Zealand Greenshell Mussel Research Articles

Histopathological changes in the greenshell mussel, Perna canaliculus, in response to chronic thermal stress

Climate change associated temperature challenges pose a serious threat to the marine environment. Elevations in average sea surface temperatures are occurring and increasing frequency of marine heatwaves resulting in mortalities of organisms are being reported. In recent years, marine farmers have reported summer mass mortality events of the New Zealand Greenshell mussel, Perna canaliculus, during the summer months; however, the etiological agents have yet to be determined. To elucidate the role of thermal stress, adult P. canaliculus were exposed to three chronic temperature treatments: a benign control of 17 °C and stressful elevations of 21 °C and 24 °C. Eight mussels per treatment were collected each month throughout a 14-month challenge period to identify and investigate histopathological differences among P. canaliculus populations exposed to the three temperatures. Histopathology revealed several significant deleterious alterations to tissues associated with temperature and exposure time. Increasing temperature and progression of time resulted in 1) an increase in the number of focal lipofuscin-ceroid aggregations, 2) an increase in focal hemocytosis, 3) an increase in the thickness of the sub-epithelial layer of the intestinal tract and 4) a decreased energy reserve cell (glycogen) coverage in the mantle. Prolonged exposure, irrespective of temperature, impacted gametogenesis, which was effectively arrested. Furthermore, increased levels of the heat shock protein 70 kDa (HSP 70) were seen in gill and gonad from thermally challenged mussels. The occurrence of the parasite Perkinsus olseni at month 5 in the 24 °C treatment, and month 7 at 21 °C was unexpected and may have exacerbated the fore-mentioned tissue conditions. Prolonged exposure to stable thermal conditions therefore appears to impact P. canaliculus, tissues with implications for broodstock captivity. Mussels experiencing elevated, temperatures of 21 and 24 °C demonstrated more rapid pathological signs. This research provides further insight into the complex host-pathogen-environment interactions for P. canaliculus in response to prolonged elevated temperature.

Effects of Greenshell Mussel (Perna canaliculus) Intake on Pathological Markers of Multiple Phenotypes of Osteoarthritis in Rats

The prevalence of metabolic osteoarthritis has been increasing worldwide, particularly among women. The aim of this study was to investigate the effects of the New Zealand greenshell mussel (Perna canaliculus; GSM) on osteoarthritis (OA) prevention in a rat model. One-hundred-and-eight female rats aged 12 weeks were divided into four test groups, containing 24 rats each, plus an additional control group. Each test group received one of the four experimental diets: normal control diet (ND), normal control diet supplemented with GSM (ND + GSM), high fat/high sugar diet (HFHS), or high fat/high sugar diet supplemented GSM (HFHS + GSM), for 36 weeks (end of the study). After 8 weeks on experimental diets, half of each group was subjected to ovariectomy (OVX) and the remaining half received a sham operation (ovaries left intact). The study evaluated body composition, bone mass, plasma cytokines, adipokines, HbA1c, CTX-II, and knee joint’s histopathology. HFHS diet and OVX significantly induced body weight gain and leptin production. OVX rats lost bone mineral density but increased adiponectin, HbA1C, and MCP-1. The OVX rats fed HFHS showed the highest Mankin scores. Importantly, inclusion of GSM reduced these pathological features. In conclusion, GSM might be beneficial in halting the progression of OA.

Comparison of Lipid Classes and Fatty Acid Profiles of Lipids From Raw, Steamed, and High-Pressure-Treated New Zealand Greenshell Mussel Meat of Different Genders

ABSTRACT The lipid classes and fatty acid profiles of oils extracted from male and female New Zealand Greenshell (Perna canaliculus) mussel samples either raw, or treated with heat or with high-pressure processing were compared. The Bligh and Dyer solvent extraction method was performed for mussel oil extraction. Iatroscan was used for lipid class determination, and gas chromatography—mass spectrometry was used for the fatty acid composition determination. Eight minutes of steaming time was required for the medium-size mussel meat placed as a single layer in a plastic pouch to achieve an internal temperature of at least 75°C. Female mussels had greater oil yield than male mussels on a dry weight basis, and female mussel oil extracts had a greater content of fatty acids than male mussels in general. No significant differences were observed in yield, lipid classes, and fatty acid compositions as a result of different treatments (raw, steamed, and high-pressure processing).

