Increased production of faecal pellets by the benthic harpacticoid Paramphiascella fulvofasciata: importance of the food source

The re-use of faecal pellets in the water column before sinking to the seafloor is known as an important pathway in marine food webs. Especially planktonic copepods seems to be actively use their faecal pellets. Since benthic copepods (order Harpacticoida) live in the vicinity of their pellets, it remains unclear how important these pellets are for their feeding ecology. In the present study a laboratory experiment was conducted to analyse the importance of faecal pellets for the feeding ecology of the harpacticoid Paramphiascella fulvofasciata and its grazing pressure on two diatom species (Seminavis robusta, Navicula phyllepta). By quantifying the amount and volume of the produced faecel pellets in different treatments, it was tested to what extent the food source and the lack of faecal pellets would influence the production of faecal pellets. We found that the grazing pressure of P. fulvofasciata depended on the diatom density since only a top-down effect could be found on the smaller Navicula cells during its initial exponential growth phase. The grazer had a negative effect on the diatom growth and controlled the cell density to about 4,000 cells/cm². In spite of the fact that the addition of faecal pellets did not show a significant positive effect on the assimilation of diatoms, the removal of faecal pellets strongly promoted the pellet production. Especially when grazing on Navicula the harpacticoid P. fulvofasciata produced significantly more and smaller faecal pellets when the pellets were removed. This outcome illustrates the need for faecal pellets of this harpacticoid copepod when grazing on the diatom Navicula. Apart from its selection for smaller diatom cells, it was suggested that the colonisation of heterotrophic bacteria enriched these pellets. This study is the first to indicate that trophic upgrading occurs on faecal pellets and not only on the initial autotrophic food sources per se.     

Biochemical constituents and bioaccumulation as biomarkers in the green mussel Perna viridis with reference to silver and chromium toxicity

The sublethal effect of silver and chromium on some biochemical constituents was studied in the green mussel Perna viridis. The results revealed an overall reduction in total protein, total DNA, total RNA, glycogen, protein bound sugars and total lipid in the gill, hepatopancreas, and ovary of the mussels exposed to metals individually and in combination when compared with control. It was apparent that mussels exposed to mixtures of metals exhibited highly significant (P?P?P?相似文献   

Interspecific variation of heavy metal concentrations in the different tissues of tropical intertidal gastropods from Malaysia

The present study aims to determine the concentrations of Cd, Cu, Fe, Ni, Pb, and Zn in the different tissues of five species of tropical intertidal gastropods from Malaysia. Each of the species have organs/tissues that highly accumulated certain metals. For Cu, the mantles of Cerithidea obtusa, Pugilina cochlidium, and Murex trapa; and the digestive caeca of Thais sp. and Chicoreus capucinus highly accumulated Cu. The shells of Chi. capucinus and M. trapa, the digestive caeca of P. cochlidium, and the digestive glands of Thais sp. and Chi. capucinus highly accumulated Cd. The tentacles and the digestive caeca of Cer. obtusa and P. cochlidium, respectively, highly accumulated Zn, the digestive glands of Thais sp., Chi. capucinus, and M. trapa also highly accumulated Zn. The shells of most of the gastropods accumulated high levels of Pb and Ni. The opercula of most of the gastropods, besides the digestive glands for Thais sp., accumulated high levels of Fe. The present study on interspecific variations of heavy metals in gastropods provided information on differences of metal distributions in the different tissues, which could be useful in proposing potential tissues as better biomonitoring tools of heavy metal bioavailabilities in the coastal waters of Peninsular Malaysia.     

Utilization of partially predated snail shells by the hermit crab Pagurus longicarpus Say, 1817

The hermit crab Pagurus longicarpus was shown to inhabit shells that were partially predated from intertidal areas of Long Island, New York. Among field collections of P. longicarpus, 2.13% of the hermit crabs (46 of 2155) were found with shells with snail tissue present. Over 90% of these partially predated snail shells were occupied by male hermit crabs. Although hermit crabs were in 8 species of snail shells, only Littorina littorea and Nassarius obsoletus were found occupied by hermit crabs and containing snail tissue. In the laboratory, we found that specimens of the spider crab Libinia emarginata were able to pull off the operculum of snails, leaving damage as found in field collections. In contrast, specimens of P. longicarpus were not able to prey on live, healthy snails. When specimens of P. longicarpus were placed in communal tanks, hermit crabs preferred partially predated snail shells to empty and original shells. However, original shells and empty shells were occupied with more frequency than partially predated shells when crabs were isolated. These findings indicate P. longicarpus actively seeks shells soon after attack and abandonment by snail predators, especially in the presence of competitors.     

