Physical microhabitat requirements of freshwater pearl mussels,Margaritifera margaritifera (L.)

Surface sediment diatoms from the east coast of Lake Tanganyika were analysed using ordination and classification techniques, and compared with assemblages previously described from the northern part of the lake. Grain-size analyses were performed on subsamples. Four groups of diatom assemblages were recognised. The first group clusters samples taken in the north, far from the Rusizi river mouth. The second group comprises samples taken on silty sediment along the Tanzanian coast, including one sample taken near the mouth of the Malagarazi river and those from the northernmost part of the lake. The third group comprises surface sediments along the Burundian coast (near Ramba and Magara), and the fourth is characterised by epipsammic taxa. A sample taken near the central arm of the Malagarazi river is included in the latter group. The impact of small rivers on the diatom assemblages in the surface sediments is restricted to the mouth area.     

Discontinuities in technological and natural systems caused by exotic species

This discussion focuses on discontinuities in both natural and technological systems caused by the introduction of exotic species into areas which they would not have been able to reach without human assistance or other alterations to native communities. The case histories of both the Asian clam and the zebra mussel are particularly instructive because of their recent introductions and the dramatic impact they have had on both natural and technological systems. Control of these mollusc species in technological systems (e.g. water intake systems) is effective to a degree but requires constant attention and utilization of resources. If control is neglected there could be extremely serious consequences. At present, no inexpensive means exist for controlling their effects, and further geographical distribution in North America is highly probable. The mollusc case histories do not appear to be linear and, in some instances, may not be continuous. Some importations of exotic species were deliberate (such as the gypsy moth, Porthetria dispar), but their escape into natural systems has often been accidental or, a less charitable person might say, careless. A viable strategy for coping with discontinuities is elusive. Discontinuities will, undoubtedly, have a major effect on the possibility of sustainable use of the planet or, to use the currently popular term, sustainable development.     

Seasonal reproductive cycle in the mussel,Lamellidens corrianus

Seasonal reproductive cycle of the freshwater mussel, Lamellidens corrianus has been studied. These mussels are functional or simultaneous hermaphrodites. The spawning was at its peak during the months of September to December. The gonads were in growing stages with reduced gonadal activity during January to April, whereas the maturation of gonads was found to be intense during May to August.     

The Crown Pearl: a draft genome assembly of the European freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758)

Since historical times, the inherent human fascination with pearls turned the freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) into a highly valuable cultural and economic resource. Although pearl harvesting in M. margaritifera is nowadays residual, other human threats have aggravated the species conservation status, especially in Europe. This mussel presents a myriad of rare biological features, e.g. high longevity coupled with low senescence and Doubly Uniparental Inheritance of mitochondrial DNA, for which the underlying molecular mechanisms are poorly known. Here, the first draft genome assembly of M. margaritifera was produced using a combination of Illumina Paired-end and Mate-pair approaches. The genome assembly was 2.4 Gb long, possessing 105,185 scaffolds and a scaffold N50 length of 288,726 bp. The ab initio gene prediction allowed the identification of 35,119 protein-coding genes. This genome represents an essential resource for studying this species’ unique biological and evolutionary features and ultimately will help to develop new tools to promote its conservation.     

Morphological and morphometrical description of the glochidia of Westralunio carteri Iredale, 1934 (Bivalvia: Unionoida: Hyriidae)

Most freshwater mussel (Bivalvia: Unionoida) larvae (glochidia in Margaritiferidae, Hyriidae and Unionidae) are fish parasites. Knowledge of the larval morphology and the mechanism of release in freshwater mussels is useful in species systematics and ecology. Westralunio carteri is the only unionoid from south-western Australia. Little information is available on its biology and its glochidia have never been described. The aim of this study was to describe the glochidia of W. carteri and method of their release. Glochidia within vitelline membranes were embedded in mucus which extruded from exhalent siphons of females during spring/summer; they then hatched from vitelline membranes but remained tethered by a larval thread and began characteristically “winking”. Shells (n=120) were subtriangular, 308 μm long (±0.83 SE), 251 μm high (±0.73 SE) and had a hinge length of 212 μm (±0.78 SE). Larval teeth were singular with interlocking cusps and convex or concave basal protuberances on opposing valves.     

