Is Manila Clam Farming Environmentally Sustainable? A Life Cycle Assessment (LCA) Approach Applied to an Italian Ruditapes philippinarum Hatchery

Abstract

Italy supplies approximately 96% of EU-farmed Manila clams. Following a reduction in wild seed availability, farmers started to depend on hatchery-produced seed, mainly imported from other countries. Indeed, only one hatchery is currently operating in Italy. This study quantifies the environmental impacts of seed production in this Italian hatchery facility to inform future planning for improving the sustainability of the supply chain. The environmental performance of the Manila clam hatchery was evaluated using the Life Cycle Assessment methodology. A cradle-to-gate analysis was performed, covering the following production phases: (1) microalgae production, (2) broodstock maintenance and conditioning, and (3) larval rearing until marketable size. The functional unit adopted was 1 kg of live clam seed. The main driver of the environmental impacts was electricity consumption, contributing over 80% for all impact categories. Other inputs showed minor contributions to different impact categories, including liquid oxygen, water pumps, and high-density polyethylene. This study highlights that the environmental burden associated with seed production could be reduced by switching to alternative technologies to meet energy needs, such as investments in photovoltaic and wind energy production systems.

1. Introduction

The aquaculture sector and its contribution to global seafood production have climbed steadily in the last decades. Global aquaculture production increased by more than 600% from 1990 to 2020 [1], showing an average annual growth rate higher than that of any other animal production system. The contribution of aquaculture to the total aquatic food production reached approximately 50% in 2020, on pair with capture, substantially contributing to the ever-growing gap between the demand and supply of seafood. Although with a slowdown compared to recent decades, aquaculture production is expected to continue to grow and exceed fisheries production by 2030, the latter coping with declining natural stocks of fish and mollusks [2,3] mainly due to overfishing, habitat degradation, and climate change effects.

Bivalve mollusk aquaculture, which in the past twenty years increased its production by approximately 82%, represents more than 14% of global aquaculture production (17.7 million t in 2020) [1]. In particular, this sector dominates Italian aquaculture, where it represented more than 60% of total production and 48% of the economic value in 2020 [4].

In addition to providing high-quality animal protein and being rich in omega-3 polyunsaturated fatty acids (PUFA) [5,6], the bivalve aquaculture sector also provides several other ecosystem services. It can contribute to the restoration of deteriorated seabed habitats and the protection of the shoreline from erosion [7]. Mollusk aggregation can provide refuge and substrates for several species; thus, bivalve aquaculture can facilitate increased abundance and richness of species at different trophic levels, thereby enriching the biodiversity of the ecosystem [8,9]. Bivalves are filter feeders; as such, they take part in the nutrient cycle and mitigation of the effects of eutrophication [9]. In addition, their shells can provide an excellent biomaterial to be used as fertilizer, lime, or construction material [9].

One of the most economically important farmed bivalves and the prime clam species produced in Europe is the Manila clam (Ruditapes philippinarum, Adams & Reeve 1850). The Manila clam is native to the Indo-Pacific region. This species was introduced in Europe between the ’70s and ’80s and was first imported to the Venice lagoon in Italy for experimental aquaculture purposes in 1983 [10,11]. Given its high adaptability, it is now commonly distributed in the Mediterranean Sea and Atlantic coast [10]. The Manila clam is also characterized by a fast growth rate, tolerance to salinity and temperature variations, and eutrophication [12]. These characteristics make its farming less risky and more profitable compared to the autochthonous carpet shell clam (Ruditapes decussatus, L. 1758). In 2020, Manila clam production in EU-27 surpassed 25,290 t, 96% of which was supplied by Italy (24,337 t) [4]. The prominent position of Italian production is derived from optimal ecological conditions favoring the growth and reproduction of this species in coastal lagoons of the Northern Adriatic Sea, in front of the Po River delta, and along the Sardinian coast [13,14,15,16]. In Italy, Manila clam production represents approximately 36% of the total aquaculture production value [4].

Manila clam farming consists of the following phases: seed collection and sowing, management of the farming area and clam density in the seabed, harvesting, and depuration (according to EU Reg. 2019/627). Manila clam seed is mainly collected in natural marine nursery areas [17,18] outside coastal lagoons, where it was historically very abundant. However, during the past two decades, a serious decline in wild clam populations, and therefore spat availability, has been observed [10]. The causes behind this reduction are poorly understood, but likely reside in phenomena acting synergistically, such as overharvesting, increased seawater temperature, anoxia, eutrophication, environmental quality degradation, and diseases [10,19]. Although Manila clam is less sensitive to poor environmental conditions than autochthonous carpet shell clams, it is still affected by limiting ecological factors with potential negative influences on reproduction success, settlement, and growth. Among them, temperature (maximum survival at 31 °C), food availability (mainly diatoms), sediment grain size (optimum 70–80% sand), turbidity, and dissolved oxygen (optimum 6–8 mg L⁻¹, minimum 3.5 mg L⁻¹) are known limiting factors when exceeding tolerance ranges [10,20].

