The effect of a toxic dinoflagellate (Alexandrium tamarense) on the oxygen uptake of juvenile filter-feeding bivalve molluscs

• 1.1. Oxygen uptake and grazing rates of juvenile bivalve molluscs Mytilus edulis, Mya arenaria, Geukensia demissa, Placopecten magellanicus and Crassostrea virginica were measured following 1 hr exposure to bloom concentrations (10⁶ cells/1) of the toxic dinoflagellate Alexandrium tamarense (GT429) using a non-toxic clone of the same species (PLY 173) as control.
• 2.2. For all bivalves, prefeeding estimates of V̇O₂ were similar to postfeeding values and values recorded 24 hr after exposure to bloom conditions.
• 3.3. V̇O₂ was similar for bivalves fed on both the toxic and non-toxic strains of A. tamarense suggesting that there were no adverse effects on V̇O₂ following 1 hr exposure to toxic GT429.
• 4.4. Bivalves differed in their rates of grazing between toxic GT429 and non-toxic PLY 173. Similar grazing rates were recorded for M. edulis and G. demissa. For P. magellanicus and M. arenaria reduced rates of clearance were recorded in GT429 compared with the non-toxic strain.

     

Mass mortality in a population of the mussel Mytilus edulis L. Caused by high temperature on rocky shores

Mass mortality in a population of the mussel Mytilus edulis L. occurred in early August, 1981, on rocky intertidal shores in Mutsu Bay, northern Japan, due to unusually high temperatures. The decomposed tissues disappeared within 3 days after death. Higher mortality was observed in the upper part of the Mytilus zone than in the lower zone. As temperatures rose the mussels expelled water contained in the shells and 50% individuals died within 1 h from high body temperature rising up to >40°C. Septifer (Mytilisepta) virgatus (Wiegmann), which occupied the zone above Mytilus, showed low mortality (maximum 16.8%). Heat tolerance seems stronger in Septifer than in Mytilus. Many small animals including polychaetes, amphipods and nemerteans etc., lived among the empty shells and when the shells were removed by wave action, these animals disappeared from the bared rock surface. One year after the mass mortality the rock surface was covered by the barnacle Chthamalus challengeri Hoek. The ecological effect of mass mortality on the intertidal community is discussed.     

Water loss from aerially exposed mussels

The valve activity and water loss from aerially exposed Mytilus edulis L. and Modiolus modiolus (L.) have been investigated in a series of laboratory experiments. Mytilus is capable of maintaining long periods of complete, or almost complete, valve closure when exposed in air, and this allows the retention of water in the mantle cavity and protects the tissues from evaporative water loss. Over periods of three days or more the amount of water lost from emersed Mytilus was found to be less than that retained in the mantle cavity at the beginning of exposure, suggesting that during normal periods of exposure the tissues are never directly subject to water loss. In contrast, Modiolus shows periods of gaping during which water loss is rapid due to drainage from the mantle cavity and evaporation from the tissues. The exposure of the tissues to air that results from gaping, makes the water loss susceptible to environmental influences of which wind was found to be the factor which caused the greatest increase in water loss and, as a consequence, an important factor in causing death through dehydration. The different abilities of Mytilus edulis and Modiolus modiolus to control water loss may be related to their intertidal distributions.     

A first report on coexistence and hybridization of <Emphasis Type="Italic">Mytilus trossulus</Emphasis> and <Emphasis Type="Italic">M. edulis</Emphasis> mussels in Greenland

Semi-sessile Mytilus mussels are used as indicators of climate changes, but their geographic distribution is not sufficiently known in the Arctic. The aim of this study was to investigate the taxonomic status and genetic differentiation of Mytilus populations in a Northwest Greenlandic fjord at Maarmorilik, impacted by contaminations from a former mine. In this study, mussels were collected at three sites differing in exposure to environmental factors. A total of 54 polymorphic SNPs found in the Mytilus EST and DNA sequences analyzed were successfully applied to 256 individuals. The results provided the first evidence for the existence of M. trossulus in Greenland. The mussel from M. trossulus and M. edulis taxa are shown to coexist and hybridize in the fjord. The three studied sites were found to differ significantly in the distribution of taxa with a higher prevalence of M. trossulus in the inner fjord. The identified M. edulis × M. trossulus hybrids mostly had a hybrid index score of about 0.5, indicating a similar number of alleles characteristic for M. trossulus and M. edulis. There was a low number of backcrosses between ‘pure’ taxa and hybrids. This newly discovered hybrid zone between the two taxa is unique in comparison with the Canadian populations. As Mytilus mussels in Greenland hitherto have been regarded as the one taxon M. edulis, the results have importance for biogeography and future monitoring and environmental studies.     

