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2 Theoretical Framework

2.2 Investigated Food Chain

It has been documented that over 180 species ingest plastic debris such as plastic fragments. The potential for ingestion and accumulation of smaller plastic pieces is far greater than with larger pieces because they are to be taken up by the smaller fish, as such they are able to accumulate up the food chain.

Concentrations of pollutants increase in the aquatic food chain. Phytoplankton, as primary producer plays a key role in transport of organic contaminants through food chains to the higher trophic levels. The primary consumer, as zooplankton for example copepods, plays an important ecological role in aquatic ecosystems by controlling the phytoplankton communities and by acting as a direct or indirect food source for higher trophic animals. The first step in the transfer of chemicals through the food chain is the bioaccumulation at lower trophic levels. High concentration in fish is partly a result of transfer throughout the food chain (Xinhong & Wang, 2005).

Figure 5 Pollutants in a Food web (Ivar do Sul & Costa, 2013)

Some toxic effects are chronic, less evident and act on a long time-scale such as

genotoxicity and reproductive failure. Anyhow they are considered as an important risk to the ecosystem. Bioaccumulation and the change in primary production at the bottom of the food chain have an effect on the concentration of organic matter throughout the whole system. If there is a higher bioavailability of contaminants in the primary producers it has an impact on the whole ecosystem. Environmental perturbation can alter dynamics and coastal structures substantially which can produce the occurrence of trophic cascade and with that the

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extinction of species. Sudden regime shifts and ecosystem collapses are likely to occur in stressed ecosystems, due to top-down (e.g. overfishing) versus bottom-up (e.g. increase of nutrition input that causes eutrophication) (Bacelar, Dueri, Hernandez-Garcia, & Zalddivar, 2008). As shown in figure 6 the representative food chain of the ecosystem in the area and season are S. viridensis, T. mediterraneus, B. boops and zooplankton in surface water.

Figure 6 Investigated Food Chain

Zooplankton

Figure 7 Zooplankton with Ingested Fluorescent Beads (Setälä, Fleming-Lehtinen, & Lehtiniemi, 2013)

The first species, in a traditional marine food web, is phytoplankton as the primary producer. It transfers organic carbon to higher trophic level such as zooplankton (Anjusha, et al., 2013). Zooplankton is a key component in the structure and correct functioning of a marine planktonic food web. It links planktonic primary production with the top pelagic consumer levels. In addition, it plays an important role in nutrient recycling within the water columns and exports particulate matter out of the photic-zone (Saiz, Calbet, Atienza, &

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Alcaraz, 2007). These species can act as an indicator of the heath of an ecosystem. (de Puelles, Alemany, & Jansa, 2007). The zooplankton community is dominated by

crustaceans and copepods (Anjusha, et al., 2013).

There has already been research carried out regarding microplastic presence in zooplankton.

One study showed ingestion of microplastic in various zooplankton communities (Figure 7) (Setälä et al., 2013) however it only identified microplastics which are flouresecent as figure 7 shows.

Boops boops

Figure 8 Boops Boops School (Archipelagos, Institute for Marine Conservation, 2013)

B. boops or Bogue is a fish of the family Sparidae. Characteristically it is 10-25 cm long, fusiform, oval body, big eyes, brownish lateral line and brown blotch on base of pectoral fin. (Archipelagos, Institute for Marine Conservation, 2013). It is a demersal fish, as well as semi-pelagic, species living on all types of bottom, such as sand, mud, rock and sea grass beds. Furthermore, Bogue can be found in a depth until 350 meters, but it is more abundant in the upper 100 meter and coastal waters. Further, it is found in schools (Figure 8). In the Mediterranean Sea it reproduces around April to May (Fisheries and Aquaculture

Department, 2015).

Figure 9 Global Capture Production for Species (Tonnes) (Fisheries and Aquaculture Department, 2015)

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Greece is one of the countries with the largest catch of this species. The global capture has been increasing within the last 60 years as the figure “Global Capture Production for species (tonnes)” shows (Figure 9). B. boops is caught on line gear, with bottom trawls and purse seines but also with beach seins and trammel nets (Fisheries and Aquaculture Department, 2015).

Trachurus mediterraneus

T. mediterraneus or Mediterranean horse mackerel (Figure 10) is a benthopelagic pisivores (Food and Agriculture Organization of the United Nations, 2015) that preys mainly on fish (Cresson, Ruitton, Ourgaud, & Harmelin-Vivien, 2013). It can be found in the Eastern Atlantic and Mediterranean Sea. Also, it mainly occurs in deeper waters of 5 to 250 m, but also in surface waters (Food and Agriculture Organization of the United Nations, 2015).

Figure 10 T. mediterraneus School (Horst, 2012)

Its characteristics are an elongate and fairly compressed body with a large head. Commonly it has a length of 10 to 30 cm. The upper part of the body and top of head are dusky to near black, or grey to bluish green. The lower two thirds of body and head are usually paler, whitish to silvery. The caudal fin is yellowish (Food and Agriculture Organization of the United Nations, 2015).

The Mediterranean horse mackerel migrates in large schools and often shoals with other Trachurus species as T. trachurus or T. picturatus (Food and Agriculture Organization of the United Nations, 2015). T. mediterraneus preys on B. boops, Phycis phycis, Phycis

blennoides, Scopraena porcus, Conger conger and Sepiola sp. (Santic, Jardas, & Pallaora, 2003). As the figure below shows, the peak catch production of this species was in the 80s after European fish stock legislation was introduced in the 1970’s (European Commission, 2015). Nowadays, it is lower, but more or less a steady amount of catches (Figure 11)

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Figure 11 Global Capture Production for Species (Tonnes) (Food and Agriculture Organization of the United Nations, 2015)

Sphyraena viridensis

S. viridensis or yellowmouth barracuda (Figure 12) is one of the most common coastal pelagic predators in the Mediterranean Sea and northeast Atlantic. The geographical range of this species might be wider because it is often confused with S. Sphyraena (Perdro Barreiros, Serrao Santos, & de Borba, 2002).

Figure 12 S. Viridensis School (Koszorek, 2013)

Characteristically the yellowmouth barracuda has a slender fusiform body with conical, hydrodynamical snout. It has a long mouth with low protractile capacity and with a prognatic lower jaw which contains two rows of long canine-like teeth. One characteristic that allows differentiation from S. Sphyraena is the absence of a scale on the preopercullum (Perdro Barreiros et al., 2002). S. viridensis has a darkish grey to bluish dorsally and silvery ventrally body. The upper half has numerous vertical dark bands that extend below the lateral line in the anterior part of the flanks. A juvenile individual of this species is more greenish to dark yellow (Perdro Barreiros et al. , 2002).

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It can be found in schools of larger than 10, small groups of less than 10, pairs or isolated individuals.The most important prey for S. viridensis is Carangidae species which vary in different regions. For example Trachurus picturatus near the Azores (Perdro Barreiros et al., 2002) and Trachurus mediterraneus in the Aegean Sea. Furthermore, it preys on Boops boops, Sardine pilcharduy, Mullus surmuletus, Chromis chromis, Diplodus annularis, Sparisoma cretende, Sepia officinalis, Atherina boyeri and Spica smaris in the Aegean Sea (Kalogirou, Mittermayer, Pihl, & Wennhage, 2012).

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3 Materials and Methodology