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In order to develop land based IMTA production systems integrating exclusively low trophic species experiments performed as part of the INTEGRATE project, at the IU-ECOAQUA Institute of the University of Las Palmas de Gran Canaria, tested the integrated production of Haliotis tuberculata coccinea, Holothuria sanctori and two species of algae (Ulva rigida and Gracilaria cornea. The studies contributed to determine the adequate biomass of abalone required to provide a food source suitable for sea cucumbers grow out, to determine the amount sediment ingested by the cucumbers and to establish their bioremediation potential in such IMTA production systems.

Two assays were performed at different scales to first estimate abalone faeces production and sea cucumber ingestion and defecation rate and to test their acceptability at pilot scale to estimate the production potential of abalone and sea cucumbers in land based IMTA systems.

During the first assay performed in triplicate in 100 liters tanks, each replicate contained 50 abalone with a total biomass of 717±14 grams, 3 small sea cucumbers with an average weight of 13.09± 0.68 grams and 3 medium size sea cucumbers with an average weight of 22.67±1.39. grams

Sea cucumbers were fed daily, during 15 days, with 15 gr of abalone feces. to estimate sea cucumbers ingestion rate. Sea cucumber faeces and leftover abalone faeces were daily collected weighed on a precision balance and dried in an oven for 48 hours until reaching constant weight to estimate their dry weight and determine sea cucumber ingestion and defecation rates.

Abalone were fed during 15 days on a mixed diet of algae Ulva rigida and Gracilaria cornea (at 28% of their weight) and compound feed (at 2% of their weight).

Faeces were daily collected, weighed on a precision balance and dried in an oven for 48 hours until reaching constant weight to estimate their dry weight and abalone defecation rate.

During the second assay performed in triplicate, in pilot scale 300 liters integrated production systems, each replicate contained abalone with a total biomass of 995±0.33 grams per tank and 1 small sea cucumber with an average weight of 12.08± 0.34 grams together with a medium size sea cucumber with an average weight of 20.37±1.47 grams. Abalone were daily fed at 2% of their weight with compound feed and at 30% of their weight a mixture of Ulva rigida and Gracilaria cornea.

To estimate sea cucumber defecation rate sea cucumber feces were daily collected during 15 days. In the case of abalone feces, they were collected once a week, to ensure enough feeding material remained available to the sea cucumbers. Sea cucumbers and abalone feces were weighed on a precision balance and dried in an oven for 48 hours until reaching constant weight to estimate their dry weight.

Ingestion rate (IR), defecation rate (FPR) and growth performance (SGR & WG) were estimated according to the following formulas:

IR (mg/g/h) = ((Wo − _Wu) / Wsc) / t

Where Wo is dried weight of the offered food (mg), Wu is dried weight of the remaining food (mg), Wsc is the wet weight of the sea cucumber in the tank (g), and t is the duration of the experiment (h).

FPR (mg/g/h) = (Wf / Wsc) / t

Where Wf is dry weight of the faeces (mg), Wsc is wet weight of the sea cucumber or abalone in the tank (g), and t is duration of the experiment (h).

WG (%) = 100 * (W_f − _W_i) / W_i

SGR (%.day^-1) = 100 * (lnW_f − _lnW_i) / number of days

Where W_i is the initial wet weight (g) and W_f is the final wet weight (g).

Results:

Significant differences in ingestion rates were observed between small and medium size sea cucumbers while their defecation rates were similar independently of their sizes.

At pilot scale, sea cucumbers ingestion and defecation rates observed sustained the ones observed during the first assay indicating their soundness to be applied and taken into account for larger scale integrated production of these species.

Growth performance of Holothuria sanctori specimens varied according to their initial size; being higher for smaller specimens as previously observed in other studies; and overall was within the range of growth performance observed for other species of sea cucumbers produced using mollusks refuse.

Overall, the integration of sea cucumbers to abalone production units in land-based IMTA systems did not affect abalone growth potential. These results highlight the interesting potential of the two species integration for future production in IMTA systems.

During the extension of the INTEGRATE project, L’Institut Agro aimed at testing the feasibility of associating for the first time the rearing of sea cucumber Holothuria forskali with the flat oyster, Ostrea edulis in open sea near-shore. The experiment was designed to verify if this association can be a successful IMTA system, meaning that the holothurians benefit from the waste of the oysters. L’Institut Agro also tested different stocking densities of Holothurians to identify the best rearing conditions to maximize growth and survival. To realistically qualify the system an IMTA, trophic links between the two species need to be demonstrated, this was performed by analysing the fatty acid and isotope signatures of the different compartments of the system.

The experimental flat oysters and holothurians were stocked separately in plastic cages of dimensions 87 cm x 45 cm x 12 cm (Figure 1A) stacked in the experimental structures. Below multiple layers of flat oyster cages, different densities of holothurians per cages were tested (Figure 2B) : 8, 16, 24, and 32 individuals per cage bottom square meters. A last condition consisted in stocking the lowest density above the flat oyster. The experiment was ran in triplicated structures with the order of the conditions below the flat oysters changed. Two temperature probes were installed on two structures. The holothurians were 5g juveniles bred in the experimental facilities of L’Institut Agro.

Figure 1. Experimental cages (A) and experimental set up (B) to test growth and survival potential of holothurian juveniles (C) stocked at different densities underneath flat oysters.

The experiment started in March 2022 and ended in May 2023. The water temperature fluctuated the experimental period from 9 to 20.5 °C with a mean around 15°C. A total of 4 biometries were performed after the start of the experiment. Results show excellent survival for all conditions (99%) and exceptional growth of the holothurians with individuals reaching up to 20x their initial weight in 15 months (Figure 3A). Surprisingly, the holothurians stocked above the flat oysters showed a growth very similar to the same stocking condition (8 holothurians.m-2) stocked underneath, with even a better growth at the end of the experiment (Figure 3A). A clear decrease in growth potential was observed with increasing stocking densities underneath the flat oysters, translating into an exponential decrease in the final mean weights (Figure 3B). Yet, the highest densities were found to be still interesting since they show the highest total final weight (Figure 3C).

