HELGOL.~NDER MEERESUNTERSUCHUNGEN
Helgol~nder Meeresunters. 45, 317-344 (1991)
Sublittoral hard substrate communities ofi H e l g o l a n d
M. J. de Kluijver
Institute of Taxonomic Zoology, University of Amsterdam;
P.O. Box 4766, NL-IO09 A T Amsterdam, The Netherlands
and
SBNO: P.O. Box 16915, NL-IO01 RK Amsterdam, The Netherlands
ABSTRACT: In the Helgoland region eight subhttoral hard substrate communities occur. These
communities were stationary in time during the years 1987-1989. The major governing parameters
are the available amount of daylight and the degree of exposure to water movement. In the photic
zone, three communities are met with, one of which is widespread and appears to be independent of
the exposure to water movement. Under exposed conditions, at the lower border of the photic zone, a
second community is observed. A third community is estabhshed on erosive muschelkalk substrates.
In the aphotic zone also, three communities are found. The distribution of these communities is
related to the rate of water movement. One community is divided into three variants, with different
preferences regarding the angle of inclination and nature of the substrates. In the artificially
constructed harbours, where sedimentation exceeds erosion, two different communities have setfled. In the community under moderately sheltered conditions many species are found which also
occur in the natural photic zone. Under extremely sheltered conditions a group of species has
become dominant which is very rare in the Helgoland region outgide the quay-walls but which has
been described as being characteristic for sheltered localities elsewhere.
INTRODUCTION
A l t h o u g h m a n y investigations h a v e b e e n p e r f o r m e d in the H e l g o l a n d region, the
sublittoral communities on hard substrates h a v e b e e n largely n e g l e c t e d until now. Recent
investigations on rocky eulittoral c o m m u n i t i e s w e r e carried out by M a r k h a m & M u n d a
(1980), M u n d a & M a r k h a m (1982) a n d J a n k e (1986). Sublittoral studies w e r e started by
Caspers, wh o m a d e inventories of the fauna of the "Tiefe Rinne" (Caspers, 1938), oysterb a n k s (Caspers, 1950), and buoys (Caspers, 1952). Investigations o n the d e v e l o p m e n t of
sublittoral co m m u n it ie s w e r e carried out by A n g e r (1978) and Harms & A n g e r (1983).
Sublittoral a l g a e w e r e studied by Lfining (1970) an d Kornmann & S a h h n g (1977).
Subhttoral b e n th ic c o m m u n i ti e s are s u b j ect ed to stable e n v i r o n m e n t a l p a r a m e t e r s
an d are thus a s s u m e d to h a v e a p r e d i c t a b l e specific composition. This w o u l d m a k e t h e m
particularly useful for the detection of short-term disturbances in the m a r i n e ecosystem.
In order to use b e n th ic communities for ecological monitoring, a reproducible description
of both the communities a n d the e n v i r o n m e n t a l p a r a m e t e r s must be available. Reproducibility m a k e s d e m a n d s u p o n the m e t h o d s of investigation. In the first place, communities must b e studied as a whole. M a n y of the publications on m a r i n e h a r d substrate
communities deal with only one particular taxonomic group, for e x a m p l e a l g a e (L(ining,
1970) or Polychaeta (K16ckner, 1976; Gillandt, 1979a, 1979b). Secondly, the data m u s t be
9 Biologische Anstalt Helgoland, Hamburg
318
M . J . de Kluijver
quantified as m u c h as possible. Studies on sublittoral h a r d substrate c o m m u n i t i e s as a
w h o l e are often qualitative (Hiscock & Hiscock, 1980; KSnnecker & K e e g a n , 1983). T h e
m a i n b e n e f i t of quantitative s t u d i e s - i s the .description of c o m m u n i t i e s b y m e a n s of
characteristic species (common species, b u t restricted to just one c o m m u n i t y ) a n d
d o m i n a n t species (occurring in m o r e communities, but a b u n d a n t in j u s t a few communities). E x a m p l e s of such quantitative studies on m a r i n e h a r d s u b s t r a t e c o m m u n i t i e s
are: Gislen (1930), Van Soest & W e i n b e r g (1981), K a a n d o r p (1986), De Kluijver (1989)
a n d De Kluijver et al. (in prep.).
