234 P
. Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
occasions and averaged to get a measure of the overall initial variability. The results from the simulated transplantations were analysed using SPSS.
3. Results
3.1. Visualisation and analytical testing of mesocosm performance Macrofauna raw data are initially presented to get a rough picture about the absolute
differences between the studied groups Table 1: mesocosm abundance data Table 1a, mesocosm biomass data Table 1b, field abundance data Table 1c and field biomass
data Table 1d. NMDS-ordinations of Fucus macrofauna abundance Fig. 1 and biomass data Fig. 2 using the five to six subsamples available from all nine control
mesocosms labelled with the letters A–I all 4 years, demonstrate that parallel mesocosms are fairly different the degree of replicability is poor. One-way ANOSIM
tests based on the same similarity matrices and with subsamples used as replicates confirm that these differences are statistically significant before correcting for multiple
testing all 4 years for both abundance and biomass data Table 2.
From the figures Figs. 1 and 2 it is also obvious that there are differences among different years, since 1989 mesocosm samples are almost exclusively found in the lower
middle or at the bottom, 1990 samples to the upper left, 1991 samples more or less in the middle, whereas 1992 samples may be found most to the right of the two ordination
maps. The suspected differences among years could be confirmed for both abundance and biomass data with a two-way nested ANOSIM using the mesocosms as replicates
with subsamples nested in the analysis. The uncorrected probability values P-values for global tests of equal community structure among years are 0.030 for abundance and
0.019 for biomass data Table 3.
Presentations of the initial start communities and the mesocosm and field mother system communities in November in the same NMDS-ordinations demonstrate that the
mesocosms have diverged considerably not only from each other poor replicability and poor repeatability but also from the field during the experimental periods both
considering abundance Fig. 3 and biomass data Fig. 4. In these figures a poor replicability is shown by the angles and different lengths of the arrows connecting the
mesocosms with the respective original start community transplantation data from field samples in early summer. A poor repeatability is visualised by the different characteris-
tics of the three ‘arrow complexes’ with 1990 to the left, 1991 in the middle and 1992 to the right. A poor ecological realism is finally indicated by the ‘mesocosm’ and ‘field’
arrows spreading out in almost all directions, although they are originating from a theoretically similar community structure each year at the start of experiments. When
just mesocosm samples from November and pooled November field samples are presented in the same NMDS-ordination, the actual dissimilarities between mesocosms
and the field become even more evident for both abundance Fig. 5 and biomass data Fig. 6. These differences in community structure are established as statistically
significant, with uncorrected P-values at 0.009 for both abundance and biomass data, using two-way crossed ANOSIM Table 4.
P . Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
235 Table 1
Distribution of macrofauna in samples from control mesocosms and the field 1989–1992 values per 100 g Fucus DWT: a abundance in mesocosms, b biomass g WWT in mesocosms, c abundance in the field,
d biomass g WWT in the field
a Abundance in mesocosms A
B C
D E
F G
H I
Cerastoderma 0.46
3.89 0.11
0.45 –
16.19 4.37
150.38 2.93
Gammarus spp. 65.46
8.85 8.41
10.50 6.96
9.02 3.49
6.54 9.81
Gasterosteus –
0.83 0.24
0.26 –
– –
0.52 –
Idotea spp. 51.86
8.30 4.55
2.35 0.90
37.77 2.20
6.10 0.69
Lymnaea spp. 6.18
0.38 1.43
– –
24.28 6.04
70.32 33.30
Mytilus 22.05
42.17 32.06
33.79 65.70
80.47 91.51
184.77 205.35
Palaemon 0.46
0.22 0.23
0.77 –
– 0.20
– 0.46
Theodoxus 200.49
230.64 464.05
387.55 171.83
277.13 383.00
209.47 210.81
Total 346.96
295.28 511.08
435.67 245.39
444.86 490.81
628.10 463.35
b Biomass in mesocosms A
B C
D E
F G
H I
Cerastoderma 0.092
0.118 0.014
0.057 –
0.529 0.358
3.101 0.149
Gammarus spp. 3.846
0.379 0.511
0.804 0.435
0.460 0.258
0.260 0.748
Gasterosteus –
0.231 0.051
0.083 –
– –
0.076 –
Idotea spp .
