.11). 67. 0 .01. (0.04). 33. # Ceramium sp . 0 .24. (0 .46). 44. 0 .01. 10. (0 .23). (0.47). 44. 0 .01. (0 .01). 40. 1 .04. (1 .07). 100. 1 .48. (1 .36). 100. Chondrus crispus.
Environmental Biology of Fishes 39 : 271-288,1994. ©1994 Kluwer Academic Publishers . Printed in the Netherlands.
Fish assemblage structure in relation to macrophytes and filamentous epiphytes in shallow non-tidal rocky- and soft-bottom habitats
Leif Pihh, Hakan Wennhage t & Sven Nilsson2 1 University of Goteborg, Marine Research Station at Kristineberg, 450 34 Fiskebackskil, Sweden 2 University of Goteborg, Department of Zoology, Box 25059, 400 31 Goteborg, Sweden Received 17 .5.1993
Accepted 30.9 .1993
Key words : Substrate, Vegetation, Filamentous algae, Habitat complexity, Shallow-water estuary, Skagerrak - Kattegat Synopsis The fish assemblage in nineteen shallow water (0-3 m) areas on the Swedish west coast, including an estuarine zone, was assessed during spring and autumn 1989 and autumn 1990, using semi-quantitative survey nets. Samples of macrovegetation were collected concurrently for estimates of species composition and biomass . Nine stations had rocky-bottom substrata and ten had soft-bottom substrata all characterized by high coverage of macrovegetation and variously overgrown with epiphytic filamentous algae . Fish assemblage structures were compared and related to vegetation biomass, substrata and estuarine influences . At rocky-bottom stations total fish biomass was positively correlated with total vegetation biomass and negatively correlated with the proportion of filamentous algae during autumn samplings . In soft-bottom habitats variation in vegetation was small between stations, and no correlation existed between vegetation biomass and fish biomass . However, the number of fish species in soft-bottom habitats decreased significantly with increasing dominance of filamentous algae . The component species of the fish assemblage varied in their relation to the vegetation biomass and structure suggesting differences in degree of association with vegetation at the species level . Multivariate analysis based on fish species composition and on vegetation assemblages at the individual stations, yielded two major groups in accordance with division of the substrate into rocky- and soft-bottom habitats . Vegetation biomass superimposed on the fish assemblage ordination indicated a relationship between vegetation biomass and fish assemblage structure . Location of stations, in relation to the estuary was reflected in subgroups formed in the fish assemblage based cluster and ordination, suggesting a substantial estuarine influence on the fish assemblages . Thus, substrate type, vegetation biomass and structure, and estuarine influence are all potential structuring factors for the fish assemblages . In our study, vegetation structure s eems . t o be of major importance and changes such as increased dominance of filamentous algae, like that observed in coastal areas in Sweden, might cause significant changes in fish assemblage structure .
Introduction
which utilize shallows as a nursery (Zijlstra 1972), and pelagic and demersal species which temporari-
The marine coastal zone is important to many litto-
ly migrate to, and forage in coastal areas (Muus 1967, Pihl 1982) . Many fish species are associated
ral fish assemblages consisting of several components : resident species (Hillden 1984), juvenile fish
with coastal habitats such as rocky-bottoms, mud
272 flats and sandy beaches during different life-history stages. The most temporally and spatially complex
& Pihl 1992) . Nutrient enrichment, through sewage inputs and runoff from river catchments, is consid-
coastal habitats include those found within estuar-
ered to enhance the growth of such opportunistic
ies which are characterized by variations and gradients in salinity and turbidity and often nutrient
filamentous algae (Raffaelli et al . 1989, Lavery et al. 1991) .
concentrations . Fish assemblages in these areas also
This investigation examined density, biomass and
include transient diadromous species, fresh water species and marine species with seasonal migra-
structure of fish assemblages relative to vegetated
tions (Elliott et al . 1990) .
rocky- and soft-bottom habitats on the Swedish west coast . In particular, we characterized fish as-
In many coastal areas macrovegetation has a major influence on habitat complexity and conse-
semblages in these vegetated habitats within coastal embayments and along an estuarine gradient
quently fish assemblage structure (Sogard & Able
with an emphasis on the increasing dominance of
1991) . Together with estuarine physical factors
filamentous algae.
these habitats are spatially and temporally variable environments . Vegetated areas support higher abundances and biomasses of fish compared with
Methods
unvegetated areas (reviewed in Orth et al . 1984) . The importance of vegetated areas as habitats for
Area investigated
fish is mainly attributed to the food supply of invertebrates associated with vegetation (Rozas &
The investigation was carried out in 19 shallow
Odum 1988, Lenanton & Caputi 1989) . Algae are of
(0-3 m) bays on the Swedish west coast (11° 34' to
minor importance as a direct food resource for fish
11° 57' E and 57° 20' to 57° 52' N) during 1989 and 1990 (Fig . 1) . The study area was situated in an ar-
in boreal and temperate waters (Wheeler 1980) . Another important function of vegetation is protection from predation (Keats et al . 1987) . The latter is considered especially important in beds of Ruppia megacarpa, a growth form poorly colonized by epiphytic invertebrates (Humphries et al . 1992) .
