2.1 Sustainable Aquaculture
The development of sustainable aquaculture is aimed at insuring that commercial
aquaculture has minimal adverse effects on the environment. One way to achieve
this goal is through the development of improved methods of waste management
for land based, coastal and offshore aquaculture by combining extractive and fed
aquaculture, also referred to as integrated multi-trophic aquaculture (IMTA)
systems.
Fish excrete nitrogen (N), phosphorus (P) and carbon (C) (Beveridge 1987;
Mugg et al. 2000; Neori et al. 2004, 2007; Corey et al. 2014). Nearly 50 kg N and
7 kg P can be released per ton of finfish produced per year (Chopin et al. 1999;
Kautsky et al. 1999; Troell et al. 2003; Kim et al. 2013). In coastal waters, high
levels of these nutrients can trigger harmful microalgal blooms (red tides) and
contribute to excessive growth of nuisance or opportunistic macroalgae (green and
brown tides), which in turn have negative consequences on coastal ecosystems and
economies. These nutrients could instead be used to support the growth of economically important seaweeds, which would compete for nutrients with nuisance
species, especially in nearshore coastal environments, hence mitigating these
potentially adverse environmental impacts (Neori et al. 2004, 2007; Chopin et al.
2008; Pereira and Yarish 2008; Abreu et al. 2009, 2011b; Buschamnn et al. 2008;
Corey et al. 2012, 2014; Kim et al. 2013, 2014a, 2015a). Seaweeds take up N, P
and C, which they use for growth and production of proteins and energy storage
products (mostly carbohydrates). When seaweeds are harvested from IMTA or
nutrient bio-extraction systems, the nutrients are also removed from the environment. Seaweeds can then be used on for bio-based, high-valued compounds for
human consumption, protein sources in finfish aquaculture diets, sources of phycocolloids, cosmeceuticals, nutraceuticals and other biochemicals, and for
low-value commodity energy compounds such as biofuels, biodiesels, biogases and
bioalcohols (Horn et al. 2000; Smit 2004; Chopin et al. 2011; Cornish and Garbary
2010; Gellenbeck 2012; Kim 2011).
Integration of shellfish with cage culture of fish can also help to reduce the risk
of eutrophication since the particulate organic matter (POM) produced by fish
(wasted feed and faeces) and the increased plankton production serve as excellent
feed and are filtered out by these organisms. Faster growth (between 30 and 40%
greater) of bivalves near fish cages has been reported with contributions of fish feed
and fish faeces varying between 5–28% and 4–35%, respectively (Wallace 1980;
Jones and Iwama 1991; Stirling and Okomus 1995; Buschmann et al. 2000;
Lefebvre et al. 2000; Lander et al. 2004; Peharda et al. 2007; Chopin et al. 2008;
Sara et al. 2009; Handå et al. 2012; Jiang et al. 2013; Dong et al. 2013). Other
studies, however, did not observe a difference in growth near fish cages (Mazzola
and Sara 2001; Navarrete-Mier et al. 2010). Several explanations for these contradicting results have been given by e.g. Troell and Norberg (1998), Troell et al.
(2011), Handå (2012) and Reid et al. (2013): (1) the POM generated by the fish
culture doesn’t increase the seston concentration significantly due to dilution;
24
B.H. Buck et al.
The development of sustainable aquaculture is aimed at insuring that commercial
aquaculture has minimal adverse effects on the environment. One way to achieve
this goal is through the development of improved methods of waste management
for land based, coastal and offshore aquaculture by combining extractive and fed
aquaculture, also referred to as integrated multi-trophic aquaculture (IMTA)
systems.
Fish excrete nitrogen (N), phosphorus (P) and carbon (C) (Beveridge 1987;
Mugg et al. 2000; Neori et al. 2004, 2007; Corey et al. 2014). Nearly 50 kg N and
7 kg P can be released per ton of finfish produced per year (Chopin et al. 1999;
Kautsky et al. 1999; Troell et al. 2003; Kim et al. 2013). In coastal waters, high
levels of these nutrients can trigger harmful microalgal blooms (red tides) and
contribute to excessive growth of nuisance or opportunistic macroalgae (green and
brown tides), which in turn have negative consequences on coastal ecosystems and
economies. These nutrients could instead be used to support the growth of economically important seaweeds, which would compete for nutrients with nuisance
species, especially in nearshore coastal environments, hence mitigating these
potentially adverse environmental impacts (Neori et al. 2004, 2007; Chopin et al.
2008; Pereira and Yarish 2008; Abreu et al. 2009, 2011b; Buschamnn et al. 2008;
Corey et al. 2012, 2014; Kim et al. 2013, 2014a, 2015a). Seaweeds take up N, P
and C, which they use for growth and production of proteins and energy storage
products (mostly carbohydrates). When seaweeds are harvested from IMTA or
nutrient bio-extraction systems, the nutrients are also removed from the environment. Seaweeds can then be used on for bio-based, high-valued compounds for
human consumption, protein sources in finfish aquaculture diets, sources of phycocolloids, cosmeceuticals, nutraceuticals and other biochemicals, and for
low-value commodity energy compounds such as biofuels, biodiesels, biogases and
bioalcohols (Horn et al. 2000; Smit 2004; Chopin et al. 2011; Cornish and Garbary
2010; Gellenbeck 2012; Kim 2011).
Integration of shellfish with cage culture of fish can also help to reduce the risk
of eutrophication since the particulate organic matter (POM) produced by fish
(wasted feed and faeces) and the increased plankton production serve as excellent
feed and are filtered out by these organisms. Faster growth (between 30 and 40%
greater) of bivalves near fish cages has been reported with contributions of fish feed
and fish faeces varying between 5–28% and 4–35%, respectively (Wallace 1980;
Jones and Iwama 1991; Stirling and Okomus 1995; Buschmann et al. 2000;
Lefebvre et al. 2000; Lander et al. 2004; Peharda et al. 2007; Chopin et al. 2008;
Sara et al. 2009; Handå et al. 2012; Jiang et al. 2013; Dong et al. 2013). Other
studies, however, did not observe a difference in growth near fish cages (Mazzola
and Sara 2001; Navarrete-Mier et al. 2010). Several explanations for these contradicting results have been given by e.g. Troell and Norberg (1998), Troell et al.
(2011), Handå (2012) and Reid et al. (2013): (1) the POM generated by the fish
culture doesn’t increase the seston concentration significantly due to dilution;
24
B.H. Buck et al.