Effects on the Ecosystem
The size and scale of marine cultivation has a direct impact on the surrounding ecosystem. In terms of negative factors one must look for the following: the accumulation and distribution of waste; accumulation of blue mussels underneath the cultivation area; and changes in benthic species. Also, there is the risk of plankton volume change in the immediate vicinity of the breeding ground (Gunnarsson, 2004; Wilding T., 2012).
To date, Icelandic areas involved with blue mussel farming have not reached significant production volume. In comparison, blue mussel farming areas in Scotland are much bigger and built on the so-called âraft techniqueâ, where, instead of single lines, large quantities of growing ropes are pulled together, which again occupy a larger area. In Iceland, the single line technique is the most common method to grow blue mussels. Due to the enhanced breakdown of biological residue in blue mussel farming, oxygen shortage at or near the bottom is, if conditions are unfavourable, possible. Here, the cultivation method is the decisive factor. Another important variable is the method used when cleaning the ropes from the attached mussels. Using conventional methods, it is most likely that some mussels separate from the ropes by themselves, and therefore fall to the bottom where they start to rot (ÃÃ³rarinsdÃ³ttir and Antonsson, 1993; Loo and Rosenberg, 1984).
Excessive rotting of biological residue can lead to a decrease in species diversity and population numbers close to the farming site. In the water column, reduction of food supply for fish juveniles occurs, which again results in lower local fish populations and catches. Changes to species and population numbers can additionally occur at or near the bottom, where more mussel residue accumulates and less plankton is available (Inglis et.al, 2000). Nevertheless, these effects are dependent on the level of pressure from the area pressure. Where the farming pressure is lower, the species diversity can increase, meaning that other forms of marine life, such as crabs and other fish, will be attracted to the farming site (Cole 2002).
Because blue mussels filter the oceanâs phytoplankton they are a direct competition to other animals in the local ecosystem. Large blue mussel volumes mean less phytoplankton for other species that feed on it in their vicinity. Furthermore, since blue mussels also feed on the eggs and larvae of other marine animals they can affect recruitment of commercial stocks (Gunnarsson et.al, 2004).
Introducing mussel farming into tidal areas makes use of the constant changing distribution of organic waste. Here, the total amount of organic matter in the ecosystem remains unchanged, since no organic substances or additives are added into the system, as is done in salmon farming. The amount of organic residue mussel farms release and accumulate depends on their scope and size. Other factors include food availability and the digestibility of that food (Inglis et.al, 2000). Risks can arise from lack of oxygen in the sediment. In Iceland, however, the current speed is high, meaning low nutrient enrichment inside the fjords. Hypoxia from mussel
cultivation is therefore unlikely (Gunnarsson et.al, 2004).
Blue mussel farming does not have a solely negative ecosystem effect. Increases in the aquaculture industry (salmon) raise the demand for sustainability. Blue mussel farming has been mentioned as a good example for a sustainable form of farming. The interest in holistic farming, where farming fish, a seaweed-like kelp zone, and blue mussel takes place in the same area, has grown strongly in recent years. Blue mussel farming can utilise existing organic waste and algae from aquaculture and thus benefit second-hand from their fertiliser consumption and cultivation (Personal contact, Eva D. JÃ³hannesdÃ³ttir, April 9 2013). An increased natural growth of blue mussels has been observed near to salmon grown in sea cages, where fish density and food availability are high, but currents small. However, these effects are considered to apply only where there is little natural food in the sea and the organic material received from salmon farming thereby affects the growth (Gunnarsson et.al, 2004; Cramford et.al, 2009; WildingT., 2012). Additional blue mussel farming has been made a condition for fish farming licences in one county of Sweden because blue mussel farming serves the role of a filter in the ecosystem and therefore lowers the nutrient enrichment effects originating from fish farming.
The nitrogen and phosphorus waste produced to grow 200 tonnes of aquaculture fish compares to the amount produced by approximately 200 people in an inhabited area (Hovgaard et.al, 2001). Cultivation can trigger a change in the local habitat and its diversity as a result of increased food supply. Studies have shown that some quantities of blues mussels drop to the sea floor which originated from their breeding lines. Cases of vegetation attaching itself on the breeding lines and so forming conditions for a new habitat that creates shelter for juveniles have also been reported (Gunnarsson o.fl.2004; Eva D. JÃ³hannesdÃ³ttir. 2013).
Blue mussel farming clearly affects the ecosystem. Its environmental impact is a major factor in the assessment of culture conditions and their permits in Iceland. To present a positive image, it is essential for growers to establish procedures that affect the ecosystem minimally. Periodic monitoring for changes, such as accumulation of waste or mussels that have fallen out of cultivation, can minimise the impact on the ecosystem during breeding (Gunnarsson et.al, 2004; Palsson, 2009). One way which has proven successful in research and monitoring is underwater cameras that regularly examine the bottom with regard to changes in the ecosystem;which applies equally to structural changes, as well as regular breeding (Crawford et.al, 2003; Telfer, 2009).
Northlight Seafood will make every effort to assess environmental conditions with effective monitoring. Their costs are included in the estimated costs of the cultivation process itself. Furthermore, already available technologies associated with rafts may minimise the hazards of oxygen depletion for such large crops.