N. I. Selin

Shell form, growth and life span of Astarte arctica and A. borealis (Mollusca: Bivalvia) from the subtidal zone of northeastern Sakhalin

This study investigates changes in body proportions during ontogenesis of the bivalves Astarte arctica and A. borealis from the subtidal zone of northeastern Sakhalin. Marked differences in the shell form of bivalves were found. The shell of A. arctica is convex and compact, shell length and height are comparable, and shell width is more than 50% of shell height. A. borealis has a slightly elongate and flattened shell, its width is less than 50% of its height. Shell proportions can provide a reliable criterion for differentiating the species. Mollusks grow at nearly the same rate but attain different maximum sizes. Linear growth is described by Bertalanffy’s equation: Lt = 48.2[1 − e −0.4850(t − 0.4396)] for A. arctica and Lt = 53.1[1 − e−0.4106(t − 0.4253)] for A. borealis. In northeastern Sakhalin, the life span of A. arctica is 7 years and of A. borealis, 8 years. By life span, the two bivalve species from Sakhalin slightly differ from their counterparts in other regions, particularly the arctic seas.

Current status of coral reefs of islands in the Gulf of Siam and Southern Vietnam

In 2010, an expedition of the Institute of Marine Biology on the R/V Akademik Oparin revisited and surveyed a number of coral reefs of Vietnam, whose species composition and structure had been first described a quarter of century ago. No substantial changes were found in the geomorphological structure of reefs of the Nam Su and Tho Chu islands in the Gulf of Siam and the Con Dao and Thu islands situated outside the gulf. Marked changes were found in the abundance of some species of associated macrobenthos. The current status of coral reefs is described and the causes of the observed changes are analyzed (anthropogenic influence, etc.).

The peculiarities of foraging migrations of the Korean-Okhotsk gray whale (Eschrichtius robustus) population in russian waters of the Far Eastern seas

Photographic identification of the Korean-Okhotsk gray whale Eschrichtius robustus population has been conducted since 2002 by researchers of the Institute of Marine Biology at the Far East Branch of the Russian Academy of Sciences (IMB FEB RAS), with financial support provided by Exon Neftegas, Ltd. and Sakhalin Energy Investment Co., in order to study the migration features and biology of this species. In 2008, photo-ID studies were carried out in two areas, off the northeastern coast of Sakhalin Island and off the southeastern coast of Kamchatka. As a result of the studies, 122 whales known from the Sakhalin gray whale catalogue were photographed. Of them, 97 individuals were registered off Sakhalin, 24, off Kamchatka, and one whale was observed at both sites. In addition, 25 more gray whales that had not been sighted off Sakhalin Island before were found off the coast of Kamchatka. Based on these photographic materials, the whales physical and skin conditions were also analyzed. Cases of sightings of gray whales in areas that are remote from their traditional summer and fall feeding grounds in the Far Eastern seas of Russia are discussed.

The growth and life span of bivalve mollusks at the northeastern coast of Sakhalin Island

Numerous shells of bivalves, which study attributed to 37 species, were collected from samples of ground taken with a Van Veen dredge sampler at the northeast coast of Sakhalin Island at depths of about 10–60 m in June–October 2003–2009. Tellina lutea, Mactromeris polynyma, Serripes groenlandicus, Macoma spp., Liocyma fluctuosum, and Siliqua alta occurred most often in the samples. The assessment of growth in 18 bivalve species revealed common patterns of age variations that were irrespective of their way of life, maximum body size, and maximum age. The greatest annual increment in shell length was observed in the first 4 years of life, and the asymptotic size of the mollusks was reached with a 10-fold decrease in the annual growth rate. The life span of the mollusks varied from 2 up to 41 years and sometimes significantly differed from that of the studied species in other areas of their range, clearly displaying the ecological conditionality of this parameter. Species with maximum ages of less than 10 years were the most numerous in the bivalve community of the region. The results of the research are discussed in relation to the nature of the environment at the northeast coast of Sakhalin Island.

Effects of Environmental Factors on Byssal Thread Formation in Some Members of the Family Mytilidae from the Sea of Japan

The ability to attach repeatedly to a substrate (glass, boulders, sand) in three common mussel species of the upper sublittoral zone of the Sea of Japan, Grayans mussel Crenomytilus grayanus, the Korean mussel Mytilus coruscus, and northern horse mussel Modiolus modiolus, was studied under experimental conditions. It was found that during 120 h of the experiment C. grayanus and M. modiolus produced more byssal threads than M. coruscus. A decrease in the water temperature from 20 to 0°C slowed the rate of production of byssal threads down to full passivity in some experimental mollusks. This was more typical of M. coruscus and less typical of C. grayanus. Renewed threads differed in their length, thick, size of the adhesive plate, and strength. M. coruscus formed the shortest, thickest, and strongest threads with rather a large adhesive disk. The observed differences are discussed from the position of morphophysiological adaptations of species for colonization of different natural substrata under contrasting conditions of the upper sublittoral zone.