H e l g o l a n d is situated in the G e r m a n Bight some 50 k m from the n e a r e s t m a i n l a n d
(Eiderstedt). Because of its isolated position, the m a r i n e e n v i r o n m e n t a r o u n d H e l g o l a n d
displays an offshore character. For the major part of the y e a r it is u n d e r t h e influence of
the North Sea w a t e r b o d y (Martens, 1978), which g u a r a n t e e s a r e l a t i v e l y constant
environment. Despite the inflow of fresh w a t e r with diluted pollutants into the s o u t h e r n
North S e a a n d the e a s t e r n G e r m a n Bight from the rivers W e s t e r s c h e l d e , M a a s , Rhine,
Elbe a n d W e s e r (Korringa, 1968; De Ruijter et al., 1987), the a r e a a r o u n d H e l g o l a n d must
b e c o n s i d e r e d relatively u n p o l l u t e d c o m p a r e d to more inshore locahties in the southern
North Sea.
MATERIALS A N D METHODS
Sampling
H a r d substrate biota w e r e s a m p l e d at 80 stations, distributed o v e r 14 localities
(Fig. 1). In T a b l e 1, the characteristics of the stations are shown. T h e d e p t h of a station is
given relative to M e a n Sea Level ( b e t w e e n h i g h a n d low tide). In g e n e r a l , the biota are
c o m p o s e d of different structural layers. In the studiec~ area, a d i s t i n g u i s h a b l e top l a y e r
(TL) of thalli of b r o w n a l g a e of the g e n u s Laminaria m a y b e d e v e l o p e d . A m i d d l e l a y e r
(ML) is f o r m e d b y organisms g r o w i n g erect from t h e substrate, but w h i c h d o not b e l o n g to
the top layer. This layer also contains the epiphytic, epizoic a n d e n d o z o i c o r g a n i s m s . The
encrusting l a y e r (EL) consists of organisms a d h e r i n g to the substrate.
In e a c h different structural layer, the p e r c e n t a g e cover of the vertical p r o j e c t i o n of all
sessile o r g a n i s m s was estimated, using a q u a d r a t of 50 x 50 cm. V a g i l e o r g a n i s m s w e r e
scored qualitatively at all stations, b u t w e r e not u s e d for cluster analysis.
Minimal sampling area
In order to obtain a r e p r e s e n t a t i v e sample, 3 to 4 q u a d r a t s of 50 x 50 cm w e r e
s a m p l e d at e a c h station. The m i n i m a l s a m p h n g a r e a r e q u i r e d was d e t e r m i n e d for station
2 (West Seite - 9.9 m), b y s a m p l i n g 10 q u a d r a t s of 32 • 32 cm. Data w e r e p r o c e s s e d using
the p r o g r a m MINAR (Kaandorp, 1986) with logarithmically t r a n s f o r m e d data. The
algorithm a n d transformation u s e d in this process w e r e the s a m e as t h o s e u s e d d u r i n g
cluster analysis. Similarity w a s plotted as a function of the s a m p l e d surface (Fig. 2).
W e i n b e r g (1978) s u g g e s t e d a similarity level of 0.70 at which the m i n i m a l a r e a is
obtained. This level is r e a c h e d within 2 q u a d r a t s (20.5 dm2).
The size of the u s e d q u a d r a t s does not influence the m i n i m a l s a m p l i n g area. F i g u r e 3
shows a c o m p u t e r simulation for r e a c h i n g these m i n i m a l s a m p l i n g a r e a s for different
q u a d r a t sizes b o t h in a h o m o g e n e o u s l y a n d a patchily distributed c o m m u n i t y . A l t h o u g h
S u b l i t t o r a l c o m m u n i t i e s off H e l g o l a n d
319
Fig. 1. Map of Helgoland showing the localities {after Lfining, I970). 1: Nordreede (West/Ost); 2:
West Seite., 3: Vorhafen; 4: Dfine (Kalberdans/Wittkliffbrunn}~ 5: Kringel~ 6: Nordmole~ 7: Repulsegrund~ 8: SelIebrunnknoll~ 9: Dfine-Sfid~ 10: Nordhafenknoll; 11: H a m b u r g e r Loch; 12: Sfidhafen~
13: Skittgatt~ 14: Steingrund (54 ~ 14' N, 08 ~03' E) [not on the map)
320
M.J.