Investigation of metallothionein level,reduced GSH level,MDA level,and metal content in two different tissues of freshwater mussels from Atatürk Dam Lake coast,Turkey

Atatürk Dam Lake is one of the important freshwater ecosystems in the world in terms of the size of the surface area and the biodiversity. The objective of this study was to determine the effects of metal pollution in the Atatürk Dam Lake on some biochemical markers in the gills and digestive glands of mussels (Unio mancus). Mussel samples were collected in July-2018 from four stations. The metal residues (Cd, Cu, Pb, Zn, and Ni) in the tissues were determined by ICP-MS. The MT, reduced GSH, and MDA levels were analysed using the proposed spectrophotometric methods. According to the results, toxic metals such as Cd and Pb in both tissues were determined mostly in mussels collected from St1. The highest MT and MDA levels in the gills were determined in St3 and St2 respectively, while the highest MT and MDA levels in the digestive glands were determined in St1. Although there was no significant difference in the reduced GSH level in the gills among the stations, the highest reduced GSH level in the digestive glands was determined in St4. These results indicated that mussels are appropriate sentinel organisms for metal contamination with effects on oxidative stress and metal exposure biomarkers.     

The trophic linkage between zooplankton and benthic suspension feeders: direct evidence from analyses of bivalve faecal pellets

Using radiotracer (¹⁴C) and microscopic observation, we demonstrated that mussels (Mytilus edulis and Perna viridis) could be predators of mesozooplankton (rotifer Brachionus plicatilis). At radio-labelled rotifer densities of 0.1, 0.2, 0.5, 1.0 individual ml⁻¹, faecal pellets of mussels showed different degrees of radio signals and most of the faecal pellets were expelled 4 h after pulse feeding on rotifers. The maximum gut retention time (GRT) of ¹⁴C-labelled rotifers in the digestive diverticula did not o show any significant difference between the two mussel species or the different densities of rotifers, and the averaged GRT was 43.4±3.06 h (mean ± SE). At a rotifer density of 4.5 individual ml⁻¹, rotifer lorica pieces and rotifer bodies without eggs were found in faeces of M. edulis, while in the pseudofaeces, only complete rotifer bodies were found.     

The role of marine aggregates in the ingestion of picoplankton-size particles by suspension-feeding molluscs

Suspension-feeding molluscs are important members of coastal communities and a large body of literature focuses on their feeding processes, including the efficiency of particle capture. Some molluscs, such as bivalves, capture individual picoplankton cells (0.2–2.0 μm) with a retention efficiency of less than 50%, leading to the assumption that such particles are not an important food resource. Picoplankton, however, are often concentrated in particle aggregates of much larger size. This study investigates the ability of suspension feeders to ingest picoplankton-size particles (0.2–2.0 μm) bound in marine aggregates. We fed clams (Mercenaria mercenaria), mussels (Mytilus edulis), oysters (Crassostrea virginica), scallops (Argopecten irradians) and slipper snails (Crepidula fornicata) 1.0- and 0.5-μm fluorescent particles (either polystyrene beads or bacteria) that were (1) dispersed in seawater, or (2) embedded within laboratory-made aggregates. Dispersed 10-μm beads were also delivered so that feeding activity could be determined. Ingested fluorescent particles were recovered in feces or isolated digestive glands and quantified. Results indicate that aggregates significantly enhance the ingestion of 1.0- and 0.5-μm beads by all species of bivalves, and enhance the ingestion of bacteria (greatest cell dimension ca. 0.6 μm) by all suspension feeders examined. Differences among species in their ability to ingest aggregates and picoplankton-size particles, however, were evident. Compared to mussels and clams, scallops and oysters ingested fewer aggregates with 1.0-μm beads or bacteria, and slipper snails ingested the most dispersed beads and bacteria. These differences may be a consequence of variations in gill structure and mechanisms of particle processing. Our data demonstrate that suspension feeders can ingest picoplankton-size particles that are embedded within aggregates, and suggest that such constituent particles may be an important food resource.     