To cope with the shortage of natural seed, Italian clam farmers have recently started to rely on seed obtained under controlled hatchery conditions. Despite the importance of the Manila clam for the Italian economy, there is currently only one hatchery operating in Italy. It produces approximately 5 t of seed/year, which is insufficient to guarantee the national demand of the growing sector. Therefore, most of the hatchery seed necessary to integrate natural recruitment is imported from other EU countries (mainly Spain, France, and The Netherlands) and the United States.

In addition to its use for increasing Manila clam production, hatchery-produced clam seed could be certified as organic and favor the expansion of organic aquaculture shellfish production, which represented less than 3% of total Italian production in 2018. Because of increasing consumer awareness on sustainability and animal welfare issues, the EU recommended Member States to quickly switch towards organic aquaculture production [21], and bivalve mollusks farming could represent the best opportunity to achieve this goal [22,23]. Indeed, as these species do not require external feed inputs, the main difference between organic and conventional supply chains is the origin of the seed. To be certified as organic, clam seed must come from certified hatcheries.

Considering: (1) the need to increase bivalve mollusk production in view of climate change mitigation; (2) the downward trend of natural clam seed recruitment, and (3) the opportunity to increase organic shellfish aquaculture production, it is likely that clam farmers will be even more dependent on hatchery-produced seed in the future. However, the economic costs associated with the production of Manila clam seed in a hatchery are higher than natural seed collection.

In this view, it is be important to balance economic, environmental, and ecological trade-offs and quantify possible positive externalities of hatchery-seed production. However, a precise estimation of the environmental impacts of artificial clam seed production is still lacking.

This communication reports the first results of a Life Cycle Assessment (LCA) model applied to the only Italian Manila clam hatchery. To the authors’ knowledge, this is the first attempt of LCA carried out on a clam hatchery. A similar approach was used to assess the environmental performance of an oyster hatchery in the United States [24]. In this study, the environmental impacts of hatchery seed production are quantified, potential hotspots are identified, and we provide suggestions for improving the environmental performance of the clam supply chain.

2. Materials and Methods

The case study referred to a Manila clam hatchery (reference year: 2020, production volume: 5.3 t) located on the North Adriatic Sea coast, Goro (FE, Italy), one of the most productive areas for clam farming. The LCA approach followed the guidelines of ref. [25]. The objective of this study was to assess the environmental performance of the clam hatchery by analyzing material and energy flows through the system. A cradle-to-gate analysis was carried out, considering the following processes: (1) microalgae production, (2) broodstock maintenance and conditioning, and (3) larval rearing until marketable size (>6 mm). The system boundaries (Figure 1) included the above processes and all material and energy inputs and outputs to and from the system. Allocation as a methodological approach to solving cases of multifunctionality was not necessary, as the only output was clam seed ready to be sown. Data on the land-based building and ancillary facilities making up the hatchery were not included in the study since the lifetime is >40 years and information was difficult to gather. For all the durable equipment used in the facility (tanks, photobioreactors, heaters, steel machinery, containers, bins, etc.), according to the information obtained from the respondent, an average lifespan of 25 years was assumed, except for the water pumps, which last approximately 10 years. Waste materials were not included in the analysis since their amount appeared to be negligible during the facility’s inspection. The functional unit (FU) chosen was 1 kg of live clam seed. The Life Cycle Inventory (

Table 1. Life Cycle Inventory (LCI) of the material and energy inputs for the production of 1 kg of live clam seed.

INPUT-MATERIAL	Value	Unit
Liquid carbon dioxide (CO2)	120.23	g
Hydrochloric acid (HCl) 37%	34.76	g
Liquid oxygen (O2)	1.26	mc
Sodium hypochlorite NaClO 14%	87.73	g
Sodium nitrate (NaNO3)	0.45	g
Sodium phosphate (Na₃PO₄)	0.09	g
Sodium chloride (NaCl)	93.93	g
Polypropylene (PP) bottles	1.41	g
Glassware	0.0010	pieces
High-density polyethylene (HDPE) water container	0.38	g
Polymethyl methacrylate (PMMA) photobioreactor	12.62	g
Fiberglass tanks	2.44	g
Polypropylene (PP) tanks	21.39	g
Polyvinylchloride (PVC) sieves	0.66	g
Titanium coil heaters	0.0001	pieces
Bins (HDPE + aluminum)	0.0075	pieces
Polypropylene (PP) raceways	90.18	g
Silica sand	5.64	g
UV lamps	0.0023	pieces
LED lamps	0.0019	pieces
Polyvinyl chloride (PVC) pipe	3.01	g
Water pump	0.0001	pieces
Steel machinery	3.76	g
Electricity	55.5	kWh
Seawater	1127	mc

) was based on data provided by the technical personnel of the hatchery through questionnaires and interviews (foreground data). The Ecoinvent 3 database was used to collect data about the production of electricity and raw materials (background data). The Life Cycle Impact Assessment was carried out using SimaPro 9.1.0.7 software (PRé Consultants), adopting the ReCiPe 2016 (H) method.

