Clam Production Research Articles

Prefacing the challenge – Assessment of the environmental efficiency of Manila clam (Ruditapes philippinarum) production based on hatchery-produced and wild seed

In 2021, Italy produced 23 thousand tons of Manila clam (Ruditapes philippinarum, Adam & Reeve 1850) from aquaculture, worth € 212 million, ranking as the world's second-largest producer. Production volumes of Manila clam have started to decline over the past 10 years due to, among other reasons, a decrease in the availability of wild seed on which clam farmers rely. This has led Italian clam farmers to buy seed from both national and foreign hatcheries. The Manila clam supply chain based on hatchery seed brings benefits to farmers, ensuring the continuity of production, but, on the other hand, production and environmental costs increase. As wild seed supply is expected to further decline due to climate change effects and habitat degradation, it is important to assess the environmental impacts of the actual production chains (conventional-wild seed and hatchery-based) to identify the hotspots and possible mitigation strategies. To this aim, this work applies the Life Cycle Assessment methodology to two case studies: a production chain based on wild seed, and, for the first time, a production chain based exclusively on seed produced in hatcheries. The results confirmed the general good environmental performance of mollusk aquaculture. For example, the Global Warming potential ranged from 0.85 to 1.05 kg CO2 eq kg−1 of clams, where the worst results refer to the production chain based on seed from the hatchery, as expected. Some production chain hotspots were highlighted: especially regarding the Global Warming potential, electricity consumption for the hatchery and depuration phases, and the use of fuels during the growth-out phase. Finally, scenario analysis has been applied to the worst-performing case study to understand the magnitude of the environmental benefits deriving from the adoption of some improvement strategies.

Low Carbon Development Strategy in the Rambat Menduyung Mangrove Forest Area of West Bangka

Indonesia is committed to reducing carbon emissions through low-carbon development. Mangrove ecosystems have a high carbon storage value that can support this development. There is a problem of high mangrove degradation caused by economic activities. One of the sectors causing mangrove degradation is the mining sector in the province of Kepulauan Bangka Belitung. Low-carbon development strategies in mangrove areas are needed to support the increase of sustainable economic activities such as capture fisheries, aquaculture, and mangrove conservation. The objective of this research is to calculate the potential value of sustainable economic activities and develop a low-carbon development strategy in the Rambat Menduyung Mangrove Area. The methods used in this research are economic benefit analysis, benefit transfer analysis of carbon emission factors, and strategy analysis using interpretative structural modeling with Exsimpro software. The results of research suggest that potential economic activities that support low carbon development in mangrove areas, namely mangrove conservation, capture of marine biota, and blood clam production, produce economic benefits of IDR105,723,552,069/year. Prioritizing low-carbon development strategies by improving protection and law enforcement policies and increasing institutional capacity and community participation supported by adequate infrastructure from stakeholders, namely DKP West Bangka, KPHP Rambat Menduyung, and Belo Laut Village Government.

Low Carbon Development Strategy in the Rambat Menduyung Mangrove Forest Area of West Bangka

Indonesia is committed to reducing carbon emissions through low-carbon development. Mangrove ecosystems have a high carbon storage value that can support this development. There is a problem of high mangrove degradation caused by economic activities. One of the sectors causing mangrove degradation is the mining sector in the province of Kepulauan Bangka Belitung. Low-carbon development strategies in mangrove areas are needed to support the increase of sustainable economic activities such as capture fisheries, aquaculture, and mangrove conservation. The objective of this research is to calculate the potential value of sustainable economic activities and develop a low-carbon development strategy in the Rambat Menduyung Mangrove Area. The methods used in this research are economic benefit analysis, benefit transfer analysis of carbon emission factors, and strategy analysis using interpretative structural modeling with Exsimpro software. The results of research suggest that potential economic activities that support low carbon development in mangrove areas, namely mangrove conservation, capture of marine biota, and blood clam production, produce economic benefits of IDR105,723,552,069/year. Prioritizing low-carbon development strategies by improving protection and law enforcement policies and increasing institutional capacity and community participation supported by adequate infrastructure from stakeholders, namely DKP West Bangka, KPHP Rambat Menduyung, and Belo Laut Village Government.

