Mussel Condition Index Research Articles

Seasonal variation in the nutrient composition of mussels (Mytilus galloprovincialis) from farms in Boka Kotorska Bay, Southern Adriatic Sea

The aim of this study was to investigated the seasonal variation in the nutrient composition of Mytilus galloprovincialis, cultivated in Boka Kotorska Bay, Montenegro, during all seasons in one year. Biometric parameters, meat yield, condition index, proximate composition, minerals, and the lipid and fatty acid compositions of mussels were analyzed. The most significant factors determining these parameters were temperature, food amount and gametogenesis The biometric parameters showed no significant differences during the sampling period. In the spring, meat yields and mussel condition index increased at substantial levels. Low values od meat yield and condition index during cold months have resulted from food shortage and reproductive cycle, when mussels use carbohydrates and protein reserves. The highest amount of protein was detected in mussels harvested in August (10.76%), while the highest amount of lipids was recorded in the winter months (2.11%). Docosahexaenoic acid and eicosapentaenoic acid were the most abundant PUFA. The concentration of metals found in mussels from the study area is within the range of mean values reported in the literature. Our results indicate that the best period for mussels harvesting was during the spring and summer (April and August), opposite the winter months when the mussels were not favorable for harvesting.

Raft and Longline Culture of Green Mussel, Perna viridis, in Cañas Bay, Iloilo, Philippines

Grow-out methods like the raft and longline have been utilized by various countries in growing green mussel, Perna viridis. In the Philippines, the stake method using bamboo poles is still widely used, which is believed to cause siltation that negatively affects green mussel production. In this study, the feasibility of raft and longline methods was determined based on mussel growth and the condition index (CI). Environmental conditions in Cañas Bay, Iloilo were also presented. Results showed that there was no significant difference in mussel growth except for final weight, where mussels in the raft were found to be significantly heavier than those in the longline. Meanwhile, the CI of mussels did not significantly differ between the two methods. Physico-chemical parameters of the water in Cañas Bay were found to be suitable for growing green mussels. Phytoplankton was composed of diatoms (86%), dinoflagellates (6%), green algae (5%), and blue-green algae (3%). This study showed the feasibility of using suspended methods like raft and longline in areas where environmental conditions favor mussel growth.

An IMTA in Greece: Co-Culture of Fish, Bivalves, and Holothurians

Integrated multitrophic aquaculture (IMTA) is an innovative mariculture methodology that reduces the environmental footprint and increases the profitability of the farm. It combines the cultivation of species belonging to different trophic levels, simulating a natural food web. In this study, five Mediterranean species were co-cultured in three operating fish farms in the Aegean (E. Mediterranean) Sea with different trophic conditions. The co-cultivated species were sea bream (Sparus aurata), European sea bass (Dicentrarchus labrax), Mediterranean mussel (Mytilus galloprovincialis), rayed pearl oyster (Pinctada imbricata radiata), and sea cucumber (Holothuria polii). Bream, bass, and mussels were cultivated according to the traditional on-growing methods (fish cages and longlines), whereas the pearl oysters and sea cucumbers were cultivated in baskets designed specifically for oyster farms. To estimate the growth of the co-cultivated species, growth indicators were calculated using length and weight measurements. Furthermore, the growth measurements from co-cultivated species were compared to the respective ones from natural populations. All the species showed high survival rates in the integrated multitrophic aquaculture (IMTA) conditions. Pearl oysters and Mediterranean mussels had positive growth in fish farms with high concentrations of nutrients. Mussel condition index (CI) was 42% in Aquaculture 1 (Aq1) and 33% in Aquaculture 2 (Aq2), compared to 35% in a typical Mediterranean mussel farm. Pearl oysters CI in Aq1 was 53%, in Aq2 56%, in Aquaculture 3 (Aq3) 19%, and in natural populations ranging from 30% to 45%. In contrast, holothurians did not gain weight under the fish cage regime despite the high survival rate. Their final total weight was 17.3 g in Ag1, 8.3 g in Aq2, and 18.3 g in Aq3, but in the natural population, the mean weight was 80 g.

