Metallothioneins and lysosomes in metal toxicity and accumulation in marine mussels: the effect of cadmium in the presence and absence of phenanthrene

It has been confirmed that metallothioneins play an important role in the accumulation of cadmium (Cd) in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.). The content of Cd in the tissue of mussels exposed for 9 d to the metal (estimated dosage of 180 g Cd mussel^-1 d^-1) was 66.2 ppm. This value is about the same as the metal content found in the digestive gland of Cd-exposed mussels kept in clean water for a recovery period of 28 d. At the end of the recovery period, however, the Cd bound to thionein had increased by approximately 250%. Our data demonstrate that the stability of lysosomes, a biological parameter adopted as a cellular stress index, is extremely low in mussels exposed to Cd for 9 d, but returns to control values in the digestive gland cells of mussels allowed to recover for 28 d in uncontaminated sea water. At this point most of the Cd present in the cytosol is bound to thionein. These data demonstrate the importance of metallothionein induction in the reduction of the cytotoxic effects exerted by high levels of Cd accumulation. The results of tests designed to clarify the reasons for the long biological half-life of Cd demonstrated that, in the digestive gland of mussels, the lysosomes are not able to eliminate Cd either bound to insoluble thionein polymers or to lipid peroxidation products such as lysosomal lipofuscin, both of which are apparently involved in the elimination of copper. The absence of these two mechanisms of metal sequestration and elimination via excretion of residual bodies (tertiary lysosomes) is in agreement with the persistence of cadmium in the digestive gland of mussels. Finally, the results also demonstrate that simultaneous exposure of mussels to Cd and phenanthrene, an established lysosomal membrane destabilizer, did not significantly alter the accumulation of Cd or the kinetics of the metal in mussels.     

Possible causes of temporal fluctuations in primary production of the microphytobenthos in the Danish Wadden Sea

The effects of prior exposure to unlabelled naphthalene on the processes of uptake, tissue distribution and elimination of [1-¹⁴C] naphthalene by mussels (Mytilus edulis) were examined. Mussels collected from Whitsand Bay (S. W. England) in October 1980 were either held unexposed or exposed to unlabelled naphthalene (0.5 μg 1^?1) for 4 wk, prior to receiving a 4 h pulse of [1-¹⁴C] naphthalene in the medium (7 μg 1^?1). After 4 h exposure to [1-¹⁴C] naphthalene, the major tissues (digestive gland, gills, kidneys, mantle and remaining tissue) showed exponential depuration curves which could be resolved into two statistically significant components. The kinetics of elimination and the biological half-times of [1-¹⁴C] naphthalene in the tissues were determined. Mussels pre-exposed to unlabelled naphthalene had a significantly higher rate of elimination of [1-¹⁴C] naphthalene from the gills and kidneys. These results indicate that the toxicant, naphthalene, is actively excreted from the body by the gills and kidneys and the process is enhanced by prior exposure to the toxicant.     

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.     

Field depuration and biotransformation of paralytic shellfish toxins in scallop<Emphasis Type="Italic"> Chlamys nobilis</Emphasis> and green-lipped mussel<Emphasis Type="Italic"> Perna viridis</Emphasis>