Influence of climate on Pelorus Sound mussel aquaculture yields: predictive models and underlying mechanisms

Multiple regression models were used to predict aquaculture production in Pelorus Sound, a 50 km long estuary supporting 68% of New Zealand's greenshell mussel Perna canali - culus aquaculture industry (worth NZ$ 204 million per annum). Mussel meat yield was modelled using both biological predictors, including seston (indexed by particulate nitrogen, PN), phyto- plankton and nutrients collected over 9 yr (July 1997 to November 2005) by the mussel industry, and physical, climatic predictors, including Southern Oscillation Index (SOI), along-shelf winds, sea surface temperature (SST) and Pelorus River flow, held in New Zealand national databases. Yield was best predicted using biological predictors collected locally at the farms inside the sound, but it was also predictable using only physical predictors collected distant from the farming region. Seston (mussel food) was also predictable using the physical predictors. Optimal predictor sets for yield and seston differed between summer and winter half-years. In summer, deep water (which enters the sound through the estuarine circulation) at the sound entrance was nitrate (NO3 � )-rich during upwelling conditions (negative SOI, NNW wind stress and cool SST). The increased NO3 � levels, in turn, triggered increased PN within the sound. In the winter half-year, PN was unrelated to upwelling and NO3 � effects at the entrance and was instead related to river flow. Remotely-sensed SST data showed that in summer, upwelling affected the entrance waters of the sound under negative SOI and upwelling-favourable wind stress, patterns which dissipated in winter. Overall, these results show that time series of physical drivers can be useful for explain- ing production variation of farmed bivalves and indicate the prospects for using data routinely col- lected in national databases for predicting mussel yield.

Population genetic variation in the New Zealand greenshell mussel: locus-dependent conflicting signals of weak structure and high gene flow balanced against pronounced structure and high self-recruitment

A pronounced north–south multitaxon genetic discontinuity occurs in central New Zealand (NZ). Polymorphic microsatellite markers have been used to test the location and structure of this discontinuity in the endemic greenshell mussel, Perna canaliculus. Nine neutral loci revealed limited evidence of genetic structure, but one outlier locus (Pcan1-27) which may be under selection provided evidence of the discontinuity in central NZ. Whilst the limited multilocus evidence of structure is assumed to result from high levels of gene flow among populations of this continuously distributed species, assignment tests indicated high to very high mean levels of self-recruitment within the 14 populations and the north and south regions. The nine neutral loci were unable to provide further clarification as to the geographic location of the discontinuity, whereas the Pcan1-27 locus was particularly informative. These results highlight a tension between limited evidence of genetic structure and presumptive high gene flow among populations versus high levels of self-recruitment and pronounced structure depending on microsatellite loci and analyses in question. Evidence from all 10 loci indicates that the genetic discontinuity is maintained by high levels of self-recruitment, and evidence from Pcan1-27 suggests that selection may also be important in explaining the existence of the discontinuity.

Challenge of New Zealand Greenshell™ mussel Perna canaliculus larvae using two Vibrio pathogens: a hatchery study

Bacterial diseases remain a large problem in aquaculture hatcheries. The successful design and implementation of protective measures in the hatchery depends on an understanding of the dynamics of the infection process. Developing an in situ experimental protocol for pathogen challenge is therefore of paramount importance. Here, we demonstrated the minimum effective pathogenic dose (MEPD) of Vibrio splendidus (10(5) CFU ml(-1)) and a Vibrio coralliilyticus/neptunius-like isolate, Vibrio sp. DO1 (10(6) CFU ml(-1)), for New Zealand Greenshell mussel (GSM, Perna canaliculus) larvae during hatchery production. In a flow-through water hatchery system, larvae given 1 to 2 h of static water exposure to these pathogen doses showed respective average cumulative mortalities of 58 and 69% on the fourth day following pathogen exposure. After the 1 to 2 h static exposure, larvae were returned to flow-through water. Larvae exposed to a dosage one order of magnitude greater than the MEPD had higher mortalities of 73 and 96% for V. splendidus and Vibrio sp. DO1 respectively. These 4 levels of mortality were significantly greater than those of the non-exposed control larvae which respectively averaged 23 and 35% in experiments involving V. splendidus and Vibrio sp. DO1. Experiments were repeated 4 times to confirm reproducibility. After pathogen exposure, pathogens were detected in the larvae and tank water of treatments with dosages of > or =10(5) CFU ml(-1) (V. splendidus) and 10(6) CFU ml(-1) (Vibrio sp. DO1), but not in treatments with lower pathogen dosages. The challenge protocols are reproducible and provide an opportunity to assess measures for the protection of GSM larvae against infection in the hatchery environment.