Microplastics and food shortage impair the byssal attachment of thick-shelled mussel Mytilus coruscus

Microplastics (MPs) have become a ubiquitous emerging pollutant in the global marine environment. The potential toxic effects of MPs and interactions of MP pollution with other stressors such as food limitation on marine organisms’ health are not yet well understood. This study investigated the effects of three-week exposure to different MPs and food shortage on the physical defense mechanisms (byssus production and properties) of Mytilus coruscus. Starvation significantly reduced the number of byssus threads, and combined exposure to MPs and food shortage suppressed the adhesion ability and condition index of mussels. The length of the byssus threads was not affected by all experimental exposures. Transcript levels of genes encoding key proteins involved in byssus formation (the mussel foot proteins mfp-1, -2, -3, -4, -5 and -6, and prepolymerized collagen proteins preCOL-D, -P and -NG) were altered by interactions between the MPs and food shortage. These findings show that insufficient food supply can exacerbate the adverse effects of MPs on mussel defense which might have implications for survival and fitness of mussels under food limited conditions (e.g. in winter) in polluted coastal habitats.

Not only greening: The effects of marennine produced by Haslea ostrearia on physiological traits of three bivalve species

The marine diatom Haslea ostrearia is known for its ability to produce marennine, a blue-green water-soluble pigment, which is responsible for the oyster greening phenomenon in the French Atlantic Coast. Marennine can be considered a bioactive extracellular compound (BEC) as it exhibits activities against detrimental pathogens in bivalve aquaculture. However, marennine could also be toxic to animals. The aim of this experimental study was to assess the effect of marennine produced by H. ostrearia upon three commercially important bivalve species, the American oyster Crassostrea virginica, the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus. Effect of this BEC was also assessed on different ontogenic stages of scallops. The animals were exposed to 3 mg L−1 of marennine and physiological response associated with clearance rates (CR), oxygen consumption and condition index (CI) were measured after 16 h of exposure (day 0), and after one subsequent week of recovery (day 7). In the short term, CR and oxygen consumption on mussels and oysters were significantly altered by marennine but not for scallops. CR recovery was observed in oysters after seven days, but no depuration was observed in mussels. Nevertheless, oxygen consumption in both mussels and oysters recovered on day 7. CI in the marennine-exposed group for both adult oysters and scallops was not significantly different, yet CI of mussels was lowered by 18.2 % compared to control. Scallop adults seemed largely resistant to marennine, but juveniles were more susceptible with a reduced CR and oxygen consumption by 71.9 % and 24.5 %, respectively, and no depuration activity observed until day 7. Additionally, CI in marennine-exposed juvenile scallops was 27 % lower than that of control. This study demonstrates species- and age-specific effect of marennine on bivalves, thus highlighting the importance of further assessment on the utilization of this pigment as a natural product decreasing pathogenicity of bacteria in shellfish aquaculture systems.

Net cages enhance golden mussel (Limnoperna fortunei) larval density and condition factor

Abstract Cage fish farming is an important economic activity in Brazil where tilapia (Oreochromis niloticus) is the main cultivated species. To investigate the cage fish farm as a vector for golden mussel invasion, we hypothesised that: (1) Limnoperna fortunei, a freshwater bivalve mollusc, finds greater food availability in the cage fish farm; (2) the cage fish farm favours mollusc colonisation and its nutritional status; and (3) its performance in the reservoir would vary over the year. We obtained data from limnological variables as well as the number of larvae and adult individuals, to evaluate condition index (CI) monthly from February 2015 to January of 2016. We established sampling stations at three points with fish farming and three points without fish farming (controls) in the Canoas II Reservoir, Paranapanema River, Brazil. We used principal component analysis (PCA) to identify spatial and temporal distribution of samples according to limnological variables. We performed a linear mixed model analysis to test the hypothesis of no difference between areas (fish farm and control) and time (months) for larval density and CI of L. fortunei. The first PCA axis (28.48% of variance) revealed a temporal gradient, showing the separation between cold and hot months. The second PCA axis (19.61% of variance) separated the samples of control and fish farms; fish farms displayed higher concentrations of total phosphorus, nitrite, and chlorophyll a. Larval densities of L. fortunei were higher in fish cage areas with time being responsible for 35% of this variation. Mussel CI was also higher in fish farms and time was responsible for 36% of the variation. We conclude that fish production in cages contributes to the establishment of golden mussels in the reservoir. Our results serve as a warning that other molluscs or invasive species may be favoured by aquaculture activities in aquatic environments. The colonisation of the mussel in the reservoir varies during the year in response to seasonality.