Under laboratory conditions, the scallop Chlamys nobilis and the mussel Perna viridis were exposed to N-sulfocarbamoyl toxins (C2 toxin), a paralytic shellfish toxin (PST), by feeding a local toxic strain of the dinoflagellate Alexandrium tamarense (ATDP) that produced C2 toxin exclusively. The bivalves were subsequently depurated in the field, and their depuration kinetics, biotransformation and toxin distribution were quantified. Depuration was characterized by a rapid loss within the first day, followed by a secondary slower loss of toxins. In the fast depuration phase, scallops detoxified PSTs more quickly than the mussels (depuration rate constants for scallops and mussels were 1.16 day^–1 and 0.87 day^–1, respectively). In contrast, the mussels detoxified PSTs more quickly than the scallops in the slow depuration phase, and the calculated depuration rate constants (mean+SE) from day 2 to day 13 were 0.063+0.009 day^–1 and 0.040+0.019 day^–1 for mussels and scallops, respectively. The differences in the appearances of gonyautoxins, GTX2 and GTX3, and their decarbamoyl derivatives, dcGTX2, dcGTX3 and GTX5, which are all derivatives of C2 toxin, indicated active and species-specific biotransformation of the algal toxins in the two bivalves. In both species of bivalves, the non-viscera tissue contained fewer toxins and lower concentrations than the viscera-containing tissue compartment. In scallops, very little toxin was distributed in the adductor muscle. In mussels, most of the PSTs were found in the digestive gland with significant transport of toxins into the digestive gland from other tissues during the course of depuration. The toxin profiles of scallops and mussels differed from each other and from that of the toxic algae fed. A significant fraction of GTX5 was detected in the mussels but not in the scallops. Our study demonstrates a species specificity in the depuration kinetics, biotransformation and tissue distribution of PSTs among different bivalves.Communicated by T. Ikeda, Hakodate     

Assessment of the effect of environmental pollution in a marina on caged mussels using chemical and genotoxic analysis

An integrated approach using the contamination levels and DNA damage in mussels (Mytilus galloprovincialis) was applied in order to assess the chemical contamination in a marina (Eastern coastline of Aegean Sea). Mussels, which were harvested from a reference site (Foca), were transplanted into a marina situated along the coast of Izmir Bay. The transplanted mussels were collected at the 14th, 30th and 60th day of the experimental period. Polycyclic aromatic hydrocarbon (PAH) levels (27–51?ng?g^?1?wet?weight) detected in the mussels were similar to the levels detected in other coastal areas of the Mediterranean Sea. The marina’s sediment was found to be contaminated with PAHs (∑PAH?=?25?µg?g^?1) of pyrolytic origin and may become a source of pollution and a threat to the marine environment. In order to assess the DNA damage, the haemolymph and gill cells of the mussels were used for the comet analysis and considered as an indicator of exposure to genotoxic chemicals including 16 PAH compounds and metals. The highest levels of DNA damage expressed as %Tail-DNA (%T-DNA) were observed at the end of the experiment (21.5% T-DNA). The correlation analyses conducted between 2-, 3-, 4-ring PAHs in mussels and %T-DNA in haemolymph and gill cells showed a significant positive correlation. This investigation confirmed that transplanted mussel can be a useful tool to determine PAH contamination in marinas.     

Sensitivity of veliger larvae of Mytilus edulis and mussel of various sizes to chlorination

The blue mussel Mytilus edulis is one of the dominant fouling organisms in cooling water systems. In this work, how veliger larvae and different size groups of the mussels responded against chlorine dosage was examined. Veliger larvae mortality was studied at different residual chlorine concentrations (0.05–0.5 mg L^?1), and it was found that a chlorine dose of 0.5 mg L^?1 is 4 times as effective as 0.05 mg L^?1 and twice as effective as 0.1 mg L^?1. Mortality of 100% for three size groups (1.4, 14, and 25 mm) and relative physiological activities of two size groups (14 and 25 mm) were observed. The exposure duration for 100% mortality of mussels decreased with the increasing residual chlorine concentration (0.1–4.0 mg L^?1). Mussel size was also found to be an important factor, considering that the continuation times for mussel mortality were 28 h for the 1.4 mm and 410 h for the 25 mm size groups. All size groups showed progressive reduction in physiological activities, such as oxygen consumption, foot activity, and byssus thread production with increasing chlorine dose (0.05–1.0 mg L^?1); the two data-sets were strongly correlated with each other. The results of this study should be of significance for optimizing the chlorine content, and minimize the environmental threat to industries where mussels are the dominant fouling organisms.     

