Integrated Multitrophic Aquaculture: Filter Feeders Bivalves as Efficient Reducers of Wastes Derived from Coastal Aquaculture Assessed with Stable Isotope Analyses - Aquaculture and the Environment: A Shared Destiny - page 113

δ 13 C δ 15 N
Sources of variation df SS MS Pseudo-F df SS MS Pseudo-F
Tr 2 17 .403 8 .7017 16 .71* 2 22 .21 11 .105 37 .24*
Ye 2 29 .116 14 .558 27 .97* 2 2 .8058 1 .4029 4 .70*
Se(Ye) 4 24 .883 6 .2208 11 .95* 4 40 .425 10 .106 33 .89*
TrxYe 0 0 No test 0 0 No test
TrxSe(Ye) 1 0 .099525 0 .099525 0 .19 1 1 .0493 1 .0493 3 .51
Res 83 43 .2 0 .52048 83 24 .745 0 .29814
Total 92 88 .919 92 92 .935
Table 3. Results of the 3-way PERMANOVA, mixed design, with “Treatment" (Tr), “Year”
(Ye) and "Season"(Se) “as fixed factors. The analysis is based on the modified Euclidean
distance dissimilarity of the Chlamys varia isotopic signatures of δ 13 C and δ 15 N (999
permutations). The studied factors were 3 treatments (cage, control 1 and control 2), three
years (2008, 2009 and 2010) and three seasons (spring, summer and autumn). *p<0.05
enrichment of 0.52 ‰ in 13 C and 0.75 ‰ in 15 N compared to bivalves from control 1; greatest
differences were found when comparing cage site with control 2, with an enrichment of 0.75
‰ in 13 C and 1.69 ‰ in 15 N (p<0.05) (Figure 5 and 6). Chlamys varia from cage site showed a
large amount of enrichment compared to control 2, 1.11 ‰ and 1.71 ‰ in 13 C and 15 N,
respectively (Figure 7 and 8).
3.2 Contribution of organic and inorganic matter sources to different consumers of
the multitrophic system
According to the bayesian mixing model, the main food source for the fish Argyrosomus
regius was pellet food, with a mean global contribution of 80.43 % (from pellet 1, 2 and 3),
while the remaining 19.57 % corresponded to fresh food. Contributions varied annually, 67.7
%, 91.53 % and 82 % for pellet food and 32.3 %, 8.5 % and 18 % for fresh food in years 2008,
2009 and 2010, respectively (Figure 9). In the first year of study, pellet 1 was the main pellet
food source, while Sardina pilchardus and Spicara smaris were the main fresh food sources;
the main pellet food source changed to be pellet 2 the following year, while in 2010 the main
source was again pellet 1; Sardina pilchardus and Spicara smaris remained the main fresh food
sources along the remaining years of study.
In filter feeder bivalve Chlamys varia , pellet food was the main food source, with a mean
contribution of up to 62.68 % of their isotopic composition in the three years of study, followed
by fresh food, POM, fish faeces and phytoplankton, with a mean contribution of 18.28 %, 11.26
%, 5.18 % and 2.58 %, respectively. Contributions of the five organic matter sources varied
both seasonally and annually (Figure 10), however, aquaculture derived products, as pellet
and fresh food and fish faeces remained the main food sources along the three years of study
varying from 70.03 % in spring 2009 to the maximum of 93.81 % in autumn 2010. Regarding
the seasonal variation, there was a fluctuation in the contribution of pellet food, with a
medium contribution in spring, fewer in summer and a higher contribution in autumn.
Summer 2009 showed a different pattern with a contribution of 81.74 % of pellet food.
Regarding pellet food sources, pellet 1 was the main source in the three years of study, with a
contribution fluctuating between 18.72 % and 81.74 %, while for fresh food the main
contribution was from Sardina pilchardu s and Spicara smaris . Particulate organic matter (POM)
also showed variation, with the lowest contribution in autumn 2009 (4.24 %) and the