Alexey Sukhotin

Influence of age and size on pumping activity and stress resistance in the marine bivalve Mytilus edulis L.

Abstract We studied age and size dependence of pumping and respiration rates, mortality during prolonged air exposure and the changes in behavioural response to cyclic salinity fluctuations combined with elevated temperatures in the White Sea blue mussels Mytilus edulis L. Five age groups (2–9 years) and three size groups: small (S, mean wet tissue mass 0.12 g), medium (M, mean wet tissue mass 0.39 g) and large (L, mean wet tissue mass 0.78 g) were analysed. Respiration rate was measured in closed respirometers. Pumping rate was determined by a laser beam to monitor the changes in water level when the inhalant and exhalant siphons were in separate compartments of the aquarium. To study their response to environmental stress, the mussels were subjected to cyclic salinity fluctuations at normal (10 °C) and elevated (20 °C) temperatures. Two parameters were noted: (1) the salinity at which shell valves either opened or closed at both temperatures, and (2) intra-individual variation of the behavioural response to salinity changes at both temperatures. Size and age affect physiological processes in the blue mussel. The responses of M. edulis to environmental stress including low salinity, elevated temperature and air exposure as well as respiration rate are generally size-dependent. Effects of age on sensitivity to low salinity and survival in air are minor. Pumping rates of mussels are significantly affected by both size and age of the animals. The disproportional decrease of pumping rate is observed at the age of about 7–8 years old.

Age-dependence of metabolism in mussels Mytilus edulis (L.) from the White Sea

Age structure, natural mortality and growth, as well as age- and size-dependent changes in parameters of energy metabolism were studied in blue mussels Mytilus edulis (L.) from the White Sea. Mussels were sampled in August (Summer sample, SS) and October (Autumn sample, AS) and contained animals of three size groups, 2-9 years old. Field data showed an increase of mortality of mussels and strong decrease in growth rates after 6 years of age. Absolute tissue growth increment (AI) reconstructed from winter growth marks on the shells decreased with age and was strongly size-dependent, while relative tissue growth increment (RI) did not depend on size of the animals. Respiration rates and citrate synthase activity demonstrated power regression versus tissue weight with regression coefficients -0.231 and -0.170, respectively. After weight correction both parameters showed a decrease with increasing age. ATP and phosphagen levels also showed a pronounced decrease in animals older than 5-6 years despite considerable differences in the absolute values of both parameters in SS and AS. pH(i) in mussels was also age-dependent and decreased with increasing age after 5 years. In air exposed mussels, pH(i) was reduced only at young age such that pH(i) was low and constant within the whole age range. Our data give evidence that aerobic metabolic rate in M. edulis from the studied population declines when animals reach an age of about 6 years. The decrease in oxygen consumption reflects the drop in mitochondrial respiration, which is mirrored by the decrease in CS activity. A concomitant fall in ATP turnover may include a downregulation of the mechanisms of acid-base regulation. pH(i) will then approach equilibrium indicated by lower pH(i) values in older animals. Our data suggest that intrapopulational comparisons of physiological parameters in mussels should take into account age composition of compared samples.

Oxidative stress and expression of chaperones in aging mollusks

The mechanisms of aging are not well understood in animals with continuous growth such as fish, reptiles, amphibians and numerous invertebrates, including mollusks. We studied the effects of age on oxidative stress, cellular defense mechanisms (including two major antioxidant enzymes, superoxide dismutase (SOD) and catalase), and molecular chaperones in two mollusks--eastern oysters Crassostrea virginica and hard clams Mercenaria mercenaria. In order to detect the age-related changes in these parameters, correction for the effects of size was performed where appropriate to account for growth-related dilution. Fluorescent age pigments accumulated with age in both species. Protein carbonyls did not change with age or size indicating that they are not a good marker of aging in mollusks possibly due to the fast turnover and degradation of oxidized proteins in growing tissues. SOD did not show a compensatory increase with aging in either species, while catalase significantly decreased with age. Mitochondrial heat shock protein (HSP60) decreased with age in mollusks suggesting an age-related decline in mitochondrial chaperone protection. In contrast, changes in cytosolic chaperones were species-specific. HSP70 increased and HSP90 declined with age in clams, whereas in oysters HSP70 expression did not change, and HSP90 increased with aging.