Feeding ecology of the loggerhead sea turtle Caretta caretta in the Northwestern Gulf of Mexico

Digestive tract contents collected from carcasses of 82 loggerhead sea turles (Caretta caretta) found on the south Texas coast from 1986 through 1988 were examined. Benthic invertebrates were the predominant prey. Sea pens (Virgularia presbytes), crabs, and mollusks accounted for 94% of the dry weight of the digestive tract samples. Temporal changes in the percent occurrence and percent dry weight of sea pens, crabs, and mollusks in the digestive tract samples were significant. Loggerheads fed primarily on sea pens during spring, then primarily on crabs during summer and fall. The increase of crabs in the loggerhead diet paralleled the annual increase in the abundance of crabs in the Gulf of Mexico. Sea pens were located nearshore at depths of 6 to 12 m and had a disjunct distribution. Present address: Texas A&M University, Department of Biology, College Station, Texas 77843-3258, USA     

Zooplankton grazing on the coccolithophore Emiliania huxleyi and its role in inorganic carbon flux

Grazing and faecal pellet production by the copepods Calanus helgolandicus and Pseudocalanus elongatus, feeding on the coccolithophore Emiliania huxleyi, were measured under defined laboratory conditions, together with the chemical characteristics and sinking rates of the faecal pellets produced. Ingestion rates of both copepods were equivalent at comparable cell concentrations, the relationship between ingestion rate (I, cells copepod^-1 h^-1) and food concentration (C, cells ml^-1), being I=0.558C for both species. P. elongatus produced a larger number of smaller faecal pellets than C. helgolandicus, but egested a larger volume of material per individual. Only between 27 and 50% of the ingested coccolith calcite was egested in the faecal pellets, and it is possible that acid digestion in the copepod gut is responsible for these considerable losses. Average sinking rates of faecal pellets containing E. huxleyi coccoliths, produced by both species, were >100 m d^-1. The implications of the quantitative laboratory estimates for the vertical flux of inorganic carbon are considered using recently studied shelf-break and oceanic E. huxleyi blooms in the N. E. Atlantic as examples.     

Cyclical contributions of the digestive epithelium to faecal pellet formation by the copepod Calanus helgolandicus

Faecal pellet formation within the gut of Stage V and adult females of the copepod Calanus helgolandicus Claus involves (1) cyclical processes of digestion and (2) the contribution of parts of the gut epithelium to the pellets. During an experimental regime in which dim lighting was restricted to day-time and feeding to night-time (17.00 to 09.00 hrs), the copepods responded with cyclical changes in both the quantity of pellets they produced and the fine structure of the contents. During the feeding period, the contents showed changes in the relative amounts of materials originating from disintegrated cells of the digestive epithelium and those derived directly from the ingested food. The vacuolar B-cells of the gut contribute to the content of the pellets and the distal, necrotic N-cells appear to be involved in forming the peritrophic membrane which encloses each pellet. Cells of the gut epithelium which are broken down during feeding are all replaced during the non-feeding period. Other individuals were taken directly from the sea and in these, also, the cells of the gut broke down during feeding and contributed to the faecal pellets. The supply of epithelial cells may limit the duration of the feeding period.     

Acute toxicities of eleven metals to early life-history stages of the yellow crab Cancer anthonyi

We report findings from the first laboratory experiments to assess toxicities of metals found in drilling muds to embryos and prezoeae of a brachyuran crab. Embryos of Cancer anthonyi are brooded externally on the abdomen of female crabs; thus, embryos may be continuously exposed to pollutants contained in sediments of contaminated benthic habitats. Lethal concentrations of metals to embryos after 7 d exposures were: iron and barium (sulfate), 1 000 mg l^–1; barium (chloride), 100 mg l^–1; aluminum and nickel, 10 mg l^–1; copper and lead, l mg l^–1; cadmium, chromium VI and manganese, 0.01 mg l^–1; mercury, 0.001 mg l^–1. All metals effectively retarded embryos from hatching at concentrations equal or lower to those causing mortality, except for cadmium. Particularly impressive was iron, which suppressed hatching at l to 10 mg l^–1, concentrations previously found non-deleterious to marine organisms and 100 times more dilute than concentrations causing significant embryo mortality. The effects of metals on embryos increased as a function of exposure duration. Embryo mortality was delayed for at least 120 h at concentrations 1.0 mg l^–1, with the exception of mercury. Lethal concentrations established at 96 h were meaningless for crab embryos, because acute toxic thresholds were not attained by that time. Larval survivorship to chromium VI, copper, and zinc increased following exposure of embryos to these metals at low concentrations (1.0 mg l^–1), suggesting induction of biochemical pathways for products which bind or metabolize metals. Identical exposures of embryos to lead failed to enhance subsequent larval survivorship, showing that inductions may be metal-specific. We suggest that exposures of brachyuran embryos at field sites and the success of their subsequent hatching in the laboratory may be a means of assessing environmental contamination otherwise difficult to monitor.     