Calanoid copepod,cladoceran, and rotifer eggs in sea-bottom sediments of northern Californian coastal waters: Identification,occurrence and hatching

In Ireland, mussels on exposed rocky shores constitute an interbreeding mixture of two forms of mussels,Mytilus edulis L. and the Mediterranean musselM. galloprovincialis Lmk. This paper presents an in-depth analysis, carried out between October 1984 and December 1986, of genetic variability at two partially diagnostic loci,Odh andEst-D, in two exposed-shore populations ofMytilus spp. in the west of Ireland. Significant differences at theOdh locus were observed in the genetic composition of adult mussels from different tidal levels. These differences were repeatable whether one was analysing replicate samples at a single point in time, samples collected at different points in time, i.e., in different years, or samples collected from different shores. Mussels recruiting to artificial substrates set out for a period of one month at different tidal levels at one of these sites were also observed to be genetically different; mussels higher up the shore exhibited higher frequencies of those alleles characteristically at high frequency inM. galloprovincialis for both theOdh andEst-D loci. Hence, the genetic differences observed in adult mussels are much more exaggerated in juveniles and are already apparent within the first month of benthic life. Possible reasons for the observed microgeographic differentiation are discussed. It is concluded that the observed genetic differences between mussels at different tidal levels arise either in the pelagic/attachment stage or very shortly after settlement.     

Effect of Cd on accumulation and loss of 210Po in the mussel Mytilus edulis

As a result of ²¹⁰Po's previously identified association with sulphur-rich proteins, metallothioneins could have a significant effect on the behaviour and fate of ²¹⁰Po in molluscs. Starved control and cadmium-exposed mussels, Mytilus edulis, were fed ²¹⁰Po-labelled algae (Isochrysis galbana) for 5 d and then allowed to depurate in clean sea water. Cadmium-exposed M. edulis accumulated less ²¹⁰Po in the digestive gland and the remainder of the tissue than control mussels, although this was due to a decrease in tissue weight. More than 40% of ²¹⁰Po was identified as being associated with high molecular weight and heat-treated cytosol proteins in M. edulis. Mussels in a starved state are known to recycle as much as 90% of their amino acids. It is proposed that ²¹⁰Po associated with these and other proteins is recycled, explaining why no significant loss of ²¹⁰Po was observed from the remainder of the tissue in either control or Cd-exposed mussels. Cadmium-induced metallothioneins had no effect on the distribution of ²¹⁰Po in M. edulis; <5% associated with the cytosolic fraction was considered to principally contain metallothioneins. It is suggested that ²¹⁰Po's apparent relationship with metallothioneins is coincidental rather than connected with its role in the regulation of metals. Received: 30 March 1998 / Accepted: 3 August 1998     

Effects of chemical contaminants on the health of Mytilus edulis from Puget Sound,Washington. II. Cytochemical detection of subcellular changes in digestive cells

Activities of the enzymes NADPH-dependent ferrihemoprotein reductase (NFR), NADH-dependent DT-diaphorase (DTD), gamma-glutamyl transpeptidase (GGT), and catalase (CAT) and peroxisome proliferation (PP) in the digestive cells of Mytilus edulis from nine sites in Puget Sound, Washington (USA) sampled in September 1992 were measured cytochemically using image analysis. Mussels from these areas are known to be exposed to a wide range of chemical contaminants. At urban-associated sites, mussels generally showed increased activities of NFR, DTD, and CAT, suppressed GGT activity, and peroxisome proliferation, relative to mussels from the non-urban reference sites. Significant positive relationships were observed between tissue concentrations of polyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and DDTs and activities of NFR, DTD, CAT, and peroxisome proliferation. Structural changes in the digestive gland of mussels also appear to be more responsive to chemical contaminant exposure than changes in enzyme activity. These relationships suggest that NFR, CAT, and the induction of peroxisome proliferation represent complimentary indicators of biological effects from chemical-contaminant exposure in the marine bivalve M. edulis. The current findings support the use of selected cytochemically measured subcellular responses as biomarkers of contaminant exposure in environmental monitoring programs.     