3.455 0.574
0.361 0.157
0.128 2.205
0.065 0.146
0.061 Lymnaea spp.
1.531 0.128
0.070 –
– 1.795
1.020 4.078
5.902 Mytilus
6.126 10.732
9.077 12.568
15.509 14.155
18.850 5.336
21.610 Palaemon
0.203 0.137
0.126 0.625
– –
0.294 –
0.356 Theodoxus
6.452 6.349
9.062 7.770
4.123 5.380
7.659 3.393
5.142 Total
21.706 18.648
19.272 22.063
20.194 24.523
28.504 16.389
33.970 c Abundance in the field
N89 S90
N90 S91
N91 S92
N92 Cerastoderma
0.65 –
– –
2.07 1.28
1.50 Gammarus spp.
26.77 179.73
14.19 57.29
86.53 302.20
42.75 Idotea spp.
4.85 36.18
1.02 6.60
1.38 8.56
1.67 Mytilus
37.40 78.32
58.61 44.71
100.53 151.94
111.55 Palaemon
– –
– 3.70
– –
– Theodoxus
2.01 187.35
8.58 4.05
7.92 25.12
2.27 Total
71.68 481.59
82.40 116.35
198.42 489.10
159.75 d Biomass in the field
N89 S90
N90 S91
N91 S92
N92 Cerastoderma
0.008 –
– –
0.015 0.034
0.025 Gammarus spp.
0.346 1.029
0.432 0.182
2.039 1.963
0.374 Idotea spp.
0.240 1.115
0.015 0.240
0.199 0.337
0.233 Mytilus
4.058 10.436
10.136 7.728
7.189 4.684
4.036 Palaemon
– –
– 2.532
– –
– Theodoxus
0.010 5.300
0.141 0.088
0.177 –
0.025 Total
4.660 17.880
10.724 10.770
9.619 7.418
4.693
The P-values that have been corrected for multiple comparisons, using Holm’s 1979 sequential Bonferroni, are still significant for the test of repeatability Table 3, P 5 0.038
for both abundance and biomass and the test of ecological realism Table 4, P 5 0.018 for both. For the replicability test Table 2 only one out of eight ‘significant’ P-values
P 5 0.002 for abundance comparison between A and B 1989 is still significant after
236 P
. Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
Fig. 1. NMDS-ordination of square-root transformed Fucus macrofauna abundance data in control mesocosms 1989–1992 stress 0.18.
correction, if a is set at 0.05. Since a P-value of 0.008 for abundance comparisons between F and G as well as H and I and biomass comparisons between H and I is the
minimum attainable significance level with 126 distinct permutations, while a sequential Bonferroni would demand a P-value , 0.004 for statistical significance, such correc-
tions may be too conservative and have a limited usefulness Clarke, 1999. Due to the increased risks of Type II errors to conclude no difference when one exists comprised
by these adjustments and the fact that Type II errors are at least equally serious as Type I errors to conclude a difference when none exists in environmental sciences Peterman,
1990; Fairweather, 1991; Mapstone, 1996, also the uncorrected P-values will be retained and considered in the discussion together with the corrected P-values.
P . Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
237
Fig. 2. NMDS-ordination of fourth-root transformed Fucus macrofauna biomass data in control mesocosms 1989–1992 stress 0.21.
3.2. Species responsible for the observed differences 3.2.1. Mesocosm replicability
The contributions of individual species to Bray–Curtis dissimilarities between parallel mesocosms replicability were determined by similarity percentage analyses SIMPER
on square-root transformed abundance Table 5a and fourth-root transformed biomass data Table 5b. The highest average dissimilarities are found for A and B 1989
d 532.80 for abundance and d 531.70 for biomass data, F and G 1991 d 528.28 for
i i
i
abundance data and H and I 1992 d 530.60 for abundance data, whereas C and D
i
1990 were the most similar of all parallel controls d 519.45 for abundance data, which
i
238 P
. Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258 Table 2
One-way ANOSIM test of differences in community structure square-root transformed abundance and
a
fourth-root transformed biomass data between parallel controls 1989–1992 Controls
Statistical Possible
Significant Significance
Adjusted compared
value permutations
statistics level
sign. level Abundance
A–B 1989 0.511
462 1
0.002 0.024
C–D 1990 20.002
126 55
0.437 0.714
C–E 1990 0.612
126 2
0.016 0.198
D–E 1990 0.244
126 11
0.087 0.348
F–G 1991 0.740
126 1
0.008 0.088
H–I 1992 0.664
126 1
0.008 0.088
Biomass A–B 1989
0.492 462
4 0.009
0.088 C–D 1990
0.072 126
30 0.238
0.714 C–E 1990
0.432 126
4 0.032
0.198 D–E 1990
0.064 126
33 0.262
0.714 F–G 1991
0.304 126
4 0.032
0.198 H–I 1992
0.628 126
1 0.008
0.088
a
The right column shows P-values corrected by a sequential Bonferroni. The symbol means that 0.01,P 0.05 and means that P 0.01.
