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 105

(De Niro & Epstein, 1978; McCutchan et al., 2003). Since the ratio of 12 C/ 13 C isotopes
changes little through the food web, this ratio is commonly used to distinguish between
carbon sources, typically C 3 or C 4 and pelagic or benthic. In contrast, consumers showed a
large amount of enrichment in nitrogen, thus, the 14 N/ 15 N ratio is commonly used to
estimate trophic positions. Integrated multitrophic aquaculture involves species with
different trophic strategies which can be positioned in the food web as a function of the
13 C and 15 N stable isotope signatures.
1.3 Objectives
To decipher whether integrated multitrophic aquaculture is an effective method for
minimizing and reducing waste inputs into the Mediterranean coastal ecosystem we have
designed a multitrophic integrated system involving filter feeders bivalves ( galloprovincialis
(Lamarck, 1819) and Chlamys varia (Linnaeus, 1758)), and fin fish Argyrosomus regius (Asso,
1801) . Through determination of carbon and nitrogen stable isotopes analyses to the several
organisms and trophic strategies, the following aims will be accomplished:
i. Define the isotopic composition of the trophic food web of integrated multitrophic
aquaculture in relation to two reference stations
ii. Study the temporal variability in waste matter fluxes at the different treatments, hence
annual and seasonal variability
iii. Calculate the relative contributions of wastes (fresh food, pellets, plankton) to the fish
farmed and to the filter feeders at the IMTA
2. Methods
2.1 Experimental design for IMTA
The study was conducted during years 2008, 2009 and 2010 at a research experimental
station (LIMIA), on the SW coast of Mallorca, in Andratx Bay (39º 32' 38.13” N, 2º 22' 51.08”
E) (Figure 1). The installations included 6 floating cages for fish reproductive stages in the
middle of the bay, with cultured Argyrosomus regius , with a total fish stock of 12-15 t year -1 .
Water depth ranged between 5 to 8 meters. Sediments surrounding fish cages were mostly
unvegetated, except for disperse patches of Caulerpa prolifera (Forsskal) J.V.Lamouroux, 1809
within tens of meters distance. Current velocity below fish cages varied between 0 to 10
cm/s, with higher prevalence of very low current speeds (0 to 5 cm/s) (own data). Feed
regime consisted in a combination of commercial dry pellets, CV4, Mar-9 vitalis repro and
Gemma (Trouw S.A), hereafter called pellet 1, pellet 2 and pellet 3, respectively; and fresh
food based on fishes Sardina pilchardus (Walbaum, 1792) (34.48 %), Spicara smaris (Linnaeus,
1758) (24.14 %), Trachurus trachurus (Linnaeus, 1758) (31.03 %) and squid Loligo vulgaris
Lamarck, 1798 (10.34 %) on average ten times per month, with 10kg supplied each time.
Two reference sites were selected to evaluate the effects of aquaculture wastes in the adjacent
environment. An external site (control 1) (39º 32' 29.37” N, 2º 22' 56.45” E) located
approximately 350 m away from the fish cages within the Andratx Bay, was selected to study
the influence of the natural variability in the bay. The second site, (control 2) was located 21
nautical miles away from fish cages (39º 28' 4” N, 2º 42' 53” E) in order to compare the isotopic
values of the different components of the food web without the fish farm influence.