Three species of Mytilus and their hybrids identified in a Scottish Loch: natives, relicts and invaders?

Three species of the mussel, Mytilus, occur in the North Atlantic region, M. edulis, M. galloprovincialis and M. trossulus, and hybrid zones are present where their distributions overlap. M. edulis is a native species in the UK. M. galloprovincialis originated in the Mediterranean and its distribution extends northwards along the Atlantic seaboard to Scotland. Baltic Sea mussels have a M. trossulus ancestry but are highly introgressed by M. edulis. In recent decades, farming of mussels on long-line rope culture systems has been introduced into Scotland. On farms in Loch Etive, a form of mussel with a fragile shell and a different shape to either M. edulis or M. galloprovincialis has been increasing in frequency over recent years. Samples of fragile shelled, normal strong shelled and intermediate mussel types were sampled from two farms in 2006 and compared with samples of M. edulis, M. galloprovincialis and M. trossulus from other sources where their species identity is well established. Abundance relative to depth, shell strength, condition index and shell morphology were analysed together with 5 allozyme loci and one nuclear DNA genetic marker (Me 15/16). The fragile shelled mussels, and many of those classed as intermediate, were identified as a mixture of M. trossulus and M. trossulus x M. edulis hybrids. This identification was strongly supported by both morphological and genetic data and is the first record of the presence of M. trossulus in UK waters. M. trossulus in Loch Etive are most likely to be a post-glacial relict population restricted to the low salinity area of the Loch that has recently increased in abundance due to commercial mussel growing activity. In addition, individual mussels of all three species and their hybrids were detected amongst Loch Etive mussels. This is the first genetic demonstration of all three species and their hybrids occurring together in one location in the Atlantic region and provides a unique opportunity to study the processes of speciation, divergence, and introgression in the genus Mytilus.     

Species status and population structure of mussels (Mollusca: Bivalvia: Mytilus spp.) in the Wadden Sea of Lower Saxony (Germany)

Three species of mussel (genus Mytilus) occur in Europe: M. edulis (Linnaeus 1758), M. galloprovincialis (Lamarck 1819) and M. trossulus (Gould, Boston Society of Natural History 3: 343?C348, 1850). Although these species are indigenous to the North Sea, the Mediterranean and the Baltic Sea, respectively, they form an extended patchy species complex along the coasts of Europe (??the Mytilus edulis complex??) and are able to hybridize where their distributions overlap. Recent studies examining the taxonomic status and genetic composition of Mytilus populations in the Netherlands and the British Isles have revealed introgressive hybridization processes within this species complex, with hints of an invasion of nonindigenous M. galloprovincialis into the North Sea. Furthermore, an extensive international mussel fishery industry in Europe (i.e., Great Britain, the Netherlands, Denmark, and Germany) is also in discussion for a possibly anthropogenically induced bioinvasion of nonindigenous Mytilus traits into the Wadden Sea area. Although it is assumed that the Wadden Sea of Germany comprises M. edulis only, this has never been confirmed in a molecular genetic study. To assess the situation for the Wadden Sea of Lower Saxony, we conducted the first molecular study of the Mytilus genus in the region. Taxonomic identification of 504 mussels from 13 intertidal mussel banks using the nDNA marker Me15/16 revealed a population composition of 99% M. edulis and 1% M. edulis X M. galloprovincialis hybrids. Hence, the Wadden Sea population is unaffected by range expansion of nonindigenous Mytilus traits. The genetic structure of the M. edulis populations was investigated using the phylogenetic and population genetics analyses of the mitochondrial DNA cytochrome-c-oxidase subunit I (COI) and the first variable domain of the control region (VD1), which were sequenced for >120 female individuals. These results showed a heterogeneous, panmictic population due to unrestricted gene flow. This can be attributed to extensive larval dispersal linked to the tidal circulation system in the back barrier basins of the Wadden Sea.     