chipelago with islands of varying size and a shoreline characterized by rocky- and soft-bottom substrate . We investigated nine bays with rocky bottom (R1-R9) and ten bays with soft sediment (S1-S10) . Each bay had an area of 1-2 hectares and attached
There are also species which breed in vegetated
macrovegetation was present from the shoreline to
habitats by either spawning (Aneer et al . 1983) or
a minimal depth of 5 m. Surrounding areas were characterized by soft-bottoms and water depth
building nests of plant material among vegetation (Curry-Lindahl 1985) . Alterations in fish assemblages might therefore be directly attributed to changes in the floral characteristics of estuarine habitats . During the last two decades Scandinavian
ranging from 10 to 50 m . Stations were chosen along an estuarine gradient from the inner to the outer archipelago and were oriented perpendicular (i .e . from north to east) to the coast (see Fig . 1) . Thus,
coastal habitats have experienced dramatic changes in algal distribution and species composition in-
stations experienced a moderate exposure gradient and were protected from the prevailing west and
cluding decreased depth distribution of vegetation
southwest winds . Mean surface water temperature is similar in such shallow bays on the Swedish west
and an increased dominance by benthic filamentous algae (Kautsky et al. 1986, Wennberg", Breuer & Schramm 1988, Svane & Grondahl 1989, Isaksson
coast, varying between 5 and 14° C in spring and autumn and 14 and 20° C in summer (Pihl & Rosenberg 1982) . Ice normally occurs for 2 to 8 weeks dur-
1
Wennberg, T. 1987. Langsiktiga forandringar av makroflorans sammansattning och utbredning i sodra Laholmsbukten sedan 1950-talet (Long-term changes in the composition and distribution of the macroalgal vegetation in the southern part of Laholm Bay, south-west Sweden, during the last thirty years) . Swedish Environmental Protection Agency, Report No . 3290. 47 pp .
ing winter. The surface salinity in the study area is influenced by the north-flowing brackish water Baltic Current . Salinity is further decreased by outflow of fresh water from the northern and southern branches of the
273 Gota River in the center of the area investigated . Approximately 75% of the river water enters the sea through the northern branch of the River . Monthly salinity measurements at 6 stations within the study area in 1990 (marked A to F in Fig . 1), 22) .
ranged from 0 .5 to 28 .2% (Table 1 Mean and maximum salinity values were similar at all stations, whereas minimum values showed greater variation . Salinity measurements indicate that stations close to the river mouth (R3, S4, S6) are subjected to larger salinity fluctuations compared with other stations . Exchange in the upper water layer is affected by river water outflow and prevailing meteorological conditions since the tidal range is less than 0 .2 m (Svansson3 ) . This results in unpredictable seasonal fluctuations in salinity . Total annual transport of nitrogen by the Gota River amounts to between 1 and 2 x 104 tons . In addition, a waste water treatment plant adds another 2 x 10 3 tons of nitrogen per year, mainly as ammonium, to the southern branch of the river (Selmer & Rydberg 1993) .
KATTEGAT
Sampling
.~.O ~R6
Fish and vegetation were sampled in June 1989 and August, 1989 and 1990 . Habitat structure was visual-
11
ly categorized as % vegetation cover of total bottom area and bottom substrate type (rocky- or softbottom) . 6-10 random samples were taken at each
NORWAY DEN
'
Annonymous, 1990 . Kustvattenkontrollen i Goteborgs och Bohuslan (Coastal monitoring in the county of Goteborg) . County of Goteborg and Bohus . 74 pp.
..
' Svansson, A . 1975 . Physical and chemical oceanography of the ry
Skagerrak and the Kattegat. Fish. Board of Sweden, contribution no. 1 . 95 pp.
Table 1. Salinity
%o
(mean with SD and range), at the six stations
shown in Figure 1, during 1990 . Salinity was measured monthly (n = 12) at 0.5 m depth . A
B
C
Mean
21 .4
17 .2
20.0
13 .4
SD Max Min
3 .0 27 .2 16 .3
4 .9 24 .7 7 .3
4.5 27.1 10.1
8.0 24.9 0.5
E
F
17 .2 7 .8
20 .0 5 .6
25 .5 1 .2
28 .2 8 .6
DENMA
r
Fig. 1 . Map of the Swedish west coast archipelago with the estuary of the northern and southern branch of Gota River . Location of rocky-bottom stations (Rl-R9) and soft-bottom stations (SlS10) are shown. A to F denotes the positions where salinity measurements were conducted monthly in 1990 (see Table 1) .
