High prevalences of disseminated neoplasia in the Baltic tellin Limecola balthica in the Wadden Sea.

The Baltic tellin Limecola balthica is one of the most common bivalves in intertidal areas in the Northern Hemisphere. Over the last 2 decades, the species has been suffering from a decrease in adult survival in the European Wadden Sea. While several factors such as global warming and fisheries have been suggested to influence the population dynamics of this bivalve mollusc, the potential role of diseases has never been investigated. In this study, we investigated whether disseminated neoplasia, a common proliferative disorder in bivalve molluscs, could play a potential role in the recent population decline of Baltic tellins in the Wadden Sea. We conducted a field survey in the Dutch Wadden Sea to (1) determine whether the disease occurs in Baltic tellins in the Wadden Sea and (2) quantify the occurrence and severity of the disease via histology. Disseminated neoplasia occurred in L. balthica at each of the 10 sampled locations with very high prevalences (21-89%) compared to those reported elsewhere for this species. The highest severity category was found in 8 to 87% of affected individuals, with severity generally increasing with prevalence. Disseminated neoplasia usually increases mortality among affected individuals and may also be associated with important sub-lethal effects, especially regarding gametogenesis. Thus, we suggest that disseminated neoplasia may play a key role in the population dynamics of the Baltic tellin, the extent of which remains to be investigated in future studies.

Cellular level response of the bivalve Limecola balthica to seawater acidification due to potential CO2 leakage from a sub-seabed storage site in the southern Baltic Sea: TiTank experiment at representative hydrostatic pressure.

Understanding of biological responses of marine fauna to seawater acidification due to potential CO2 leakage from sub-seabed storage sites has improved recently, providing support to CCS environmental risk assessment. Physiological responses of benthic organisms to ambient hypercapnia have been previously investigated but rarely at the cellular level, particularly in areas of less common geochemical and ecological conditions such as brackish water and/or reduced oxygen levels. In this study, CO2-related responses of oxygen-dependent, antioxidant and detoxification systems as well as markers of neurotoxicity and acid-base balance in the Baltic clam Limecola balthica from the Baltic Sea were quantified in 50-day experiments. Experimental conditions included CO2 addition producing pH levels of 7.7, 7.0 and 6.3, respectively and hydrostatic pressure 900 kPa, simulating realistic seawater acidities following a CO2 seepage accident at the potential CO2-storage site in the Baltic. Reduced pH interfered with most biomarkers studied, and modifications to lactate dehydrogenase and malate dehydrogenase indicate that aerobiosis was a dominant energy production pathway. Hypercapnic stress was most evident in bivalves exposed to moderately acidic seawater environment (pH 7.0), showing a decrease of glutathione peroxidase activity, activation of catalase and suppression of glutathione S-transferase activity likely in response to enhanced free radical production. The clams subjected to pH 7.0 also demonstrated acetylcholinesterase activation that might be linked to prolonged impact of contaminants released from sediment. The most acidified conditions (pH 6.3) stimulated glutathione and malondialdehyde concentration in the bivalve tissue suggesting potential cell damage. Temporal variations of most biomarkers imply that after a 10-to-15-day initial phase of an acute disturbance, the metabolic and antioxidant defence systems recovered their capacities.

Seafloor sediments as microplastic sinks in the northern Baltic Sea - Negligible upward transport of buried microplastics by bioturbation.

Microplastics (MPs) are ubiquitous in the marine environment. High concentrations of MPs are found from seafloor sediments, which have been proposed to act as their final sinks. Because bioturbation is an important process affecting the burial of MPs, a mesocosm experiment was established to study whether sediment infauna may also promote MP return to the sediment surface. Thin layers of frozen sediment containing an environmentally realistic concentration (<1300 MPs per kg of dry sediment) of MP fragments in two size classes (>500 µm and 100-300 µm) were added to depths of 2 cm and 5 cm in the experimental cylinders filled with sediment. The displacement of these MPs, made of acrylonitrile butadiene styrene (ABS), by a community of common benthic invertebrates in the northern Baltic Sea (clam Limecola balthica, polychaete Marenzelleria spp., gammarid Monoporeia affinis) was studied in a 10-week experiment. After the experiment, the MPs were extracted from each sediment layer and the animals were examined for MP ingestion. The results indicated that the transportation of MPs to the sediment surface by bioturbation was negligible. Thus, in the Baltic Sea, the seafloor may act as a sink for once sedimented MPs, reducing simultaneously the MP exposure of the macrofauna feeding on the sediment surface.

Transcriptome of the bivalve Limecola balthica L. from Western Pacific: A new resource for studies of European populations.

The Baltic clam Limecola balthica L. (Tellinidae) is broadly used in ecophysiological, toxicological, evolutionary and environmental monitoring studies. However, it is poorly studied in respect of genome and gene functions. We obtained a transcriptome of Limecola b. balthica from Kamchatka (Western Pacific) generated with the use of Illumina high-throughput sequencing. We annotated 11,374 proteins, including 53 from the oxidative phosphorylation pathway and a number of pollution-stress biomarkers, recovered 254,540 single nucleotide variants within two annotated transcriptomes including 25,330 scorable in the previously published European data. Our results confirmed the available allozyme data indicating that nuclear genomes of the clams from the Baltic Sea were intermediate in their genetic composition between the Pacific (L. b. balthica) and the Atlantic (L. b. rubra) subspecies. At the same time, the mitochondrial genomes of Limecola from Kamchatka were nearly identical to the single published genome from the Baltic. The genomic diversity in Limecola was found to be high and comparable with that of other marine mollusks (0.0138 and 0.0142 heterozygous positions in the two studied transcriptomes). The data obtained in our study are a valuable resource for further development of genomic markers for evolutionary genetic and ecophysiological studies of L. balthica complex.