Long-term monitoring studies as a powerful tool in marine ecosystem research

Global environmental challenges, such as climatic shifts, ocean acidification, and anthropogenic pressures urgently require detailed knowledge on functioning of the marine biota in order to create realistic models that predict future changes in populations, communities, and ecosystems. The long-term monitoring observations remain one of the best and sometimes the only way of acquiring knowledge on the complex seasonal and multiannual processes taking place in marine realms. This volume focuses on the long-term studies conducted for the past several decades in the White Sea, a relatively small marine basin located in sub-Arctic and Arctic zone in the northwest of Russia. It has a peculiar hydrologic structure: the upper water layers which experience strong seasonal temperature fluctuations and are inhabited by boreal organisms almost do not mix with the deeper waters which have negative temperatures the year round and are occupied by the Arctic species complex. The White Sea has a long-standing history of extensive environmental monitoring spanning all levels of the ecosystem. The goal of this special issue is to present the key findings of these studies to international research community and to identify environmental and biological processes that are involved in the ecosystem change of this important sub-Arctic marine basin.

Spatial and temporal variation of hydrological characteristics and zooplankton community composition influenced by freshwater runoff in the shallow Pechora Sea

Polar shallow marginal seas are of high importance as they are the most productive regions of the Arctic Ocean and serve as filters for terrestrial runoff. Salinity and turbidity gradients create diverse habitats for planktonic organisms in coastal areas. In the present study we aimed at assessing the degree to which environmental gradients influence the abundance and community structure of the zooplankton in a shallow Arctic sea affected by terrestrial runoff. Zooplankton distribution was studied in a coastal zone in the southeastern part of the Barents Sea (Pechora Sea) in July 2014 and September 2016 along the archipelago that stretches from the continent towards the open sea. The ecosystem was in a spring state in July (2014) and in a summer state in September (2016). A clear positive gradient of salinity and a negative cline of turbidity were revealed, directed from the coast towards the open sea. A horizontal salinity gradient was detected in both seasons. The turbidity gradient was most pronounced during summer. Distribution of several species of marine zooplankton (e.g. Pseudocalanus spp., Temora longicornis, Microsetella norvegica) was associated with the salinity gradient. Parameters of community structure (species richness, diversity, evenness, total zooplankton abundance) correlated with turbidity while only diversity and evenness were influenced by salinity. A gradient was observed from a more diverse and less abundant zooplankton community in areas with high turbidity and low salinity towards a less diverse and more abundant community in the open sea. This heterogeneity influences higher trophic levels including commercial fishes and reflects how marginal filters function.

Introduction to the Proceedings of the 49th European Marine Biology Symposium

In September 2014 a group of 130 marine biologists from 26 countries assembled in the 49th European Marine Biology Symposium (EMBS) held in Saint Petersburg, Russia. The EMBS is a series of annual conferences providing presentations and dialogue in a fairly informal atmosphere – the perfect conditions for encouraging interactions on state-of-art issues in marine science in Europe and beyond. The 49th symposium, organized by the Zoological Institute of the Russian Academy of Sciences, included four keynote lectures, 65 oral presentations and 92 poster contributions under the overarching theme ‘A variety of interactions in the marine environment’.

The rational use of the White Sea biological resources and production potential

This article is based on a paper heard at a meeting of the RAS Presidium. The state of the biological resources of the White Sea is characterized, and a conclusion about the high production potential of its biota is made in the article. It is shown that the reserves of herring (herring being the main fishery object), overexploited by excessive fishing and other anthropogenic impacts, are not limited by zooplankton production. In the authors’ opinion, the rational use of the White Sea’s production potential and the recovery from a fishery depression is the mariculture of White Sea organisms.