Predator-induced alarm responses in the common periwinkle, Littorina littorea: dependence on season, light conditions, and chemical labelling of predators

Chemically mediated alarm reactions of the common periwinkle, Littorina littorea (L.), were studied in laboratory experiments during two consecutive summers, and one intermediate autumn season. Responses to chemical stimuli were detected as crawl-out responses, i.e. movements of snails out of the water. Snails were exposed to extracts of injured conspecifics, extracts of the mussel Modiolus modiolus (L.), and water conditioned by the predatory crab Carcinus maenas (L.), which had been maintained on different diets. In experiments carried out during the summer, a significantly larger number of snails moved out of the water when exposed to chemical stimuli from injured conspecifics, compared to chemical stimuli from injured mussels or filtered seawater. These results suggest that chemical alarm substances are present in L. littorea. Water conditioned by crabs that had been fed L. littorea released significantly more crawl-out responses compared to water conditioned by crabs that had been kept on a fish diet. When tested in autumn, no significant differences were found in responses to the above-mentioned water samples. Crawl-out responses under different light regimes were also investigated. All series of experiments carried out in the dark evoked a higher number of responses compared to series that took place in light. These findings may indicate an adaptation of snails to night-active predators. In total, the current results suggest that a L. littorea diet may chemically “label” the predator crab with snail alarm substances, and that predator-induced responses of L. littorea are actually responses to conspecific alarm substances released from crabs that have been maintained on a L. littorea diet. The response to the alarm signal, however, appears to be dependent on season and light conditions; some ecological implications of these findings are also discussed. Received: 8 January 1999 / Accepted: 29 March 1999     

Ecology of subtropical hermit crabs in SW Madagascar: short-range migrations

Many mobile animals migrate because of the different benefits provided by different localities in time and space. For hermit crabs, such benefits include resource (shell, water, food) acquisition and gamete release. One of the more successful crustacean land-invaders, Coenobita hermit crabs, undertake complex short-range migrations in SW Madagascar. Number of active hermit crabs was inversely related to wind strength and positively related to tidal range, emphasising that movement would conserve water. A circadian component was also recorded in the locomotory activity of Coenobita pseudorugosus and C. rugosus. Path linearity varied with many of the same parameters, but also with beach slope. Movement was primarily perpendicular to shore in small individuals, but the parallel proportion increased with hermit crab size and tidal range, probably driven mostly by shell and food searching. Despite the costs of movement and shell carriage in the terrestrial environment, C. pseudorugosus and C. rugosus were as fast as their marine counterparts. Their speeds varied principally with individual size and were approximately 20% faster without shells and about 20% slower when climbing up a 20° slope, compared to horizontal or downhill travel. Hermit crabs, which are highly numerous and speciose in SW Madagascar, do not seem to partition niches by differential movement patterns. Aside from provision of shells in middens and capturing large adults for bait or pets, human activity may have a profound effect on hermit crab movement: observations at rare uninhabited marine reserves like Nosy Ve show that considerable diurnal activity may take place despite the apparent hostility of the environment to an essentially marine animal.     

Role of bacteria in decomposition of faecal pellets egested by the epiphyte-grazing gastropod Gibbula umbilicaris

The significance of the microheterotrophic utilization of faecal pellets derived from Gibbula umbilicaris — one of the most important gastropod species in the Posidonia oceanica ecosystem around the Isle of Ischia (Italy) — was investigated by means of microcosm-experiments. Initial total organic carbon (TOC) content of faecal pellets was 32 gC (mg faeces dry wt)^-1 and declined continuously over a 2-month incubation period. The low values of TOC coincided with SEM observations of pellets which were found to consist mainly of diatom frustules and other slowly utilizable material. In a long-term experiment freshly egested faecal pellets were rapidly colonized by bacteria, which reached densities of up to 14x10⁵ cells (mg faeces dry wt)^-1 within 12 h. Thereafter bacterial numbers declined and fluctuated in a very narrow range between 2 and 3.5x10⁵ cells (mg faeces dry wt)^-1 during the two months of the investigation period. In short-term experiments (over 5 d) similar trends were observed. Peak densities of attached bacteria were followed by a decline of this population. Concurrently the number of free-living bacteria increased. This observation was confirmed by O₂ consumption measurements of freshly egested faecal pellets over 24 h, where the highest O₂ consumption rates were obtained after 12 h, followed by a rapid decline, thus supporting the view that detachment of bacteria may occur. Moreover, the respiration data indicate that about 4% of faecal TOC are remineralized within the first day.     