de Kluijver
T a b l e 1. D e s c r i p t i o n of th e stations s a m p l e d , s e q u e n c e a c c o r d i n g to t h e d e n d r o g r a m (cf. F i g u r e 4)
Station
Location
Depth
(m}
Date,
Slope
Orient
Area
{dm 2)
Substrate
01
09
37
05
72
03
07
30
76
63
65
20
28
Nordreede-West
Nordreede-West
Nordreede-West
Dfine-Kalberdans
Nordreede-West
W e s t Seite
Kringel
Nordreede-West
W e s t Seite
NordhafenknoU
Skittgatt
Nordmole
Kringel
6.5
6.1
5.7
4,8
4,5
5,9
4.7
6.1
4.6
6.5
10.8
8.7
5.4
Community A
03-07-87
I0
21-07-87
I5
05-07-88
15
13-07-87
i0
15-06-89
20
07-07-87
25
20-07-87
25
10-09-87
15
21-06-89
30
07-06-89
10
08-06-89
20
01-09-87
5
09-09-87
25
90
50
90
110
60
30
220
340
90
240
60
280
270
100
100
75
100
75
100
100
75
75
75
75
75
75
sandstone
sandstone
sandstone
limestone
sandstone
sandstone
sandstone
sandstone
sandstone
limestone
limestone
limestone
concrete
06
10
14
59
34
Kringel
Kringel
Kringel
Hamburger Loch
Kringel
9.2
10.0
9.2
9,7
9.3
Community B
14-07-87
25
21-07-87
35
24-07-87
70
27-07-88
25
16-09-87
10
180
20
350
90
-
100
100
75
75
75
sandstone
limestone
sandstone
hmestone
sandstone
16
23
Dfine-Wittkliffbrunn
Dtine-Wittkliffbrunn
2.1
3.7
Community C
27-07-87
5
03-09-87
25
270
90
75
75
muschelkalk
muschelkalk
02
08
21
31
18
17
53
42
43
44
47
52
39
41
51
58
49
73
61
54
12
69
78
19
W e s t Seite
Kringel
Repulsegrund
Repulsegrund
W e s t Seite
Nordmole
W e s t Seite
Repulsegrund
Sellebrunnknoll
Nordhafenknoll
Repulsegrund
Repulsegrund
W e s t SeRe
Repulsegrund
Repulsegrund
Nordhafenknoll
H a m b u r g e r Loch
Repulsegrund
Kringel
W e s t Seite
W e s t Seite
W e s t Seite
Sellebrunnknoll
W e s t Seite
9.9
11.0
14.3
12.7
13.2
11.6
11.3
10,0
10.8
11.8
12.2
11.2
13.5
14.1
12.6
12.7
11.6
13.9
14.2
12,8
17.3
14.7
16,6
I5.3
Community D
06-07-87
10
20-07-87
5
02-09-87
10
14-09-87
10
30-07-87
30
29-07-87
15
21-07-88
10
08-07-88
70
11-07-88
80
1t-07-88
5
14-07-88
I0
20-07-88
I0
06-07-88
I0
07-07-88
5
20-07-88
10
27-07-88
5
15-07-88
10
19-06-89
0
05-06-89
0
21-07-88
I0
22-07-87
5
13-06-89
0
23-06-89
0
31-08-87
5
240
130
0
170
210
240
240
240
150
300
270
220
270
90
240
220
210
102
100
100
100
100
75
75
100
100
i00
75
75
75
I00
75
75
I00
75
75
75
100
75
75
75
sandstone
sandstone
sandstone
sandstone
limestone
sandstone
limestone
limestone
limestone
limestone
limestone
limestone
limestone
sandstone
sandstone
sandstone
limestone
sandstone
sandstone
sandstone
sandstone
sandstone
sandstone
sandstone
S u b l i t t o r a l c o m m u n i t i e s off H e l g o l a n d
321
Table 1 (continued)
Station
Location
Depth
(m)
Date
,Slope
Orient
Area
Substrate
(din2)
Community D
35
33
22
24
50
25
64
70
75
80
67
Nordhafenknoll
West Seite
Sellebrunnknoll
Repulsegrund
14.2
16.5
6.3
11.1
7.3
15.1
10,6
12.4
11.7
12.2
14.7
13
40
48
71
79
38
46
68
74
45
Nordmole
Dfine-Sfid
Nordreede-West
W e s t SeRe
Repulsegrund
Dfine-Sfid
Nordmole
Nordmole
Steingrund
Dfine-S0.d
22,9
15.5
11,9
19.5
19.6
12.6
18.3
14.3
10.2
19.2
27
62
29
56
32
36
Nordreede-West
Nordreede-Ost
Nordreede-Ost
Nordreede-Ost
Nordreede-West
Nordreede-West
9.3
10.4
9.3
8.0
10.5
9.5
04
15
11
55
77
26
Vorhafen
Vorhafen
Vorhafen
Vorhafen
Vorhafen
Vorhafen
7.3
6.3
7.4
7.1
6,1
6.5
57
60
66
Stidhafen
Siidhafen
Sfidhafen
4.2
4.5
5,1
Dfine-Sfid
West Seite
Repulsegrund
Nordhafenknoll
Sellebrunnknoll
Repulsegrund
Sel]ebrunnknoll
17-09-87
16-09-87
02-09-87
03-09-87
19-07-87
04-09-87
08-06-89
13-06-89
20-06-89
27-06-89
12-06-89
10
5
65
95
90
45
100
90
20
80
30
70
110
220
30
40
250
310
180
30
75
100
75
75
75
75
75
75
75
75
75
sandstone
sandstone
sandstone
limestone
limestone
limestone
limestone
limestone
limestone
limestone
limestone
5
10
5
60
25
20
60
30
0
60
240
210
30
60
300
270
150
100
100
75
75
75
100
75
75
75
75
sandstone
sandstone
sandstone
sandstone
sandstone
limestone
sandstone
sandstone
sandstone
sandstone
10
20
10
20
10
65
0
190
80
150
100
100
75
75
100
100
sandstone
sandstone
sandstone
sandstone
sandstone
sandstone
90
90
90
90
90
5
0
210
30
20
50
-
100
100
100
75
75
75
concrete
concrete
concrete
concrete
concrete
sandstone
90
90
90
120
120
80
75
75
75
iron
iron
iron
Community E
23-07-87
07-07-88
14-07-88
14-06-89
26-06-89
06-07-88
13-07-88
12-06-89
19-06-89
12-07-88
Community 1~
08-09-87
06-06-89
09-09-87
26-07-88
14-09-87
05-07-88
Community G
10-07-87
27-07-87
22-07-87
22-07-88
21-06-89
07-09-87
Community H
26-07-88
27-07-88
09-06-89
322
M . J . de Kluijver
o.