Spatio-temporal differences and simulation studies of the carbon budget from fisheries in the northern marine economic circle of China

With the proposal of dual carbon goals, enhancing carbon sinks and reducing carbon emissions has become a critical issue. Fisheries, as a component of agriculture, possess the dual attributes of being a “carbon sink” (biological carbon fixation) and a “carbon source” (the carbon emissions from fishing vessels). Therefore, it is necessary to assess the carbon sink and carbon emission levels of fisheries. The northern marine economic circle, which includes Liaoning, Hebei, Tianjin, and Shandong, is an important site for fisheries in China, characterized by abundant aquatic resources. However, a comprehensive assessment of the carbon budget for fisheries in this region is still unclear. This study calculated the carbon sinks, carbon emissions, and net carbon emissions associated with fisheries in the region from 2013 to 2020. Additionally, we used sensitivity analysis and scenario simulation to explore the factors influencing the net carbon emissions. The results revealed that the carbon budget of the northern marine economic circle was in a carbon deficit (the amount of carbon emissions was higher than that of carbon sinks) from 2013 to 2020. However, a downward trend in the net carbon emissions was observed, indicating the potential of achieving carbon neutrality. From the perspective of provinces, significant differences among provinces (cities) were found in terms of carbon sinks, carbon emissions, and net carbon emissions, with Shandong having the largest net carbon emissions. Furthermore, the production of clams and the use of seawater trawl net have a significant impact on the net carbon emissions. Increasing the production of clams while reducing the power of trawling operations can significantly decrease net carbon emissions. Based on these results, this study provides relevant suggestions to enhance the carbon sink capacity and decrease the carbon emissions of fisheries in the northern marine economic circle.

A demographic model to forecast Dinophysis acuminata harmful algal blooms

Harmful algal blooms (HABs) in marine environments have significant adverse effects on public health, aquaculture and recreational activities. Surges of certain phytoplanktonic toxin-producing microalgae (mostly dinoflagellates or diatoms species) can induce Amnesic, Diarrhetic or Paralytic Shellfish Poisoning (ASP, DSP and PSP). Among HAB species, the genus Dinophysis leads to DSP in human consumers; this being the most recurrent problem in the Iberian Peninsula with the biggest economic impact on clam production and harvesting. While complete elimination of HABs is not feasible, timely implementation of appropriate measures can prevent their negative consequences. This is critical for aquaculture. Research on D. acuminata (dominant Dinophysis species in the North Atlantic) has been focused on ecophysiology and population dynamics, although with few modelling attempts. Weekly monitoring along the Portuguese coast since 2006 has revealed that D. acuminata thrives under spring/summer photosynthetically active radiation (PAR) coupled with water temperatures below 20°C, which typically coincide with the local upwelling regime. In order to advance this knowledge numerically, we developed a demographic model linking D. acuminata growth rate to PAR and sea surface temperature (SST). The 13-year (1-Jan-2006 to 31-Dec-2018) time-series of observations was closely fit by model forecasts. However, the model demonstrated limitations in issuing timely warnings of harmful proliferation of D. acuminata, failing to do so in 50% of cases, and issuing incorrect warnings in 5% of the cases. Furthermore, improving the odds of emitting timely warnings always worsened the odds of emitting false warnings, and vice-versa. To simultaneously improve both aspects, the modelling results clearly indicated the need of implementing both census/projection intervals smaller than 7 days and a laboratory detection limit below 20 cell/L. The time resolution of the census and of the model proved to be the most limiting factor that must be addressed in order to improve numerical forecasting of HABs.

Spatiotemporal variation in clam recruitment among beaches in Washington State (USA)