An integrated investigation of biomarkers’ response in crabs (Liocarcinus depurator) and benthic indices at a metalliferous waste discharge area in North Evoikos gulf,Greece

This study applied biomarkers and benthic indices at an area in North Evoikos Gulf, Greece, affected by metalliferous slag disposal. Biomarkers of antioxidant defense (catalase, glutathione S-transferase), and neurotoxicity (acetylcholinesterase) were measured in crabs Liocarcinus depurator. Iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), and zinc (Zn) concentrations in sediments and crabs were also measured. High levels of all metals were found in sediments at the disposal area. Metal levels in the crabs were also higher in the disposal area although spatial differences were not as marked as in the sediments. Accordingly, biomarker responses of crabs in the disposal area were also noted suggesting impact on the antioxidant defense of the organisms against oxidative stress. Benthic indices showed disturbance in the disposal area. The combined approach of measuring biomarkers and contaminant levels in the crabs and sediment was complementary to the benthic indices approach providing indications of metal exposure related effects. Our results support the idea that a twofold monitoring approach of assessing both the benthic community structure shifts and the biomarkers and metal accumulation levels may integrate and capture both the structural and the toxicological effects of dumping onto the benthic communities.     

Food webs and fishing affect parasitism of the sea urchin Eucidaris galapagensis in the Galápagos

In the Galápagos Islands, two eulimid snails parasitize the common pencil sea urchin, Eucidaris galapagensis. Past work in the Galápagos suggests that fishing reduces lobster and fish densities and, due to this relaxation of predation pressure, indirectly increases urchin densities, creating the potential for complex indirect interactions between fishing and parasitic snails. To measure indirect effects of fishing on these parasitic snails, we investigated the spatial relationships among urchins, parasitic snails, commensal crabs, and large urchin predators (hogfish and lobsters). Parasitic snails had higher densities at sites where urchins were abundant, probably due to increased resource availability. Commensal crabs that shelter under urchin spines, particularly the endemic Mithrax nodosus, preyed on the parasitic snails in aquaria, and snails were less abundant at field sites where these crabs were common. In aquaria, hogfish and lobsters readily ate crabs, but crabs were protected from predation under urchin spines, leading to a facultative mutualism between commensal crabs and urchins. In the field, fishing appeared to indirectly increase the abundance of urchins and their commensal crabs by reducing predation pressure from fish and lobsters. Fished sites had fewer snails per urchin, probably due to increased predation from commensal crabs. However, because fished sites also tended to have more urchins, there was no significant net effect of fishing on the number of snails per square meter. These results suggest that fishing can have complex indirect effects on parasites by altering food webs.     

Characterisation of cysteine proteinase activities in the digestive tract of juvenile <Emphasis Type="Italic">Paragnathia formica</Emphasis> isopods,ectoparasites of estuarine fish

Juveniles of Paragnathia formica Hesse (Isopoda; Gnathiidae) are haematophagous ectoparasites, feeding on fish blood which supplies the nutrients for their development through growth and moulting, and the subsequent survival and reproduction of the free-living adults. Little is known of the mechanisms of digestion in juvenile gnathiids, and biochemical studies on the digestive tract of these interesting estuarine isopods have not been undertaken previously. Here, functionally active cathepsin-like cysteine proteinases are identified in the digestive system of juvenile praniza (fed) and zuphea (unfed) forms. The physiological pH of the digestive tract and the optimum proteolytic activities detected in praniza 3 homogenates using the cathepsin B/L, cathepsin B, and cathepsin H fluorogenic substrates, N-Carbobenzoxy-Phe-Arg-4-methoxy-2-naphthylamine (Z-phe-arg-MNA), N-Carbobenzoxy-Arg-Arg-4-methoxy-2-naphthylamine (Z-arg-arg-MNA) and Arg-4-methoxy-2-naphthylamine (H-arg-MNA), respectively, are in the acidic range (pH 5.8–6.7). Inhibition profiles against Z-phe-arg-MNA and Z-arg-arg-MNA using the cathepsin B inactivator urea, and cysteine proteinase inhibitors, support the presence of cathepsin L- and B-like enzymes. These proteolytic activities are 10–50 times higher in homogenates of praniza 3 compared with zuphea 3 forms. Histochemistry of praniza 3 sections reveals that the predominant enzyme activity towards Z-phe-arg-MNA is limited to the digestive glands during early and mid stages of digestion; later, this activity appears in the lining of the anterior hindgut. Moreover, activity towards Z-arg-arg-MNA is generally restricted to the digestive glands, and only occasionally present in the anterior hindgut. In conclusion, the digestive glands are the main site of cathepsin-like cysteine proteinase activities in P. formica juveniles; these enzymes appear to be important to the digestion of host fish blood enabling development through to the free-living adult.     

