Mussel Stocks Research Articles

Longevity of subtidal mussel beds (Mytilus edulis) in eutrophic coastal areas

Mussel populations (Mytilus edulis) around the coasts of Europe and the North Atlantic are often ephemeral and have notably experienced a large decline in abundance. Since 1993, annual blue mussel stock surveys have been carried out in the Limfjorden, Denmark. We used the stock survey data combined with electronic monitoring fishing data and Mechanistic Models for the Limfjorden, providing environmental data to investigate the impact of various stressors. Multiple factors were found to affect the longevity of subtidal mussel beds in Limfjorden. Predation by starfish, fishing activities, shell length of the mussels, amplitude in summer temperature and consecutive days of oxygen depletion decreased the longevity of the beds. Conversely, increased biomass, multiple cohorts and increasing water depth demonstrate stabilising effects. Water column stratification had both a negative and positive impact on bed longevity depending on the duration. These analyses can help inform environmental, conservation, and fisheries managers on the long-term trends of population dynamics and gain a deeper understanding of what factors can affect mussel bed longevity in the context of declining stocks.

Selective pressure on ontogenic stages of blue mussels (Mytilus edulis, L.)

Our previous work confirmed that the higher survival, growth, and commercial performance of a mussel stock collected from a specific lagoon have been maintained over the last 25 years at a microgeographic scale despite intensive transfers of its spat to other local mussel sites. The objective of this study was to identify potential selection mechanisms supporting the quality of this stock. We used a mesocosm approach to examine the effect of maximum seawater temperature measured in the field on the different ontogenic stages of Mytilus edulis to simulate similar patterns in the laboratory. We demonstrated that thermal selection did not affect the development of peri-metamorphic stages (< 1 mm) since no effects were observed on growth, survival, or prodissoconch II size under natural thermal variations. However, our experimental results clearly indicated the existence of a thermal selective pressure (24 °C for 85 h) on 4.5–7 mm juvenile mussels, with growth performance enhanced in surviving individuals. Mortality was 37% higher compared to the control group, suggesting the elimination of more sensitive and less performant mussels. Interestingly, surviving individuals showed improved shell and tissue growth rates, by 22 and 51%, respectively. Our results support the hypothesis that the thermal selection of highly performant stock is size-dependent. The selective pressure demonstrated in this study along with our previous work highlighting the physiological and genetic differences between local stocks constitute the key mechanisms leading to the observed stable production performance over decades at a microgeographic scale.

Determining restoration potential by transplanting mussels of different size classes over a range of aerial exposures

Restoration of mussels typically focuses on either subtidal or intertidal habitats, although it is important to consider the full historical range of a species. However, it remains unclear how environmental changes can impact the ability of mussels to survive in tidal heights where they occurred historically. Additionally, there is limited research on the viability of reducing mussel stock size for restoration purposes. In this study, green-lipped mussels Perna canaliculus of 2 size classes (80 and 60 mm) were assessed when transplanted as a single size class or as mixed cohorts in 9 m2 plots at 3 shore heights (i.e. neap low tide, spring low tide, and subtidal). The mussels were sampled over a 1 yr period to understand the effect that shore height and size class had on mussel metrics, such as survival, growth, and condition. The results revealed that shore height had a greater effect than size class on mussel survival, with a total loss of mussels transplanted into areas that were exposed at neap tides in contrast to 39% mussel survival transplanted into areas that were only exposed on spring low tides. Further, mussels transplanted in the adjacent subtidal had higher overall survival (74%). This suggests that aerial exposure time determines the upper vertical limit for restoration by transplantation of mussels sourced from aquaculture, despite their historical distribution. The results of this study also support the use of smaller mussels (~60 mm) for transplantation for mussel reef restoration, as a 25% reduction in size resulted in 50% more mussels being deployed.

