Abstract
Future scarcity in phosphorus resources is a challenge directly linked to food
security (Desmidt et al., 2015; Cordell et al., 2009), and solutions are needed to shift the current phosphorus use into more sustainable forms (Cordell et al., 2009, 2011). The release of biological waste from finfish aquaculture along coast lines can have negative impacts on marine ecosystems (Jansen et al., 2018), as well as being a wasteful practice with limited resources like phosphorus. Recirculation of biological waste from aquaculture can be done by co-cultivating species like Saccharina latissima, in integrated multi-trophic aquaculture (IMTA) systems (Buschmann et al., 2001; Chopin et al., 2001; Ridler et al., 2007). This study characterizes storage of phosphorus in S. latissima and evaluates the recycling potential through the IMTA cultivation of this species.
A 4-month cultivation study was conducted by deploying vertical ropes (5 m) with S. latissima seedlings (Forbord et al., 2018) along a gradient within and downstream from a salmon farm. The ropes were grouped as integrated among pens (I-SL, -150 to 0 m), and downstream from farm edge (D-SL, 100 to 280 m), assuming different nutrient availability between groups from farm proximity. Biomass registration, water- and tissue samples were collected for the period and analyzed from samplings after 2 (April) and 4 (June) months. Tissue samples were analyzed for carbon (C) and nitrogen (N) (acetanilide as standard), and phosphorus (P) (Koroleff, 1976) content at three different areas of the seaweed to characterize internal distribution: basal- (B), mid- (M), and apex area (A).
Tissue content of P (Figure 3.6) varied significantly between I-SL and D-SL group. The content was highest in the B area in April for both groups (p<0.05), indicating prioritized accumulation of nutrients in the meristematic tissue to facilitate growth in young individuals. This support phosphorus being an element important for physiological functions involved in growth (Hurd et al., 2014). The A and M area was significantly different (p<0.05) in the D-SL group but not for the I-SL group, indicating an effect of nutrient availability affecting internal biochemical composition. Overall, the magnitude of P content suggest that algae cultivation solely for recycling P is not recommended.
Biomass yields were significantly higher in the I-SL with a peak yield of 7.01±0.88 kgFWm−1 in June, supporting studies with increased biomass yield by cultivation near salmon farms ( Broch et al., 2013; Marinho et al., 2015). However, within the I-SL group the biomass yield was highest at the farm edge, decreasing further in-between salmon pens (Figure 3.5). Being an indication of other factors for instance limiting light and water movement patterns, which can affect seaweed growth (Klebert et al., 2013). This supports cultivation of seaweed closely downstream from salmon farms, to ensure the highest biomass yield. Further, biomass yield was promoted as a main factor for estimating the magnitude of bioremediation potential.
security (Desmidt et al., 2015; Cordell et al., 2009), and solutions are needed to shift the current phosphorus use into more sustainable forms (Cordell et al., 2009, 2011). The release of biological waste from finfish aquaculture along coast lines can have negative impacts on marine ecosystems (Jansen et al., 2018), as well as being a wasteful practice with limited resources like phosphorus. Recirculation of biological waste from aquaculture can be done by co-cultivating species like Saccharina latissima, in integrated multi-trophic aquaculture (IMTA) systems (Buschmann et al., 2001; Chopin et al., 2001; Ridler et al., 2007). This study characterizes storage of phosphorus in S. latissima and evaluates the recycling potential through the IMTA cultivation of this species.
A 4-month cultivation study was conducted by deploying vertical ropes (5 m) with S. latissima seedlings (Forbord et al., 2018) along a gradient within and downstream from a salmon farm. The ropes were grouped as integrated among pens (I-SL, -150 to 0 m), and downstream from farm edge (D-SL, 100 to 280 m), assuming different nutrient availability between groups from farm proximity. Biomass registration, water- and tissue samples were collected for the period and analyzed from samplings after 2 (April) and 4 (June) months. Tissue samples were analyzed for carbon (C) and nitrogen (N) (acetanilide as standard), and phosphorus (P) (Koroleff, 1976) content at three different areas of the seaweed to characterize internal distribution: basal- (B), mid- (M), and apex area (A).
Tissue content of P (Figure 3.6) varied significantly between I-SL and D-SL group. The content was highest in the B area in April for both groups (p<0.05), indicating prioritized accumulation of nutrients in the meristematic tissue to facilitate growth in young individuals. This support phosphorus being an element important for physiological functions involved in growth (Hurd et al., 2014). The A and M area was significantly different (p<0.05) in the D-SL group but not for the I-SL group, indicating an effect of nutrient availability affecting internal biochemical composition. Overall, the magnitude of P content suggest that algae cultivation solely for recycling P is not recommended.
Biomass yields were significantly higher in the I-SL with a peak yield of 7.01±0.88 kgFWm−1 in June, supporting studies with increased biomass yield by cultivation near salmon farms ( Broch et al., 2013; Marinho et al., 2015). However, within the I-SL group the biomass yield was highest at the farm edge, decreasing further in-between salmon pens (Figure 3.5). Being an indication of other factors for instance limiting light and water movement patterns, which can affect seaweed growth (Klebert et al., 2013). This supports cultivation of seaweed closely downstream from salmon farms, to ensure the highest biomass yield. Further, biomass yield was promoted as a main factor for estimating the magnitude of bioremediation potential.