3. Results and Discussion

The environmental performance related to the production of 1 kg of hatchery-produced seed is reported in

Table 2. Impact assessment of hatchery seed production–characterization. Results refer to 1 kg of live clam seeds.

Midpoint Impact Category	Unit	Total
Global warming (GW) 1	kg CO2 eq	2.63 × 101
Stratospheric ozone depletion (SOD)	kg CFC11 eq	2.00 × 10−5
Ionizing radiation (IRAD)	kBq Co-60 eq	3.30 × 100
Ozone formation, human health (OF-HH)	kg NOx eq	5.00 × 10−2
Fine particulate matter formation (FPMF)	kg PM2.5 eq	3.40 × 10−2
Ozone formation, terrestrial ecosystems (OF-TE)	kg NOx eq	5.09 × 10−2
Terrestrial acidification (TA)	kg SO2 eq	9.69 × 10−2
Freshwater eutrophication (FE)	kg P eq	9.04 × 10−3
Marine eutrophication (ME)	kg N eq	8.42 × 10−4
Terrestrial ecotoxicity (T-ECOTOX)	kg 1,4-DCB	8.25 × 101
Freshwater ecotoxicity (F-ECOTOX)	kg 1,4-DCB	2.83 × 100
Marine ecotoxicity (M-ECOTOX)	kg 1,4-DCB	3.52 × 100
Human carcinogenic toxicity (HCT)	kg 1,4-DCB	9.53 × 10−1
Human noncarcinogenic toxicity (HnCT)	kg 1,4-DCB	2.61 × 101
Land use (LU)	m2a crop eq	1.01 × 101
Mineral resource scarcity (MRS)	kg Cu eq	7.34 × 10−2
Fossil resource scarcity (FSR)	kg oil eq	8.20 × 100
Water consumption (WC)	m3	5.70 × 10−1

¹ The Global warmingimpact category does not consider the biogenic carbon flows related to shell formation.

. The contribution analysis of the inputs to the considered impact categories is given as histograms in Figure 2.

As depicted in Figure 2, the main driver of environmental impacts was electricity consumption, contributing more than 80% for all the selected impact categories and reaching 91% and 94% for Global warming (GW) and Stratospheric ozone depletion (SOD) impact categories, respectively. The only exception was found for the Mineral resource scarcity (MRS) impact category, for which electricity accounted for 70% of the impact. It should be kept in mind that the burden associated with electricity consumption is mainly derived from the processes required for its production, such as fuel use and combustion, and air, soil, and water pollution due to the mining and drilling activities associated with fuel extraction. The major contribution of the production and use of electricity to all the midpoint impact categories is due to the fact that electricity in Italy is still mainly derived from the combustion of fossil resources. In 2016, the reference year available in the Ecoinvent database for the shares of electricity technology in Italy, 63% of the electricity produced came from non-renewable sources. This share shows a decreasing trend, reaching approximately 59% in 2020 [26]. It should be noted that, nowadays, Italian thermoelectric generation depends almost exclusively on natural gas, with consequent benefits compared to thermoelectric generation from oil resources on the environment, e.g., reduced GHG emissions [26].

Other inputs showed minor contributions to different impact categories. These were liquid oxygen, water pump, and high-density polyethylene (HDPE). The contribution of liquid oxygen used for water treatment (oxygenation) varied among impact categories, ranging from 1.6% to 15%. In particular, the impact categories most affected by the utilization of liquid oxygen (>10%) were IRAD (15%) and FE (11%). It is worth mentioning that the use of liquid oxygen for the reference year was still not fully optimized and that its consumption was set at approximately 1500 mc/year in the following years. On the other hand, the use of water pumps appeared to have the greatest impact (>10%) on the following impact categories: F-ECOTOX (13%), M-ECOTOX (13%), and MRS (10%). Finally, the use of HDPE materials contributed 10% to the MRS impact category.

The results confirmed that electricity consumption, which still substantially depends on fossil fuels, is one of the major bottlenecks to the environmental sustainability of food supply chains, and with particular reference to this study, is the main contributor to the hatchery phase of the Manila clam supply chain in Italy. Furthermore, if the indirect contribution of the consumption of electricity from non-renewable resources derived from the production of liquid oxygen, water pumps, and plastic materials is considered, the importance of this input is even higher.