AbstractAbundant clam populations provide ecosystem services and commercial and recreational shellfish harvests worldwide. Two non‐native clams (Manila clams, Ruditapes philippinarum; eastern soft‐shell clams, Mya arenaria) commonly populate mid‐intertidal zones of coarse‐sediment beaches in Washington State, USA. To better understand factors influencing their abundance, we used passive mid‐intertidal spat collectors to determine the density and distribution of clam recruits (150–500 μm shell length) at eight beaches spanning over 500 km and over two reproductive seasons (2016 and 2017). Cumulative seasonal recruitment (clams <500 μm) in 2016 and 2017 at +1.0 m MLLW ranged from 800 to 125,000 m−2 for Ruditapes philippinarum and 50–85,000 m−2 for M. arenaria, and did not differ by substrate type at small scales (gravel vs. crushed shell). At larger scales, different interannual recruitment patterns across sites did not dramatically shift the ranked order of highest and lowest recruitment sites. Cumulative recruitment tended to be lower at warmer sites, while timing of peak recruitment was not consistently related to temperature. Sites also differed in the relative recruitment of the two clam species, but most beaches had greater densities of R. philippinarum than M. arenaria at both recruitment and juvenile stages. Although recruitment densities differed by two orders of magnitude across sites, post‐settlement factors eliminated initial spatial variation within a year, dampening recruitment variability among these beaches that all contribute to commercial and recreational clam production.

Spatiotemporal variations in migratory bird diversity and abundance along the coast of Gochang getbol.

Tidal flats provide critical habitat for migratory waterbird species; however, populations of migratory waterbirds have significantly declined due to tidal flat loss and degradation caused by human activities, particularly in Asia. Gochang getbol is one of tidal flats located on the southwest coast of South Korea and a center of clam production. Using bird monitoring data collected at five zones (zone1 to zone5) established across Gochang getbol and near coastal area, we examined distribution patterns of migratory bird diversity and conservation-related species along the coast of Gochang getbol. The intensity of human activity ‒ mudflat culture (mostly bivalve) and aquaculture was relatively high at zone2 and zone3, occupying > 30% of 2km circular area surrounding most sample points of these zones. Zone1 and particularly zone4 contained more natural/semi-natural habitats (less disturbed mudflats and wetlands) and zone5 had smallest mudflat than others. Shannon diversity, species richness, and abundance of migratory birds differed between zones (Anova test, P ≤ 0.02) except Shannon diversity in winter. In fall, all values were higher at zone4 than zone3 and zone5. In winter, zone1 showed greatest species richness and higher abundance than zone2, zone3, and zone5. In spring, while most differences were found between zone4 and zone5, abundance at zone4 was somewhat higher than zone2. The results from the fourth corner analysis indicated that abundance of species foraging at mudflat level was positively associated with zone1 (winter) but negatively with zone3 (fall). Sandpipers were positively associated with zone4. Abundance distribution maps of conservation-related species, created by inverse distance-weighted interpolation modeling, also showed high abundance of most conservation-related species at zone4 and 1. The findings of our study suggest the importance of natural/semi-natural habitat, and the possible link between human activity and distribution patterns of migratory birds in Gochang getbol. While we need further investigation on direct response of migratory birds to human activity, areas with low human activity with more natural/semi-natural habitat, e.g., zone4 and zone1 may be crucial for the conservation of migratory birds.

Consumer Preferences and Willingness to Pay for Clams with Sustainability Certification in Mediterranean Countries

For some types of seafood, such as clams, there are now sustainability certificates that guarantee their sustainable production. However, their consumption may be associated with some ethical and sustainability concerns, as clams are harvested in ways that may be harmful to the environment. The aim of this study is therefore to investigate consumers’ sustainability concerns based on their purchasing preferences and WTP for clams with sustainability certification in three Mediterranean countries—Italy, Spain and Croatia. Data were collected online and consumer preferences were elicited using a labelled discrete choice experiment. The results show that in general all consumers prefer clams from their country of origin, while there are differences in their appreciation for the sustainability certification. While Croatian consumers are not very interested in the current Marine Stewardship Council (MSC) sustainability certification, consumers in Spain are willing to pay a higher price for it. At the same time, consumers in Italy are more interested in new certifications such as Responsible Fisheries Management (RFM). These results could be of interest to clam production and distribution companies trying to advance their corporate social responsibility activities and positioning.