Large-scale changes in marine and terrestrial environments drive the population dynamics of long-tailed ducks breeding in Siberia

Migratory animals experience very different environmental conditions at different times of the year, i.e., at the breeding grounds, during migration, and in winter. The long-tailed duck Clangula hyemalis breeds in the Arctic regions of the northern hemisphere and migrates to temperate climate zones, where it winters in marine environments. The breeding success of the long-tailed duck is affected by the abundances of predators and their main prey species, lemmings Lemmus sibiricus and Dicrostonyx torquatus, whose population fluctuation is subject to climate change. In the winter quarters, long-tailed ducks mainly eat the blue mussel Mytilus edulis. We examined how North-west Siberian lemming dynamics, assumed as a proxy for predation pressure, affect long-tailed duck breeding success and how nutrient availability in the Baltic Sea influences long-tailed duck population size via mussel biomass and quality. Evidence suggests that the long-tailed duck population dynamics was predator-driven on the breeding grounds and resource-driven on the wintering grounds. Nutrients from fertilizer runoff from farmland stimulate mussel stocks and quality, supporting high long-tailed duck population sizes. The applied hierarchical analysis combining several trophic levels can be used for evaluating large-scale environmental factors that affect the population dynamics and abundance of migrants from one environment to another.

Mytella strigata and Mytella guyanensis as an object of study: scientific and popular nomenclature review, morphological aspects and occurrence in Babitonga Bay-SC/ Mytella strigata e Mytella guyanensis como objeto de estudo: revisão da nomenclatura científica e popular, aspectos morfológicos e ocorrência na Baia da Babitonga-SC

Bivalve molluscs are an object of great economic interest, in the genus Mytella, it is possible to highlight the species Mytella strigata and Mytella guyanensis. The aim of this study was to carry out a review about the popular and scientific nomenclature of these species, evaluate the main characteristics used to differentiate them, as well as to carry out a quali-quantitative analysis of the mussels from the bay of Babitonga-SC. During the popular nomenclature review it turned out that the mussels M. guyanensis and M. strigata have gone through numerous revisions and nomenclature changes, as well as have several synonymous species. According to the studies reviewed to the popular nomenclature subject, 75% of the publications related to M. guyanensis and M. strigata were made in the Northeast, regarding the popular names “bacucu” and “sururu”, the second term was the most widespread. The analysis of the mussel stocks of Babitonga Bay demonstrated the predominance of M. guyanensis (96%). No significant difference was observed for the sample survey and collection station factors. However, the variations in abundance and diversity were significant for the stratum factor, where the highest values were recorded in the lower mesolittoral, suggesting a tendency for these organisms to be distributed in environments with less air exposure at low tide.

Eiders, nutrients and eagles: Bottom-up and top-down population dynamics in a marine bird.

The main objective of this long-term study (1978-2016) was to find the underlying factors behind the declining trends of eider Somateria mollissima in the Baltic/Wadden Sea. Specifically, we aimed at quantifying the bottom-up effect of nutrients, through mussel stocks, on reproduction and abundance of eider, and the top-down effects caused by white-tailed eagle Haliaeetus albicilla predation. Bottom-up effects increase marine primary productivity with subsequent effects on food availability for a major mussel predator. Top-down effects may also regulate eider populations because during incubation female eiders are vulnerable to predation by eagles. Our structural equation modelling explained a large percentage of the variance in eider abundance. We conclude that the Baltic/Wadden Sea eider population was regulated directly by white-tailed sea eagle predation on incubating females and indirectly by the amount of nutrients in seawater affecting both mussel stocks and the breeding success of eiders, reflecting density dependence. These findings may explain the decreasing trend in the Baltic/Wadden Sea eider population during the last decades as an additive effect of top-down and bottom-up factors, and likely as an interaction between them.

-Blue mussel (Mytilus spp.) cultivation in mesohaline eutrophied inner coastal waters: mitigation potential, threats and cost effectiveness.