0
0
T
c~
N
0
c~
]
0.0
10.2
I
20.5
I
30.7
I
41:0
I
51.2
$ in dm2
Fig. 2. Bray-Curtis coefficient (SI) as a function of the sampled surface (S) for station 2 (West Seite 9.9 m depth)
t h e m i n i m a l s a m p l i n g a r e a is i n d e p e n d e n t of the q u a d r a t size, it is l a r g e r in a patchily
distributed c o m m u n i t y t h a n in a h o m o g e n e o u s l y distributed c o m m u n i t y . Station 2 is
d o m i n a t e d b y the a n t h o z o a n Metridium senile, a species which tends to occur in a p a t c h y
distribution. The a r e a of 3 to 4 q u a d r a t s of 50 x 50 cm (75-100 d m 2) is t h e r e f o r e certainly
sufficient to y i e l d a r e p r e s e n t a t i v e s a m p l e of the communities off H e l g o l a n d .
Environmental parameters
T h e s u b m a r i n e d a y l i g h t was m e a s u r e d using a relative " U n d e r w a t e r H e m i s p h e r i c a l
Irradiance Meter" (UHIM) d e s c r i b e d b y W e i n b e r g (1979). T h e spectral sensitivity of the
U H I M (peak v a l u e 480 nm; b a n d - w i d t h 60 nm) roughly corresponds to t h e transmission
characteristics of water. F r o m the m e a s u r e m e n t s in midwater, the v e r t i c a l extinction
coefficient (k in m - t ) was calculated, using the L a m b e r t - B e e r l a w [Eq. (1)] for monochromatic light.
Id = Io" e-~d
(i)
From measurements at the stations and at the same depth in midwater, the station
coefficient (sc in %) of each station was obtained.
The exposure of the sublittoral communities to water movement was determined in
two ways. For some stations, the rate of exposure was related to the erosion of gypsum
blocks. The erosion value is expressed as the average weight loss of four gypsum blocks
(g-h -I) during one lunar day (24.45 h). A description of this method, including a
mathematical framework, is given by De Kluijver & Kaandorp (in prep.). A second
Subhttoral communities off Helgoland
323
"o
03
E
~ H
0~m
ogeiiiiiillI i ~tri~~icitY'
ld illy
Quadrat size
Fig. 3. Computer simulated determination of the minimal area of a homogeneously and a patchily
distributed community. For explanation see text
method, which was performed for all stations, used the sediment characteristics as a n
indicator of the exposure to water movement. In order 'to determine these s e d i m e n t
characteristics, samples of about 100 g of the upper 1 cm layer of the s e d i m e n t s were
sieved through 7 graded sieves (2.8-0.053 ram). The characteristics were expressed as
the proportional contribution of the dry weight of the different sieved fractions. The
contribution of the various fractions was analysed with n o n - t r a n s f o r m e d data, u s i n g the
computer programs CLUSTAN1C2 (Wishart, 1978) and SRTORD (Kaandorp, 1986). The
lower m a r g i n a l value of the smallest characteristic fraction was used as a n indication of
the current velocity.
The potential sedimentation in the communities was m e a s u r e d u s i n g s e d i m e n t traps.