Comparison of high-hydrostatic pressure and frozen treatments on raw freshwater clam marinated in soy sauce: Impact on microbiological and organoleptic qualities

The purpose of this study was to compare how the two different methods of food processing, high pressure processing (HPP) under 300–500 MPa for 3 min and freezing, affect the microbiological, chemical, and organoleptic qualities of soy sauce-marinated freshwater clams (Corbicula fluminea) during refrigeration. The aerobic plate count (APC), psychotropic bacteria count (PBC), Salmonella spp., and coliform of high pressure processed soy sauce-marinated clams (HPP marinated-clams) were obviously lower than conventionally frozen soy sauce-marinated clams (frozen marinated-clams), or were not detected. In addition, after all samples’ 15-day refrigeration period, HPP was found to significantly inhibit the growth of APC, PBC, Salmonella spp., and coliform, while the microbial counts of frozen marinated-clams increased gradually with time. However, the surface areas, moisture contents, and salt contents of all samples of both HPP marinated-clams and frozen marinated-clams slightly increased during refrigeration. Furthermore, the results of organoleptic analyses exhibited that the storage life of marinated clams can be increased from 9 days under freezing treatment to 15 days under HPP (300 MPa and 500 MPa). Using high-throughput sequencing, HPP treatment significantly changed the microbiota of marinated clam and delayed the spoilage process. Therefore, the study suggests using HPP at least 300 MPa for 3 min to effectively inhibit the microbial growth and significantly extend the storage life of the samples during the refrigeration period. This is a first study to use HPP technology to replace the traditional freezing technology in the application of raw soy sauce-marinated freshwater clam products, and at the same time, HTS was used to evaluate the changes of microbiota during refrigeration.

Effects of ultrasound-assisted high temperature-pressure treatment on the structure and allergenicity of tropomyosin from clam (Mactra veneriformis).

Tropomyosin (TM) is the major allergen in clams. This study aimed to evaluate the effects of ultrasound-assisted high temperature-pressure treatment on the structure and allergenicity of TM from clams. The results showed that the combined treatment significantly affected the structure of TM-converting the α-helix to β-sheet and random coil, and decreasing the sulfhydryl group content, surface hydrophobicity, and particle size. These structural changes caused the unfolding of the protein, disrupting and modifying the allergenic epitopes. The significant reduction in the allergenicity of TM was approximately 68.1% when treated with combined processing (P<0.05). Notably, an increase in the content of the relevant amino acids and a smaller particle size accelerated the penetration of the enzyme into the protein matrix, resulting in strengthening the gastrointestinal digestibility of TM. These results prove that ultrasound-assisted high temperature-pressure treatment has great potential in reducing allergenicity, benefiting the development of hypoallergenic clam products.

Innovative Approaches towards Utilisation of Clams

Clams are recognized as a valuable food source, and their consumption has grown worldwide. However, this increased consumption has also been associated with various cases of foodborne illnesses. This is primarily linked to the feeding behaviour of clams, as they are filter feeders and tend to accumulate harmful substances. This review paper examines different traditional and advanced methods for processing clams, encompassing thermal and non-thermal techniques. These methods are designed to effectively control harmful microorganisms and extend the shelf life of clam products, ensuring the safety and quality of clam meat for human consumption. The review covers traditional methods such as chilling, marination, fermentation, chelation, boiling, roasting, and more, as well as advanced technologies like Microwave-Assisted Induction Heating (MAIH), High Hydrostatic Pressure (HHP), and Retort Pouch Processing (RPP). Additionally, it explores the creation of value-added clam products. The comprehensive information presented in this article aims to raise awareness among consumers and processors about properly handling and processing this nutritious seafood resource, promoting safer and higher-quality clam products.

Isotope Geochemistry for Seafood Traceability and Authentication: The Northern Adriatic Manila Clams Case Study.

In Italy, the production of manila clams (Ruditapes philippinarum, Adams and Reeve, 1850) is mainly localized in northern Adriatic lagoons in the Po River delta, where shellfish farming provides important socio-economic revenue. However, in our globalized world, the seafood market is threated by fraudulent activities, in which agri-food products whose provenance is not certified are sold, posing a risk to consumer health. Multi-isotope ratio analysis is commonly used to trace the provenance of goods produced in different countries with different climatic and environmental conditions. Here, we investigated the reliability of this approach in terms of tracing the exact provenance of manila clams harvested in three Adriatic northern lagoons that are close to each other. We also verified the origin of samples bought at a local supermarket with a certificate of provenance. We carried out elemental analyses of carbon (C), nitrogen (N), and sulfur (S) and the respective isotopic ratios (13C/12C; 15N/14N; 34S/32S) on manila clam tissues, plus isotopic analyses of carbon (13C/12C), oxygen (18O/16O), and strontium (87Sr/86Sr) on manila clam shells. Each isotopic parameter can be used to identify the marine and continental contributions of water and/or nutrient supplies occurring in the lagoons. Therefore, the combination of isotopic parameters in a linear discriminant analysis (LDA) allowed for the identification of the lagoons in which the manila clams were produced.