Assessment of Environmental Quality in the Tamaulipas Laguna Madre, Gulf of Mexico, by Integrated Biomarker Response Using the Cross-Barred Venus Clam Chione elevata

The entire Laguna Madre of Tamaulipas is a natural protected area and a Priority Marine Region of Mexico. However, its important biodiversity and high levels of endemism are threatened by the discharge of different pollutants and activities related to the ocean oil and gas industry. Therefore, the assessment of these effects on this marine ecosystem is of paramount importance. At present, the joint approach of monitoring chemical contaminant levels, alongside the use of pollution biomarkers as surrogate measures of biological impact within the environment, provides the better evaluation of the environmental hazard. Within this context, a biomonitoring study using native Chione elevata mussels sampled from four locations along the Mexican Laguna Madre coasts evaluated whether a battery of select biomarkers was suitable for identifying and quantifying pollution-induced stress in mussels. The levels of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), alkaline phosphatase (ALP), glutathione s-transferase (GST), and the oxygen radical absorbance capacity (ORAC) were measured in soft tissues samples. Different metals (Cd, Pb, Cu, Zn, and Fe) as well as total heavy hydrocarbons were also determined in sediments. Higher concentrations of metals were observed in sampling localities with marine influence possibly related to the presence of marine grass. The concentration of total heavy hydrocarbons, as expected, was higher in sites with intensive fishing activity. The integrated biomarker response (IBR) and the condition index of mussels allowed discriminating between localities of continental and marine influence, revealing that the sampling stations with continental influence were subjected to a greater stress as a result of anthropogenic effects.

Nutritional value of the Tunisian mussel Mytilus galloprovincialis with a special emphasis on lipid quality

This study reports, for the first time, data on nutritional quality parameters in Tunisian mussels, Mytilus galloprovincialis, with an especial emphasis on lipid compounds. Mussel condition index (CI), proximate composition and fatty acid profiles were investigated for a one year period in order to identify the best harvesting period. Analysis revealed that polyunsaturated fatty acids (PUFA) were the dominant fatty acids with a prevalence of n-3 over n-6 forms. Pearson’s correlation indicated a strong relationship between CI and PUFA compound and Principal Components Analysis suggested that, from winter to summer, the product maintained a condition sufficiently good for marketing. The best CI and lipid quantity/quality occurred during summer and this may be used as criteria for product labelling. The study also included a thorough literature review that allowed data comparison on mussels from various Mediterranean sites and allowed the mussels from the Bizerte lagoon (North of Tunisia) to be differentiated.

Comparison between IMTA and monoculture farming of mussels (Mytilus galloprovincialis L.) in the Boka Kotorska Bay

This paper presents the results of growth rate and condition index analysis of Mytilus galloprovincialis in integrated system and monoculture. The aim of this study was to show if there are differences in growth and condition index of mussels between integrated multi-trophic aquaculture (IMTA) and monoculture farming. The growth rate and condition index were monitored during a 13-month study at three different sites: 1) close to fish cages (NBL), 2) 100 m removed from fish cages (NUD), 3) at a monoculture mussel farm (SVN) around 8 km far away from cages. The most intense growth of mussels was recorded in spring, and the least intense in summer. After 13 months, monitored individuals at all three locations achieved commercial size. The growth rate was very similar at all sites. The condition index showed spatial and temporal differences. Condition index values on site NUD were mostly higher compared to SVN and NBL, which were very similar, exept for the period from October to December when CI was similar on NBL and NUD site and higher in comparation with SVN. CI values on NBL an NUD site during cold period indicate on fact that mussels probably feed on the nutrients from fish farm origins.The highest mortality rate was recorded at the NBL site, probably due to the effects of fouling organisms.