As advised by Bloesch & Burns (1980), simple cyhnders were used with a n i n n e r diameter
of 11.7 cm. Because of the bottom relief, the ratio of length to diameter was restricted to
5 : 1. S e d i m e n t a t i o n was expressed in g - m -2. d -1, dry weight, m e a s u r e d over 21 days.
T e m p e r a t u r e was m e a s u r e d u s i n g a modified mercury t h e r m o m e t e r (Weinberg,
1979). Both the surface a n d bottom t e m p e r a t u r e were m e a s u r e d at each station. Additional data were o b t a i n e d from the w e a t h e r station Helgoland.
Cluster analysis and inverse analysis
For the cluster analysis, the p e r c e n t a g e cover of all sessile organisms of the quadrats
of a station was averaged. This yielded a data table of 80 stations a n d 142 sessile species.
Before analysis, all data were logarithmically transformed using Eq. (2); in which x is the
p e r c e n t a g e cover a n d T(x) the transformed value.
324
M . J . de Kluijver
x=0.0
0.1 --< x -----100.0
~T(x) =0
--~ T(x) = log(10x) + 1
(2)
The cluster analysis was carried out uslng the computer p r o g r a m C L U S T A N 1 C 2
(Wishart, 1978). T h e A v e r a g e L i n k a g e m e t h o d (Sokal & Michener, 1958) w a s u s e d in
c o m b i n a t i o n with the Bray-Curtis coefficient [Eq. (3)].
Ixi-vil
S(X, Y) =
i~1
(3)
~, (Xj +Yj)
j=l
This c o m b i n a t i o n of algorithm a n d coefficient l e a d s to r e p r o d u c i b l e results (Shin,
1982; Kaandorp, 1986; De Kluijver, 1989; De Kluijver et al., in prep.).
0.761
0.696
0.650
0.565
I
0 499
1-
0 454
0
~68
0:30::3
l
0 2:37
,1
0
17.2
A
B
C
D
E
F
G
Fig. 4, Dendrogram resulting from the cluster analysis of the data. The clusters distinguished are
marked A-H
H
Subhttoral communities off H e l g o l a n d
325
In addition to the n o r m a l analysis an inverse analysis was performed, w h i c h p r o c u r e s
information a b o u t the composition of the clusters. With the p r o g r a m SRTORD (Kaandorp,
1986), the distribution of the quantities of the species over the clusters w a s calculated.
Characteristic species w e r e d i s t i n g u i s h e d at a concentration level of 90 % within a
community. D o m i n a n t a n d characteristic species m u s t b e p r e s e n t in at l e a s t 67 % of the
stations with the c o m m u n i t y concerned.
For comparison, the d a t a w e r e also a n a l y s e d using the p r o g r a m T W I N S P A N (Hill,
1979), with the following i n p u t p a r a m e t e r s : for p s e u d o s p e c i e s the cut levels 0.0, 2.0, 5.0,
10.0 a n d 20.0 w e r e used, a n d all w e i g h t s for levels of p s e u d o s p e c i e s w e r e set to 1, without
indicator potentials for the cut levels.
RESULTS
Cluster analysis and inverse analysis
Figure 4 shows the d e n d r o g r a m resulting from cluster analysis, t h e o r d e r e d d i a g r a m s
resulting from the inverse analysis are g i v e n in T a b l e s 3, 4, 5, 6 a n d 7. T h r e e m a i n g r o u p s
of stations can b e discriminated u s i n g the fixed stopping rule. The first cluster (A, B a n d
C) consists of stations s a m p l e d in the photic zone, b e t w e e n 2.1 a n d 10.8 m, d o m i n a t e d b y
algae. The s e c o n d cluster (D, E a n d F) is formed b y stations s a m p l e d in the aphotic zone,
b e t w e e n 6.3 a n d 22.9 m. The third cluster (G a n d H) is s a m p l e d in the sheltered,
artificially constructed, Vor- a n d Siidhafen, b e t w e e n 4.2 and 7.4 m.
A further division, using the v a r i a b l e stopping rule, yields 8 m e a n i n g f u l clusters
which can b e r e g a r d e d as subhttoral communities on account of species composition a n d
differences in the e n v i r o n m e n t a l p a r a m e t e r s . The variable stopping rule is p r e f e r r e d to
the fixed stopping rule, b e c a u s e it allows differences in the mosaic composition of the
species in the different communities, which l e a d to different similarity levels.