Optimizing Hard Clam Production in Taiwan by Accounting for Nonlinear Effects of Stocking Density and Feed Costs on Farm Output of Clams

Despite mass mortality, hard clams remain among the main cultured shellfish in Taiwan. Using cross-sectional data, this study applies threshold regression modeling with stocking density and feed costs as the threshold variables to explore the nonlinear relationship between input and output factors. The findings show that the production output levels may be increased by different combinations of factor inputs and variations in input factors. More specifically, the higher output levels may be achieved by increasing labor input while reducing capital input factors in farming households with a higher stocking density (HSD &gt; 1,087,870 inds/ha) or higher feed cost (HFC &gt; 13,889 NTD/ha). Farming households with a lower stocking density (LSD ≤ 1,087,870 inds/ha) may enhance production output levels by increasing feed input while reducing capital inputs. Moreover, the maximum output level of HSD and HFC farming households was estimated to reach 9255 kg/ha and 9807 kg/ha, respectively. Results of the production output simulation suggest that the feeding cost per hectare in LSD households should not exceed 25,119 NTD to avoid overfeeding, which may cause culture deterioration and lower survival rates. As such, farmers are advised to adjust their feed costs according to the stocking density to maximize production output.

Characterization of a novel activating protein-1 (AP-1) gene and the association of its single nucleotide polymorphisms with vibrio resistance in Tegillarca granosa

The blood clam Tegillarca granosa is a commercial marine bivalve of economic value, accounting for approximately 50% of clam production in China. In recent years, the yield of blood clams has been threatened by bacterial infections caused by marine Vibrio species that thrive under a rising sea temperature. The transcription factor activating protein-1 (AP-1) is emerging as an important player in the innate immunity of marine bivalves against viral or bacterial infections. In this study, the full-length cDNA of a novel T. granosa AP-1 (TgAP-1) was cloned for the first time. The 1591-bp cDNA encoded a protein of 292 amino acid residues with a calculated molecular weight of 32.8 kDa. The TgAP-1 protein contained an N-terminal Jun domain and a C-terminal basic region leucine zipper domain typically found in Jun proteins (a subfamily of AP-1 proteins). TgAP-1 was ubiquitously expressed in T. granosa, with the highest expression detected in the gill and foot, followed by the mantle, hemolymph, and hepatopancreas. Exposure to Vibrio harveyi induced TgAP-1 expression in gill tissues and the expression levels of TgAP-1 of resistant blood clams were always lower than that of control population whether Vibro infection or not. A total of 18 single nucleotide polymorphisms (SNPs) of TgAP-1 were detected in T. granosa. SNP-typing and haplotyping of resistant and susceptible populations revealed that six SNPs (AG type of TgSNP-1, GA type of TgSNP-2, TG type of TgSNP-4, CT type of TgSNP-7, AG type of TgSNP-11, and GA type of TgSNP-12) and four haplotypes (fHap2, fHap3, fHap6, and fHap7) were significantly associated with V. harveyi resistance. Risk assessment showed that fHap2 (CG) and fHap7 (GA) were associated with an increased resistance, while fHap3 (CT) and fHap6 (AG) were associated with an increased susceptibility. The results from this study supported a potential role of TgAp-1 in the anti-Vibro immunity of T. granosa. The discovery of the genetic molecular markers and haplotypes related to Vibrio resistance can provide guidance for selective breeding of T. granosa in the future.