4 .53 0 .03 11 .46
(0 .51) 56 (0 .01) 22 (52 .67)
(3.99) (0.17) (4.92)
100 20
40
30 40 60
(1 .56) (0.09) (1 .80)
(0 .15)
0 .31 0 .06 1 .29
1 .15
(0 .03)
10 10 20
1 .09 0 .01 54 .91
0 .24 0 .17 2 .03
0 .39 (0 .23) 0 .86 0 .05 * 7 .96 0 .52 0 .15 0 .17
11 22
(31 .75)
(2.06)
(0.29) (0.28) (3 .68)
78 11
78 67 67
(0.67) 89 (0.47) 44 (1 .00) 100 (0.14) 22 11 (5 .78) 100 (0.90) 56 (0.31) 44 (0.82) 33
(0 .22)
0.01 0 .04
10
33 56 22
20
10 10
(5 .37) (0 .52) (0 .49) (0 .49) (0 .28) (0 .68) (1 .04) (0 .58)
* 0.01 0.04
(0 .20)
0.06
70 30
(2 .30) (0 .49) (0 .01)
(0 .28) 78 (0 .01) 33 (0 .44) 44 (0 .41) 100
Oc.%
(0 .01) 22 (27 .98) 100 (5 .09) 67 (4 .90) 67 11 (3 .48) 89
0.52 0.15 *
0.15 * 0.10 0.34
(SD)
* 31 .17 2.55 2 .08 1 .30 2 .64
10 10 30
50 80
Oc.%
0 .02 *
(0 .44) (0 .46) (1 .50) (0 .06)
(1 .59) (0 .78)
(0 .04)
0.05 0.02 0.01
2.70 0.28
(1 .32) (0 .62)
0.34 0.55
(SD)
44 44 56 33 11 89 78 33 33 22 56 22 89
22 89 44 33 22 67 11
(0 .02) (47 .67) (1 .93) (1 .45) (22 .75) (5 .87)
(0 .09) 33
11 (0 .18) 22 11 (0 .30) 89
S
R
Oc.%
R
(SD)
Aug 89
Jun 89
Chlorophyta # Cladophora sp. # Enteromorpha sp. 0 .03 # Ulva lactuca # Filamentous - green 0 .23 Phaeophyta Ascophyllum nodosum Chorda filum 0 .05 # Chordaria sp. # Dictyosiphon sp . # Elachista sp . 0 .01 Fucus serratus 33 .15 Fucus vesiculosus 0 .74 Halidrys siliquosa 0 .30 3 .92 Laminaria digitata Laminaria sacharina 3 .99 Sphacelaria sp . 0 .08 # Spermatochnus sp. # Filamentous - brown Rhodophyta # Ahnfeltia sp. 0 .15 # Ceramium sp. 0 .24 Chondrus crispus 0 .44 Cystoclonium sp. 0 .02 Dumontia sp . 0 .06 Furcellaria lumbricalis 5 .86 Phyllophora 0 .38 Phycodrys rubens 0 .25 # Polysiphonia sp . 0 .15 Porphyra•s p. 0 .05 # Rhodomela sp . 0 .39 # Filamentous - red 0 .20 # Filamentous - GBR 0 .66 Spermatophyta Zostera marina 0 .20 Ruppia sp. * Mean total biomass 51 .56
Taxa
0 .22
4 .89 1 .04 *
0.04 0 .01
0.03 1 .24 0.87
13 .25 0 .42 25 .15
0 .17 0 .53 0 .02 0 .03 0 .07 0 .41 0 .25 1 .02
0 .01 * 0 .11
0 .51 0 .04
S
(7 .50) (1 .47) (7 .57)
(0 .50) (1 .14)
(1 .16) (0 .16) (0 .02) (0 .12)
(0 .01) (0 .01)
(0.67)
(0.84)
(2.65) (2.29)
(0.09) (0 .01)
(0 .11) (3 .60) (1 .12)
(SD)
100 70
10 70 20 20 40 10 50 100
40 20 10
80 10
50
80 60 10
50 20
40 70 100
Oc.%
0 .19 * 79 .09
0 .13
1 .52 2 .50 0 .22 0 .01 0 .18 * 0 .06
0 .09 1 .04 0 .17
0 .03
55 .11 9 .14 1 .62 1 .19 2 .29 *
0.03
2.96 0.02
* 0.18 0.17 0.25
R
Aug 90
17
83 17
50 50 33 83
Oc.%
33
(48 .23)
(0 .37)
(0 .52)
50 17
33
(0 .11) 67 (1 .07) 100 (0 .23) 83 17 (6 .44) 33 (2 .01) 83 (0 .70) 50 (0 .00) 50 (0 .10) 67 17 (0 .03) 33
(0.08)
(49.58) 100 (13 .16) 83 (4.38) 67 (1 .88) 67 (2.41) 67 17
(3.03)
(0 .00) (0 .48) (0 .67) (0 .59)
(SD)
0 .03 0 .05
7.19 0.38 19.71
0.02
22 33
(4 .67) 100 (0 .55) 78 (11 .30)
11
(0.04) 33 (1 .36) 100 (0 .07) 56 11 11 (0 .14) 78 11 11 11
(0.17) (0.13)
22 11
(0.08)
0 .01 0 .31
22 67 11 11
67 56 89
Oc.%
(5.50) 100 (2.08) 67
(4 .60) (1 .69)
(1 .80) (1 .03) (1 .42)
(SD)
3 .51 1 .31
2 .67 0 .72 * *
0.55 0 .40 0 .90
0 .01 1 .48 0 .03 * * 0.11 * 0.01 0.02
S
Table 2 . Vegetation biomass (mean and SD, g dry weight (DW) 0.06 m2) for the different taxa at rocky (R) and soft (S) bottom stations during sampling in June and August 1989 ((R) n = 9, (S) n =10) and in August 1990 ((R) n = 6, (S) n = 9) . The proportion of stations at which as taxon was encountered as given as percentage occurence (% Oc .) . Filamentous algae which could not be separated in the samples were grouped as filamentous green, brown, red or as a mixture of the three groups (GBR) . # = Taxa included in the group of filamentous algae. * = Mean biomass < 0 .01 g DW 0.06 m-2.