Effect of food quality on energy uptake

The dynamic energy budget (DEB) theory assumes that the feeding of an organism in relation to food density follows the type-II functional response when food consists of purely digestible organic matter. However when faced with a food source high in inorganic content, an organism needs to adapt physiologically to maximise organic extraction. Indeed filter-feeding marine bivalves inhabiting turbid coastal waters cope with large fluctuations in food quality by selectively ingesting and pseudofaeces production. Data from feeding experiments with the New Zealand greenshell mussel Perna canaliculus have demonstrated that inorganic particles contribute some uncertainty to the estimate of the half-saturation coefficient. Incorporating inorganic matter into the functional response would improve the prediction of energy uptake.

Research Issues in Inactivation of Listeria monocytogenes Associated with New Zealand Greenshell Mussel Meat (Perna canaliculus) Using High-Pressure Processing

ABSTRACT New Zealand Greenshell mussels are currently shucked by heat processing, and this can be used as a listericidal step. Shucking by high pressure processing (HPP) has potential benefits in product quality and increased yield, but processors need to understand the effects of this technology on the safety of their product with respect to Listeria monocytogenes. L. monocytogenes was mixed with minced mussel meat, and 2 g samples (in foil pouches) were subjected to HPP at various pressures, times, and temperatures. Of 10 tested strains of L. monocytogenes, the most resistant to HPP at 400 MPa (Food Science Australia strain 2655 isolated from Australian processed meat) was selected for subsequent work. This strain showed two-phase inactivation kinetics in response to time at 400 MPa. Approximately 5 log10 cells/g were rapidly inactivated in a log-linear fashion with time while the remaining cells were inactivated at a slower rate. There was also some evidence of a shoulder in the inactivation curves. In the temperature range tested (10°C–40°C), the log-linear inactivation rates showed linear increases with increasing processing temperature at 400 MPa with a z value of 29.1 min.

Effect of Heat Treatment on Hepatitis A Virus and Norovirus in New Zealand Greenshell Mussels (Perna canaliculus)by Quantitative Real-Time Reverse Transcription PCR and Cell Culture

Quantitative real-time reverse transcription PCR (qRT-PCR) and cell culture (50% tissue culture infectious dose [TCID50]) were used to determine the effect of heat treatments on norovirus and hepatitis A virus (HAV) in the New Zealand Greenshell mussel (Perna canaliculus). Since it is common practice to cook mussels until the shells open, internal temperatures and opening times of mussels on boiling and steaming were determined at regular time intervals. Fifty mussels in batches of six were exposed to boiling and steaming. A mean internal temperature of 90°C (recommended for virus inactivation when maintained for 90 s) was reached after boiling for 170 s, with all 50 mussels open at 210 s. For steaming, the mean internal temperature achieved was only 83°C after 300 s, and all 50 mussels were open. When mussels were steamed for 180 s (mean internal temperature of 63°C), a significant 1.5-log decrease in the HAV titer (log TCID50) was observed. Following the immersion of mussels in boiling water for 180 s (mean internal temperature of 92°C), no viable HAV was detected. For both boiling and steaming experiments, there was no significant change in the norovirus or HAV qRT-PCR titers compared with the controls. Our results show that when New Zealand Greenshell mussels open on heating, their internal temperature may not reach the parameters required for virus inactivation. Immersion for a minimum of 3 min in boiling water rather than steaming is recommended to reduce the risk of viral foodborne illness from contaminated shellfish.