Distribution pattern, population structure, and growth of Septifer bilocularis (Bivalvia: Mytilidae) on reefs of Southern Vietnam

The features of the spatial distribution, size and age structure of populations, and growth of the bivalve mollusk Septifer bilocularis (Linnaeus, 1758) were investigated for the first time in the waters of Vietnam. It is shown that in the subtidal area, on reefs well protected from wave effects, S. bilocularis occupies a corallogenous substrate constructed of dead branchy colonies of Acropora and Porites and forms settlements there with a population density and biomass exceeding those in populations located along the open coast and developing on massive coral colonies of the genera Porites, Favia, and Favites. The extensive accumulation of sediments in the inner part of Vanphong Bay (Khanh Hoa Province) correlated with a decrease in the size and age ranges for populations of S. bilocularis. It is found that in places with regularly active hydrodynamics the mollusks grew somewhat more slowly and formed a more convex shell than on reefs protected from surf. The longevity of S. bilocularis estimated both from the greatest observed age and from the growth equation of Bertalanffy was somewhat greater in the former case compared with the latter one, but in general did not exceed 11 years for both cases. The results of the studies are discussed from the position of morphophysiological adaptations of sessile bivalve mollusks to life in contrasting environmental conditions of the upper subtidal zone.

Some peculiarities of the population biology of the ghost shrimp Nihonotrypaea petalura (Stimpson, 1860) (Decapoda: Callianassidae) in coastal waters of Vostok bay, the Sea of Japan

In June 2012, some features of the population biology of the ghost shrimp Nihonotrypaea petalura were studied first for the Russian waters in sublittoral populations of the Vostok Bay (Peter the Great Bay, Sea of Japan). It was found that N. petalura formed aggregations of an average density of 9–19 ind./m2 at the depth of 0.2–3 m on rocky and mixed bottoms. The biomass of the aggregations was 15–27 g/m2 or 1–33% of the average total biomass of macrozoobenthos, which included animals of 48 taxa. The maximum depth of the shrimp burrows was 52 cm. The populations consisted of animals with body lengths of 17–63 mm. In the size-frequency distribution, two peaks in the number, attributed to the shrimps of 24–29 and 39–48 mm size groups, were observed. The ratio of males to females almost did not vary with size and remained in general close to 1: 0.9 for the surveyed shrimp populations. The local differences in the studied parameters of N. petalura from the Vostok Bay, as well as from other areas of the range, are discussed in relation to features of the habitation of these animals that living in different biotopes.

The distribution and some features of the biology of the ghost shrimp Nihonotrypaea japonica (Ortmann, 1891) (Decapoda: Callianassidae) from the Volchanka River estuary (Vostok Bay, Sea of Japan)

In August and October of 2013, the patterns of the spatial distribution, size, and sex composition of the estuarine population of the ghost shrimp Nihonotrypaea japonica were studied in the Vostok Bay (Peter the Great Bay, Sea of Japan) for the first time in Russian waters. It was found that this species inhabits waters under monthly mean temperatures from −1.6 to 21.7°C and salinity from 11.2 to 32.5‰, populating silted sand below the ice cover that is typical for December-March. The maximum population density of N. japonica reached almost 200 ind./m2, and a biomass of 120 g/m2 with average values of these parameters of 18 ± 43 ind./m2 and 10.83 ± 25.50 g/m2, respectively, which is almost one-third of the total biomass of the macro-zoobenthos. The population consisted of males with body lengths of 14–61 mm and females from 17 to 58 mm. In the size composition four groups of individuals were distinguished: underyearlings, 1-, 2-, and, apparently, 3-year old animals. The male/female ratio is close to 1 : 1.2. Males prevailed in animals with body lengths of less than 20 mm, while females prevailed among larger individuals. Features of the spatial distribution, size, and sex composition of populations of N. japonica are discussed in relation to the environment and reproduction at the northern boundary of its range.

Use of the photo method in the study of the composition and abundance of soft-bottom macrobenthos

The composition and abundance of the macrobenthic fauna associated with soft-bottom beds of the large bivalve mollusks Crenomytilus grayanus and Modiolus modiolus were studied in the inner part of Vostok Bay (Sea of Japan) in spring 2010. More than 30 taxa of animals were found in the mussel beds. Comparison of the data obtained with three different methods of studying muddy-bottom mussel communities showed that 80% of their biomass and only up to 25% of the species composition and 19% of the abundance can be estimated by the photo method. Photo surveys disregard small and/or juvenile animals, as well as infaunal organisms, and thus do not give a complete picture of the species, size, and age composition and abundance of biota.

Coral communities of barrier reefs of Vietnam

The composition and spatial distribution of the coral communities of the barrier reefs of Jiang Bo and of Re Island were described in detail for the first time for Vietnamese waters. Their comparability to the ribbon reefs of the Great Barrier Reef in Australia and to the barrier reefs of the Philippines and Indian Ocean was revealed by morphological parameters, species diversity and zonal distribution. Their geomorphological status, the presence of fore reef, epi-reef and back reef complexes with their specific composition of flora and fauna, and an obligatory lagoon separating the reef from fringing inshore reefs, enabled the attribution of the surveyed reefs to the barrier type of reef.