The EU-water framework directive (WFD) focuses on nutrient reductions to return coastal waters to the good ecological status. As of today, many coastal waters have reached a steady state of insufficient water quality due to continuous external nutrient inputs and internal loadings. This study focuses first on the current environmental status of mesohaline inner coastal waters to illustrate their needs of internal measures to reach demanded nutrient reductions and secondly, if mussel cultivation can be a suitable strategy to improve water quality. Therefore, nitrogen, phosphorus, chlorophyll a, and Secchi depth of nine mesohaline inner coastal waters in north east Germany were analyzed from 1990 to 2018. Two pilot mussel farms were used to evaluate their effectiveness as a mitigation measure and to estimate potential environmental risks, including the interactions with pathogenic vibrio bacteria. Further, estimated production and mitigation potential were used to assess economic profitability based on the sale of small sized mussels for animal feed and a compensation for nutrient mitigation. The compensation costs were derived from nutrient removal costs of a waste water treatment plant (WWTP). Results show that currently all nine water bodies do not reach the nutrient thresholds demanded by the WFD. However, coastal waters differ in nutrient pollution, indicating that some can reach the desired threshold values if internal measures are applied. The mitigation potential of mussel cultivation depends on the amount of biomass that is cultivated and harvested. However, since mussel growth is closely coupled to the salinity level, mussel cultivation in low saline environments leads to lower biomass production and inevitably to larger cultivation areas. If 50% of the case study area Greifswald Bay was covered with mussel farms the resulting nitrogen reduction would increase Secchi depth by 7.8 cm. However, high chlorophyll a values can hamper clearance rates (<20 mg m−3 = 0.43 l h−1 dry weight g−1) and therefore the mitigation potential. Also, the risk of mussel stock loss due to high summer water temperatures might affect the mitigation potential. The pilot farms had no significant effect on the total organic content of sediments beneath. However, increased values of Vibrio spp. in bio deposits within the pilot farm (1.43 106 ± 1.10 106CFU 100 ml−1 (reference site: 1.04 106 ± 1.45 106 CFU 100 ml−1) were measured with sediment traps. Hence, mussel farms might act as a sink for Vibrio spp. in systems with already high vibrio concentrations. However, more research is required to investigate the risks of Vibrio occurrence coupled to mussel farming. The economic model showed that mussel cultivation in environments below 12 PSU cannot be economic at current market prices for small size mussels and compensations based on nutrient removal cost of WWTPs.

Freshwater pearl culture in Mexico: historic context, present status and future perspectives

AbstractWe revise the historic context of freshwater pearl culture in Asia, updating the present situation and perspectives of this activity in Mexico, and, possibly, in some Latin American countries. The review is based on the results of ten years of research conducted in southeast Mexico (state of Tabasco) to firstly determine the demography of freshwater mussel stocks and, based on this information, identify a target species with a higher potential for pearl farming: the fatmucket mussel Psoronaias crocodilorum. The main advances relative to the seeding technique for keshi pearl production and composite technique for half‐pearl (mabe) production are detailed and placed under perspective with China, as today's greatest producer of freshwater pearls. After ten years, several cohorts of keshi and mabe pearls have been produced, representing the first of their kind in Latin America. Although the yield and quality of these pearls has gradually been improved, some aspects of the keshi technique (preparation and seeding of the donor's mantle into the host's mantle) still require further optimisation. To promote social development, one of the goals of the project included the involvement of local communities in the manufacture and selling of handcrafts made from the shell. The other goal was to share the main outcomes derived from the keshi and mabe techniques with academics, producers, and government authorities through a series of training workshops aimed to create awareness in the local communities for the potential of freshwater pearl culture in Tabasco as an aquaculture‐based, environmentally friendly and viable model for socioeconomic development.

The impact of mussel seed fishery on the dynamics of wild subtidal mussel beds in the western Wadden Sea, The Netherlands

