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 112

enrichment of 4.38 ‰. For δ 15 N values, phytoplankton from cage site, was enriched on
average a 1.35 ‰ relative to control 1 and 1.56 ‰ relative to control 2. The same pattern
existed for zooplankton, with an average enrichment of 2.63 ‰ and 3.73 ‰ in 13 C relative to
control 1 and control 2, respectively; while for nitrogen, the enrichment relative to control 1
and control 2 was on average, 0.09 ‰ and 2.15 ‰, respectively.

Particulate organic matter (POM) from cage site showed mean values of -15.98 ± 1.43 ‰ and
3.78 ± 2.06 ‰ for δ 13 C and δ 15 N, showing an enrichment in 13 C and 15 N relative to control 1
and control 2, with average values of 1.93 ‰ and 0.62 ‰ in 13 C and 0.62 ‰ and 1.10 ‰ in
15 N, respectively. As in phytoplankton and zooplankton, differences were more pronounced
when comparing cage site with the distant control site, control 2. On the contrary, δ 13 C and
δ 15 N sedimentary organic matter (SOM) values from cage site and control 1 were relatively
similar, with mean values of -17.13 ‰ and 2.04 ‰ for δ 13 C and δ 15 N in cage site and -17.04
‰ and 3.34 ‰ for δ 13 C and δ 15 N in control 1. Relative to control 2, cage site was enriched in
13 C a 0.67 ‰ while for 15 N the enrichment was only 0.06 ‰

Sedimentivorous echinoderm Holothuria forskkalii showed mean values of -13.95 ± 0.28 ‰
and 7.77 ± 0.56 ‰ for δ 13 C and δ 15 N, respectively in cage site. Average values in control 1
were -14.10 ± 0.64 ‰ and 7.04 ± 0.27 ‰ for δ 13 C and δ 15 N, respectively and in control 2 of -
13.19 ± 0.62 ‰ and of 4.82 ± 0.65 ‰ for δ 13 C and δ 15 N, respectively. Comparing cage site
with control sites, an enrichment of 0.79 ‰ in 13 C relative to control 2 was observed, while
control 1 values were depleted in a 0.15 ‰ for 13 C. For 15 N, it was observed an enrichment of
0.73 ‰ and 2.93 ‰ relative to control 1 and 2, respectively.

3.1.2 Filter feeder bivalves and temporal variability in isotopic signals among
treatments

Filter feeders bivalves collected in the cage site exhibited similar isotopic values, ranging
from -20.73 ‰ to -20.90 ‰ for 13 C and 6.26 ‰ to 6.36 ‰ for 15 N in Mytilus galloprovincialis ,
and between -19.41 ‰ to -19.76 ‰ for 13 C and 7.33 ‰ to 7.64 ‰ for 15 N in Chlamys varia.
Statistical analyses showed significant differences between cage and control treatments in
the three years of study with filter feeder bivalves from fish cages enriched in both 13 C and
15 N (PERMANOVA, p<0.05) (Table 2 and 3). Mytilus galloprovincialis of cage site showed an

δ 13 C δ 15 N

Source of variation df SS MS Pseudo-F df SS MS Pseudo-F

Tr 2 18 .07 9 .0352 20 .743* 2 17 .327 8 .6634 19 .53*

Ye 2 10 .524 5 .2618 12 .08* 2 2 .1712 1 .0856 2 .44

Se(Ye) 4 17 .003 4 .2509 9 .75* 4 31 .434 7 .8584 17 .72*

TrxYe 1 1 .6363 1 .6363 3 .75 1 8 .6544 8 .6544 19 .51*

TrxSe(Ye) 1 3 .9901 3 .9901 9 .16* 1 0 .47796 0 .47796 1 .078

Res 107 46 .607 0 .43558 107 47 .442 0 .44338

Total 117 93 .894 117 135 .58

Table 2. 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 Mytilus galloprovincialis 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