Figure 2. Growth differences between stocking conditions over time (A), final mean (B) and total (C) per replicated cage for each density below the oyster cages.

Finally, the fatty acids compositions of the holothurians showed clear differences for conditions above and below the oysters (at the lowest stocking densities), which translated into a significant difference on the second dimension of the Principal Composant Analysis ran on all fatty acids (Figure 4). Isotope analyses are still in progress to confirm these results.

Figure 4. Coordinates on the second axis of a Principal Component Analysis performed on the fatty acids profiles of holothurians reared at 3 different conditions. The first two boxplots represents 2 densities of holothurians reared underneath flat oysters, while the last one illustrates results of holothurians reared above oyster cages.

Altogether, this pilot study shows the great potential of using Holothuria forskali to rear in combination with flat oysters. Such a system would at least allow to diversify the production. The biochemical composition analysis (Fatty acids) suggests that food sources are different for individuals stocked underneath the flat oysters compared to individuals above. This provides the first argument to stipulate that H. forskali is able to use oysters’ waste when stocked underneath. If this is confirmed by isotope analyses, this will provide proofs that the pilot study is a successful IMTA, and that H. forskali help to reduce organic waste accumulation under bivalves production.

These results will be presented at the European Aquaculture Society conference in Vienna (2023) during an oral presentation.

Experts in integrated multi-trophic aquaculture met to present the results of INTEGRATE. CTAQUA held the final technical hybrid conference of the project on June 13, in CTAQUA’s facilities located in El Puerto de Santa Maria from 10:00 to 17:00.

One of the purposes of this event was to create a network of knowledge transfer between scientific and innovation organizations to companies in the sector. This event provided the opportunity to share experiences of other relevant projects in the field of aquaculture sustainability and IMTA systems such as ASTRAL, Aquavitae and BIOGEARS.

We also counted with the participation of the 7 organizations from the 5 countries that are part of the project consortium. Along with CTAQUA (Spain), leader of the project, INTEGRATE partners include the Agrocampus Ouest Research Institute (France), the Portuguese Institute of the Sea and Atmosphere (Portugal), Bangor University (United Kingdom), Irish Seaweed Consultancy (Ireland), Universidade do Algarve (Portugal), University of Las Palmas de Gran Canarias (ULPGC) and GreenCoLAB (Portugal)”.

During the event, various experts explained their contribution to the project and the multiple benefits of these systems. Among others, the optimization of the nutrients necessary for the growth of different species at different trophic levels. A smart way to encourage diversification of aquaculture production, which has great potential to improve the resilience and economic stability of producers with a holistic approach.

New techniques have also been explored to increase IMTA’s commercial potential. Among other activities, the most relevant results were focus on the diversification of cultivated species and simulation models of IMTA productive scenarios in estuaries, highlighting opportunities and species of interest in IMTA aquaculture production.

In addition, as was reflected during the intervention of Anna Soler and Susan Whelan from Irish Seaweed Consultancy, important technical knowledge has been generated on the cultivation of the macroalgae Himanthalia elongata. Other species for which technical knowledge has been improved are Porphyra spp, Codium spp, Palmaria palmaria and Ulva spp, species of high economic value and that can be perfectly integrated into these multi-trophic systems.

In the case of other low trophic level animals, as Gercende Courtois explained, knowledge of several species of sea cucumbers such as Holoturia forskaii, Holoturia tuberculata and Holuturia arguinensis, which are in high demand on the international market, has been promoted. The project also contributed to the gastronomic valorization of these species as part of the important work of making them known to society.

GreenCoLAB’s researchers, Lais Galileu Speranza, Sustainability Group Leader, and Ahmad Furqan Hala, Specialist in Life Cycle Assessment, presented the WP5 results on “Exploring the Sustainability of IMTA”, during Session 2 – IMTA Best Practices in the IMTA Atlantic Arc  of the INTEGRATE final event.

The potential environmental impact and benefits of IMTA systems compared to the traditional practices (monoculture fish farming) were evaluated by using life cycle assessment (LCA). LCA was performed based on international standards (ISO14040/14044) using OpenLCA v2.0.0 software and Ecoinvent v3.7 and Agribalyse v3.01 databases with a cradle-to-gate approach (impacts until the products are harvested). During the project, four scenarios were assessed: polyculture fish farming system (used as the reference), seaweed and fish system, semi-intensive IMTA, and semi-extensive IMTA.

Results showed that IMTA systems are able to reduce the total environmental impact of all impact categories when compared to polyculture fish farming. Feed is the major contributor to the impacts, followed by the energy/electricity use to support the farming activity. A more extensive system and a diversification of species in the IMTA community have proven to reduce the environmental impact of the system. It was important to notice that the chosen functional unit when conducting an LCA may affect the results and standardization in the methodologies of conducting such studies are required.

To bring these sustainability concepts to the market and boost the value of the IMTA products, regulations, directives and ecolabel certifications have been created in the EU. The currently available ecolabels face the lack of transparency and integrity of the certification program, high cost, and failure to fully address major problems such as carbon footprint. Therefore, a strategy to raise awareness and give recognition to IMTA for the amelioration of the environmental impact of fish farming needed to be developed. The technical standard that was developed in INTEGRATE I was a great initiative to be a public standard for aquaculture in general and IMTA specifically. The WP5 activities evaluated the regulatory landscape for ecolabeling and defined a strategic plan route for an ecolabel certification taking into consideration the LCAs performed.