For the cultivation of mussels, wild stocks of juveniles are harvested to collect mussel seed as starting material for the culture. These wild stocks are found in the sublittoral western Wadden Sea (NL). After summer spat fall, fisheries in Autumn on newly formed beds is carried out in areas that have the risk of washing away due to storms, or are vulnerable for starfish predation. These wild beds are considered as relatively unstable. On remaining more stable wild beds, seed fishery is carried out in next Spring. As the Wadden Sea is a nature conservation area, mussel seed fisheries is only allowed if no negative impacts on the nature management objectives can be expected. Seed fishery impacts were addressed in an extensive study including effects on sediment composition, macrobenthos and epifauna. In this paper we describe the effects of mussel seed fisheries on the development of the mussel stocks with and without fisheries in 39 pairwise studied impact and control plots.Stocks on seed beds in areas of the sublittoral Western Wadden Sea that are known as unstable, show a large decline within one year after settlement, also when there is no seed fishery. Harvesting seed on more stable beds in Spring results in a statistical significant reduction in stock size, which lasts for a period of two years after the first fishery. For the longer term, there is a gradual decline of the mussel stocks on all studied plots. On three out of the 39 plots, mussel biomass showed a large increase, both on control and impact parts. Also these mussel beds declined and eventually disappeared. A difference in life expectancy of fished and unfished beds was not demonstrated.It is concluded that sublittoral beds gradually disappear, also without fisheries. As a consequence, new recruitment is of critical importance for the long-term survival of sublittoral mussel beds. As we found no significant difference between recruitment on fished and control parts, there are no indications for negative impacts of seed fishery on new recruitment.

Commercial Performance of Blue Mussel (Mytilus edulis, L.) Stocks at a Microgeographic Scale

Bivalve aquaculture is an important component of the economy in eastern Canada. Because of current social, environmental, economic, and resource constraints, offshore mussel cultivation seems to be a promising strategy. With the objective of optimizing farming strategies that support the sustainability and development of the mussel industry at a microgeographic scale, we evaluated, after a traditional two year production cycle, the commercial performance of spat from several mussel (Mytilus edulis) stocks originating from sites separated by less than 65 km and cultivated at two different grow-out sites (shallow lagoon and offshore waters). The spatiotemporal variation in spat performance was studied through a multiyear in situ “stock-site” spat transfer design. The spat supply originating from the Bassin du Havre-Aubert lagoon systematically exhibited a larger size at sleeving time when compared to other stocks, and a better productivity level when harvested. Nevertheless, an alternative strategy would be to collect spat from the Havre-aux-Maisons lagoon, mostly because of the important commercial volumes of spat that can be collected there. Commercial performance (net income) was three times higher in the deep offshore grow-out site than in the shallow lagoon site. This better productivity in the open sea confirms the highly valuable strategy of offshore mussel farming in this area, where it was hypothesized that the less stressful environmental conditions positively influence reproduction, survival, and growth trends.

Implementation of various approaches to study the prevalence, incidence and progression of disseminated neoplasia in mussel stocks

Marine mussel production is of substantial economic interest in numerous coastal areas worldwide, making crucial the study of pathologies that affect them. Disseminated neoplasia (DN) has recently been suggested to be linked to blue mussel, Mytilus edulis, mortality outbreaks observed in France since 2014, although the evidence remains indirect. In order to improve DN detection and monitoring, we compared the sensitivity of four diagnostic tools, namely haemocytology, histology, flow cytometry, and genetics. Haemocytological examination gave the best results in sensitivity and had the advantage of being non-invasive, allowing disease progression to be followed in affected mussels. Using this approach, we showed that DN progression is usually slow, and we provide evidence of remission events. We observed a high diversity of forms and mitotic features of neoplastic cells located in the vesicular connective tissue but rarely in the haemolymph. Circulating cells occur as four main types but are homogenous in morphology and DNA content within a single individual. Polyploidy proved very high, from 8 N to 18 N. Genetic analysis of haemolymph DNA showed that a Mytilus trossulus genetic signal was associated with almost all the DN cases here diagnosed by haemocytological examination, regardless of the DN type. This result corroborates DN is a transmissible cancer that first originated in a M. trossulus host and subsequently crossed into M. edulis. No pre-neoplastic conditions were detectable. The prevalence of the disease was quite low, which, together with the low morbidity observed in the lab, suggest DN is unlikely to be the direct cause of mortality outbreaks in France.