Biomonitoring of heavy metal (Cd,Cu, Pb,and Zn) concentrations in the west intertidal area of Peninsular Malaysia by using Nerita lineata

Snails, Nerita lineata, were collected from 15 sites along the west intertidal area of Peninsular Malaysia from December 2005 until April 2006. The concentrations of heavy metals (Cd, Cu, Pb, and Zn) were determined in the total soft tissues, operculums, and shells of the snails. Different patterns of heavy metal distributions were found in the different tissues (shell, operculums, and soft tissues) as well as spatial variations of heavy metal concentrations in the snails. This shows that the distribution of metals in the shells and the total soft tissues of N. lineata were not similar which could be due to different rates of metal accumulation, excretion, and sequestration. Since N. lineata is abundant on the rocky shores, below jetties and mangrove trees along the west intertidal area of Peninsular Malaysia and accumulate heavy metals, the snails are therefore potential biomonitors of heavy metal contamination for the west intertidal area of Peninsular Malaysia.     

Freshwater Mussel,Lamellidens Marginalis (Lamarck) (Mollusca: Bivalvia: Unionidae) As an Indicator of River Pollution

Abstract

Analyses were made of heavy metals, manganese, nickel, copper, zinc and lead in water samples and soft body, shell and different tissues (gills, digestive glands, mantle and viscera) of the Unionid mussel, Lamellidens marginalis collected from two tributaries of the Cauvery river. Water samples from Station I contained higher concentrations of the metals than those from Station II. the concentration of metals in water at both stations were in the descending order: Mn > Zn > Pb > Ni > Cu. However, the concentrations of metals in the soft body were in the descending order: Zn > Mn > Pb > Ni > Cu at both stations in all size groups of mussels tested. the concentration of zinc maintained a linear relationship with the size of the mussels, but manganese showed a reverse trend. Small size (4-5 cm) mussels accumulated more manganese (105.5 μg.g^?1 dry wt.) than larger ones (7-8 cm; 6.5 μg.g^?1 dry wt.). Both young and old is accumulate the same level of lead, copper and nickel in the soft body. the order of concentrations of metals (Mn, Pb, Zn, Ni and Cu) in the shell of mussels from both stations coincided with the order of concentrations of background water except for lead. the accumulation of lead was higher in shell (30.4-36.2 μg.g^?1 dry wt.) than in soft body (6.4-12.0 μg.g^?1 dry wt.). the pattern of concentration of metals in the various tissues reveal that the digestive glands have greater ability than other tissues to concentrate most metals under study. the concentration factors for soft body, shell and different tissues are presented. the advantages in using the common mussel for biomonitoring of contaminants in water is also discussed.     

Imposex in Hexaplex trunculus (Gastropoda: Muricidae): first results from biomonitoring of tributyltin contamination in the Mediterranean

Imposex (the occurrence of penis and vas deferens in females) in Hexaplex trunculus collected from Malta (Central Mediterranean) in 1992 is reported. This phenomenon is related to the levels of tributyltin (TBT) in the organisms as well as in sediments. Imposex indices (relative penis size and vas deferens sequence) are used to biomonitor coastal contamination by TBT for the first time in the Mediterranean. In its response to TBT, H. trunculus is ranked as one of the most sensitive neogastropod species studied so far. Accumulation of TBT and its metabolites in the digestive glands, gonads and the rest of the body are described, and sex-related differences are shown. No preferential female mortalities are recorded in populations exposed to high levels of TBT. However, a reported shift in the size frequency distribution of H. trunculus in contaminated sites, towards bigger snails, may suggest reduced reproductive potential.