Environmental parameters
The southern North S e a w a t e r mixes with fresh w a t e r s u p p l i e d b y the rivers Elbe a n d
Weser, which causes a d e c r e a s e in salinity towards the coast. During spring, the salinity
of the surface w a t e r at H e l g o l a n d m a y d e c r e a s e to 30-31%o S, while d u r i n g w i n t e r t i m e
the salinity m a y i n c r e a s e to 34 %o S (Hagmeier, 1930). The annual c h a n g e s in t e m p e r a t u r e
of the surface w a t e r r a n g e s from 2 ~ to 18~ (Lfining, 1985). Salinity a n d t e m p e r a t u r e
values for 1986 are given by Gillbricht (1987). The fluctuations of salinity a n d t e m p e r a ture at greater d e p t h s (Tiefe Rinne, 50 to 60 m) are smaller than in the surface l a y e r
(K16ckner, 1976).
The current p a t t e r n a r o u n d H e l g o l a n d is strongly influenced b y the g e o m o r p h o l o g y
of the sea bed. I n t e g r a t e d m e a s u r e m e n t s of the total amount of w a t e r m o v e m e n t , using
g y p s u m blocks, w e r e p e r f o r m e d d u r i n g July 15-16, 1987 on a calm day. The w e s t side of
H e l g o l a n d is the most e x p o s e d (0.14-0.16 g ' h-1), followed b y the N o r d r e e d e (0.14 g . h - l )
a n d D f i n e - K a l b e r d a n s a n d Vorhafen (0.10 g- h - 1). In shallow places (station 3, W e s t Seite,
d e p t h 6.0 m), this v a l u e r a p i d l y i n c r e a s e d during stormy w e a t h e r conditions. M e a s u r e ments during July 23-24, 1987 (westerly wind, force 4-5) show erosion v a l u e s of 0.28
g. h -1. The p r e v a i l i n g w i n d s a r o u n d H e l g o l a n d are westerly (Fig: 5). The i n f l u e n c e of
326
M . J . de Kluijver
w i n d i n d u c e d water m o v e m e n t can almost b e n e g l e c t e d at a depth of half the wave
l e n g t h (Van Straaten, 1973).
The current velocity also influences the particle size of deposited material. Cluster
analysis of 88 s e d i m e n t samples yielded a d e n d r o g r a m with 7 different types of sediments. The result of the inverse analysis is given in Table 2. The s e q u e n c e i n the ordered
d i a g r a m is that of decreasing d o m i n a n c e of the coarse fractions. S e d i m e n t type I is
characterized b y a d o m i n a n c e of the coarse sand fraction (2.8-1.4 ram), w h i l e type VII is
characterized b y the d o m i n a n c e of silt a n d clay fractions (< 0.15 ram). Below the diagram,
the proportional contribution of stations of different communities are listed. T h e s e q u e n c e
of the communities, ordered according to the fineness of the sediments, corresponds with
the results of the exposure experiments u s i n g g y p s u m blocks. The potential s e d i m e n t a -
N
NW
NNW
WNW/7....
~
\\
, .~NNE_NE
ENE
ESE
vSE
WSW
SSE
SW
SSW
S
Fig. 5. Wind energy rose for Helgoland for 1983 (data from Wetterstation Helgoland). Increased
thickness of lines indicates strengths of 1-3, 4-5, 6-7 and more than 8 Beaufort
Sublittoral communities off H e l g o l a n d
327
T a b l e 2. O r d e r e d
diagram
resulting
from the inverse analysis of the sediment
data and the
proportional
contribution of the different sediment types over the communities.
* * * The clusters in
which a concentration
level of 90 % is reached
Type
I
02.8-01.4
II
.
.
.
01.4-0.60
0.60-0.30
0.30--0.15
0.15-0.09
0.09-0.05
< 0.05
.
III
.
.
.
.
IV
.
.
.
.
.
.
.
.
.
.
.
.
VII
.
.
.
VI
V
$$$
.
.
. .
. . . . .
. . . . .
$1e
$$~
$$m
$$$
*"
Communit~
B
40.0
40.0
20.0
-
-
-
D
C
E
A
F
G
H
3.3
.
56.7
100.0
55.5
33.3
20.0
-
33.3
.
11.1
16.7
.
-
6.7
-
.
.
.
.
.
8.3
-
33.3
58.3
60.0
16.7
20.0
66.7
100.0
.
tion in the natural e n v i r o n m e n t varied b e t w e e n 19.5 an d 42.1 g - m - 2 ' d-1, w h i l e in the
artificially constructed harbours this a m o u n t e d to 65.1 g . m - 2 . d -1 in the V o r h a f e n and
only 13.7 g - m - 2 . d -1 in the Sfidhafen. In an samples, more than 75 % of the s e d i m e n t
consists of fractions smaller than 0.05 ram. In Figure 6, the proportional contribution of
the dry w e i g h t s is plotted against the different fractions. Tab l e 2 clearly shows that in the
natural e n v i r o n m e n t the l o w e r hmit of the characteristic fraction is almost l a r g e r than 0.09
-O- Nordreede-Ost, 9.7 m;
totally 27.5 g/m2/d
90.
s0
,~
70
/ ~
9ll- Vorhafen, 8.6 m; totally
~ /
60'
65.1 g/m2/d
50'
o.