Bioaccumulation of metals in three freshwater mussel species exposed in situ during and after dredging at a coal ash spill site (Tennessee Valley Authority Kingston Fossil Plant).

On December 22, 2008, a dike containing coal fly ash at the Tennessee Valley Authority Kingston Fossil Plant (TN, USA) failed, and within months, dredging operations began to remove ash-contaminated sediments. The purpose of this study was to investigate differences in the bioaccumulation of metals in three mussel species during and after dredging operations. Mussels were caged for approximately 1 year during dredging and after, and then mussel condition index values and As, Cd, Cr, Pb, Ni, Se, Hg, U, Fe, Mg, Al, Sb, Ba, Be, Co, Cu, Mn, Mo, Ag, Sr, Tl, V, and Zn concentrations in soft tissue were determined via inductively coupled plasma-mass spectrometery. Overall, the differences observed in metal bioaccumulation and mussel health suggest that mussels in the immediate downstream area of the dredging site may have been impacted, as evidenced by a significant decrease in mussel condition index values, but that this impact did not result in increased tissue concentrations of metals.

Spatial distribution pattern of Mytilus chilensis beds in the Reloncaví fjord: hypothesis on associated processes

Natural M. chilensis populations dominate habitats with a steep environmental gradient, and that are characterized by abrupt changes in salinity and exposure to desiccation. Although these populations are the source of seed supplies for the Chilean mussel culture industry (annual production around 250 thousand Tons), knowledge about natural populations is scarce. Based on video transect recordings, this study carries out research into one of the principal mussel beds and its associated epibenthic community in the Reloncaví Fjord, both along cross-shore and along-shore distribution gradients. Mytiluschilensis was observed between the middle intertidal zone and the upper subtidal zone (between approximately 9 and 26 psu), with a richer associated community towards the subtidal zone and the fjord mouth. The mussel Condition Index (total meat weight/shell length*100) in the intertidal zone was significantly greater than in the subtidal zone, which raises questions about the reproductive contribution of mussels along the intertidal mid-subtidal gradient. Salinity and tidal variations, together with biological interactions, would seem to be key factors for explaining M. chilensis spatial distribution in the Reloncaví fjord, where beds appear to be in a contraction stage, as evidenced by M. chilensis scarcity towards the subtidal zone. The importance of these populations and their persistence in environments with high perturbation frequency, suggests a monitoring program should be implemented that considers both population spatial distribution and the changing environmental conditions.

Estimating the Potential Production of the Brown MusselPerna perna(Linnaeus, 1758) Reared in Three Tropical Bays by Different Methods of Condition Indices

Perna perna(Linnaeus, 1758) is the main marine bivalve mussel yielded commercially in Brazil. In spite of this, scientific data is very scarce regarding its productivity in tropical shallow waters. The Condition Index (CI) is used worldwide in mariculture to assess animal health, harvest time, and yield. In this study, the authors used CI results from nine different methods to assess the season effect on the mussel CI and also to evaluate the potential yield of three southern Brazilian bays. The results from nine CI methods were used for the comparison of the seasonality and yield of mussels reared in three marine bays. Sampling was carried out monthly within two 4-month periods, from December 2008 to August 2009. The results show a trend for seasonal effects on the CI results. The winter months showed the highest and the lowest values. Between bays, higher CI values were detected in animals reared at Sepetiba Bay, followed by Guanabara Bay and Ilha Grande Bay. We suggest that the CI (that considers the ratio between bivalve soft tissue wet weight and total length) should be used by fishermen, since this formula was able to detect differences between sites and is more easily applied.