Response to selection for increasing resistance to the spring mortality outbreaks in Mytilus edulis occurring in France since 2014

Massive spring mortality outbreaks have been reported in Mytilus spp. in France since 2014. The main areas affected are the Pertuis Charentais Sounds and the coast of the Pays de la Loire, which cultivate mainly M. edulis, and the putative causal agents remain unknown. We report the results of the first generation of mass selection focused on survival and resistance to the spring mortality in M. edulis. Two stocks of mussels were sampled in the Pertuis Charentais Sounds in 2014; one of these went through a spring mortality outbreak and the survivors were used to produce the selected stock, while the second stock was M. edulis considered to be naïve against the putative causal agents of the mortality outbreak and was used to produce the control stock. A first cohort was produced in 2015 and tested at one site in the Pertuis Charentais Sounds. In April and May 2016, a spring mortality outbreak was observed when seawater temperature ranged from 10 to 15 °C. In October 2016, the selected stock had a lower mortality (44%) than the control stock (78%). To confirm this result and investigate genotype by environment interaction, a second cohort was produced in 2016 and tested at six sites. Although no significant mortality was reported at the four sites in the Pertuis Charentais Sounds in 2017, the selected stock had a lower mortality (17–27%) than the control stock (61–74%) at the two sites along the coast of the Pays de la Loire. The survival had increased of 34–48% after one generation of mass selection and the realized heritability was high, ranging from 0.55 to 1.15, but further generations of selection are required to obtain a better estimation of the heritability. Our study showed a positive response to selection in three environments that were different to the site from which mussels were selected, suggesting the absence of strong genotype by environment interaction in sites where spring mortality outbreaks occurred. Selection to enhance M. edulis survival of the spring mortality should be efficient and should be capable of easy implementation through mass selection. Apparently, selection to enhance the survival of M. edulis did not affect the mussel growth in comparison with the controls, but automatically improved the yield of M. edulis in sites affected by the spring mortality outbreaks.

Effects of stock origin and environment on growth and reproduction of the green-lipped mussel Perna canaliculus

The effect of stock origin and growing environment on growth and reproduction of the green-lipped mussel Perna canaliculus was investigated on the marine farms in the Marlborough Sounds, New Zealand. Following the normal commercial practice, mussel stocks from three widely separated origins in New Zealand were transplanted to six sites in Marlborough Sounds and grown on ropes hung from commercial longlines for eleven months. Stock origin had significant effects on growth rates as measured by shell length and flesh weight. Growing sites also showed a significant effect on flesh growth rate but only a small effect on shell length growth, with considerable variation among sites. Two sites (Beatrix Bay and Hallam Cove) had the fastest growth in flesh weight. One stock (Golden Bay) showed the fastest growth and lowest mid-winter reproductive rates, while the Kaitaia stock (the most commonly used one in industry) showed highest winter reproductive rate. Spawning was responsible for mid-winter declines in flesh weight among all stocks, but the Golden Bay stock recovered flesh weight more rapidly than other stocks after spawning. The stock differences in growth suggest that genetic traits of stock origin remained after mussels were grown in different environments (sites). In addition, we speculate that there would be a large variation of physiological rates between stocks including filtration, ingestion and respiration rates. The variation in growth and reproduction suggests that there would be a significant difference in energy allocation for reproduction, flesh and shell growth among stocks. The study has obvious application to the mussel industry for planning and selective seeding of stocks to maximise economic benefits. The use of fast-growing stocks and timing of harvesting in mid-winter can dramatically improve quality and quantity of production.

Allocation of body reserves during winter in eider Somateria mollissima as preparation for spring migration and reproduction

Capital breeders, such as the eider duck Somateria mollissima, accumulate resources before the start of breeding. Eiders preferentially feed on blue mussels Mytilus edulis to build up body condition during winter. We explored how body condition and gizzard mass of wintering eiders relate to mussel quality and quantity, winter climate and body condition of females at the breeding grounds. Body condition during winter (defined as scaled body mass index) of eiders increased during winter and the magnitude of the effect depended on age and mussel quality. Gizzard mass of eiders increased during winter with effects of mussel quality, mussel stocks and sex. Body condition in winter of adult females increased from the first half of January to the second half of February on average by 1.5%, equal to c. 96 g. During the same period gizzard mass of adult females increased by 12.2%, i.e., a nearly ten-fold increase compared to that observed in body condition in winter. Body condition of females at the breeding grounds in Finland (defined as body condition at hatching) was significantly positively correlated with gizzard mass in winter, but not significantly correlated with body condition in winter. Thus, eiders allocate body reserves to increase gizzard mass but less so to increase body condition in winter. This can be considered an adaptive migratory strategy of these eiders, whereby large winter (pre-migratory) gizzards increase food processing capacity, making it possible for eiders to arrive at the breeding grounds with superior body condition and a high reproductive potential.