Differing responses of the estuarine bivalve Limecola balthica to lowered water pH caused by potential CO2 leaks from a sub-seabed storage site in the Baltic Sea: An experimental study.

Sub-Seabed CCS is regarded as a key technology for the reduction of CO2 emissions, but little is known about the mechanisms through which leakages from storage sites impact benthic species. In this study, the biological responses of the infaunal bivalve Limecola balthica to CO2-induced seawater acidification (pH7.7, 7.0, and 6.3) were quantified in 56-day mesocosm experiments. Increased water acidity caused changes in behavioral and physiological traits, but even the most acidic conditions did not prove to be fatal. In response to hypercapnia, the bivalves approached the sediment surface and increased respiration rates. Lower seawater pH reduced shell weight and growth, while it simultaneously increased soft tissue weight; this places L. balthica in a somewhat unique position among marine invertebrates.

Abnormalities in bivalve larvae from the Puck Bay (Gulf of Gdansk, southern Baltic Sea) as an indicator of environmental pollution.

This study described the occurrence of abnormalities in bivalve larvae from the Puck Bay. Analyses of plankton samples collected in 2012-2013 showed that larval Mytilus trossulus, Mya arenaria, and Cerastoderma glaucum exhibited abnormalities that could indicate adverse environmental impacts. The deformities were mainly in shells, but missing soft tissue fragments and protruding vela were also noted. In addition to larval studies, we analyzed benthic postlarvae of Mytilus trossulus. Interestingly, grooves and notches at different locations of the prodissoconch, dissoconch, and shell margin were observed. Some of these deformations were reminiscent of the indentations found on the shell edge of larvae. Comparing the proportion of abnormal postlarvae to larvae with shell abnormalities suggested that the survival of larvae with shell abnormalities was low. Overall, our results suggested that the ratio of abnormal bivalve larvae could be used as an indicator of the biological effects of hazardous substances in the pelagic environment.

Impact of environmental hypercapnia on fertilization success rate and the early embryonic development of the clam Limecola balthica (Bivalvia, Tellinidae) from the southern Baltic Sea - A potential CO2 leakage case study.

Carbon capture and storage technology was developed as a tool to mitigate the increased emissions of carbon dioxide by capture, transportation, injection and storage of CO2 into subterranean reservoirs. There is, however, a risk of future CO2 leakage from sub-seabed storage sites to the sea-floor sediments and overlying water, causing a pH decrease. The aim of this study was to assess effects of CO2-induced seawater acidification on fertilization success and early embryonic development of the sediment-burrowing bivalve Limecola balthica L. from the Baltic Sea. Laboratory experiments using a CO2 enrichment system involved three different pH variants (pH 7.7 as control, pH 7.0 and pH 6.3, both representing environmental hypercapnia). The results showed significant fertilization success reduction under pH 7.0 and 6.3 and development delays at 4 and 9 h post gamete encounter. Several morphological aberrations (cell breakage, cytoplasm leakages, blastomere deformations) in the early embryos at different cleavage stages were observed.

Bioturbation activity of three macrofaunal species and the presence of meiofauna affect the abundance and composition of benthic bacterial communities.

Given concerns of increasing rates of species extinctions, the relationship between biodiversity and ecosystem functioning has become a major research focus over the past two decades. Many studies have shown that biodiversity per se (e.g. species richness) or species-specific traits may be good predictors of changes in ecosystem function. Although numerous studies on this subject have focused on terrestrial systems, few have evaluated benthic marine systems. We used the Limecola balthica community as a model to test whether the number or identity of three well-studied macrofaunal species influence the sediment bacterial compartment, which drives important biogeochemical processes and influence ecosystem functioning. We also investigated the poorly known role of meiofauna in the interactions between macrofauna and bacteria. Eight combinations of 0-3 species were maintained in microcosms for 34 days in the presence or absence of meiofauna. The abundance and composition of the bacterial community, defined by the relative percentage of cells with a high (HNA) vs low (LNA) nucleic acid content, were measured. Species identity of macrofauna was a better indicator of changes in the microbial compartment than was species richness per se. In particular, the gallery-diffuser behaviour of the polychaete Alitta virens likely induced strong changes in sediment physical and geochemical properties with a major impact on the bacterial compartment. Moreover, the presence of meiofauna modulated the influence of macrofauna on bacterial communities. This study provides evidence that species identity provides greater explanatory power than species richness to predict changes in the bacterial compartment. We propose that multi-compartment approaches to describe interactions amongst different size classes of organisms and their ecological roles should be further developed to improve our understanding of benthic ecosystem functioning.

The effects of low seawater pH on energy storage and heat shock protein 70 expression in a bivalve Limecola balthica.

Though biological consequences of CCS (Carbon Capture and Storage) implementation into the marine environment have received substantial research attention, the impact of potential CO2 leakage on benthic infauna in the Baltic Sea remained poorly recognized. This study quantified medium-term (56-day laboratory exposure) effects of CO2-induced seawater acidification (pH 7.7, 7.0 and 6.3) on energetic reserves and heat-shock protein HSP70 expression of adult bivalve Limecola balthica from the southern Baltic. While no clear impact was evident in the most acidic treatment (pH 6.3), moderate seawater hypercapnia (pH 7.0) induced elevated catabolism of high caloric reserves (carbohydrates including glycogen and lipids) in order to provide energy to cover enhanced metabolic requirements for acid-base regulation. Biochemical response did not involve, however, breakdown of proteins, suggesting that they were not utilized as metabolic substrates. As indicated also by subtle variations in the chaperone protein HSP70, the clams demonstrated high CO2 tolerance, presumably through development of efficient defensive/compensatory mechanisms during their larval and/or ontogenic life stages.