Seasonal and PAH impact on DNA strand-break levels in gills of transplanted zebra mussels

Genotoxicity endpoints are useful tools to biomonitor the physicochemical and biological quality of aquatic ecosystems. A caging study on the freshwater bivalve Dreissena polymorpha was planned to run over four seasons in the Seine River basin in order to assess whether DNA damage measured in transplanted mussels to polluted area vary according to seasonal changes. Three sites were chosen along the Seine River, one upstream from Paris and two downstream, corresponding to a chemical gradient of water contamination. The DNA strand break (comet assay) and chromosomal damage (micronucleus test) were measured in caged mussels at each site and in winter, spring and summer, along with PAH water contamination, PAH bioaccumulation, the mussel condition index (CI), the gonado-somatic index (GSI) and the filtration rate (FR). The level of DNA strand break measured in winter was low and increased in spring, concomitantly with FR and GSI. Over the same period, micronucleus (MN) frequency and PAH bioaccumulation decreased significantly in caged mussels, with both parameters positively correlated to each other. DNA strand-break levels and MN frequencies showed inter-site variations corresponding to the chemical contamination gradient. These two genotoxicity endpoints usefully complement each other in field studies. These results show that the MN test and comet assay, when applied to gill cells of caged zebra mussels, are sensitive tools for freshwater genotoxicity monitoring.

Haemocytic neoplasia in Mediterranean mussels (Mytilus galloprovincialis) in the Slovene Adriatic Sea

The health status of cultured and wild Mediterranean mussels in the Slovene Sea has so far been unexplored. Initially, 1280 adult Mediterranean mussels (Mytilus galloprovincialis), 960 from a shellfish farm and 320 from natural beds, were collected over a one-year period. Water temperature, oxygenation and salinity were measured at each sampling. Mussels were measured and weighted to calculate the condition index and microscopically examined for the presence of haemocytic neoplasia. Haemocytic neoplasia was detected in 14 mussels (1.1%) with a higher prevalence in cultured mussels. Neoplastic cells singularly infiltrated the connective tissue, in small foci or diffusely. Necrosis and multifocal atrophy of digestive tubules were noticed in mussels with diffuse neoplasia, whereas severe haemocytic infiltration of connective tissue was seen in mussels with single neoplastic cells. Haemocytic neoplasia was more frequently observed in spring and autumn. The average condition index of mussels with haemocytic neoplasia was slightly higher than in healthy ones. This is the first report of haemocytic neoplasia in Mediterranean mussels in the Northern Adriatic Sea. The disease occurs only sporadically and to date no significant impact on the mussel population has been noted.

Variation in tissue stoichiometry and condition index of zebra mussels in invaded Swedish lakes

We examined the spatial variation in carbon:nitrogen:phosphorus (C:N:P) stoichiometry and condition index of the zebra mussel (Dreissena polymorpha), non-indigenous species, in four Swedish lakes with different productivity. Within-lake variability was observed in tissue C:N molar ratios of Dreissena in all lakes and in tissue C:P ratio only in three lakes. Depth had no effect on tissue C:P and N:P ratios of Dreissena. A positive correlation was found between C:N:P stoichiometry of seston and elemental composition of zebra mussel in one of the lakes. Tissue C:N and N:P ratios were the main factors that related to zebra mussel condition index. Zebra mussel condition was positively related to tissue C:N ratio. Smaller Dreissena had higher C:N ratio than larger Dreissena in two of the four lakes. Zebra mussels in the lake with highest productivity had lower C:P and N:P ratios than zebra mussels in the lake with lowest productivity. Our study suggests that the zebra mussel may modify their phosphorus content in relation to lake trophic state, and therefore cope with stoichiometric constraints which may explain the invasion success of this and other related species.

