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 117

highest in spring 2009 (29.39 %). Especially remarkable is the low contribution of
phytoplankton, with values from 0.06 % in summer 2009 to 5.27 % in summer 2008.

Similarly, pellet food was the main food source for Mytilus galloprovincialis, with a mean
contribution of 57.95 %, followed by fresh food (21.46 %), fish faeces (8.90 %), POM (7.84 %)
and phytoplankton (3.83 %). Contributions also varied seasonally and annually, but again
aquaculture derived products remained the main food sources in the three years of study,
with mean values varying from 82.79 % in spring 2009 to 97.7 % in spring 2008. Contrary to
Chlamys varia, pellet food contribution was higher in spring and decreased in summer and
autumn (Figure 11). Regarding the different commercial pellet food, similar to Chlamys varia
pellet 1 was the main contributor, especially in spring 2008 were it represented up to 82 % of
the total isotopic composition. Sardina pilchardus and Spicara smaris were the main sources
among the fresh food supplied in fish cages. POM showed a lower contribution in the
isotopic composition of Mytilus galloprovincialis than in Chlamys varia , with values ranging
between 1.85 % in spring 2008 to 14.79 % in spring 2009. Contribution of phytoplankton was
slightly higher than in Chlamys varia , with values between 0.87 % in spring 2008 to nearly
17.50 % in autumn 2009.

Mytilus galloprovincialis

100

90

80

70

60

Phytoplankton
Fish faeces
POM
Fresh food
Pellet food

50

40

30

20

10

0

Spring Summer Spring Summer Autumn Spring Summer Autumn

2008 2009 2010

Fig. 11. Seasonal and annual variability of the feasible contribution of the main organic
matter sources to the diet of Mytilus galloprovincialis cultured in fish cages calculated by
Bayesian mixing models.

The mean feasible contribution of organic matter sources in sedimentivorous Holothuria
forskalii was also analysed to study whereas there was an influence of organic enrichment in
the benthic population (Figure 12). According to Bayesian mixing model, POM was the
main food source, with a mean contribution of 48.56 % in the years of study. Contribution of
aquaculture derived products as pellet and fresh food, and fish faeces was remarkable, with
a 28.11 %. Bayesian mixing model was also applied to POM to elucidate its composition,
with nearly the 50% of its isotopic signature coming from phytoplankton (Figure 13). The
contribution of aquaculture derived products was also remarkable, with nearly 30 %.