4.1 Attempted Method Development to Dissolve Fish Stomachs
After conducting desk research into the different ways of dissolving fish stomachs, three options became apparent. The first possible method to dissolve the organic tissue is with a sodium hydroxide solution. In February, the first method was tried with a 1 and 2 M sodium hydroxide solution using hydroxide as an reaction agent. The stomach was not dissolved within a week in either of the two solutions. A reason for that might have been the low molarities or temperature. A second trial was carried out at a higher temperature of 25
°C, room temperature in an incubator. The results were the same (see Appendix 1). After contacting some researchers who had already experimented with this method, it was advised to try it at 60 °C or with a potassium hydroxide solution. Some studies used alkaline solution method and showed that optimal alkaline digestion protocol is 1 and 2 M NaOH which digest a sample by 90.0 ± 2.9% and 85.0 ± 5.0%, whereas 10 M NaOH has a digestion efficacy of 91.3 ± 0.4 % (Cole, et al., 2014). As a laboratory hood is not available, neither trying out the sodium hydroxide method at a temperature of 60°C nor changing the concentration nor the potassium hydroxide method are options for this research.
To continue, two more methods were tested: dissolving the fish stomach with coca cola, with phosphoric acid as the active ingredient; and baking soda solutions, also called sodium hydrogen carbonate solution, at a temperature of 25°C in the incubator. The results showed that the baking soda solution dissolved the stomach better than the coca cola, with which the stomach just expanded in size. The same method was tested at a temperature of 41°C and again the baking soda solution dissolved more. To hasten the process, the sodium hydrogen carbonate solution was heated up and stirred for about three hours. The fish stomach
dissolved quite well with this procedure (see Appendix 1).
4.2 Microplastic Fibres in Surface Water
Microplastic fibres have been found in all of the investigated transects and ranged from 5 to 16 fibres see table. This table refers to the five surface water samples taken (Z. 1-5) and describes the total number of microplastic fibres present. An average of the sample set was taken as well as a standard deviation.
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Table 1 Microplastic Fibres Present in the Surface Water
Sample
Filtered
Volumen (m3) Total Fibres
Total Fibres per 1000 m3
Z. 1 18.30 5.00 273
Z. 2 16.11 13.00 807
Z. 3 14.22 5.00 352
Z. 4 18.61 16.00 860
Z. 5 17.30 9.00 520
Average 16.91 9.60 568
The Appendix 3 “Surface Water Microplastic Fibres Presence” shows that black, blue and transparent fibres were present in all of the samples showing that black fibres are the highest in number.
The average amount of microplastic fibres per 1000 m3 present in the surface water is 568±
264 with an average filtered volume of 16,91±1,79 (see Appendix 12 “Surface Water Sample Standard Deviation” and graph below).
4.3 Microplastic Fibres in Boops boops
For the second trophic level the table below shows the results of microplastic
presence in the representative species Bogue. B. boops stomachs showed microplastic in all of the investigated specimens. The amount of microplastic fibres ranges from 12 to 20 as the table below shows.
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Table 2 Microplastic Fibres Present in B. boops
Sample
The colouration of fibres differs between black, blue, red, transparent, green and others. In number, black and transparent are the most abundant with 26 and 24 (see Appendix 5 “B.
boops Microplastic Fibres Presence”). The average weight is 76 ± 7.4, the average length is 19,4 ± 0.8 and average number of fibres is15,4 ± 3,2 in this species (see Appendix 13,15 and 17). The average fibres per weight are 204 ± 49,9 and fibres per length are 79 ± 16,9 (see Appendix 14 and 16).
4.4 Microplastic Fibres in Trachurus mediterraneus
T. mediterraneus represents the third trophic level of the investigation. The analysis of the T. mediterraneus stomachs showed presence of microplastic ranging from 14 to 62 pieces (see table below).
Table 3 Microplastic Fibres in T. mediterraneus
Sample Weight Length Total Fibres
Fibres per
The fibre colouration within these individuals ranges from blue most numerous, black second highest to yellow with the lowest as shown in the Appendix 7 “T. mediterraneus Microplastic Fibres Presence”. The first individual had the most fibres present. The four other specimens have one third the number of fibres than the first (see table above). The average weight is
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175,4 ± 43,9, the average length is 27 ± 3,1 and average number of fibres is 28 ± 19,5 (see Appendix 13,15 and 17). The average fibres per weight are 157 ± 173,1 and fibres per length 101 ± 86,2 (see Appendix 14 and 16).
4.5 Microplastic Fibres in Sphyraena viridensis
The S. viridensis stomach all contained micro fibres and the amount of fibres range from 23 to 75 (see table below).
Table 4 Microplastic Fibers Present in S. viridensis
Sample Weight Length
Total Microplastic
Fibres per Length (m)
Fibres per Weight (kg)
S.v. 1 229 37 35 95 153
S.v. 2 1750 74 75 101 43
S.v. 3 656 56 48 86 73
S.v. 4 390 53 23 43 59
S.v. 5 819 62 30 48 37
Average 769 56 42 75 55
All kinds of fibre colours are present in the investigated species. The highest amount of microplastic was found in the second individual. It also contains the highest amount of black and transparent fibres see Appendix 9 S. viridensis Microplastic Fibres Presence. The average amount of fibres in this species is 769 ± 594,3 weight, 56 ± 13,5 of length and 42 ± 20,5of total fibres. The average fibres per weight are 55 ± 46,9 and fibres per length 75 ± 26,9.
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4.6 Overall Food Chain
Figure 19 Correlation Length And Number of Fibres
Figure 21 Correlation Weight and Number of Fibres
Comparing weight and length of the average species in the food chain shows that there is a positive correlation between weight or length and the number of fibres due to the correlation coefficient (R) being high (almost 1) in both cases. The fibres per weight and weight show a negative correlation. Contrary to that the fibres per length and specimen length show little correlation due to the correlation coefficient being low (see Figure 20). The graphs above show also that the number of fibres is higher whenever fish are heavier or taller. Conversely the ratio of fibres to length/ weight is greater in smaller fish. This correlation implies that the hypothesis of this investigation, that consumption per gram of lower trophic level fish is more harmful than of higher levels is correct.
y = 1.2292x0.8901
Fibres per Length (m)
Length (cm)
Fibres per Length
Figure 18 Correlation Length and Fibres perLength
y = 2765x-0.582
Figure 20 Correlation Weight and Fibres per Weight
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