Table 2 Comparison of trematode species richness and diversity of the analyzed component communities in the 2010s and earlier time periods, using the Sørensen similarity index and Shannon diversity t-test

Compared time periods

1963–2000 vs. 2011–2020

1991–2000 vs. 2011–2020

1963–1990 vs. 2011–2020

1981–1990 vs. 2019–2020

1991–2000 vs. 2011–2020

1963–1980 vs. 1981–2020

Shannon diversity t-test (t; df; P)

16.0; 1663.6; < 0.001

−0.4; 74.6; 0.72

5.9; 514.0; < 0.001

3.1; 43.5; 0.003

−2.0; 16.6; 0.07

N/A (Σ_n2 = 0)

Sørensen similarity index

0.545

0.600

0.400

0.800

1.000

0.000

Number of trematode species found in both study periods

3

3

1

2

2

0

Number of trematode species found only in the first study period

3

2

3

1

0

8

Number of trematode species found only in the last study period

2

2

0

0

0

0

Number of host individuals examined (first/last study period)

35/66

58/85

45/76

39/41

211/515

16/33

Number of trematode individuals found (first/last study period)

3690/1046

154/47

514/14

678/37

16/31

179/0

Number of trematode species found (first/last study period)

6/5

5/5

4/1

3/2

2/2

8/0

Intensity of infection (first/last study period)

113.1/15.9

2.7/0.6

11.4/0.2

17.4/0.9

0.08/0.06

11.2/0.00

Chao-1 (first/last study period)

6.0 ± 0.5/6.0 ± 2.2

6.0 ± 2.2/5.5 ± 1.3

5.0 ± 2.2/1.0 ± 0.0

1.0 ± 0.0/2.0 ± 0.0

2.0 ± 0.3/2.0 ± 0.0

8.5 ± 1.3/N/A (0)