Population dynamics of the invasive Pacific oyster Crassostrea gigas during the early stages of an outbreak in the Wadden Sea (Germany)

Table 1 Spatial extent of all investigated mussel beds, with mean abundance ± SE and maximum abundance of Pacific oyster in 2003, 2004 and 2005

Mussel bed	Mussel bed area 2003 [ha]	Crassostrea gigas (ind./m²)			Significant change of the abundance
		2003	2004	2005
		Mean ± SE	Mean ± SE	Mean ± SE
#1	3.13	11.11 ± 2.65	55.40 ± 12.05	150.56 ± 25.71	a, b, c
#2	22.83	42.44 ± 5.34	136.24 ± 14.90	302.04 ± 40.96	a, b, c
#3	37.09	13.32 ± 1.92	70.92 ± 8.92	107.97 ± 16.12	a, b, c
#4	7.67	0.41 ± 0.08	0.83 ± 0.27	0.23 ± 0.12	a, c
#5	18.98	1.47 ± 0.25	4.22 ± 1.02	10.73 ± 3.24	a, b, c
#6	11.09	0.96 ± 0.21	7.99 ± 1.05	93.80 ± 21.16	a, b, c
#7	28.54	1.59 ± 0.31	3.91 ± 0.94	77.36 ± 19.94	a, b, c
#8	48.85	0.01 ± 0.01	0.18 ± 0.18	2.42 ± 0.74	a, b, c
#9	28.69	0.12 ± 0.05	1.66 ± 1.66	6.47 ± 2.53	a, b, c
#10	6.77	0.09 ± 0.03	0.2 ± 0.05	0.62 ± 0.42	a, b, c
#11	14.21	0.04 ± 0.02	0.46 ± 0.11	27.85 ± 5.20	a, b, c
#12	6.51	0.91 ± 0.12	6.67 ± 0.85	205.56 ± 23.61	a, b, c
#13	14.15	0	0.03 ± 0.02	0.06 ± 0.04
#14	5.91	0.13 ± 0.03	0.67 ± 0.11	2.58 ± 0.67	a, b, c
#15	12.29	0.09 ± 0.03	1.42 ± 0.18	1.24 ± 0.16	a, b

Significant increase is shown (P ≤ 0.05): a = Friedman-test (all 3 years of investigation), b and c = Wilcoxon-test (b = 2003–2004) (c = 2004–2005). At mussel bed #4 the change between 2004 and 2005 was a significant decrease

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