Effects of copper on the latency of lysosomal hexosaminidase in the digestive cells of Mytilus edulis

Mytilus edulis collected from Tomales Bay, California, USA, during mid-winter 1979 were exposed to increased concentrations of dissolved copper under controlled laboratory conditions. A dose-dependent reduction in the latency of lysosomal hexosaminidase activity in digestive cells was induced after a 30 d exposure to copper. The half-time of the hexosaminidase staining reaction in sections of digestive gland from control mussels was 15.5 min; for mussels exposed to 25, 50, and 75 g Cu l^-1 it was 11.8, 8.5 and 5.5 min, respectively. In addition, the dyecoupled reaction product was seen earlier in sections from individuals exposed to 50 and 75 g Cu l^-1 (after 30 s) and 25 g Cu l^-1 (1 min) than in sections from control individuals (2.5 min). Copper accumulations were demonstrated histochemically to have the same distribution as the hexosaminidase reaction product, indicating that copper is sequestered in lysosomes. Copper concentrations in digestive gland tissue, were related to the concentrations of copper in the water to which the mussels were exposed.     

Factors affecting the flux of arsenic through the mussel Mytilus galloprovincialis

Radiotracer experiments were designed to study the effects of certain environmental and biological factors on arsenic accumulation and elimination processes in the Mediterranean mussel Mytilus galloprovincialis. Arsenic (as arsenate) uptake increased with increasing arsenic concentration in the water; however, the response was not proportional, indicating that accumulation was partially suppressed at higher external arsenic concentrations. In general, approximately 80% of the ⁷⁴As taken up was associated with the soft parts, with small mussels concentrating ⁷⁴As to a greater degree than larger individuals. The highest ⁷⁴As concentrations were recorded in the byssus and the digestive gland. Increased temperature enhanced both arsenic uptake and loss. Mussels in sea water at 19 S accumulated approximately three times more ⁷⁴As than those held at 38 S. Arsenic loss was much less affected by salinity, with only a tendency for greater arsenic retention noted at lower salinities. Studies carried out in the laboratory and in situ revealed that arsenic turnover was significantly more rapid in actively growing individuals living under natural conditions. Arsenic-74 loss from the in situ group was essentially biphasic, with biological half-times of approximately 3 and 32 days for the fast and slow compartments, respectively. The active secretion of arsenic in the byssal threads contributed to the total elimination of the element from the mussels.     

Causative species of diarrhetic shellfish poisoning (DSP) in Norway

This study was performed at Vikane in the Sognefjord, Norway, from September 1987 to October 1988 on the blue musselMytilus edulis collected monthly at three different depths (3 to 6, 6 to 8 and 8 to 12 m). Cell numbers of three species ofDinophysis from mussel digestive glands and in seawater were counted for each specimen. Multivariable statistical methods were used to detect annual cycles of phytoplankton abundance in the fjord and to examine the contribution of each species to toxification of mussels. Cluster analysis and principal component analysis indicated the following results: (1) an annual cycle and an inter-specific association of threeDinophysis species populations were pointed out.D. acuta andD. norvegica were well associated over the entire period of this study, and exhibited an autumnal peak.D. acuminata was dissociated from these species and reached its maximum abundance between spring and early summer. (2) The threeDinophysis species induced toxicity in the blue mussels in different manners.D. acuta andD. norvegica were responsible for high autumnal toxicity, andD. acuminata for the spring peak. (3) A long persistence of diarrhetic shellfish poisoning (DSP) in blue mussels (from April to February), and a depth gradient of toxicity were observed — the toxicity value in the upper layer being double those of other depths.     