-D- Sr, dhafen, 5.4 m; totally
13.7 g/m2/d
40'
" 9 West Seite, 15.0 m;
totatly 42.1 g/m2/d
30'
20"
-A- D0ne-Wittkliffbrunn,
10.
4.0 rn; totally 19.5
- , ' , ~
0 ~'-'-----'-;~======'==~
2.81.4
9o- Nordreede-West,4.9 m;
totally 41.2 g/m2/d
1.40.6
0.60.3
~ '~r-'--
m
0.30.15
0.150.09
Fraction in
F i g . 6. P r o p o r t i o n a l
contribution
m
0.090.05
#
g/m2/d
<0.05
mm
of the dry weights
of the different
fractions
in the sediment
traps
328
M . J . de Kluijver
Fig. 7. Minimal vertical extinction coefficients (k m-1) in midwater measured in July 1987
mm, while in the artificial e n v i r o n m e n t the lower limit of the characteristic fraction is
generally smaller t h a n 0.05 ram. This implies that in the natural e n v i r o n m e n t erosion
takes place, while in the harbours s e d i m e n t a t i o n occurs.
Light-penetration is strongly i n f l u e n c e d by seasonal c h a n g e s a n d w e a t h e r conditions
(Lfining & Dring, 1979). Figure 7 shows the lowest values of the vertical extinction
coefficient m e a s u r e d in July 1987. Localities on the relatively shallow east side of
Helgoland show higher values of the vertical extinction coefficient than localities on the
west side. T h r o u g h stirred up sediments a n d erosion products, the vertical extinction
coefficient increased to 0.59 m -1 d u r i n g stormy w e a t h e r in July 1987.
A r o u n d Helgoland, three m a i n types of natural h a r d substrates occur: r e d sandstone,
m u c h s e l k a l k a n d h m e s t o n e facies (Wills, 1968). Two additional types of artificial substrates were sampled: concrete at Kringel a n d in the Vorhafen, a n d iron in the S/idhafen.
Subhttoral communities
off H e l g o l a n d
329
T a b l e 3. O r d e r e d d i a g r a m r e s u l t i n g from t h e i n v e r s e a n a l y s i s for t h e s p e c i e s o c c u r r i n g in b o t h t h e
n a t u r a l e n v i r o n m e n t a n d t h e artificially c r e a t e d h a r b o u r s . T h e clusters in w h i c h a c o n c e n t r a t i o n level
of 90 % is r e a c h e d a r e m a r k e d w i t h . . . . . or ~. . . . '. P r i n t e d a s t e r i s k s i n d i c a t e a p r e s e n c e level of at
l e a s t 67 % w i t h i n t h e c o m m u n i t i e s . A b b r e v i a t i o n s : A n -' a n t h o z o a n , Br - b r y o z o a n , BA - b r o w n alga,
Bi - bivalve, Cr - c r u s t a c e a n , G A - g r e e n alga, H y - h y d r o z o a n , P - p o l y c h a e t e , RA - r e d alga, S s p o n g e , T - tunicate, TL - top layer, M L - m i d d l e l a y e r a n d EL - e n c r u s t i n g l a y e r
Community:
T u b i c o l o u s o r g a n i s m s (Cr/P)
EL-Phymatoh'thon sp. (RA)
Audouinella rnembranacea (RA)
EL-Hildenbranch'a rubra (RA)
Obelia dichotoma (Hy)
Leucosolenia variabilis IS)
Urticina felina (An)
Alcyonium digitatum (An)
Scypha c///ata (S)
Didemnurn maculosum (T)
Botrylloides leachi (T)
Haficlona rosea (S)
CIy~'a hemisphaerica (Hy)
Ulva lactuca (GA)
Halichondria panicea (S)
Polysiphonia urceolata (RA)
Phyllophora pseudoceranoides (RA)
Ceramium deslongchampsii (RA)
Ceramium rubrum (RA)
Enteromorpha linza (RA)
Sidnyum turbinatum (T)
Calh'thamnion hookefi (RA)
Phycodrys rubens (RA)
Desmarestia viridis (BA)
Alcyonidium mytili (Br)
Bryopsis lyngbyei (GA)
Sphacelaria plumosa (BA)
Dynamena pumfla (Hy)
Lomentaria clavellosa (RA)
Spirorbis sp. (P)
Chaetomorpha melagonium (GA)
A
B
C
D
E
***
F
***
***
G
***
=**
***
***
S
0 *
0
*
H
***
***
O
Um*
Scrupocellaria scruposa (Br)
Bowerbankia sp. (Br)
Bugula plumosa (Br)
EL- Cryptosula pallasiana (Br)
Table 4
Table 5
Table 6
Table 7
330
M . J . de Kluijver
The sublittoral communities
In the d e n d r o g r a m (Fig. 4), eight subhttoral communities, forming three m a i n groups,
are distinguished. The contribution of different taxa to the c o m m u n i t y composition, split
up for the different structural layers, are hsted in Table 9. Species characteristic of both
the n a t u r a l offshore e n v i r o n m e n t a n d the artificially created harbours are listed in Table 3. Species restricted to the photic a n d aphotic zone in the n a t u r a l e n v i r o n m e n t are
given in Table 4.