Effects of fishing closure and mechanized clam dredging on a Callista chione bed in the western Mediterranean Sea

Clam production from wild fisheries has declined dramatically in Europe from 169,917 (2000) to 99,917 tonnes (2018). This negative trend has been particularly severe along the Mediterranean coast of Spain, where most clam stocks have collapsed in the last decades. Management responses to reconcile declining fisheries typically include closing areas to fishing. This study evaluated the effect of fishing closure on the Callista chione bed on the Maresme coast, which was among the most productive fishing grounds. At the same time, this study examined the direct impact of mechanized clam dredges on the megabenthic assemblages. The same locations were surveyed in 2005 (regular fishing activity) and 2020 (5 years after the official fishing closure). The closure of the clam fishing area has not helped in the recovery of the C. chione stock. Changes in C. chione biology and population dynamics were found. However, the diversity in the macrobenthic community has increased. Species with fragile shells or vermiform soft bodies have become more abundant or have appeared. These species are also among those most affected by mechanized clam dredging activity. The data suggest that active management actions are required (e.g. restocking) to recover the C. chione population in the medium term.

Analysis of Groundwater Quality for Clean Water Supply in Pasaran Island, Bandar Lampung City, Indonesia

Pasaran is the only productive small island functioning as the anchovy and green clam production center in Bandar Lampung. Its water use has, however, increased since its designation as an economically fishery-based development area or minapolitan in 2012. This is due to the fact that groundwater resources in small island ecosystems surrounded by seawaters with a narrow diameter are easily affected by the insistence of seawater. Moreover, population pressure and land-use change are also feared to be affecting groundwater quality. Therefore, this research was conducted to analyze and evaluate groundwater resource quality in Pasaran Island using five wells on the entire island as sampling points selected based on census. The samples were tested for physical, chemical, and biological parameters in the laboratory and compared with water quality standards (Minister of Health’s Regulation No. 32/2007). The results showed relatively low water quality because the samples contained up to 3900 μS/cm salinity, 3771.9 mg/l chlorides, 31.7–141.52 mg/l nitrates, and 6.8–170 MPN/100ml total coliform which exceed the standards for drinking water. Meanwhile, wells 1, 4, and 5 were found to be safe for sanitation-hygiene purposes and well 1 was suitable for public baths even though they are not of drinking quality. This means the groundwater quality generally met Class II-water requirements for clean water supplies.

Effects of ammonia nitrogen on early growth and survival of the ‘Zebra 2’ strain of the manila clam ( Ruditapes philippinarum )

The ‘Zebra 2’ strain of the Manila clam (Ruditapes philippinarum) is a newly bred for aquaculture in the low temperature Bohai and Yellow seas in northern China. The goal of this study was to determine the tolerance of ‘Zebra 2’ clams at early developmental stages to total ammonia nitrogen (TAN) under acute stress and continuous subacute stress levels. ‘Zebra 2’ were cultured under TAN stress at water salinity of 27–28, temperature of 21–28°C and pH of 8.0–8.2. Survival rate and production of clams from the fertilized egg to juvenile stages were measured. The acute stress test revealed that the median effective concentrations of TAN for hatchability and deformity of fertilized eggs at 24 h were 7.08 and 15.12 mg/L, with the unionized ammonia (UIA) at 0.22 and 0.36 mg/L respectively. The 50% lethal concentrations for D-shaped larvae (shell length 101.50 μm), umbo larvae (179.67 μm) and juveniles (610.50 μm) at 96 h were 3.28, 48.90 and 57.57 mg/L, with UIA at 0.10, 2.08 and 2.99 mg/L respectively. These results suggested that the ‘Zebra 2’ clams hatching and D-shaped larvae stages were most sensitive to TAN and that the tolerance significantly increased after the umbo larval stage. In the continuous subacute stress test, ‘Zebra 2’ juveniles were observed under all the treatments after 53 days of exposure to TAN stress at 5.45 mg/L (0.23 mg/L UIA). The maximal acceptable toxicant concentration of UIA used to determine the mortality rate, yield and relative yield was ranged from 0.12 to 0.23 mg/L. These findings suggested that maintaining TAN <0.22 mg/L and UIA ≤0.021 mg/L at seawater pH ≤8.5, salinity ≥25 and water temperature ≤25°C would improve larval rearing of ‘Zebra 2’ clams.