Quantitative determination of metallothionein-like proteins in mussels. Methodological approach and field evaluation

Electrochemical quantitation of metallothionin-like proteins (MLP) in mussels was based on the determination of their constituent cysteinyl residues according to Brdika's catalytic reaction. Calibration was performed by an internal MLP standard isolated from the digestive gland of Mytilus galloprovincialis for which protein concentration had been estimated by Bradford's spectrophotometric method. For that purpose three metal-binding proteins [MLP-I, MLP-II and Cu-BP (binding protein)] were separated by DEAE-Sephadex A-25 chromatography from the digestive gland of mussels previously exposed to Cd. The most negatively changed MLP-II fraction was characterized by the fact that it contained the largest amount of both total metal and sulphydryl (-SH) content per mass of protein, although this was approximately two times lower than the-SH level of commercially available MT from rabbit liver. Exposure of mussels to a relatively low level of cadmium (0.2 g Cd l^-1) added into the seawater either by itself or as a mixture with other metals (2 g Cu l^-1 and 1.6 g Pb l^-1) resulted in a measurable level of MLP induction within 14 d in comparison to the control specimens. The effect of the metal mixture on MLP synthesis appears to be less than additive, suggesting a competitive interaction between metal ions for uptake and binding sites as well as differing potentials for MLP induction. Variations in the MLP content observed in the digestive gland of mussels seasonally collected from the same location are in the range 2.1±0.4 mg g^-1 on a wet weight basis. The methodological and conceptual aspects of the application of MLP induction in the Mytilus sp. as a biomarker in seawater trace metal monitoring are critically evaluated.     

Co-ordinated rhythms of digestion,absorption and excretion in Mytilus edulis (Bivalvia: Mollusca)

Sequential alternation of extracellular digestion in the stomach and intracellular digestion in the diverticula appears widespread among bivalves. The present study documents some physiological consequences of such processes in Mytilus edulis L. collected during 1981 from Whitsand Bay, Cornwall, England. Pronounced temporal fluctuations in faecal deposition are described that relate, in terms of amplitude and period, to both sinusoidal rhythmicity established for ammonia excretion and changes in the morphology of digestive tubules. Although at least partially synchronised among replicate groups of mussels, these cycles bore no consistent relationship with exogenous influences. Hourly fluctuation in the net absorption efficiency for nitrogen, as evidenced by the mean percentage ±2 SE, measured over 24 h sampling periods, was considerable (16.0±53.7, 49.3±10.9 and 52.8±6.6 for mussels acclimated in March, June and October, respectively). This variation in absorption derived from an inverse relationship between the percentage nitrogen within faeces and the rate of faecal egestion. Accordingly, peaks of faecal deposition presumably represented the pulsed remnants of intracellular digestion. Co-ordinated rhythms of digestion, absorption and excretion were thus evident in M. edulis. These processes displayed seasonally dependent periodicities of approximately 8, 3 and 4 h in March, June and October, respectively. It was concluded that, at least for M. edulis, this previously unquantified rhythmicity of physiological processes warrants careful consideration during assays commonly undertaken in the complication of nutrient and energy budgets.     

Seasonal variation in the balance between physiological mechanisms of feeding and digestion in Mytilus edulis (Bivalvia: Mollusca)

Seasonal variations in the balance between physiological mechanisms of feeding and digestion are considered among 45 to 57 mm shell length Mytilus edulis L. from southwest England. Mussels had been acclimated to standardised conditions of food availability in March, June and October, 1981. Results indicate that despite showing a negative relationship (P<0.001) with the efficiency of ¹⁵N absorption, coincident alterations of both ingestion rate (0.17 to 0.54 mg total Phaeodactylum tricornutum h^-1) and organic gut content (1.00 to 1.80 mg) represent significant mechanisms effecting the seasonal regulation of nutrient acquisition. Concurrent changes in absorption efficiency alone clearly exerted a relatively minor influence upon seasonal rates of absorption. Associated gut residence times of ¹⁵N-labelled material varied between 4 and 10 h. Furthermore, despite the ensuing deleterious effects, together with increased gut contents, absorption efficiencies among mussels that had been starved throughout acclimation were consistently maintained equivalent to those among individuals feeding normally. Such constancy was at least partially achieved by an increased residence time of material within diverticulae, relative to the digestive system as a whole. Finally, comparison of isotopic absorption efficiencies with those recorded for total organics and organic nitrogen has demonstrated differences of as much as 30% between gross and net uptake due, we suggest, to excretion of metabolically derived material within the alimentary canal.     

