Do magnetic fields related to submarine power cables affect the functioning of a common bivalve?

The aim of the study was to determine the effect of static magnetic field (SMF) and electromagnetic field (EMF), of values usually recorded near submarine cables, on the bioenergetics, oxidative stress, and neurotoxicity in the cockle Cerastoderma glaucum. Bivalves maintained a positive energy balance, but the filtration rate and energy available for individual production were significantly lower in SMF-exposed animals compared to the control treatment. No changes in the respiration were noted but ammonia excretion rate was significantly lower after exposure to EMF. Changes in the activities of antioxidant enzymes and the lipid peroxidation were not observed however, exposure to both fields resulted in increased protein carbonylation. After exposure to EMF a significant inhibition of acetylcholinesterase activity was observed. As the present study for the first time revealed the oxidative damage and neurotoxicity in marine invertebrate after exposure to artificial magnetic fields, the need for further research is highlighted.

Next-generation phylogeography of the cockle Cerastoderma glaucum: Highly heterogeneous genetic differentiation in a lagoon species

AIM

Coastal lagoons form an intriguing example of fragmented marine habitats. Restricted gene flow among isolated populations of lagoon species may promote their genetic divergence and may thus provide a first step toward speciation. In the present study, the population genetic structure of the lagoon cockle Cerastoderma glaucum has been investigated to clarify the complex phylogeographic pattern found in previous studies, to localize major genetic breaks, and to discuss their origin and maintenance.

LOCATION

The Atlantic and Mediterranean coasts, including the Baltic, North Sea, and Black Sea.

METHODS

A total of 204 C. glaucum individuals from 14 populations were genotyped using restriction site-associated DNA sequencing (RADseq). The genetic diversity, divergence, and structure were analyzed using genome-wide single nucleotide polymorphisms (SNPs). Phylogenetic relationships were inferred under a coalescent model using svdquartets.

RESULTS

The RADseq approach allowed inferring phylogeographic relationships with an unprecedented resolution. Three deeply divergent lineages were identified within C. glaucum that are separated by many genetic barriers: one lineage in the Aegean-Black Sea region, one in the Ionian Sea, and the last one widely distributed from the Western Mediterranean to the Baltic Sea. The nested branching pattern displayed on the species tree largely agrees with the likely scenario of C. glaucum postglacial expansion from the Mediterranean to the Baltic Sea.

MAIN CONCLUSION

The genetic differentiations between geographically separated lagoons proved to be strong, highlighting the evolutionary influence of these naturally fragmented habitats. The postglacial expansion created complex patterns of spatial segregation of genetic diversity with allele frequency gradients in many outlier loci, but also discrepancies between the nuclear and mitochondrial genetic markers that probably arose from genetic surfing of mitochondrial variation.

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.

The reproductive cycle, condition index, and glycogen reserves of the cockles Cerastoderma glaucum from the Gulf of Gabès (Tunisia)

The gametogenic cycle of the Cerastoderma glaucum was analyzed using both qualitative and semi-quantitative methods. The condition index and glycogen concentrations were determined in order to provide information on energy storage. The cockles were collected monthly from a Bayyadha site located 15 km south of Sfax City (Gulf of Gabès) between January 2007 and January 2008. From histological point of view, we applied two approaches: (i) the qualitative method describing the various stages of gamete development for males and females during a cycle of 13 months, and (ii) the semi-quantitative method concerning the estimation of different tissue surfaces. The results showed that there is evidence of three periods of reproduction in this population. A comparison between the surfaces occupied by the three organs showed that the foot and the gonad surfaces are higher than the surface of the adductor muscle. This could suggest that these two organs are more involved in the process of glycogen reserve storage. The results of the glycogen concentrations in the different tissues (gonad, adductor muscle, and "remainders") show that during the second and third periods of reproduction, glycogen was stored in the adductor muscle and in the remainder during sexual rest, and in the gonad during the gametogenesis phases in order to supply the reproductive effort. On the contrary, in the first period of reproduction, the low concentrations of glycogen recorded in the gonad coincided with its high degree of development. This fact could be related to environmental conditions (low temperature and food) recorded during this period.

Transcriptional response of stress-regulated genes to industrial effluent exposure in the cockle Cerastoderma glaucum

This study assessed the responses of molecular biomarkers and heavy metal levels in Cerastoderma glaucum exposed for 1 week to two industrial effluents (1%) discharged into the Tunisian coastal area, F1 and F2, produced by different units of production of a phosphate treatment plant. A significant uptake of metals (Cd, Cu, Zn, and Ni) was observed in exposed cockles compared to controls, with an uptake higher for F1 than for F2. A decrease in LT50 (stress on stress test) was also observed after an exposure to the effluent F1. Treatments resulted in different patterns of messenger RNA (mRNA) expression of the different genes tested in this report. Gene transcription monitoring performed on seven genes potentially involved in the tolerance to metal exposure showed that for both exposures, mechanisms are rapidly and synchronically settled down to prevent damage to cellular components, by (1) handling and exporting out metal ions through the up-regulation of ATP-binding cassette xenobiotic transporter (ABCB1) and metallothionein (MT), (2) increasing the mRNA expression of antioxidant enzymes (catalase (CAT), superoxide dismutases, CuZnSOD and MnSOD), (3) protecting and/or repairing proteins through the expression of heat shock protein 70 (HSP70) mRNAs, and (4) increasing ATP production (through the up-regulation of cytochrome c oxidase 1 (CO1)) to provide energy for cells to tolerate stress exposure. The tools developed may be useful both for future control strategies and for the use of the cockle C. glaucum as a sentinel species.