27 5 station in spring and 10-15 in autumn to quantify vegetation composition and biomass . Vegetation
Data analysis
samples were collected inside a 0 .06 m 2 sampling ring by a diver . The ring was thrown backwards over
Data were tested for normality and homogeneity of variances and since some data (fish biomass and fil-
head by the diver at randomly selected sites at each station . Vegetation from each sample was identi-
amentous algae biomass) did not closely approxi-
fied, weighed (after drying at 60° C to constant weight), and mean biomass was determined by species for each station and sampling date . Algal spe-
mate normality, non-parametric statistics were used throughout . Differences in total vegetation biomass, filamentous algal biomass and % cover, be-
cies with a predominant part of the thallus less than
tween June and August 1989, were tested with a Wilcoxon signed-rank test, as were seasonal differenc-
1 mm in diameter, were classified as filamentous algae for subsequent analysis . Filamentous algae oc-
es in the number and total biomass of fish species. Differences in total abundance and biomass of fish
curring as epiphytes on kelp or Zostera marina were
between soft- and rocky-bottom stations were test-
removed, weighed and considered separately during the analysis . The algae Ulva lactuca and Entero-
ed with a Mann-Whitney U-test .
morpha spp., which are favoured by high nutrient concentrations (Lavery et al . 1991), were included
Correlations between vegetation and fish were tested with a Spearman's rank Correlation Test .
in the filamentous group. Substantial amounts of fil-
These analyses were restricted to August data only, to eliminate seasonal covariation between varia-
amentous algae occurred as indivisible aggregates
bles, and were further restricted to include only spe-
and were classified as filamentous-green, brown or red algae or as mixture of these groups . Fish sampling was carried out with 1 .5 m high and
cies present at more than 75% of all stations . Adjustment of level of significance for multiple testing
42 m long survey gllnets, divided into 14 randomly distributed three meter sections with different mesh sizes varying from 6 .25 to 70 mm (Nyberg &
Affinities between stations based on fish and vegetation assemblages were analysed by multivariate
Degerman) W . Gillnets were placed along one depth
stricted the multivariate analysis to data from August 1989 when all stations were sampled and vege-
contour . At every sampling occasion 2 survey-nets were used per hectare divided in equal proportions between the two depth intervals 1 to 2 m and 2 to 3 m. Survey-nets were randomly distributed along each depth interval for a duration of 12 hours (deployed over-night) . Fish were identified to species, counted, measured and weighed shortly after capture. Biomass (wet weight to 1 g) and abundance are expressed as weights and numbers per net, respectively. The sampling technique likely underes-
was made according to the formula Pcrit = P/n .
methods as described in Field et al . (1982) . We re-
tation biomass was high . Vegetation biomass was square root transformed whereas fish abundace was double square root transformed and standardized by total on stations . Hierarchical agglomerative clustering was performed on Bray-Curtis similarity matrices based on the transformed data using group-average linking . Similarity matrices were then used to perform a Multidimensional Scaling
timate sedentary demersal species and small fish
Ordination (MDS) . Vegetation biomass was superimposed as circles of proportional size on the fish
(gobies and juveniles) which could avoid this type
assemblage based MDS . Differences between the
of gear.
predefined groups, rocky- and soft-bottom stations, were analysed with the ANOSIM permutation test (Clarke & Green 1988) for significance .
° Nyberg, P. & E . Degerman 1988 . Standardiserat provfiske med oversiktsnat (Standardized fish sampling with survey-nets) . Fresh Water Research Laboratory, Drottningholm, Contribution no . 7 . 18 pp .
276 60 o a
60 -
60'
60"
m 40 -
40
N
N 40 -
40
N
20-
2020 0
S1
0 ja
R1
S2
60 -
60'
N °'• 20 o N
R 1
S
R2 60'
40-
*
N 57° 50'
40-
200
0
S3
R3
R4
® Zostera marina
0
Filamentous algae
0
Algae with thick or leaf like thallus
Fig. 2. Mean total vegetation biomass (g dry weight 0 .06 m-'), at rocky- (R1-R9) and soft-bottom (Sl-S10) stations, during sampling in June and August 1989 and August 1990 (represented by left, middle and right bar) . Standard error (SE) values are shown above the columns . Vegetation biomass was divided in Zostera marina, filamentous algae and algae with thick or leaf like thallus . * = no sampling conducted .
277 stations R6 to R9 . Furcellaria lumbricales occurred
Results
at all localities on two of three sample dates and had Vegetation
the highest overall biomass among red algae . Green algae contributed less than 1% of the total algal bio-
Twenty eight taxa of macrovegetation including the
mass on most sampling occasions in rocky-bottom
two spermatophytes (Zostera marina and Ruppia sp .) were collected at the 19 stations (Table 2) . Of
localities, except at station R2 and R3 . These sta-
these, 28 and 25 taxa were present in rocky- and
tions had low total vegetation biomass and green algae made up as much as 17 and 5% of the total
soft-bottom samples, respectively . These are to be regarded as minimal estimates, however, since fil-
algal biomass, respectively . All soft-bottom areas had eelgrass, Zostera mari-
amentous algae in most samples were hard to sep-
na, meadows, which comprised most of the vegeta-
arate, and therefore not always identified to spe-
tion biomass (Table 2, Fig . 2) . At most stations patches of Fucus serratus and F vesiculosus oc-
cies . Brown algae dominated in biomass and species diversity at all rocky-bottom stations . Fucus serratus was ubiquitous and dominated in biomass at most locations, on average contributing to 64, 56
curred in the eelgrass beds, and these species dominated by weight among algae in soft-bottom habitats . Z. marina was always variously overgrown with filamentous algal epiphytes . Filamentous
and 69 % of the total plant biomass in June 1989, and August 1989 and 1990, respectively (Table 2) . Lami-
(mainly green) algae contributed between 9 and 53 % of the total biomass of vegetation in June and
naria digitata and L . saccharina were second in bio-
between 0.1 and 66% in August .