Dreissena population status in nearshore Lake Ontario

Dreissenid mussels are ecosystem engineers in the Great Lakes, affecting benthic and water column communities and production. We surveyed mussel populations at four Canadian and three U.S. locations in summer 2008 to update population status and examine correlations with water column data. We measured mussel length, density, shell-free dry mass (SFDM), condition index, and phosphorus content of both shells and mussel tissue. The water column variables of chlorophyll a, turbidity, and total phosphorus (TP) were correlated with each other lake-wide, but exhibited only a few correlations with mussel metrics within seasons or shorelines. Quagga mussels (Dreissena rostriformis bugensis) represented ~99% of the mussel community in nearshore collections. Mussel length declined in a west-to-east direction and increased with depth in both U.S. and Canadian nearshore waters. Mussel density declined west-to-east in U.S. water, but exhibited no difference among sites in Canadian waters. Mussel condition index and phosphorus concentrations were correlated and increased west-to-east within the U.S. nearshore. There were significant declines in both tissue and shell P content with season in U.S. mussels, but no clear patterns in Canadian mussels. We estimated there were 9.7×1012 mussels (mean=3402.9/m2) in the Lake Ontario nearshore totalling 1.2×105mT of mussel tissue which could filter the entire Lake Ontario nearshore volume (0–20m depth=30.9km3) in roughly 1 to 7days. It appears that mussel density has declined since the last large surveys of 5 or 10years ago (Canadian nearshore or U.S. nearshore, respectively), however the data were either only slightly supportive of, or showed no support for, food limitation or goby predation as the most parsimonious explanation for the decline in mussel abundance.

A large scale survey of trace metal levels in coastal waters of the Western Mediterranean basin using caged mussels (Mytilus galloprovincialis)

A large scale study of trace metal contamination (Hg, Cd, Pb and Ni) by means of caged mussels Mytilus galloprovincialis was undertaken along the coastal waters of the Western Mediterranean Sea within the context of the MYTILOS project. Individual mussels from an homogeneous population (shell size 50 ± 5 mm) obtained from an aquaculture farm were consecutively caged and deployed at 123 sites located in the Alborán, North-Western, South-Western and Tyrrhenian sub-basins for 12 weeks (April-July) in 2004, 2005 and 2006. After cage recoveries, both the metal content in the whole mussel tissue and the allometric parameters were measured. Statistical analysis of the datasets showed significant differences in concentrations between sub-basins for some metals and mussel condition index (CI). Linear regression models coupled to the CI were revisited for the data adjustment of certain trace metals (Hg, Cd and Ni), and four level categories were statistically derived to facilitate interregional comparison. Seawater masses surrounding coastal areas impacted by run-off from land mineralised coasts and industrial activities displayed the highest concentration ranges (Hg: 0.15-0.31 mg kg(-1) dw; Cd: 1.97-2.11; Ni: 2.18-3.20 and Pb: 3.1-3.8), although the levels obtained in most of the sites fitted within moderate or low categories, and they could be considered as baseline concentrations. However, few sites considered little-influenced by human activities, at present, showed high concentrations of Cd, Ni and Pb, which constitute new areas of concern. Overall, the use of active biomonitoring (ABM) approach allowed to investigate trace metal contamination in order to support policy makers in establishing regional strategies (particularly, with regard to the European Marine Strategy Directive).

Factors affecting 210Po and 210Pb activity concentrations in mussels and implications for environmental bio-monitoring programmes

The activity of 210Po and 210Pb was determined in mussels of the same size (3.5–4.0 cm shell length) sampled monthly over a 17-month period at the Atlantic coast of Portugal. Average radionuclide concentration values in mussels were 759 ± 277 Bq kg −1 for 210Po (range 460–1470 Bq kg −1 dry weight), and 45 ± 19 Bq kg −1 for 210Pb (range 23–96 Bq kg −1 dry weight). Environmental parameters and mussel biometric parameters were monitored during the same period. Although there was no seasonal variation of radionuclide concentrations in sea water during the study period, the concentration of radionuclide activity in mussels varied seasonally displaying peaks of high concentrations in winter and low concentrations in summer. Analysis of radionuclide data in relation to the physiological Condition Index of mussels revealed that 210Po and 210Pb activities in the mussel (average activity per individual) remained nearly constant during the investigation period, while mussel body weight fluctuated due to fat storage/expenditure in the soft tissues. Similar variation of radionuclide concentrations was observed in mussels transplanted from the sea coast into the Tejo Estuary. However, under estuarine environmental conditions and with higher food availability throughout the year, transplanted mussel Condition Index was higher than in coastal mussels and average radionuclide concentrations were 210 ± 75 Bq kg −1 (dry weight) for 210Po and 10 ± 4 Bq kg −1 (dry weight) for 210Pb, therefore lower than in coastal mussels with similar shell length. It is concluded that the apparent seasonal fluctuation and inter-site difference of radionuclide concentrations were mostly caused by mussel body weight fluctuation and not by radionuclide body burden fluctuation. This interpretation can be extended to the apparent seasonal fluctuation in concentrations of lipophilic and lipophobic contaminants in mussels, and provides an explanation for occasional high concentrations of 210Po and man-made contaminants measured in mussels far from pollution sources.

