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 110

Cage

16

A. regius

P2

14

Pellet food

Fresh food L

12

ZP

FP

L

10

H. forskalii

P3

PP

T

T

S

8

SP

6

P1

POM

Filter feeders

4

2

SOM

0

- 3- 2- 1- 0- 9- 8- 7- 6- 5- 4- 3

δ

13 C

Fig. 2. Mean δ 13 C and δ 15 N values of samples in the cage site in years 2008 (▲), 2009 (■) and
2010 (●). ZP: zooplankton; PP: phytoplankton; FP : Argyrosomus regius fish faeces; S: Sardina
pilchardus ; SP: Spicara smaris , T: Trachurus trachurus ; L: Loligo vulgaris ; P1: pellet 1; P2: pellet
2; P3: pellet 3; POM: particulate organic matter and SOM: sedimentary organic matter. Filter
feeders include Chlamys varia (grey symbol) and Mytilus galloprovincialis (white symbol).
Sardina pilchardus , Spicara smaris , Trachurus trachurus and Loligo vulgaris are classified as fresh
food.

Throughout the sampling period, Argyrosomus regius' carbon isotopic signature was, on
average, -19.06 ± 0.64 ‰, (ranging between -18.72 ‰ to -19.77 ‰), while for nitrogen it was,
on average, 11.45 ± 1.12 ‰, (ranging between 10.24 ‰ to 12.83 ‰). Concerning the isotopic-
step enrichment, the value of fish faeces was 13 C - depleted compared to the muscle isotopic
signature, with a mean decrease of 1.61 ± 0.55 ‰. For 15 N, the depletion was more
pronounced, with a mean decrease of 3.34 ± 1.34 ‰.

Regarding the phytoplankton fraction, in the three years of study, phytoplankton from cage
site exhibited similar values of δ 13 C and δ 15 N, with mean values of -14.54 ± 0.29 ‰ and 7.70
± 0.22 ‰, respectively. Values in control sites showed little variability, with mean values of -
15.04 ± 0.41 ‰ and 7.10 ± 1.06 ‰ for δ 13 C and δ 15 N in control 1; and -19.44 ± 0.44 ‰ and 5.25
± 1.25 ‰ for δ 13 C and δ 15 N in control 2, respectively. For zooplankton, mean values in cage
site were -21.13 ± 1.27 ‰ for δ 13 C and 8.06 ± 0.91 ‰ for δ 15 N. Values from control 1 showed
more variability; with mean values of -18.49 ± 3.56 ‰ for δ 13 C and 7.97 ± 0.91‰ for δ 15 N,
while in control 2 values were of -17.39 ± 0.37 ‰ and 5.91 ± 1.30 ‰ for δ 13 C and δ 15 N,
respectively. Comparing δ 13 C and δ 15 N values from cage site relative to control sites,
phytoplankton from cage site showed a slightly enrichment in 13 C relative to control 1, on
average 0.59 ‰; differences were more pronounced relative to control 2, with an average