Production and Biomass of Pokea Clam (Batissa violacea var. celebensis von Martens, 1897) in the Langkumbe River Waters North Buton Southeast Sulawesi

Langkumbe River is located in West Kulisusu District and has long been used by the community for various daily activities. One of the resources often used by the people around Langkumbe River is pokea clams. The aim of this study was to determine the production and biomass of pokea clams (B. violacea) in Langkumbe River Waters of North Buton Regency from August to October 2017. The sampling method used was swept area method using a traditional fishing gear "Tangge" (fishing gear). The samples were measured for the length, width and thickness. The total weight was measured with the clam/total mass (MT) and the weight of the meat. The samples were dried using an oven for 24 hours at 70 °C to obtain the shell-free dry mass (SFDW). Data were analyzed using standard formulas. The total sample obtained was 1.307 individuals. The highest density of pokea clam was found in August at 596.8 ind/m². Annual production of pokea clam (B. violacea) in Langkumbe River with a total annual production of 1,107.33 gSFDW/m2/year. The highest and lowest production are 297.09 gSFDW/m²/year at size 2.19-2.54cm and -0.16 gSFDW /m²/year at size 4.70-5.05cm, respectively. The total population biomass was 528.03 gSFDW/m2 with the highest biomass 171.72 gSFDW/m²/year at size 2.55-2.90 cm and the lowest was 1.40 gSFDW /m²/year at size 4.70-5.05 cm, so that the recovery rate (P/B ratio) was 2.1 gSFDW/m2/year.

Effects of translocation on the asari clam Ruditapes philippinarum at small spatial scales in Matsukawaura, Japan

The asari (Manila) clam Ruditapes philippinarum is a commercially important bivalve that lives on tidal flats, but the clam landings have decreased in many estuaries in Japan. To increase the production of the clam, we conducted pilot translocation experiments at small spatial scales within the estuarine system of Matsukawaura Lagoon, Japan. Two scales were used: one was a horizontal translocation from an area with low clam productivity to an area with high productivity, and the other was a vertical translocation from the upper area to the lower area of the tidal flat. Our caging experiment with the horizontal translocation revealed that the growth rate and somatic condition of the clams translocated to favorable conditions were significantly better than those remaining in the original habitat. On a sandy fishing ground, vertical translocation of clams from the upper intertidal zone to the lower intertidal zone resulted in higher growth rates and better somatic conditions for the clams. Moreover, the clams from sandy ground showed larger growth increases than those from muddy-sand ground, indicating that the origin of clams affected translocation effectiveness. We found that clam biomass increased by 42%– 53% with the vertical translocation of small (&lt;30 mm shell length) clams during the fishery off-season from August to April. These results indicate that translocation of local clams to favorable habitats within an estuarine system can increase clam production and yield practically during the off-season.

Analysis of the Economic Value and Status of the Ecosystem Services Provided by the Ashtamudi Wetland Region, a Ramsar Site in Kerala

Wetlands provide critical services such as protection against flooding and wave action, water quality maintenance, habitat provision, food products, etc. Ashtamudi is the second-largest wetland ecosystem in Kerala state, and it provides numerous ecosystem services (ES). This study has analysed the economic value and current status of 11 important ES provided by this wetland. The considered services are fish production, clam production, shrimp/prawn larvae production, inland navigation, coir production, carbon sequestration and erosion prevention provided by mangroves, flood protection, cooling effect, tourism and future use-value. The total economic value of the wetland by considering the aforementioned services is 424 million US$ (in terms of 2017 International $ value), and every hundred square metres of the wetland provides an economic output of 820 US$ per year approximately. Even though the valuation of a few ES has been carried out in earlier studies, this particular study has incorporated more services in valuation and analysed the change in its value compared to previous years. This study also tried to analyse the status of ‘wetland features’ essential for the sustenance of ES, the spatial changes of the service providing habitats, and its impact on ES delivery. The study has been carried out in a GIS framework using inputs from various sources including remote sensing (RS) data. Landsat imageries and digital elevation model of the study area are used to understand the economic value and current status of certain services. Analysis, such as spatial change of service providing habitats, shoreline alterations, changes in NDVI of selected locations is carried out by utilizing the aforementioned RS data. Compared to the previous years, the value of supporting and regulating services is declining. At the same time, the value of certain provisioning and cultural services is improving. As the supporting and regulating services are the prerequisites for all other ES to sustain, the current trend indicates a collapse of the entire system shortly. While addressing this issue, more priority has to be given in restoring antecedent wetland condition, which will indeed lead to the improvement of supporting and regulating ES. Community-based institutional mechanisms have to be developed to ensure consistent monitoring and maintenance of the wetland.