Effects of GABA and epinephrine on the settlement and metamorphosis of the larvae of four species of bivalve molluscs

Competent larvae of different marine bivalve species were treated with GABA and epinephrine at different concentrations and times of exposure to test the ability of the drugs to induce settlement and metamorphosis. GABA induced both settlement and metamorphosis in the mussel Mytilus galloprovincialis, the clams Venerupis pullastra and Ruditapes philippinarum and the oyster Ostrea edulis. Maximum induction of settlement (>39%) was achieved after exposure of V. pullastra larvae to 10⁻⁴ M GABA; this concentration of GABA also induced the highest percentages of metamorphosis in the four species studied. Epinephrine was identified as an active inducer of settlement and metamorphosis in bivalve molluscs. Exposure to 10⁻⁵ M epinephrine induced significant levels of settlement in Mytilus, Venerupis and Ostrea. In contrast, epinephrine failed to induce settlement behaviour in Ruditapes. Maximum induction of metamorphosis was produced by 10⁻⁵ M epinephrine in mussels, clams and oysters; Ruditapes showed the highest percentage of metamorphosis (>78%). This is the first report in which the involvement of GABA in the settlement and metamorphosis of bivalve molluscan larvae is demonstrated. It was also recognised that epinephrine plays a role not only in inducing metamorphosis but also in initiating settlement.     

Bioinvasion threatens the genetic integrity of native diversity and a natural hybrid zone: smooth‐shelled blue mussels (Mytilus spp.) in the Strait of Magellan

Smooth‐shelled blue mussels of the Mytilus edulis species complex are widely distributed bivalve molluscs whose introductions threaten native marine biodiversity (non‐indigenous species – NIS). The aim of the present study was to identify the species and hybrids of Mytilus present in the Magellan Region (southern Chile). Results indicate that three mussel species of the Mytilus edulis complex are found in the region – M. edulis, M. chilensis (or the Southern Hemisphere lineage of Mytilus galloprovincialis), and M. galloprovincialis of Northern Hemisphere origin. For the first time, alleles of the introduced M. trossulus are reported from the Southern Hemisphere. In the Strait of Magellan the native Pacific blue mussel, Mytilus chilensis and the native Atlantic blue mussel, Mytilus edulis, meet and mix at a natural hybrid zone (about 125 km in length). This is the first record of a natural Mytilus hybrid zone in the Southern Hemisphere and is also the first record of the co‐occurrence of genes from all four Mytilus species in any one region. These results contribute to the knowledge of the biodiversity and delimitation of mussel species in southern South America, and highlight how introduced species may threaten the genetic integrity of native species through hybridization and introgression.     

Mytilus galloprovincialis Lmk. in Southern Africa

The Mediterranean mussel, Mytilus galloprovincialis Lmk. has been identified on the west coast of southern Africa using morphological and biochemical-genetic comparisons with samples of “pure” M. edulis L. from Denmark and M. galloprovincialis from the Mediterranean coast of Spain. Our results show that the southern African Mytilus more closely resembles M. galloprovincialis in anterior adductor, posterior adductor and hinge size. It also has a more ventrally located maximal shell width like the Mediterranean mussel. The electrophoretic examination of 23 proteins showed that many alleles diagnostic for M. galloprovincialis appeared in the southern African Mytilus. Nei's genetic distance between the southern African Mytilus and M. galloprovincialis was 0.010 ± 0.004 and the average genetic distance between these samples and M. edulis was 0.162 ± 0.077.The presence of M. galloprovincialis in southern Africa could be explained by biogeographic dispersal along the west coast of Africa during Pleistocene cooling, or by a recent inadvertant or intentional introduction by man. To test these two hypotheses, we examined ≈750 mussel shells collected from Koi-san middens and ≈350 shells from a raised-beach deposit all located on the west coast of Cape Province, South Africa. The ages of these deposits range from 1500 yr to 120000 yr and pre-date the arrival of Europeans to the Cape. This examination did not reveal any shells of Mytilus. We, therefore, conclude that the introduction of M. galloprovincialis to southern Africa was a recent event. We suggest that, since the first confirmed reference to Mytilus in southern Africa was made from a 1972 collection, the introduction occurred within the last two decades.     