Development of an expert system for the integration of biomarker responses in mussels into an animal health index

Biomarkers on sentinel organisms are utilised worldwide in biomonitoring programs. However, the lack of effective interpretational capacity has hampered their uptake for use for assessment of risk in environmental management. The aim of the present study was to develop and test an objective decision-support or expert system capable of integrating biomarker results into a five-level health-status index. The expert system is based on a set of rules derived from available data on responses to natural and contaminant-induced stress of marine mussels. Integration of parameters includes: level of biological organization; biological significance; mutual inter-relationship; and qualitative trends in a stress gradient. The system was tested on a set of biomarker data obtained from the field and subsequently validated with data from previous studies. The results demonstrate that the expert system can effectively quantify the biological effects of different levels of pollution. The system represents a simple tool for risk assessment of the harmful impact of contaminants by providing a clear indication of the degree of stress syndrome induced by pollutants in mussels.     

Application of two SH-based methods for metallothionein determination in mussels and intercalibration of the spectrophotometric method: laboratory and field studies in the Mediterranean Sea

Metallothionein (MT) induction is widely used as a biomarker of exposure to metals in mussels. The aims of the present work were first to compare the suitability of spectrophotometry and differential pulse polarography (DPP) for MT detection in mussels exposed to 200 ppb cadmium for 9 days in a laboratory experiment and in mussels sampled in different seasons from expected pollution gradients along the Mediterranean Sea; second, to intercalibrate the widely used spectrophotometric method using mussels from Saronikos Gulf. In the intercalibration of the spectrophotometric method, similar results (p>0.05) were obtained by two different research teams indicating a good reproducibility of the technique. However, polarographic and spectrophotometric methods gave significantly (p<0.05) different results in laboratory and field studies. In the laboratory experiment, MT values detected with DPP were nine times higher than with spectrophotometry. The results obtained by the two methods were significantly correlated. Both methods could discriminate between control and exposed mussels. In field studies, MT values obtained by DPP were 34–38-fold higher than with spectrophotometry, and MT concentrations measured by both methods were not correlated. This discrepancy could be due to several factors, including the low levels of bioavailable metals in the studied areas and the possibility that the different methods can measure MT isoforms differentially. Further work is needed to decipher the functions of MT isoforms in mussels. This information is relevant for the application of MT as a biomarker in biomonitoring programmes.     

Larval settlement and metamorphosis of the mussel Mytilus coruscus in response to natural biofilms

Settlement and metamorphosis of pediveliger larvae of Mytilus coruscus in response to natural biofilms was investigated in the laboratory. Pediveliger larvae settled and metamorphosed in response to biofilms and post-larval settlement and metamorphosis increased with biofilm age. The activity of the biofilm was positively correlated with biofilm age, dry weight, bacterial density and diatom density, but had no apparent relationship with chlorophyll a concentration. The change in bacterial community composition corresponding to biofilm age may explain differences in the age-dependent inducing activities of biofilms, which in turn may play an important role in larval settlement in this species.     

Detachment,displacement and reattachment activity in a freshwater byssate mussel (Limnoperna fortunei): the effects of light,temperature and substratum orientation

The ability of the freshwater bivalve Limnoperna fortunei to voluntarily detach from the substratum, crawl and reattach as a function of illumination, temperature, substratum orientation, and mussel size was investigated. Thirty-two per cent of the 879 experimental animals detached and reattached elsewhere at least once during five- to eight-day experiments. The proportions of mobile mussels were significantly higher in permanent darkness than under permanent illumination. Displacement distances were also higher in darkness, but statistical differences with illuminated individuals were inconclusive. No evidence of circadian rhythms was detected. Mobile mussels were often significantly smaller than non-mobile individuals. It was not possible to detect the effect of water temperature (22°C and 31°C), or substratum orientation (topside and underside) on mussel mobility, but because the power of the statistical tests was low, future experiments are needed to confirm this result. The ability of mussels to voluntarily detach and reattach elsewhere has important implications for biofouling control.