mass and were especially frequent at the offshore
Total mean biomass of macrovegetation varied between 4 .2 and 174 (mean 59.1) g DW 0 .06 m- ' at
Table 3. Estimates of vegetation cover (% of station area) and the relative coverage of filamentous algae as % of total vegetation cover, during sampling in June and August 1989 and August 1990 at 9 rocky-bottom stations (Rl-R9) and 10 soft-bottom stations (Sl-S10) . * = no sampling conducted .
rocky-bottom stations and between 2 .0 and 41 .9
Site
Vegetation cover J-89
R1 R2 R3 R4 R5 R6 R7 R8 R9 S1 S2 S3 S4 S5 S6 S7 S8 S9 S10
50 45 70 65 80 80 80 65 65 85 85 80 80 80 50 80 90 80 90
A-89 70 65 85 75 85 80 80 70 65 90 90 90 90 90 60 90 95 90 95
Filamentous algal cover A-90 90 * 75 85 95 85 80 * * 90 90 75 80 95 80 95 85 95 *
J-89 10 60 10 10 15 20 70 70 20 15 10 20 30 30 60 70 80 60 20
A-89 70 80 70 10 25 30 80 70 20 80 60 30 40 60 80 80 90 80 50
A-90 90 80 10 20 40 65 * * 40 50 40 55 80 60 75 90 85
(mean 16 .4) g DW 0 .06 m2 at soft-bottom stations (Fig . 2) . Vegetation biomass increased from the inner to the outer archipelago on all sampling occasions . Mean biomass of vegetation at rocky-bottom stations ranged from 51 .6 to 79.2 (mean 58 .8) g DW 0.06
M-2 during
the three sample periods (Table 2) .
Corresponding values for soft-bottom vegetation biomass were 11 .4 to 25 .2 (mean 18 .6) g DW 0.06 m-2. At soft-bottom stations there was a significant (p < 0 .005) increase in total vegetation biomass from spring to autumn in 1989, but no analogous change occurred on rocky-bottom . This increase was mainly caused by the growth of Zostera marina during the summer season (Fig . 2) . Filamentous algal biomass ranged from 0.5 to 5 .1 g DW
m2 in June 1989 0.06 m2 in August 1989 0.06
and from 0 .4 to 13 .5 g DW
(Fig . 2), and was significantly (p < 0.04) higher in autumn than spring 1989 . Vegetation cover was high at all stations, ranging from 45 to 90% in spring and 65 to 95% in autumn (Table 3) . Filamentous algae occurred mainly as epiphytes on fucoids and on Zostera marina and significantly (p < 0 .001) increased their cover on host substrates from a mean of 35% (range 10 to 80) in
S (SD)
R (SD)
S (SD)
3 .1 (6 .2) 26 .1
0 .2 63 .1
0 .7
9 .0 (24.2) 238 .2 (362 .4)
7 .2 (10 .4)
R (SD)
2 .9 (2 .5)
S (SD)
Aug 89
1 .5
2 .5 (1 .3)
S (SD)
0.3
R (SD)
Aug 90
29
8 4 13 20.8 (106.1) 17 188.0 (222.9) 13
11 .0 4.7
S (SD)
R
3 17 28 7 66 3
7 34
52 90 83 31 3 3 48 52 3 3 69 28 17 31 3 14
41 48 3 72
10 7
17
S
% Oc .