New diagnostic SNP molecular markers for the Mytilus species complex

The development of diagnostic markers has been a long-standing interest of population geneticists as it allows clarification of taxonomic uncertainties. Historically, there has been much debate on the taxonomic status of species belonging to the Mytilus species complex (M. edulis, M. galloprovincialis and M. trossulus), and whether they are discrete species. We analysed reference pure specimens of M. edulis, M. galloprovincialis and M. trossulus, using Restriction site associated DNA (RAD) sequencing and identified over 6,000 SNP markers separating the three species unambiguously. We developed a panel of diagnostic SNP markers for the genotyping of Mytilus species complex as well as the identification of hybrids and interspecies introgression events in Mytilus species. We validated a panel of twelve diagnostic SNP markers which can be used for species genotyping. Being able to accurately identify species and hybrids within the Mytilus species complex is important for the selective mussel stock management, the exclusion of invasive species, basic physiology and bio-diversity studies.

Adaptation of cultured mussel Mytilus galloprovincialis Lamarck, 1819 from the northern Adriatic Sea to nearby aquaculture sites and translocation

The ability of mussels to cope with environmental conditions depends on the species’ capacity to acclimate or adapt within its morphometric and physiological parameters. In the present study,we investigated the effect of aquaculture site and translocation on different stocks of Mediterranean mussel, Mytilus galloprovincialis Lamarck, 1819. We used shell morphological ratios (width/length, height/length and height/width) and allometric relationships (volume-length and shell weight-length) in addition to condition index (wet meat weight/total weight) and mortality to compare cultivated and translocated mussels from the northern Adriatic Sea, Croatia. Mussels were collected from five cultivation areas (Lim, Pomer, Raša, Vabriga and Budava), and then moved for three months to experimental station at marine protected area in Lim Bay. Differences between cultivated mussels suggested morphological plasticity, although translocation weakly affected allometric relationships. Decrease in condition index was pronounced in translocated mussels, indicating adaptation to different local environmental conditions. High post translocation mortality was observed in mussels transferred to the experimental area. Our study shows plastic response of M. galloprovincialis, which can provide a useful information of mussel stocks selection in aquaculture.

Ecological restoration of mussel beds onto soft‐sediment using transplanted adults

The success of restoration initiatives to restore bivalve beds relies on sufficient recruitment of larvae to offset mortality of re‐established populations. Individuals of the nearly extirpated green‐lipped mussel are capable of surviving within the current environment of the Hauraki Gulf, New Zealand; however, it is uncertain what potential factors might inhibit the establishment and persistence of restored mussel beds. Four experimental mussel beds were established within a shallow soft‐sediment embayment and assessments of population dynamics were conducted approximately every 6 months over a 2‐year period. Deployed mussels quickly congregated into contiguous mussel beds that persisted throughout the study; however, only 26.2% of mussels that were initially established survived until the end of the study. The cause of this overall loss of mussels can be attributed to a near lack of observed recruitment, with only three individual recruiting mussels observed throughout the entire study. Despite similar mortality rates within the restored mussel beds to that of natural populations, these populations will be unsustainable long term given the lack of recruitment. Potential causes of the observed mortality and lack of recruitment are discussed, including environmental factors affecting non‐natal mussel stock and sea star predation. This research provides a foundation for the development of best‐practice methods in the restoration of green‐lipped mussels. However, further investigation into recruitment pathways and sources of mortality for adult mussels will be necessary to overcome the observed limitations if future restoration is to be successful.

