozoa and large vitellogenic oocytes, especially in the early spawning period (June). All of these results suggest a reduced reproductive output for the infected mussels.

Phylogenetic and morphological characterization of the green alga infesting the horse mussel Modiolus modiolus from Vityaz Bay (Peter the Great Bay, Sea of Japan).

In this work, the ultrastructural features and taxonomic position of the green microalga infesting the horse mussel Modiolus modiolus from the north-western Pacific (Vityaz Bay, Peter the Great Bay, Sea of Japan) are reported. Mussels were collected monthly from May to September of 2009. In different months, the prevalence of mussels with green tissues was 16.6-62.5% (mean 43%). The most affected organs were the mantle, digestive gland and gonad. Histological analysis revealed severe infiltration of the connective tissue by hemocytes containing the alga cells. Electron microscopy showed that the alga was morphologically similar to the green algae from the genus Coccomyxa (Chlorophyta: Chlorococcales). Two new primers were designed to generate partial small subunit (SSU) rRNA sequences of the green alga from M. modiolus. Phylogenetic analysis based on the comparison of the SSU rRNA sequences of the trebouxiophyceans confirmed an affiliation of the green alga with the genus Coccomyxa. The sequence (1296 bases) of the green alga from M. modiolus was most closely related to the sequence CPCC 508 (AM981206) (identity 100%), obtained from an acid-tolerant, free-living chlorophyte microalga Coccomyxa sp. and to the sequences EU127470 (identity 99.3%) and EU127471 (identity 99.7%) of the green alga, presumably the true Coccomyxa parasitica, infecting the blue mussel Mytilus edulis from the Flensburg Fjord (North Atlantic).

NADPH-diaphorase activity in the central nervous system of the Gray mussel Crenomytilus grayanus (Dunker) under stress conditions: a histochemical study.

NADPH-diaphorase (NADPH-d) is a histochemical marker for nitric oxide synthase (NOS) and is widely used to identify nitric oxide (NO) producing cells in the central nervous system (CNS) of both vertebrates and invertebrates. NADPH-d histochemistry was used to quantitatively characterize putative NO-producing neurons in the CNS of the Gray mussel Crenomytilus grayanus subjected to two kinds of stress, environmental pollution and hypoxia, the latter caused by the mollusk transportation in a small volume of water. Mussels were sampled from one relatively clean (reference) and four polluted sites in Amursky and Ussuriysky Bays (Peter the Great Bay, Sea of Japan) in August, 2003. The number of NADPH-d-positive neurons was estimated and enzyme activity was determined from the optical density of the formazan precipitate in the CNS ganglia at 0, 3, and 72 h after sampling. Just after sampling, NADPH-d-positive neurons were found in the cerebropleural, visceral, and pedal ganglia. The number and staining intensity of NADPH-d-positive neurons were significantly higher in the pedal ganglia than the other two ganglia. There were significant differences in the number of NADPH-d-positive neurons and enzyme activity between the mussels from the reference and heavily polluted stations. The proportion and staining intensity of NADPH-d-positive neurons were maximum in the pedal ganglia of the mussels from the heavily polluted station in Amursky Bay. Transportation of mussels in a limited volume of water for 3h resulted in a significant increase in the proportion and staining intensity of NADPH-d-positive neurons in all ganglia. In mollusks from all stations kept in aerated aquaria for 72 h, both the proportion and staining intensity of NADPH-d-positive neurons did not differ significantly from the initial level. However, the differences in the proportion and staining intensity of NADPH-d-positive neurons between the reference and heavily polluted stations were significant. The present results suggest that NO is involved in mollusk nerve cell adaptation to environmental changes.

Sea urchins--a new model for PAF research in embryology.

This study reports on the effect of PAF on sperm motility, fertilization and early embryo development in the sea urchin Strongylocentrotus intermedius. PAF proved to be the amplifier of sperm motility and fertilizing capability at 10(-8)-10(-9) M and was toxic at higher concentrations. BN 52201 did not counteract the PAF action. The advantages of using sea urchins for PAF research in embryology are discussed.