Genetics and taxonomy of Chilean smooth-shelled mussels, Mytilus spp. (Bivalvia: Mytilidae)

It has been previously established that native smooth-shelled mussels in southern South America possess close evolutionary affinities with Northern-Hemisphere Mytilus edulis L. 1758 (McDonald et al. (1991) [5]). This result has since been challenged by authors claiming that Chilean mussels should be considered a local subspecies of M. galloprovincialis Lmk. 1819. Moreover, morphological, physiological, ecotoxicological and molecular genetic studies on Chilean smooth-shelled mussels still frequently refer to ‘M. chilensis’ Hupé 1854, even though the previous discovery of alien M. galloprovincialis and considerable heterogeneity in shell morphology among samples collected along the Chilean shores raise concerns that different Mytilus spp. species might have been included under ‘M. chilensis’. Here we reviewed the molecular and morphological data available on smooth-shelled mussels from Chile in an attempt to clarify both their genetic composition and their taxonomic status. Using multivariate analysis on sample × allozyme-frequency matrices, we confirmed the widespread occurrence of the Southern-Hemisphere form of M. edulis along the shores from the North Patagonia region of Chile to the southern tip of the South American continent. The populations sampled in southern central Chile showed some evidence of slight introgression from Southern-Hemisphere M. galloprovincialis. Morphological characterization of a sample from Dichato in southern central Chile was consistent with its previous genetic identification as Mediterranean M. galloprovincialis. The occurrence of Southern-Hemisphere M. galloprovincialis in Punta Arenas at the southern tip of the South American continent was also reported. Southern-Hemisphere M. edulis, including native Chilean smooth-shelled Mytilus, should be assigned subspecific rank and named M. edulis platensis d’Orbigny 1846.     

Development of a real-time PCR assay for detection of Mytilus species specific alleles: Application to a sampling survey in Scotland

Shellfish aquaculture is a growing industry in Scotland, dominated by the production of the mussel Mytilus edulis, the native species. Recently the discovery of Mytilus galloprovincialis and Mytilus trossulus together with M. edulis and all 3 hybrids in cultivation in some Scottish sea lochs led to questions regarding the distribution of mussel species in Scotland. The establishment of an extensive sampling survey, involving the collection of mussels at 34 intertidal sites and 10 marinas around Scotland, motivated the development of a high-throughput method for identification of Mytilus alleles from samples. Three Taqman®-MGB probes and one set of primers were designed, based on the previously described Me 15/16 primers targeting the adhesive protein gene sequence, and samples were screened for the presence of M. edulis, M. galloprovincialis and M. trossulus alleles using real-time PCR. Mytilus edulis alleles were identified in samples from all 44 sites. Mytilus galloprovincialis alleles were found together with M. edulis alleles extensively in northern parts of the west and east coasts. Mytilus trossulus alleles were identified in samples from 6 sites in the west and south-west of Scotland. Because M. trossulus is generally undesirable in cultivation and therefore preventing the geographical spread of this species across Scotland is considered beneficial by the shellfish aquaculture industry, these 6 samples were further analysed for genotype frequencies using conventional PCR. Although distribution of the non-native species M. galloprovincialis and M. trossulus have proven to be more widespread than previously thought, there is no evidence from our study of either M. trossulus or M. galloprovincialis acting as an invasive species in Scotland. The real-time PCR method developed in this study has proven to be a rapid and effective tool for the identification of M. edulis, M. galloprovincialis and M. trossulus alleles from samples and should prove useful in future surveys, ecological or aquaculture management related studies in both unispecific and mixed species areas of these species.     

Genetic traits in the bivalve Mytilus from Europe, with an emphasis on Arctic populations

Genetic and some ecophysiological traits of mussels collected in the European Arctic, up to their northeastern distribution limit in the Barents Sea, were studied and compared with traits of mussels from the Mediterranean, Atlantic and Baltic. The genetic traits of these populations were analysed by isoenzyme electrophoresis on seven loci in order to assess the Mytilus complex to which populations in the Arctic region belong. Ecophysiological variables, the weight-index and glycogen were analysed to assess the physiological fitness of the populations. Three distinct groups were recognised: (1) Mytilus (edulis) galloprovincialis in the Mediterranean and Spain, (2) M. (edulis) edulis along the Atlantic coast from the Netherlands northwards into Russia, and (3) the Baltic Mytilus (edulis) trossulus. The mussels from populations in the Russian Arctic all belong to the Atlantic Mytilus (edulis) edulis group. The genetic variability and ecophysiological measures indicated that the sub-Arctic White Sea mussel populations have a relatively lower performance capacity, whereas those in the Arctic at the edge of their northern distribution showed a surprisingly strong performance. Accepted: 14 June 2000     