Aquaculture planning for suspended bivalve farming systems: The integration of physiological response of green mussel with environmental variability in site selection

Bivalve Condition Index (CI) is widely employed in environmental monitoring programmes as it integrates physiological responses to stress with changes in somatic growth. Besides indicating, the commercial quality of a bivalve population it may be also be used to compare the relative health of animals in nearby populations. In this study, CI of green mussels, Perna viridis was evaluated as the intrinsic response to the variations in the environment in two potential mussel mariculture sites in the tropical monsoon region with diverse remoteness to riverine outflow. Condition index of mussels from site with relatively higher riverine influence (RI) was compared with mussels from area of reduced riverine (RR) influence along Karnataka coast (Eastern Arabian Sea). The dominant patterns of spatial trends in 12 environmental variables (temperature, salinity, pH, dissolved oxygen, rainfall, chlorophyll-a (chl-a), suspended particulate matter (SPM) particulate organic matter (POM), particulate inorganic matter (PIM), POM/SPM, chla/POM and PIM%) of the sites were resolved by Principal Component Analysis (PCA). The stepwise multiple regression analysis related the spatial variability in CI to variations in water temperature and organic content of the seston (chlorophyll-a and particulate organic matter). The discriminant analysis performed with monthly mean water temperature, chl-a levels and CI ratio [high CI ratio (CI high) and low CI ratio (CI low)] indicated that 83.9% of the CI high was associated with high chl-a and high water temperature group whereas, 72.4% of CI low were associated with low chl-a and low water temperature regime. The RR site presented less variation in environmental parameters offering a more conducive environment for the growth of mussels, characterised by better CI with low seasonal variations. Whereas, in the site proximate to riverine discharge, reserves were alternatively channelled into energy-consuming processes and hence unfavourable environmental conditions showed poor tissue condition due to utilization of energy reserves which were potentially destined for growth. Thus, average CI, besides its representation of the general health condition of the bivalves can potentially be used in selecting suitable sites for bivalve mariculture in comparable hydrological environment.

Simple methodology coupling microwave-assisted extraction to SPE/GC/MS for the analysis of natural steroids in biological tissues: Application to the monitoring of endogenous steroids in marine mussels Mytilus sp.

A simple analytical procedure for the simultaneous determination of eight endogenous steroids (testosterone, androstenedione, 17β-estradiol, estrone, pregnenolone, progesterone, dihydroandrostenedione, and dihydrotestosterone) in aquatic molluscs by solid-phase extraction (SPE) and gas chromatography/mass spectrometry (GC–MS) has been developed. After a microwave-assisted extraction, samples were further extracted and purified using two successive SPE (EnviChrom-P and NH 2) cartridges. Steroids were derivatized with a mixture of N-methyl-N(trimethylsilyl)trifluoroacetamide (MSTFA)/mercaptoethanol/ammonium iodide (NH 4I) and determined by GC–MS in selective ion monitoring mode. Recoveries were in the range 85–114%, although slightly lower for dihydrotestosterone, and the repeatability of the procedure, expressed as the coefficient of variation, was lower than 16%. The limits of detection determined in digestive glands of mussels were in the range 0.1–0.4 ng g −1 wet weight for all the steroids. The developed procedure was then applied to the monitoring of steroid profiles in the digestive glands of mussels from the Arcachon Bay (France) during two reproductive cycles. In parallel, two physiological parameters (lipid content and the condition index of mussels) were also monitored, as well as the seawater temperature and salinity. Only progesterone and pregnenolone were detected in the digestive glands of mussels, and the seasonal variations of progesterone levels seemed to be related to the spawning periods of Mytilus sp. in the Bay. The current challenge for the determination of natural steroids in aquatic invertebrates is also briefly discussed.