also can be anticipated from the P-values in ANOSIM tests in Table 2. Gammarus is an important discriminator between mesocosms 1989 both considering abundance and
biomass due to a mass occurrence in A, but otherwise this species does not contribute to much of the dissimilarities. Idotea is a central discriminator between A and B 1989, C
and E 1990 as well as F and G 1991 and consistently more dominant in former mesocosms each year. Palaemon adspersus is of some importance regarding biomass
comparisons between D highest biomass and the two other controls 1990 C and E. Theodoxus fluviatilis is important concerning abundance comparisons between all
parallel mesocosms, although the differences are remarkable only in 1990 and 1991. Lymnaea is mainly important for biomass data, especially in discriminating A and B
1989, as well as C and the other two control mesocosms 1990 D and E, with consistently higher biomass in former mesocosms each year. Cerastoderma is most
important during later years, i.e. in discriminating F and G 1991, and especially H and I
Table 3 Results of a global two-way nested ANOSIM on differences in macrofauna community structure abundance
and biomass among years 1989–1992 repeatability on square-root transformed abundance and fourth-root
a
transformed biomass data Variable
Global R Permutations
Number of Uncorrected
Corrected sign. statistics
P-value P-value
Abundance 0.444
1260 38
0.030 0.038
Biomass 0.533
1260 24
0.019 0.038
a
All possible permutations 1260 were used. The right column shows P-values corrected by a sequential Bonferroni. The symbol means that 0.01,P 0.05.
P . Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
239
Fig. 3. NMDS-ordination of mesocosm and field samples at the start and at the end of experiments for Fucus macrofauna square-root transformed abundance data stress 0.10. Arrows connect samples from the same year
and visualise the divergence of mesocosm and field communities. Note that no field samples from the start were available in 1989.
1992 due to a mass occurrence in H. Mytilus edulis, finally, is a central discriminator between all parallel mesocosms considering both types of data and has consistently
higher abundances and biomasses in latter pools every year, i.e. in B, E, G and I. See also Table 1a and b for the exact numerical values.
3.2.2. Mesocosm repeatability The two-way nested ANOSIM could only demonstrate global differences, i.e. that
there are overall differences in community structure 1989–1992, regarding the re- peatability of BHB-mesocosms. A closer look at the years, two at a time with SIMPER
240 P
. Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
Fig. 4. NMDS-ordination of mesocosm and field samples at the start and at the end of experiments for Fucus macrofauna fourth-root transformed biomass data stress 0.09. Arrows connect samples from the same year
and visualise the divergence of mesocosm and field communities. Note that no field samples from the start were available in 1989.
analyses Table 6a and b, reveals that the most different pair of years are 1989 and 1992 41.39 Bray–Curtis dissimilarity for abundance and 33.04 dissimilarity for biomass
data and 1990 and 1992 40.37 dissimilarity for abundance and 34.24 dissimilarity for biomass data, which also can be anticipated from the NMDS ordinations. The
molluscs Lymnaea, Cerastoderma and Mytilus edulis, which all are found at con- siderably higher abundances in 1992, are the most important abundance discriminators
between 1992 and 1989–1990. Also Theodoxus fluviatilis is an important discriminator for abundance data. Considering biomass data Lymnaea is especially important
P . Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
241
Fig. 5. NMDS-ordination of mesocosm and field samples at the end of the experiment on Fucus macrofauna square-root transformed abundance data stress 0.07.
comparing 1992 with 1989 and 1990, and Mytilus edulis when just the earlier years are compared with one another. The exact numerical values are given in Table 1a and b.