STRUCTURE OF THE CONCHIOLIN CASES OF THE PRISMS IN MYTILUS EDULIS LINNE

The prisms in the shell of Mytilus edulis Linné are calcite needles. Their small size and their thin conchiolin cases distinguish them from the prisms of many other species of mollusks. These Mytilus prisms have been studied with the electron microscope. The material consisted of positive replicas of surfaces of the prismatic layer, etched with chelating agents, and of preparations of tubular cases from decalcified prisms which were compared with the conchiolin from decalcified mother-of-pearl of the same species. In the replicas, the cases appear as thin pellicles in the intervals between the prism crystals. Both the prism cases and the nacreous conchiolin, disintegrated by exposure to ultrasonic waves and sedimented on supporting films, appear in the form of tightly meshed, reticulated sheets, described as "tight pelecypod pattern" in former studies on nacreous conchiolin of Mytilus. The results show that in the shell of this species the same conchiolin structure is associated with aragonite in mother-of-pearl and with calcite in the prismatic layer.     

Biogenic and taphonomic processes affecting the development of shell assemblages: an actuopaleontological case study from mussel banks on North Sea tidal flats

Summary From spring 1997 to winter 2000, the composition and structure of epibenthic bivalve clusters and patches on a backbarrier tidal flat of the East Frisian Wadden Sea were continoously analyzed. The studied bivalve aggregates developed from intense and approximately simultaneous spatfalls of Mytilus edulis and Cerastoderma edule in 1996, after a severe winter (1995/96) with 64 days of driftice coverage. Spatfall occurred on a bare sandy tidal flat, whereas adjacent shell layers situated at the southern margin of the spatfall site were not colonized. Usually, such shell layers are the most common secondary hard substrates in the backbarrier area favorable for initial settlement of Mytilus larvae. The shell layers predominantly originate from erosion of former Mya arenaria and C. edule populations. So far, the studied bivalve aggregates are composed of approximately equal proportions of living specimens of both species, M. edulis and C. edule. The incorporated cockles were prevented from burrowing into the rediment by the coherent byssal mesh. In contrast to the results of previous studies, the great bulk of epibenthic living C. edule did survive for several years within the clusters. Therefore, the common terms ‘Mytilus banks’, ‘Mytilus patches’ or ‘Mytilus clumps’ may be too general and may erroneously imply a dominance of (or mono-specific composition by) M. edulis. In the fossil record, i.e. in diagenetically consolidated shell layers, the enforced epibenthic life-mode of C. edule and the remarkable species composition as well as the temporal development of the aggregates would not be recognizable.     

Will the invasive mussel Mytilus galloprovincialis Lamarck replace the indigenous Perna perna L. on the south coast of South Africa?

The mussel Mytilus galloprovincialis is invasive worldwide, has displaced indigenous species on the west coast of South Africa and now threatens Perna perna on the south coast. We tested the hypothesis that Mytilus will replace Perna by examining changes in their distribution on shores where they co-exist. Total cover, adult density, recruit density, recruit/adult correlations and mean maximum lengths of both species were measured in 2001 at two contrasting sites (Plettenberg Bay and Tsitsikamma) 70 km apart, each including two locations 100 m apart. Cover and density were measured again in 2004. Total mussel abundance was significantly lower in Tsitsikamma, and recruit density was only 17% that of Plettenberg Bay. Abundance and cover increased upshore for Mytilus, but decreased for Perna, giving Mytilus higher adult and recruit density and total cover than Perna in the upper zones. Low shore densities of recruits and adults were similar between species but cover was lower for Mytilus, reflecting its smaller size, and presumably slower growth or higher mortality there. Thus, mechanisms excluding species differed among zones. Recruitment limitation delays invasion at Tsitsikamma and excludes Perna from the high shore, while Mytilus is excluded from the low shore by post-recruitment effects. Recruitment limitation also shapes population structure. Recruit/adult correlations were significant only where adult densities were low, and this effect was species-specific. Thus, at low densities, larvae settle or survive better near adult conspecifics. After 3 years, these patterns remained strongly evident, suggesting Mytilus will not eliminate Perna and that co-existence is possible through partial habitat segregation driven by recruitment limitation of Perna on the high shore and post-settlement effects on Mytilus on the low shore.     