13 .0 (20 .4) 0.2 160.4 (220 .4) 14 .7 1 .2 406 .2 (336 .5) 168 .5 (143 .3) 433 .9 (390 .8) 125 .0 (148 .2) 298 .3 (194 .8) 81 .0 (89 .5) 96 4 .0 (17 .8) 3 .5 (3 .2) 17 113 .7 (186 .3) 249 .7 (990 .4) 235 .8 (210 .1) 164.1 (285 .2) 178 .3 (213 .1) 181 .6 (325 .1) 58 2 .1 (3 .4) 44 .3 (63.9) 1 .8 (7 .5) 5 .2 (6 .7) 0 .2 2.8 (4.1) 46 6 .0 (7 .2) 3 .7 (4 .7) 9 .1 (14 .3) 8 .1 (11 .1) 9 .3 (23 .0) 9 .6 (11 .0) 50 1104 (1011.0) 65 .1 (151 .5) 397 .8 (555 .7) 53 .4 (47 .7) 464 .5 (680 .8) 76 .0 (421 .3) 58 3 .8 4 11 .8 4 .2 4 10 .1 (21 .4) 65 .9 (64.4) 252 .5 (190 .3) 41 .6 (60.1) 110.0 (95 .6) 54 35 .4 (125 .8) 25 .1 (8 .4) 433 .0 (310 .8) 110.9 (222 .5) 129 .7 (235 .3) 151 .3 (168 .7) 63 0.1 4 .0 (3 .6) 0 .9 4 .5 (10 .3) 5 .3 (1 .2) 38 116 .2 (121 .1) 433 .8 (563 .6) 18 .7 (32 .7) 350 .4 (561 .3) 61 .3 150 .2 (264 .5) 38 2 .2 29 .4 (210 .1) 19 .2 (94.7) 69 .1 (487 .2) 4 10 .0 (15.6) 3 .3 (12.0) 12 .2 (23.8) 21 72 .3 (117 .8) 12 .6 (29.7) 94 .1 (103 .5) 34 .6 (50.1) 54 0 .1 0 .3 4 8 .2 (7 .1) 9 .3 7 .1 7 .3 5 .8 8 13 .3 4 104 .4 172 .9 39 .0 (119 .5) 60 .7 (97.2) 56 .3 (158 .8) 27 .2 (23 .3) 164 .2 (421 .2) 25 22 .8 18 .3 8 4 .7 2 .1 (9 .2) 22 .3 (163 .7) 21 .4 (119 .7) 53 .1 (371 .5) 60 .8 (112 .1) 37 .0 25 0 .6 0 .6 (0 .3) 0 .5 (0 .5) 0 .4 (0 .6) 0 .4 (0 .3) 25 1 .1 0 .5 4 108 .9 (135 .0) 24 .6 (10.2) 124 .7 (151 .1) 21 .0 (22.9) 163 .8 (142 .5) 41 .4 (43 .4) 96 0 .1
11 .6 (28.0) 1 .1 46 .0
6 .2 (12.5)
R (SD)
R (SD)
R (SD)
S (SD)
Jun 89
Aug 89
Jun 89 Aug 90
Mean biomass (SD)
Mean density (SD)
Ammodytes sp. 0 .13 (0.10) 0 .13 (0 .30) 0 .22 (0 .20) 0.10 (0 .13) Anguilla anguilla Belone belone 0 .02 0.02 0 .03 Centrolabrus exoletus 0 .03 (0 .04) 0.06 0 .10 Chelon labrosus 0 .04 Ciliata mustela 0 .18 (0.39) Clupea harengus 0 .06 0 .55(l .77) 0 .11 (0 .24) 0.56 (1 .04) 0.08 0.22 (0 .25) Coregonus sp . 0.22 0 .63 (0.67) 0 .06 0.68 (0 .74) 0.08 0.82(l .03) Cottus gobio 0.02 Ctenolabrus rupestris 21 .93 (20 .51) 6 .96 (6 .67) 25 .24 (29 .56) 6.83 (8 .70) 18.97 (14.28) 3 .88 (3 .49) Entelurus aequoreus 0.37 (1 .89) 0 .13 (0 .12) Gadus morhua 0.22 (0.34) 0 .99 (3 .35) 0 .67 (0 .50) 1 .06 (1 .58) 0.89 (0.82) 1 .21 (1 .25) Gasterosteus aculeatus 2.99 (3 .46) 1 .09(l .57) 25 .29 (26.05) 0 .07 0.17 (0.26) 1 .82 (2 .20) Gobius niger 0.33 (0.25) 0 .75 (1 .10) 0 .91 (1 .00) 0 .99(l .20) 0.89(l .95) 0.82 (0 .81) Labrus berggylta 11 .18 (12 .83) 1 .21 (2.21) 2 .50 (2 .26) 0.58(l .13) 0.97(l .60) 0.18 (0 .53) Labrus bimaculatus 2.00 Limanda limanda 0.07 0.07 Merlangius merlangus 0 .20 (0.36) 6 .17 (5 .46) 23 .47 (16 .74) 3.22 (4.23) 8 .32 (8 .19) Myoxocephalus scorpius 0.41 (1 .65) 0 .38 (0.10) 5 .00 (3 .35) 1 .52 (3 .92) 1 .45 (2.25) 1 .49(l .64) Nerophis ophidion Pholis gunellus 0.18 (0.10) 0 .03 0 .18 (0.10) 0.20 (0.12) Platichthys flesus 0.61 (0.83) 2 .11(l .62) 0 .13 (0.10) 1 .64 (2 .36) 0.25 0.86(l .69) Pleuronectes platessa 0.06 0 .43 (2.35) 0 .54 (2 .35) 0.88 (5.78) Pollachius pollachius 0 .33 (0.37) 0 .20 (0 .54) 0.50 (1 .65) Pollachius virens 2 .20 (3 .09) 0 .35 (0 .73) 2.78 (2.55) 0.92 (1 .26) Pomatoschistus pictus 0.04 0.03 Psetta maxima 0 .08 (0.12) 0 .04 0 .09 0.08 0.05 Raniceps raninus 0.06 0 .06 Rutilus rutilus 0 .06 0 .76 Salmo trutta 0.17 (0.35) 0 .15 (0.47) 0 .21 (0 .23) 0.17 (0.26) 0 .35 (0 .63) Scomber scombrus 0.06 0 .06 Scophthalmus rhombus 0 .02 Solea solea 0.07 0 .21 (1 .18) 0 .15 (0.47) 0 .66 (4 .77) 0.28 (0.23) 0 .25 Spinachia spinachia 0 .09 0 .17 (0.08) 0 .16 (0 .09) 0.14 (0.12) 0 .16 (0.13) Sprattus sprattus 0 .03 0 .11 0 .05 Symphodus melops 10.26 (11 .75) 1 .23(l .40) 7 .20 (7 .73) 1 .29(l .22) 6.03 (3 .53) 3 .31 (2 .69) Syngnathus acus 0 .13 (0.12)
Species
Table 4. Mean and standard deviation (SD) of fish abundance (ind . per net) and biomass (g wet weight per net) for fish species at rocky (R) and soft (S) bottom stations during sampling in June and August 1989 ((R) n = 9, (S) n = 10) and in August 1990 ((R) n = 6, (S) n = 9) . Percentage occurrence represents the number of samples where a species was encountered relative to the total number of samples for rocky and soft-bottom stations, respectively .