Population dynamics of subtidal blue mussels Mytilus edulis and the impact of cultivation

Fishery on subtidal mussel beds and subsequent relying on culture plots in the same system is a common practice in bottom mussel culture. We address factors that determine the population dynamics of subtidal blue mussels Mytilus edulis L. and to what extent total (natural plus cultured) subtidal mussel biomass in the system is affected by fishery practices. Mussel size and density of spatially segregated natural and cultured subtidal mussel populations in the western Wadden Sea were measured over time in 2 field studies. Spatial patterns in survival rates showed better spat survival in areas with lower salinity and lower density of sea stars Asterias rubens. This suggests that mussel survival is negatively related to sea star distribution which is to a large extent controlled by salinity. The Asterias−Mytilus relation in the Wadden Sea is an example of the concept that environmental stress determines the successes of the prey by affecting the prey− predator relationship. Natural beds that escape predation are found at lower salinities, and mussels on these beds showed low growth rates, also because of lower food quality in these areas. Mussel culture is strongly affecting the population dynamics of the subtidal mussel population, through relay of mussels from natural mussel beds to culture plots. This activity increases mussel growth and survival, because food quality on culture plots is high and predation is controlled. Despite harvesting, mussel biomass production on culture plots was higher than on natural mussel beds, enhancing total subtidal mussel stock.

Rehabilitating mussel beds in Coffee Bay, South Africa: Towards fostering cooperative small-scale fisheries governance and enabling community upliftment.

Along the coast of South Africa, marine resources play a significant role in supporting livelihoods and contributing to food security in impoverished rural communities. Post-apartheid fisheries laws and policies have begun to address traditional fishing rights and development needs, and new management arrangements are being implemented. One such initiative has been the Mussel Rehabilitation Project in Coffee Bay, which piloted a resource rehabilitation technique at several over-exploited fishing sites. Mussel stocks in these exploited areas had dropped to under 1% mussel cover, and during the project period, stocks increased to>80% cover, supporting a sustainable harvest well above national daily bag limits. This stock enhancement was achieved only after the project had started to address social challenges such as the lack of local management institutions and the need to enhance food security. The project embarked on training and institution-building; it formed a robust community mussel management committee; and developed a local resource management plan, facilitating increased community participation in the day-to-day management of the resource. The project also saw the initiation of various ancillary projects aimed at improving food security and stimulating the local economy and hence alleviating pressure on the marine resources. Here we review this 10-year project's outcomes, and present lessons for small-scale fisheries governance in South Africa and internationally. We show, through empirical experience, that balancing stock rebuilding needs in a context of widespread poverty and dependency on natural resources by a local fisher community can only be addressed through an integrated approach to development. Participation of resource users and a thorough understanding of the local context are imperative to negotiating appropriate small-scale fisheries governance approaches. We recommend that the implementation of South Africa's newly minted Small-Scale Fisheries Policy should begin with bottom-up, demonstrative resource management measures such as mussel rehabilitation. This type of initiative can deliver short-term food security benefits and foster social learning towards sustainable and cooperative fisheries governance.

Salinity effects on growth and toxin production in anAlexandrium ostenfeldii(Dinophyceae) isolate from The Netherlands

Alexandrium ostenfeldii is among the most intensely studied marine planktonic dinophytes and in the last few years blooms have become a recurrent phenomenon mainly in brackish coastal waters. Since 2012, A. ostenfeldii recurs annually in the Ouwerkerkse Kreek, a Dutch brackish water creek discharging into an estuary with large stocks of mussels, oysters and cockles. The creek is characterized by highly dynamic abiotic conditions, notably salinity. Here, we investigated the impacts of salinities ranging from 3 to 34 on growth and toxin content of an A. ostenfeldii isolate from the creek. Our results demonstrate a broad salinity tolerance of the Dutch A. ostenfeldii population, with growth rates from 0.13 to 0.2 d−1 over a salinity range from 6 to 34. Highest paralytic shellfish toxin and cyclic imine toxin cell quotas were observed for the lowest and highest salinities, and were associated with increases in cell size. Lytic activity was highest at the lowest salinity, and was 5-fold higher in the cell-free supernatants compared to cell extracts. Together our results demonstrate a tight coupling between salinity and A. ostenfeldii growth rate, cell size and toxin synthesis, which may have consequences for the seasonal dynamics of bloom toxicity.