The major contribution of electricity consumption to the environmental burden associated with Manila clam seed production agreed, at least in part, with the only other study documenting the environmental performance of the shellfish supply chain that included the hatchery stage [24]. In that work, the author analyzed the environmental burden of producing a half dozen half-shell oysters (corresponding to approximately 0.17 kg of edible product) in the United States from the hatchery stage to processing. The supply chain described covered a wide geographical distribution, since the hatchery phase took place in Hawaii, the pre-growing phase in California, and the grow-out phase in Washington. Thus, the study included all the relevant transports from the different sites, which substantially contributed to the impacts. Nonetheless, a more specific comparison between ref. [24] and the current study is difficult as the differences between the two case studies are too profound and could lead to misinterpretations.

Concerning hotspot identification and room for improvement in the case of the Italian Manila clam hatchery, the environmental burden associated with the production of seed could be reduced by switching to alternative technologies to cope with the energy demands of the facility, such as investments in photovoltaic and wind energy production systems or utilization of electricity produced exclusively from renewable sources. For example, if 100% of the energy needs would be satisfied by purchasing solar energy, the Global warming potential associated with the production of 1 kg of Manila clam seed would decrease to 6.39 kg CO₂.

Although an environmental assessment of the impacts associated with seed import was outside the scope of this study, it can be argued that in terms of the entire Manila clam supply chain, the transportation phase could have a relevant environmental burden, as also shown in ref. [24]. Therefore, as it is likely that the demand for clam seed will increase in the coming years and farmers’ needs will have to be met by purchasing more and more hatchery-produced seed, an Italian network of clam hatcheries and pre-fattening farms would be desirable to reduce the environmental costs associated with the import of clam seed from other countries. However, a specific assessment of the impacts associated with Manila clam seed import will be useful to better inform future strategic planning.

Pending the LCA analysis of the complete Manila clam supply chain (from wild seed collection and/or hatchery-produced seed sourcing to the depuration phases) (Martini et al., in preparation), it is worth pointing out that this work specifically computed the environmental impacts associated with the hatchery phase of the Manila clam supply chain. For this study and according to the production processes analyzed, the FU chosen was 1 kg of live clam seed, which corresponds to approximately 20,000 individuals. The environmental impacts referred to the FU adopted here should not be confused with the environmental impacts associated with the production of 1 kg of commercial-size, marketable clams. Considering (1) a minimum survival rate (from seed sowing to adult clam harvesting) of 60%, as estimated by farmers and technical personnel interviewed, and (2) a mean individual weight of 10 g for live adult clams, 1 kg of clam seed (the FU used) would produce approximately 120 kg of commercial-sized clams. Therefore, the results reported in this study would refer to the production of the amount of seed that allows farmers to obtain approximately 639 t of live commercial-sized clams.

As a further consideration, it should be mentioned that the environmental costs associated with the production of hatchery seed may be higher than those associated with wild seed collection. Wild seed is collected in nursery areas adjacent to areas designated for the growth-out phase, thus minimizing fuel consumption (Martini et al., in preparation).

Despite the possible higher environmental impact of hatchery seed production, the possible advantages associated with capillary distribution of hatchery facilities on the national territory could be represented by the constant availability of seed product in the future. This would satisfy the demand for seed by farmers, thus securing the production of Manila clams, regardless of environmental conditions. Furthermore, given a continuing decline of wild clam populations, the reduced pressure on stocks would possibly allow for the recovery of populations. Hatchery-produced seed would also be an opportunity to improve the quality of the final product through broodstock selection, thus enhancing morphological, physiological, and organoleptic characteristics, such as shell shape and color, resistance to disease or higher temperature, growth rate, and yield [27], and promote the production of organic shellfish products. Finally, the local production of hatchery seed would be associated with reduced impacts linked to the transport of seed from other countries.

4. Conclusions

The environmental burden associated with hatchery production of Manila clam seed in Italy appeared to be strictly linked to electricity consumption. Following the main European and national strategies to address the sustainability of food production chains [21,28,29], strategic planning for the development of food production systems with lower environmental impacts is fundamental. In this framework, it is pivotal to quantify such impacts on each step of the value chain. In general, bivalve farming is considered a source of protein with high nutritional value and low impact [30,31]. However, it still faces challenges related to declining production due to the effects of climate change, overexploitation, and habitat degradation. With particular reference to the Manila clam value chain, if the bottleneck in the supply of natural seed observed in recent years continues, the development of a network of hatcheries and pre-fattening facilities, possibly at a national level, will be necessary to meet the need for clam seed. This desirable future development will reduce the pressure on natural stocks and the impacts related to seed transport from other countries, but it will require the implementation of new technologies to reduce the use of electricity from non-renewable resources in favor of electricity from renewable sources such as solar and wind energy, hydropower, and bioenergy from agricultural, urban, fisheries, or aquaculture biomass.