Zoarces viviparus
Trisopterus minutus
Trisopterus esmarkii
Triglopsis quadricornis
Trachinus draco
Taurulus bubalis
Syngnathus typhle
Syngnathus rostellatus
Species
Table 4. Continued.
0.32 (0 .21)
0.11
0.07 2.89 (3 .19) 0.04
0.05 (0 .06)
0.02
0.12 (0 .20) 1 .35 (2 .14)
0.04
0.87(l .10)
R (SD)
R (SD)
S (SD)
Aug 89
Jun 89
Mean density (SD)
0.08 (0.04)
0.03
0.03 0.40 (0.74)
S (SD)
0.14 (0 .12)
0.11
0.44 (0 .45)
R (SD)
Aug 90
0 .03 0 .10
0 .22 (0.32)
0 .03
S (SD)
S (SD)
8.3 (16 .2)
0 .9 2 .7 (4 .7)
0 .2 1 .4 (6 .7) 182.6 (168 .6) 72 .0 (122 .9) 1 .0
R (SD)
Jun 89
Mean biomass (SD)
1 .6
34 .1 (42.0)
R (SD)
Aug 89
3 .5 3 .4 (13.7)
1 .9
0 .2 15 .8 (28.0)
S (SD)
1 .9 (2 .4)
3 .7
16 .2 (17.1)
R (SD)
Aug 90
0.7 4 .4
8 .1 (9 .3)
S (SD)
8 4 25
4 71 4
R
17
7
14 59
S
% Oc.
280 spring to a mean of 58% (range 10-90) in autumn 1989 .
species (whitefish, Coregonus spp.) significantly contributed to the total fish biomass (Fig. 3) .
Fishes
Total fish biomass exhibited only slight temporal variability at most stations (Fig . 3) . The highest biomass of marine species occurred in the outer archi-
A total of 6761 teleosts representing 45 species,
pelago at both rocky- and soft-bottom localities . However, at soft-bottom stations near the river
were collected at the 19 stations during the study (Table 4) . Thirty five species were caught in spring and 40 species in autumn . Rocky habitats contained
mouths, the fresh water species, roach, Rutilus ruti-
7 to 16 species, and soft-bottom localities yielded 6
ferences (p > 0 .05) in overall fish abundance or bio-
to 18 species (Table 5) . There was a significant (p < 0 .002) increase in number of species per station be-
mass between rocky- and soft-bottom stations.
tween spring and autumn 1989 . Fish species composition was similar at all rocky-
lus, and whitefish contributed as much as 87% of the total fish biomass . There were no significant dif-
Fish-vegetation relationships
bottom stations with the assemblage dominated by the family Labridae : goldsinny wrasse, Ctenolabrus rupestris, corkwing, Symphodus melops, and ballan wrasse, Labrus berggylta, and the family Cottidae : bull-rout, Myoxocephalus scorpius, and sea scorpion, Taurulus bubalis. These species occurred at 58 to 96% of all stations during the three sampling occasions and together comprised 82% of the total number of individuals collected (Table 4) . They also contributed 82% of the total biomass in June 1989 and 69 and 74% in August 1989 and 1990, respectively. During autumn juvenile gadoids (whiting, Merlangius merlangus, saithe, Pollachius virens, and cod, Gadus morhua) became more abundant and occurred at 69 to 81% of the stations and contributed 22 to 23°o of the fish biomass (Table 4) . Species composition was similar in soft-bottom localities but exhibited some seasonal variation. High densities of goldsinny wrasse and threespined stickleback, Gasterosteus aculeatus, were observed in spring (Table 4) . These species were found at 9 of 10 stations, and comprised 75% of the assemblage . In August 1989 and 1990, juvenile whiting were caught at all stations and contributed to 52 and 31% of the total abundance, respectively. Flounder, Platichthys flesus, cod and goldsinny wrasse dominated by weight in spring together making up 57% of the total fish biomass . During autumn these species together with whiting contributed to between 38 and 55 % of the biomass . At four stations located near the mouths of the northern and southern branch of Gota River the fresh water
Relationships between fish fauna and vegetation were investigated in the rocky- and soft-bottom habitats during August 1989 and 1990 . Significance of correlation was tested between the fish parameters (number of fish species, total fish biomass and Table 5 . Number of fish species (mean and SD) at rocky (R) and soft (S) bottom stations during sampling in June and August 1989 and August 1990 . * = no sampling conducted .