Lysosomal responses to experimentally injected anthracene in the digestive cells of Mytilus edulis

Experimentally injected anthracene (10 to 100 g mussel^-1) has been shown to induce dose-dependent lysosomal destabilisation and release of hexosaminidase in the digestive cells of Mytilus edulis after 24 h. This destabilisation was accompanied by cytological evidence of cytolysis of the digestive cells. The destabilising effect of 100 g of injected anthracene persisted for 96 h with a return to the control condition by 168 h. These results are discussed in the context of environmental contamination by polycyclic aromatic hydrocarbons.     

Ingestion of bivalve larvae by<Emphasis Type="Italic"> Mytilus edulis</Emphasis>: experimental and field demonstrations of larviphagy in farmed blue mussels

Ingestion of bivalve larvae by Mytilus edulis was investigated. Laboratory experiments revealed that ~ 90% of bivalve larvae offered to mussels was ingested and apparently fully digested. The shell of the bivalve larvae offered no protection against digestive processes, resulting in high larval mortality once inside the stomach. Stomach content analysis (September 2001–January 2003) showed that bivalve larvae were ingested by farmed mussels year-round, with the exception of March 2002. Numbers of ingested larvae were highest in October 2001 and May 2002, which coincides with known spawning times of farmed mussels in Ireland. Mussels ingested a large size-range of bivalve larvae, suggesting that all stages of the bivalve life cycle are vulnerable to predation. It is suggested that adult bivalves routinely filter larvae from the surrounding water and that, given the high biomass of mussels present in mussel farms, filtration by adult bivalves significantly reduces numbers of bivalve larvae in nearby waters.Communicated by J.P. Thorpe, Port Erin     

Age,growth and population structure of <Emphasis Type="Italic">Modiolus barbatus</Emphasis> from the Adriatic

Age, growth and population structure of Modiolus barbatus from Mali Ston Bay, Croatia were determined using modal size (age) classes in length frequency distributions, annual pallial line scars on the inner shell surface, internal annual growth lines in shell sections of the middle nacreous layer and Calcein marked and transplanted mussels. The length frequency distributions indicated that M. barbatus attain a length of ∼40 mm in 5–6 years indicating that a large proportion of the population in Mali Ston Bay is <5 years old. Some mussels of ∼60 mm were predicted to be 14 years old using the Von Bertalanffy growth (VBG) equation. Up to the first 6 pallial line scars were visible in young (<6 years) mussels but in older shells the first scars became obscured by nacre deposition as the mussel increased in length and age. The age of the older shells (>6 years) was determined from the middle nacreous lines in shell section, which formed annually in winter between February and March; the wider dark increments forming during summer (June to September). The oldest mussel, determined from the middle nacreous lines, was >12 years, with the majority of mussels aged between 3 and 6 years of age. The ages of mussels ascertained using the growth lines were not dissimilar to the ages predicted from the length frequency distributions. Age at length curves produced using modal size class data were not different from the data obtained using the pallial scar rings and internal growth lines. Taken together these data suggest that M. barbatus attains a length of 40 and 50 mm within 5 and 8 years, respectively. Eighty one percent of individual M. barbatus injected with a Calcein seawater solution (300 mg Calcein l⁻¹), into their mantle cavity successfully deposited a fluorescent line, which was visible in suitably prepared shell sections under ultra violet light. Incorporation of Calcein into the mussel shells was seasonally variable with the lowest frequency of incorporation in mussels marked in February and recovered in May. Seasonal shell growth was observed with significantly higher growth rates in mussels marked in May and removed in August (ANCOVA, F _3,149 = 23.11, P < 0.001). Mussels (∼18 to 22 mm) marked in May and recovered in August displayed maximal growth rates of >2.5 mm month⁻¹ compared with a mean mussel growth rate of 1.2 ± 0.6 mm month⁻¹. At other times of the year mussel shell growth ranged from immeasurable to 1.48 mm month⁻¹.     