3.2.3. Ecological realism of the mesocosm The highest overall dissimilarities in this paper are not surprisingly found for the
comparisons of macrofauna community structure between the mesocosms and the field mother system, i.e. 58.54 for abundance data Table 7a and 44.73 for biomass data
Table 7b. These differences also proved to be statistically significant using a two-way crossed ANOSIM. SIMPER analyses demonstrate that Theodoxus fluviatilis L., whose
normal autumn migrations to deeper waters are prevented in the mesocosms thus the
242 P
. Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
Fig. 6. NMDS-ordination of mesocosm and field samples at the end of the experiment on Fucus macrofauna fourth-root transformed biomass data stress 0.08.
Table 4 Results of global tests from a two-way crossed ANOSIM on differences in macrofauna community structure
a
between mesocosms and the mother system at the end of experimental periods 1989–1992 Variable
Global R Permutations
Number of Uncorrected
Corrected sign. statistics
P-value P-value
Abundance 1.000
108 1
0.009 0.018
Biomass 0.772
108 1
0.009 0.018
a
All possible permutations 108 were used. The right column shows P-values corrected by a sequential Bonferroni. The symbol means that 0.01,P 0.05 and means that P 0.01.
P . Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
243 Table 5
Each species’ contribution d to the average dissimilarities between parallel mesocosms: a square-root
i
transformed abundance data and b fourth-root transformed biomass data Species
d 89AB d 90CD
d 90CE d 90DE
d 91FG d 92HI
i i
i i
i i
a Abundance Cerastoderma
2.16 0.60
0.27 0.55
3.47 11.19
Gammarus 7.67
2.37 2.11
2.94 2.29
1.21 Gasterosteus
0.76 0.66
0.57 0.38
– 0.52
Idotea 6.83
2.12 2.70
2.03 6.76
2.12 Lymnaea
2.62 1.63
1.81 –
3.59 3.01
Mytilus 5.53
3.92 4.10
6.55 5.43
5.97 Palaemon
0.71 1.00
0.36 1.17
0.22 0.42
Theodoxus 6.53
7.15 15.20
12.74 6.53
6.16 Total d
32.80 19.45
27.12 26.36
28.28 30.60
b Biomass Cerastoderma
3.55 1.76
0.93 –
4.00 5.05
Gammarus 4.62
2.13 1.76
2.92 2.87
2.38 Gasterosteus
2.06 2.61
2.22 1.55
– 1.86
Idotea 5.05
3.74 5.32
4.06 7.77
2.94 Lymnaea
5.06 3.84
4.23 –
3.42 1.42
Mytilus 7.27
4.79 3.50
6.63 5.05
4.36 Palaemon
2.65 4.12
1.60 4.46
– 2.59
Theodoxus 1.44
0.66 3.46
3.11 1.96
2.16 Total d
31.70 23.65
23.03 24.17
26.41 22.76
high abundance values, by far is the most important discriminator. Gammarus and Mytilus edulis, which contribute to the abundance dissimilarities with more than 10
each, are other important discriminators. Lymnaea, Mytilus edulis, Idotea and Ceras- toderma are in addition to Theodoxus central contributors to biomass dissimilarities. See
also Table 1a–d for the exact numerical values.
3.3. Spatial and temporal variability in the field mother system The field mother system was investigated in order to get basic information about the
natural spatial and temporal variability of bladder-wrack macrofauna and an idea of possible consequences for mesocosm experiments. The spatial variability between
¨ neighbouring bladder-wrack plants, differences between sampling locations Havero
1990 and 1992, Utterholm 1991 and differences between years have partly been reported previously Kraufvelin, 1998, Table 5 on p. 259. The year-to-year differences
and differences between mother systems are recapitulated in this paper together with some rough information about seasonal differences, i.e. early summer compared to late
autumn Table 1. The seasonal variability is, however, better visualised by monthly samples from Utterholm 1991 plotted out in an NMDS ordination scheme Figs. 7 and
8, where a continuous temporal change during the year is evident. Although there is a high degree of spatial variability between replicates, it may be noted that the samples
most similar to the June samples are the ones from November, i.e. the samples most
244 P
. Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258 Table 6