Station
R1 R2 R3 R4 R5 R6 R7 R8 R9 Mean R (SD) S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 Mean S (SD)
No . of species Jun 89
Aug 89
9 6 7 10 11 8 10 12 11 9 .3 (2 .0) 10 9 9 7 8 9 9 7 6 9 8 .3(l .3)
9 9 13 8 10 10 11 14 16 11 .1(2.7) 9 10 14 10 13 11 18 7 11 12 11 .5 (3 .0)
Aug 90 9 8 9 8 9 16
9.8 (3 .1) 15 10 13 8 12 14 11 7 10 * 11 .1(2.7)
281 3000
3000
2000
2000
2000
1000
1000
1000
. 0
∎ t ∎ 0 R1
S1
0
1000
S2
R2
5000
5000-
4000
4000-
4000
3000
3000-
3000
2000-
2000-
2000 -
1000-
1000-
1000-
3000
3000
3000
2000
2000
2000
1000
1000
0
0
R4
R1
N 5
1
°
50'
S3
1000
& S5
0
S6
5000-
5000
5000
4000-
4000
4000
3000-
3000
3000
2000-
2000
2000
1000 -
1000
1000
0
0
0
2
o S4
I t R3
0
S3
S
'
~ Iw 5000
0
° 4 '
1
3000
2000
E
3000
R5
S7
[]la
S8
5000-
5000
5000-
6
4000 -
4000
4000 -
R6
3000-
3000
3000-
2000-1 11
2000-
100 0 -
10000 -„ `
200010,00-
'
S9 7 °
`
R6
R7
S9
5000
5000
5000-
4000
4000
4000-
3000
3000
3000-
2000
2000
2000-
1000
1000
10000 -
0
*
R8
0
R9
*
R 8 R 9
11* S10
Fig. 3. 'lbtal fish biomass (g wet weight per net) at rocky- (R1-R9) and soft-bottom (Sl-S10) stations during sampling in June and August 1989, and August 1990 (represented by left, middle and right bar) . Fresh water species are shown separately as open sections of bars . * _ no sampling conducted.
biomass of individual dominant fish species) and the vegetation parameters (total vegetation biomass and percentage filamentous algae of total vegetation biomass) . Rocky- and soft-bottom stations were treated separately in the analysis .
At rocky-bottom stations, a significant (p < 0 .02) positive correlation was found between total fish and vegetation biomass (Table 6) . There was also a significant (p < 0 .02) negative correlation between total fish biomass and percent filamentous algae .
28 2 Among the dominant fish species corkwing showed a significant (p < 0 .01) positive correlation with vegetation biomass . The biomass of corkwing and saithe, consisting of 0-group and 1-group speci-
MDS configuration (Fig . 4b) had a low stress value (0 .083) which implied that the two dimensional plot was a reasonable representation of the similarity
mens, were negatively correlated (p < 0 .01) with
between stations . The soft-bottom station S3 included species associated with both rocky- and soft-
percentage filamentous algae.
bottom substrata and therefore showed closest af-
In soft-bottom habitats no overall correlation was found between total fish and vegetation bio-
finity to the rocky-bottom stations R1 and R2 (group I in Fig . 4b) . S3 also had the lowest biomass
mass . However, the number of species was significantly (p < 0 .01) negatively correlated with percent
of filamentous algae among soft-bottom stations (Fig . 2) . The ANOSIM test confirmed a significant
of filamentous algae (Table 6) . Goldsinny wrasse
difference between rocky- and soft-bottom stations
biomass was positively correlated (p < 0 .005) with vegetation biomass .
(R = 0 .585 ; p < 0.0001) . Rocky-bottom stations were spatially segregated according to the position in relation to the estuary (Fig . 1, 4b) . The two rocky-bottom stations R3 and
Multivariate analysis
R4 (II) outside the northern branch of Gota River estuary had high similarity and all rocky-bottom
The August 1989 similarity matrix of fish species composition, based on abundance data, yielded a
stations south of the estuary (R5 to R9) clustered into one group (III) . Among soft-bottom habitats,
cluster with the 19 stations divided into two major
the estuarine in-shore and northern stations formed
groups (Fig . 4a, b) . The analysis was also performed on biomass data which resulted in a similar pattern .
one group (IV), whereas the remaining group (V) consequently consisted of stations located in either
The division was in almost total agreement with the
the southern or off-shore part of the study area .
pre-defined rocky- and soft-bottom stations . The
In Figure 4c vegetation biomass was superim-
Table 6. Relation between macrovegetation variables (total biomass and proportion of filamentous algae) and fish variables (no . of species and biomass) in August 1989 and 1990 . Correlations were tested for both total biomass of fish and for biomass of some dominant species with Spearman's Rank Correlation Coefficient Test . When testing individual fish species level of significance was adjusted for multiple testing according to Pcrit = P/n . Variables
Vegetation biomass
Filamentous algae
rs
p
rs
p
0 .63 0 .13
0 .019 0 .627
- 0 .68 0 .35
0 .011 0.204
0 .23
0 .400 0 .050
- 0 .48 0 .30
0 .073 0 .270 0.205 0.004
Rocky-bottom Total fish biomass No . of species Ctenolabrus rupestris Merlangius merlangus Myoxocephalus scorpius Pollachius virens Symphodus melops Soft-bottom Total fish biomass
- 0 .52 - 0 .47
0 .081
0 .34
0 .45 0 .70
0 .091 0 .009
- 0 .78 - 0 .72 - 0 .23 - 0 .64
- 0 .01
0 .979
No . of species Ctenolabrus rupestris Gasterosteus aculeatus
0 .40 0 .68 0 .14
0 .086 0 .004 0 .561
Gobius niger Merlangius merlangus
- 0 .16 0 .23
0 .507 0 .324
0 .43
0 .072
Symphodus melops *=p
