The functional unit is the basis of comparison in
comparative LCAs. The functional unit follows the goal
of the study, since different goals may require different
functional units. The goal of the study and the associated
functional unit partially defines the system boundary of
the inventory. For example, if frozen fillets in supermarkets
are chosen as a functional unit, the system boundary needs to
be defined so as to include processing, transportation, and
distribution. The functional unit may, moreover, significantly
influence comparative LCAs involving different species,
since the edible portions and nutritional values of products
can differ by an order of magnitude (Roy et al. 2009). Mussels
and shrimp, for example, provide respectively, 13.6 and
140 kg of protein per ton of whole animals harvested
(Mungkung 2005; Iribarren et al. 2010; www.nutraqua.com
accessed 23-June-2010)