Glacial history of the European marine mussels Mytilus,inferred from distribution of mitochondrial DNA lineages

Mussels of the genus Mytilus have been used to assess the circumglacial phylogeography of the intertidal zone. These mussels are representative components of the intertidal zone and have rapidly evolving mitochondrial DNA, suitable for high resolution phylogeographic analyses. In Europe, the three Mytilus species currently share mitochondrial haplotypes, owing to the cases of extensive genetic introgression. Genetic diversity of Mytilus edulis, Mytilus trossulus and Mytilus galloprovincialis was studied using a 900-bp long part of the most variable fragment of the control region from one of their two mitochondrial genomes. To this end, 985 specimens were sampled along the European coasts, at sites ranging from the Black Sea to the White Sea. The relevant DNA fragments were amplified, sequenced and analyzed. Contrary to the earlier findings, our coalescence and nested cladistics results show that only a single M. edulis glacial refugium existed in the Atlantic. Despite that, the species survived the glaciation retaining much of its diversity. Unsurprisingly, M. galloprovincialis survived in the Mediterranean Sea. In a relatively short time period, around the climatic optimum at 10 ky ago, the species underwent rapid expansion coupled with population differentiation. Following the expansion, further contemporary gene flow between populations was limited.     

Effects of several peptides with pro-arg-leu-NH2 C-terminal sequence on invertebrate muscles

1. Effects of the following PRLamide peptides on some invertebrate muscles were examined: APNFLAYPRLamide (a peptide of the bivalve mollusc Mytilus), AAPLPRLamide (a peptide of the echiuroid Urechis), FTPRLamide (a fragment of a peptide of the insect Pseudaletia), YFSPRLamide (a fragment of a peptide of the insect Heliothis) and pQTSFTPRLamide (a peptide of the insect Leucophaea).2. In the ABRM of Mytilus, the Mytilus and Urechis peptides potentiated phasic contraction by repetitive electrical stimulation. The former was more potent than the latter. The three insect-origin peptides did not show any potentiating effect but showed a weak antagonistic action on the potentiating effect of the Mytilus peptide. Except the Mytilus peptide, the PRLamide peptides showed little or no relaxing effect on catch tension, though they accelerated catch-relaxing response to repetitive electrical stimulation.3. In the inner circular body-wall of muscle of Urechis, the PRLamide peptides showed a potentiating effect on twitch contraction. The Urechis peptide was most potent. In the esophagus of the annelid Perinereis, the PRLamide peptides showed a contractile effect. The Urechis peptide was also most potent.4. In the crop of the cricket Gryllus, the insect-origin peptides markedly potentiated spontaneous rhythmic contractions. The Mytilus peptide showed a weak potentiating effect, but the Urechis peptide showed little or no effect.     

Acute exposure to Catha edulis depresses contractility and induces myocardial infarction in spontaneously contracting,isolated rabbit’s heart

Khat chewing is a recreational habit known to pose major socio-economic and medical problems in countries of Southern Arabia and the Horn of Africa. Among other adverse health effects, khat chewing has been associated with an increased risk of myocardial infarction (MI) in heavy consumers. This study was carried out to examine the direct effects of Catha edulis extract on contractility of spontaneously contracting, isolated rabbit heart and to investigate its mechanism of action. Isolated six rabbit’s hearts attached to a Langendorff apparatus were perfused with extract at a constant flow rate and continuously bubbled with a 95% O₂/5% CO₂ gas mixture. Each heart served as its own control, as responses were recorded before and after administration of C. edulis extract. Varying concentrations of extract (50, 100 and 250 mg/ml) were loaded in the perfusate, their effects recorded and effluent fluid collected for assay of cardiac enzymes. Histological examination of the cardiac tissue was performed at the end of perfusion with 250 mg/ml extract. This study revealed that acute exposure to C. edulis extract exerted negative inotropic and chronotropic effects on isolated hearts. The extract also had a vasoconstrictor effect on coronary vessels, independent of α₁ adrenergic receptor stimulation. Histological examination of hearts perfused with 250 mg/ml C. edulis extract revealed the presence of histological changes unique to myocardial infarction, a finding consistent with observed increased levels of cardiac enzymes in perfusates. Thus, we have demonstrated experimentally a direct cardiac depressant- and MI inducing effects of C. edulis extract. These results are consistent with the earlier reported deleterious effects of khat on cardiovascular function among khat chewers.