It is led by HQ Seaweed, based in San Adrián de Cobres, and is currently in the environmental assessment phase. The cultivation would be done using eight ropes, each 72 meters long.
A company from Vilaboa is promoting a project for the cultivation of seaweed in the Vigo estuary. The species to be cultivated is sweet or sugar kombu (Saccharina latissima scientifically), which is the European equivalent of Japanese kelp. The cultivation would be carried out through eight lines, each 72 meters long, arranged in four double rows located within the Redondela B and Cangas D farming zones [situated in the waters of Moaña]. The initiative is currently in the simplified environmental impact assessment phase at the Ministry of Environment, since one of the zones—Redondela B—is located in the San Simón inlet, included in the Natura 2000 Network.
The goal of the project led by HQ Seaweed, based in the port of San Adrián de Cobres, is to cultivate this seaweed for human consumption using “long-lines” or ropes suspended by buoys. In each of the chosen zones, four lines of 72 meters in length will be installed, arranged in two double rows. Each row will consist of a longitudinal rope or “mother rope,” with its ends attached to a biconical buoy. This rope is called the “mother rope” because it serves as the support for the cultivation ropes on which the seaweed will grow. Due to the 1.5-kilogram concrete counterweights used to keep them suspended, this type of cultivation is called a “V” or “garland” system.
Why does the company want to cultivate this species? It is a seaweed that has great commercial value, and the project authors compare it to Japanese kelp (Saccharina japonica), which is the most widely cultivated species in the world, with an estimated production of 11 million tons per year. The problem with sweet kombu in Galicia is that, due to a combination of its ecological value and rarity, it cannot be naturally exploited. “Its collection in the natural environment is not allowed because it is, to some extent, a structural species and because the northwest of the Iberian Peninsula is its southern distribution limit […] Furthermore, its populations are relatively scattered and of limited size, which makes its exploitation unprofitable and could endanger its conservation,” the project explains.
Thus, the best alternative is industrial cultivation, and expectations are very favorable due to previous studies and experiences. The Galician estuaries have a high growth rate. In a test conducted in the Ares and Betanzos estuary, a production of 20.7 kilograms per meter of rope was obtained over a period of 140 days, whereas in Canada it took twice as long to achieve similar results.
The biconical buoys intended for use have two vertices, allowing each buoy to keep two cultivation lines afloat simultaneously. In each of the selected zones in the Vigo estuary, there will be two double lines, spaced four meters apart. Additionally, to prevent tangling, the individual ropes will be separated by 1.5 meters.
The biconical buoys at the ends will be 500 liters each, and each will be anchored to a main and a secondary deadweight, both made of concrete and weighing two tons, which will also prevent loss of tension. In turn, the mother ropes will be kept on the water surface thanks to other 200-liter buoys placed every six meters, with additional 3-liter floaters every 1.5 meters.
The dimensions of the entire system –125×100 meters in Cangas D and 102×90 meters in Redondela B– require the company to request the concession for the two contiguous grids adjacent to the requested location. They explain that with only one, the anchorages would fall outside the requested area limits, which goes against Galicia’s regulations for floating nurseries.
The project submitted for evaluation to the Ministry of Environment emphasizes that these facilities “do not require daily supervision”, so “they will not cause a significant increase” in maritime traffic in the area, with fewer than thirty visits expected per year. According to studies conducted to date, the optimal time for cultivating sweet kombu in Galicia is between November and December, while harvesting should take place in mid-spring, between April and May.
HQ Seaweed points out that once the harvest is complete, the cultivation lines will be dismantled, leaving only the anchors and marker buoys in the marine environment. This will also allow for the cleaning of algae residues and other organisms attached to the ropes and floats, a cleaning that will be done with scrapers and seawater, without using chemicals. The installation of the cultivation lines — which is estimated to take two days — and their subsequent removal will be carried out using a 15-meter mussel fishing boat.
A species with great commercial interest that would help reduce the environmental impact of mussel production
Sweet kombu is one of the macroalgae species with the greatest commercial interest in the northern Iberian Peninsula, due to its demand and economic value. According to the project submitted by HQ Seaweed to the Xunta de Galicia, retail prices for this species range between 40 and 49 euros per kilogram of dried algae. The project authors also point out another possible benefit linked to environmental sustainability and mussel production. Although this mollusk has the great advantage of not requiring additional feeding—it feeds on the phytoplankton entering the estuaries through marine currents—it does have a “significant impact” on other parts of the marine ecosystem.
Los redactores explican que la gran cantidad de fango rico en materia orgánica excretado por el mejillón y depositado bajo los polígonos de bateas cambiará las características del sedimento y de la fauna asociada. Bajo las bateas se crea un microambiente dominado por detritos orgánicos, en el que abundan especies detritívoras –como poliquetos–, que junto con los restos de mejillón supone una fuente de comida para multitud de peces y otros organismos. Esto no impide que haya que reducir su impacto ambiental para “alcanzar la sostenibilidad” de esta industria. La iniciativa que se somete ahora a estudio puede ser una buena opción porque las sustancias de desecho liberadas por el mejillón como el amonio, fósforo y otros compuestos solubles excretados pueden ser empleados por las algas como nutrientes. Dicho de otro modo, “fertilizarán de manera natural” las aguas en las que se cultivará el kombu dulce, lo que a su vez favorecerá su crecimiento y una mayor producción.