A comparison of genetic diversity between cultured and wild populations, and a test for genetic introgression in the New Zealand greenshell mussel Perna canaliculus (Gmelin 1791)

We evaluated whether genetic material from offspring of greenshell mussels, Perna canaliculus (Gmelin 1791), obtained from Kaitaia, northern New Zealand, and transferred to mussel farms around the country, had introgressed into wild (naturally occurring) mussel stocks. The potential extent of genetic introgression of this northern mussel DNA was assessed by analysis of allozyme, mitochondrial SSCP and RFLP, and nuclear RAPD markers. Cultured and wild populations throughout New Zealand showed an absence of biochemical genetic differentiation at seven protein-encoding loci, meaning that allozyme analysis was not a suitable tool to address the question of genetic introgression. For the DNA marker techniques, a haplotype specific to mussels originating from Kaitaia was identified only using mitochondrial composite markers. However, this composite marker occurred at low frequency in the Kaitaia population and not in any other populations and, therefore, could not be used to measure introgression of Kaitaia genes into wild populations. MtDNA and RAPD analyses revealed that North Island and Greater Cook Strait mussels were genetically different from lower South Island, particularly South Island west coast mussels, and the wild Stewart Island population. Furthermore, the two marker types showed that cultured mussels were significantly differentiated from wild mussels. These two findings clearly indicate that at the molecular level, population subdivision exists in P. canaliculus. The SSCP and RFLP markers did not show any evidence of genetic introgression of spat moved from the north into southern mussel populations. The RAPD markers, however, showed that the wild Stewart Island population (HSB) fell outside the northern and the southern clades of populations. The HSB population is located near an aquaculture site that has been seeded with mussels from Kaitaia for over a decade. Our RAPD data are consistent with the possibility of genetic introgression of genes from northern populations into this southern population. We recommend that genetic analysis of wild mussel populations in the vicinity of stocked areas be carried out regularly.

Genetic structuring among populations of the greenshell mussel Perna canaliculus revealed by analysis of randomly amplified polymorphic DNA

Allozyme analysis of 35 populations of the endemic New Zealand greenshell mussel Perna canaliculus (Gmelin 1791) indicated an absence of genetic structuring, whereas mitochondrial DNA (mtDNA) single-strand conformation polymorphism (SSCP) analysis of 22 of the same popula- tions indicated a pronounced genetic discontinuity between northern and southern mussels at ~42° S latitude. The present study examines the genetic structuring of a subset of 19 New Zealand mussel populations using the randomly amplified polymorphic DNA (RAPD) technique. A genetic disconti- nuity was observed between northern and southern populations, which resulted from significant allele frequency differences, but no absolute differences between populations of these regions. Southern populations were genetically more diverse than northern populations, with the west coast of the South Island being the most distinct from northern populations. The RAPD data are consistent with the mtDNA data, indicating that both studies have resolved the population structure of P. canaliculus at a higher level than previous allozyme studies. The location of the genetic discontinuity coincides with major hydrographic features at ~42° S latitude. We hypothesise that restricted gene flow (larval transport), a consequence of present day coastal surface circulation patterns, influences the population genetic structuring of this species, an effect which is relatively recent in geological time (within the last 12 000 yr).

Gene order for a segment of the mitochondrial genome of the greenshell mussel, Perna canaliculus (Bivalvia: Mytilidae)

The gene order of mitochondrial genomes has been reported to differ among distantly related taxa, but to be more or less conserved among closer relatives. 1 The two assumptions made when using mitochondrial gene organization to reconstruct phylogenetic relationships among taxa are that mitochondrial gene rearrangements are rare and that a shared organization reflects a common ancestry. 2 Although mitochondrial gene order has been reported to have arisen independently in four bird lineages, 3 convergent rearrangements in independent lineages are assumed to be highly unlikely, and mitochondrial genome organization appears to be an informative character to determine relationships among phyla or classes. 4 Here, we compare the mitochondrial DNA (mtDNA) gene organization of the endemic New Zealand greenshell mussel, Perna canaliculus (Gmelin, 1791) to those of other invertebrate species because mitochondrial gene order may prove a useful tool to reconstruct the phylogeny among New Zealand mytilid bivalves, e.g. Aulacomya maoriana, Mytilus galloprovincialis, and

Naturally low seston concentration and the net energy balance of the greenshell mussel (Perna canaliculus) at Island Bay, Cook Strait, New Zealand

