International Journal of Marine Science 2016, Vol.6, No.27, 1-22
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2.4 Data analysis
Statistical analyses were designed to assess the effect of the environmental variables and parameters that
contribute to ocean acidification on the abundance and diversity of fish species in the two fisheries, and which
species were being driven by those parameters. Species composition and abundance data and physico-chemical
data were captured in Microsoft excel 2010 prior to analysis. The Shapiro-Wilk test (Shapiro and Wilk, 1965) was
used to test for normality of data, and after data proved to be non-parametric from the test, the Kruskal-Wallis H
test was used to test for significant differences in relative abundance of species between seasons and fisheries,
using the XLSTAT 2012 computer software. Margalef, Pielou, Shannon-Weiner and Simpson diversity indices
were computed for fish data using the Diverse feature in Primer 6 software. A Principal Components Analysis
(PCA) was then conducted to identify parameters with greater influence on variations in terms of abundance and
diversity in the various sites using the RELATE and BVSTEP functions in Primer 6 software (Clarke and Warwick,
2001). All environmental data was log transformed and normalised (logx+1) to take care of all zeros, while fish
data was square root transformed in order to weight the contribution of common and rare species in the
non-parametric abundance data before analysis in the Primer 6 software. A canonical correspondence analysis
(CCA) using the CANOCO 4.5 software (ter Braak, 1986) for Windows was then conducted to ordinate the
principal variables identified from the PCA with the identified fish species.
Table 1: Mean (±standard deviation) values of physico-chemical parameters measured in the lean and peak seasons of both fisheries
in the year 2013
Physico-chemical parameters Sites/seasons
Teshie lean
Teshie peak
Tema lean
Tema peak
Salinity (ppt)
34.14±0.85
28.97±0.65
29.68±1.57
32.82±4.30
Temperature (
o
C)
28.03±0.57
26.14±2.03
26.73±1.72
23.14±1.26
Pressure (dbars)
7.63±1.60
6.07±1.65
83.90±52.75
53.34±5.04
Total alkalinity (µmol/kg)
1423.72±600.50
1182.27±72.11
2897.39±282.59
1655.17±570.42
pH
8.30±0.21
8.33±0.19
7.63±0.65
7.29±0.16
DIC (µmol/kg)
1001.94±484.11
895.93±58.14
2915.25±575.31
1663.52±572.42
pCO
2
(µatm)
72.44±30.56
98.00±48.27
511.69±526.42
1966.93±786.44
Aragonite saturation
4.43±1.72
2.60±0.94
1.59±1.10
0.51±0.26
Calcite saturation
6.67±2.60
3.99±1.43
2.44±1.69
0.78±0.40
Carbonate (µmol/kg)
333.52±18.73
157.48±55.93
133.07±38.00
31.95±16.17
Revelle factor
7.23±2.41
6.78±0.94
10.77±3.00
15.67±1.15
Nitrates (mg/l)
0.98±0.13
0.88±0.25
1.17±0.41
3.40±2.59
Phosphates (mg/l)
2.23±2.21
0.08±0.03
0.28±0.24
2.12±2.01
Sulphates (mg/l)
2050.00±176.78
5450.0±353.55
5400.00±0.00
6062.50±515.39
Silicates (mg/l)
9.73±8.03
2.23±1.96
4.90±0.64
22.78±19.23
Iron (mg/l)
0.12±0.08
0.11±0.00
0.20±0.07
0.23±0.12
Calcium (mg/l)
143.00±6.61
139.67±3.62
134.17±5.80
388.75±29.55
Magnesium (mg/l)
1400.00±141.42
2500.00±100
2075.00±106.07
2233.33±152.75