溴氰菊酯对菲律宾蛤仔体内酶活性和组织损伤的初步探索

采用不同质量浓度的溴氰菊酯(0.0070 mg·L~(-1)、0.014 mg·L~(-1)、0.020 mg·L~(-1)、0.027 mg·L~(-1))对菲律宾蛤仔进行20 d半静置染毒,测定不同时间淋巴液中乙酰胆碱酯酶(ACh E)和钠离子-钾离子-三磷酸腺苷酶(Na~+-K~+-ATPase)活性、鳃和肝脏中谷胱甘肽转硫酶(GST)活性的变化,并观察染毒20 d后鳃丝组织和消化盲囊组织的损伤情况。酶活性分析结果显示,与对照组相比,低浓度组(0.0070 mg·L~(-1))试验期间酶活性均无显著差异(P0.05);中浓度组(0.014 mg·L~(-1)、0.020 mg·L~(-1))淋巴液中ACh E和Na~+-K~+-ATPase均呈先激活后抑制的变化规律(P0.05),鳃和肝脏中GST活性均呈上升趋势(P0.05);高浓度组(0.027mg·L~(-1))淋巴液中ACh E和Na~+-K~+-ATPase、肝脏中GST活性在试验期间持续下降(P0.01),而鳃中GST活性呈先抑制后升高的趋势(P0.05)。研究表明,低中浓度的溴氰菊酯对菲律宾蛤仔体内的酶活性表现为先诱导后抑制,具有明显的时间、剂量效应;高浓度的溴氰菊酯对菲律宾蛤仔体内酶活持续抑制,且染毒浓度越高,组织细胞变异越显著,表现为鳃丝上皮细胞纤毛层萎缩、纤毛脱落,消化盲囊上皮细胞膨胀,出现包涵体样结构。     

High intertidal community organization on a rocky headland in Maine,USA

A mosaic patchwork of the barnacle Balanus balanoides L., the mussel Mytilus edulis L., and the alga Fucus vesiculosus L. was found in the transitional region between the mid and high intertidal zones on a rocky headland on Mount Desert Island, Maine, USA. The development of the mosaic was observed by following recruitment and survival of B. balanoides in denuded patches located at the same tidal level along a 60 m stretch of shore. Barnacle recruitment was least under canopies of F. vesiculosus and greatest in open areas kept moist at low tide by surf. Barnacle survival after settlement was least under the F. vesiculosus canopy due to the whiplash effect of the algal fronds in the surf and greatest in open areas free from competition from mussels. In open areas, early mortality was correlated with settlement density. In areas of dense settlement (60 spat cm^-2) up to 90% mortality resulted within 5 months from crowding associated with growth. In older individuals crowding produced hummocks of elongated, weakly attached barnacles which were more prone to removal by surf than uncrowded barnacles. Mussels exerted competitive dominance over barnacles for space and the presence of mussel beds prevented further barnacle recruitment. Mussels suffered extensive mortality during winter storms when surf removed dense mats of weakly attached mussels. The patchy distribution of mussels and barnacles results from irregular rock substrata producing numerous environmental patches with respect to wave exposure and drainage at low tide, and from densitydependent mortality of both mussels and barnacles which creates patches of new colonizable space within each environmental patch.