Each species’ contribution d to: a the average abundance dissimilarity data square-root transformed and
i
b the average biomass dissimilarity data fourth-root transformed between every pair of years 1989–1992 Species
d 89–90 d 89–91
d 89–92 d 90–91
d 90–92 d 91–92
i i
i i
i i
a Abundance Cerastoderma
1.67 2.96
7.19 3.54
8.32 6.22
Gammarus 5.05
4.95 3.81
2.28 1.66
1.63 Gasterosteus
0.62 0.35
0.52 0.26
0.43 0.26
Idotea 6.07
4.99 4.73
4.37 1.73
3.53 Lymnaea
1.79 3.97
7.75 4.74
9.09 4.42
Mytilus 5.23
6.16 10.46
5.66 9.71
6.98 Palaemon
0.72 0.47
0.52 0.47
0.54 0.32
Theodoxus 9.36
7.31 6.40
7.44 8.89
7.01 Total d
30.51 31.16
41.39 28.76
40.37 30.38
b Biomass Cerastoderma
3.07 3.56
4.90 4.69
7.09 4.02
Gammarus 3.13
3.88 2.99
2.84 2.07
2.45 Gasterosteus
1.89 1.05
1.69 1.06
1.71 0.98
Idotea 5.76
5.07 5.24
4.92 3.10
4.27 Lymnaea
3.79 5.85
8.43 7.32
11.07 4.16
Mytilus 6.17
5.79 5.30
4.67 4.05
3.96 Palaemon
2.81 2.06
2.33 2.20
2.53 1.81
Theodoxus 1.87
1.59 2.16
1.83 2.62
2.27 Total d
28.49 28.85
33.04 29.53
34.24 23.92
distant in time. The samples from July are on the other hand the ones that differ most from the June samples. This last fact has immediate consequence for transplantation to
mesocosms. The time lag in transplantation present both in 1989 and 1992 is thus an important explanation for differences between control A and B as well as H and I, i.e.
the parallel mesocosms that differed most from each other.
The results from simulated transplantations to BHB-mesocosms are presented in Tables 8 and 9. An estimate of the theoretical amount of organisms in the mesocosm
bladder-wrack zone at the start of experiments is received, if the values per 100 g DWT |500 ml of volume in Table 8 are multiplied by 16 corresponding to the total
bladder-wrack volume of 8 l. Judging from the field data from 1996 some numerically important taxa at least initially like Chironomidae about 16 500 individuals per
mesocosm, Balanus improvisus 3500, Jaera albifrons 450 and Hydrobia sp. 200 have most likely been overlooked at the analyses of mesocosm fauna. The initial
variability is estimated for 48 variables by CVs averaged from 10 simulated transplanta- tions Table 9. These CVs are also compared with a number of real end CVs from the
mesocosms 1989–1992 for evaluation of how much the initial situation determines the final mesocosm replicability. A closer look at these comparisons indicates that most of
the final variability for Cerastoderma, Mytilus, Palaemon and Theodoxus is determined already by differences in the transplanted bladder-wrack. The same seems to be true for
Lymnaea and Gasterosteus, but as we will see later, this is not the case. Regarding
P . Kraufvelin J. Exp. Mar. Biol. Ecol. 240 1999 229 –258
245 Table 7
Each species’ contribution d to the average dissimilarities between mesocosms and the mother system at the
i
end of experimental periods 1989–1992: a square-root transformed abundance data total d 558.54 and b fourth-root transformed biomass data total d 544.73
a Abundance Species
Average Average
Average Ratio
Percent Cumulative
abundance abundance
term percent
field mesocosm
d
i
Cerastoderma 0.88
19.11 3.88
0.72 6.63
98.67 Gammarus
37.90 15.31
6.02 1.23
10.29 76.37
Idotea 2.41
13.48 4.58
1.05 7.82
92.04 Lymnaea
0.00 15.24
4.60 0.96
7.86 84.22
Mytilus 69.10
81.99 8.68
1.36 14.83
66.08 Palaemon
0.00 0.26
0.45 0.45
0.77 99.44
Theodoxus 5.37
278.85 30.00
2.54 51.25
51.25 b Biomass
Average Average
biomass biomass
field mesocosm
Cerastoderma 0.01
0.47 4.48
1.06 10.02
85.96 Gammarus
0.73 0.91
3.35 1.09
7.49 93.45
Idotea 0.16
0.85 5.89
1.28 13.16
75.94 Lymnaea
0.00 1.58
6.99 1.09
15.62 47.94
Mytilus 6.63
12.48 6.64
1.34 14.83
62.78 Palaemon
0.00 0.19
1.84 0.47
4.12 97.57
Theodoxus 0.09
6.16 14.46
2.66 32.33
32.33
Gammarus and Idotea the initial differences seem to be less important as long as no time lags in transplantation are present.
4. Discussion