This paper describes an investigation of the physiological energetics of the New Zealand greenshell mussel, Perna canaliculus (Gmelin, 1791), which is aimed at determining if mussels are absent from many shores of Cook Strait as a consequence of a negative energy balance resulting from ambient low seston quantity and quality. Seston characteristics and mussel physiological functions were measured under ambient summer conditions at Island Bay, a site in Cook Strait. Estimates of total particulate matter (TPM in mg litre−1), particulate organic matter (POM in mg litre−1), and particulate organic carbon (POC in |ig litre−1) were low but of a similar magnitude to values reported for many comparable temperate regions. However, seston % organic matter (% OM) values were consistently low (<25%) and resulted in negative net absorption efficiency (AE) values and concomitant negative scope for growth (SFG = net energy balance) values. We suggest that the ongoing costs of energy loss associated with extra‐and intracellular digestion (termed metabolic faecal loss) are greater than the energy derived from seston of such low organic matter. Our data indicate that ambient levels of seston % OM of ≤25% are insufficient to promote a positive net energy balance in P. canaliculus, and as such probably play a major role in explaining the almost complete absence of mussels from many Cook Strait shores.

Absence of population genetic differentiation in the New Zealand greenshell mussel Perna canaliculus (Gmelin 1791) as assessed by allozyme variation

Genetic variation in the endemic New Zealand greenshell mussel, Perna canaliculus (Gmelin 1791), was examined using starch-gel electrophoresis at seven protein-coding loci (Idh; Acon-1; Acon-2; Gpd; Pgi; Pgm; Pgd) in 35 populations (N=1038 mussels). For all loci and all populations, Fisher's exact tests indicated highly significant departures from Hardy-Weinberg equilibrium (HWE), but this overall result was caused by significant heterozygote deficiencies at only two loci (Pgm and Pgd), and in only three northern populations (Kuaotunu, Te Haumi and Days Bay). Allelic and genotypic differentiation between population pairs at individual loci and across all loci were nonsignificant, and genotypic disequilibrium at each locus pair was also nonsignificant for all populations. Genetic variation in all populations was high (mean heterozygosity, 0.210+/-0.113), while Nei's D among populations was very low (0.002+/-0.002). Low population subdivision (&theta;=-0.001+/-0.002) and high levels of gene flow (Nm(p)=10.18; Nm(&theta;)=infinity) also indicated that the single panmictic unit model best explains population genetic homogeneity in P. canaliculus over a north-south distance >2000 km. Lack of genetic subdivision in this species is discussed in light of two previous allozyme studies, with differing results: one suggested that a north-south division exists between greenshell mussel stocks, and the other suggested that population structure in this species can be explained through isolation by distance model modified by local hydrology.

Biochemical Genetic Variation Among Populations of the Greenshell Mussel, Perna canaliculus, from New Zealand: Preliminary Findings

Seven polymorphic and four monomorphic allozyme loci were assayed from nine wild populations and one cultured population of the endemic New Zealand greenshell mussel, Perna canaliculus. Genetic variation was examined to determine the extent of intra-population subdivision and inter-population variability. Five of seven polymorphic loci exhibited significant heterozygote deficiencies compared to Hardy-Weinberg equilibrium. Population F-statistics indicated that significant genetic heterogeneity exists among populations, indicating that there is insufficient gene flow between geographically isolated populations to create panmixia. The observed genetic heterogeneity among populations is best explained by an isolation-by-distance model of gene flow, which is modified by localized hydrographic conditions. These preliminary findings are discussed in the context of the one previous survey of population genetic variation in P. canaliculus and how this information relates to the gene flow of the greenshell mussel in New Zealand, which is often mediated by human transport from the main collection site of Kaitaia to aquaculture sites throughout the country.

Biochemical genetic variation among populations of the greenshell mussel, Perna canaliculus, from New Zealand: preliminary findings

Seven polymorphic and four monomorphic allozyme loci were assayed from nine wild populations and one cultured population of the endemic New Zealand greenshell mussel, Perna canaliculus. Genetic variation was examined to determine the extent of intra-population subdivision and inter-population variability. Five of seven polymorphic loci exhibited significant heterozygote deficiencies compared to Hardy-Weinberg equilibrium. Population F-statistics indicated that significant genetic heterogeneity exists among populations, indicating that there is insufficient gene flow between geographically isolated populations to create panmixia. The observed genetic heterogeneity among populations is best explained by an isolation-by-distance model of gene flow, which is modified by localized hydrographic conditions. These preliminary findings are discussed in the context of the one previous survey of population genetic variation in P. canaliculus and how this information relates to the gene flow of the greenshell mussel in New Zealand, which is often mediated by human transport from the main collection site of Kaitaia to aquaculture sites throughout the country.