Effect of eutrophication on the distribution and ecophysiology of the mussel Mytilus trossulus (Bivalvia) in southern Baltic Sea (the Gulf of Gdańsk)

Abstract

The effect of eutrophication on benthos is usually reported as negative. In the case of the Gulf of Gdańsk, eutrophication has increased the availability of food resources to filter feeders such as mussels, affecting their physiology and vertical distribution. Comparative studies of the mussel Mytilus trossulus from two depth zones (10 m and 40 m) over a seasonal cycle revealed ecophysiologic differences between deep-and shallow-water animals. For the same shell length, the shallow-water mussels were heavier (dry weight ϭ 0.004L 2.297 ) and showed a higher weight index (dry weight/volume), averaging 3.8 Ϯ 1.9 mg cm Ϫ3 , than the deep-water mussels (dry weight ϭ 0.0002L 1.726 and 2.5 Ϯ 1.1 mg cm Ϫ3 ), primarily because of a nearly twofold greater carbohydrate store. In the shallow zone, females contained more carbohydrates (on average 5.8% dry weight) than males (3.8% dry weight) because females conserve energy for reproduction. Differences in physiologic variables, and subsequently physiologic performance of the mussels, were related to different nutritional conditions in the ambient water. The deep habitat had lower Chl a, averaging 1.1 mg L Ϫ1, total particulate matter (TPM) 4.3 mg L Ϫ1 and particulate organic matter (POM) 1.1% of TPM as compared with the shallow habitat, with average Chl a 2.5 mg L Ϫ1 , TPM 4.9 mg L Ϫ1 , and POM 1.5%. The eutrophication of the Gulf of Gdańsk has led to an increase in the food availability in the water column, which allowed efficient colonization of the deep zone by the mussels; however, the dominance of males over females (ϳ3 : 1) suggests that the food sustains only spawning-related metabolic demands and is not sufficient for energy conservation in this zone. Starch gel electrophoresis of eight enzyme loci showed no statistical differences in the allele and genotype frequencies between the shallow-and deep-water mussels; thus, the differences in ecophysiologic traits between depths are due to acclimatization.

Waterbird Populations and Pressures in the Baltic Sea

“…Current eutrophication impacts on bivalve populations are not well known, and may differ between the different coastal regions of the Baltic Sea, and even within regions impacts may show a diversity of trends (Lundberg 2005). Thus, conceptual models showing responses of bivalve-feeding waterbirds to nutrient enrichment in coastal areas of the Baltic Sea may ideally represent a dome-shaped response reflecting both the impoverished benthic conditions and hypoxia in enclosed areas with mixing constraints and even in more exposed areas during extreme events of oxygen deficiency, and positive relations between eutrophication and the growth of bivalve stocks found in more exposed areas (Cloern 2001, Wolowicz et al 2006. Areas which are consistently oxygen-depleted will suffer mortality of benthic organisms, and also more mobile species such as fish will die if unable to escape the oxygen-depleted area.…”

Seasonal variation in the reproductive activity, physiological condition and biochemical components of the brown musselPerna pernafrom the coastal waters of Yemen (Gulf of Aden)

“…Multiple intermittent spawning has been often observed in ecosystems where the resident mussels live under environmental stress, including stress from the thermal regime, prolonged aerial exposure and restricted productivity e.g. in the upwelling area (Griffiths 1977) or in eutrophicated water-basins (Newell et al 1982;Wołowicz et al 2006). It has been therefore hypothesized that under adverse hydrological conditions, e.g.…”

Estuaries — a biological point of view

“…In the following years, all populations resembled the Atlantic type, probably due to the inflow of North Sea water and/or different environmental selection pressures (Hummel et al 2000). Similarly, in Mytilus trossulus from the Gulf of Gdańsk the allele frequencies of the octopine dehydrogenase locus (Odh) showed a tendency to vary with depth, suggesting a possible role of this enzyme in adaptation to deep-water habitats , Wołowicz et al 2006. In addition to naturally occurring genetic changes, human driven alterations (for example resulting from pollution) have been shown in recent studies.…”

“…What is more, intense exploitation of the coastal zone and the open sea by humans for a wide range of uses such as industry, energy production, shipping, commercial fishing, extraction of oil, sand and gravel, and dumping of dredged materials have a major impact on the water quality. The Baltic has been subjected to significant anthropogenic inputs of nutrients and pollutant contaminants during the last century, and eutrophication and pollution now have large-scale implications (AErtebjerg et al 2001, Wołowicz et al 2006. Clear-cut alterations in the structure and function of the ecosystem have been observed in the Gulf of Gdansk, and extend, to various degree, across the entire Baltic.…”

“…The observed ecophysiological phenomena are likely to derive from acclimatisation of the bivalves to the locally different environmental conditions (e.g. temperature, salinity and dissolved oxygen), the availability of food has also been suggested as having a primary impact on the ecophysiological differentiation of the mussels (Wołowicz et al 2006). Similar depth-related local physiological differences have been also reported for the Baltic clam Macoma balthica, whose deep-water subpopulation showed distinct ecophysiological features (condition index, biochemical composition and gonadal development cycle) compared to the shallow-water subpopulation (Bonsdorff, Wenne 1989;Hummel et al 2000).…”