Table 4. Ordered diagram resulting from the inverse analysis for species restricted to the natural
environment. For an explanation of the abbreviations and symbols, see Table 3
Community:
Sagartia elegans/troglodytes (An)
Sertularia cupressina (Hy)
Obelia geniculata (Hy)
Celleporella hyalina (Br)
Calicella syringa (Hy)
Diphasia rosea (Hy)
Flustra foliacea (Br)
EL-Electra pflosa (Br)
Phyllophora traillii (RA)
Mytilus edulis (Bi)
Crisia eburnea (Br)
EL-Flustra foliacea (Br)
EL-Caflopora lineata (Br)
Diadumene cincta (An)
Verruca stroemia (Cr)
Punctaria plantaginea (BA)
Ectocarpu s sp. (BA)
Sertularella rugosa (Hy)
Tubularia larynx (Hy)
Myxilla mcrustans (S)
Sertularella polyzonias (Hy)
Crisia denticulata (Br)
Alcyonidium diaphanum (Br)
Polyplumulana setacea (Hy)
Hydrallmania falcata (Hy)
Eudendrium sp. (Hy)
Lanice conchilega (P)
Janua sp. (P)
EL-Cribrilina punctata (Br)
EL-Celleporefla hyalina (Br)
EL-Microporella ciliata (Br)
EL-Chorizopora brongniartefla (Br)
EL-Conopeum reticulum (Br)
EL-Schizomavella linearis (Br)
EL-Alcyonidium mytili (Br)
A
B
C
D
E
F
G
H
Sublittoral communities off Helgoland
331
Communities restricted to the photic zone
The first m a i n cluster (A, B and C) is composed of three communities. T a b l e 5 shows
the ordered diagram for this cluster. All communities are d o m i n a t e d by algae in the
middle layer. The cluster does not possess m a n y collective red algae restricted to this
cluster, b e c a u s e most of the d o m i n a n t algae also occur in the sheltered Vorhafen, e.g. the
red algae Polysiphonia urceolata, Phyllophora pseudoceranoides, Ceramium rubrum a n d
Ceramium deslongchampsii (cf. Table 3).
C o m m u n i t y A is found at the localities Nordreede-West, Diine-Kalberdans, West
Seite, Kringel, Nordhafenknoll, Nordmole a n d Skittgatt. With the exception of a deep
station at Skittgatt (10.8 m), all stations possess a well developed top layer of the b r o w n
Table 5. Ordered diagram resulting from the inverse analysis for species restricted to the photic zone
in the natural environment. For an explanation of the abbreviations and symbols see Table 3
Community:
Electra pilosa (Br)
TL-Laminaria hyperborea (BA)
Laminaria hyperborea (BA)
Delesseria sanguinea (RA)
Membranipora membranacea (Br)
Ulva sp. (GA)
Laomedea flexuosa (Hy)
TL-Larninaria saccharina (BA)
Laminaria sacchanna (BA)
Coralh'na officinalis (RA)
Plocamium cartilagineum (RA)
Polysiphonia nigra (RA)
Cladophora rupestris (GA)
Enteromorpha prolifera (GA)
Desmarestia aculeata (BA)
Elachista sp. (BA)
Membranoptera alata (RA)
Porphyra umbilicalis (RA)
Sphacelaria radicans (BA)
Petalonia fascia (BA)
Acervochalina loosanoffi (S)
EL-Ralfsia verrucosa (BA)
EL-Membranipora membranacea (Br)
Pol~des rotundus (RA)
Polysiphonia nigrescens (RA)
Cladophora albida (GA)
Polyclinum aurantium (T)
Molgula citn'na (T)
Esperiopsis fucorum (S)
Sphacelaria caespitosa (BA)
A
B
C
m00
QmO
aam
om~
D
E
F
G
H
332
M . J . de Kluijver
alga Laminaria hyperborea. The middle layer is dominated by red algae (dominant
species: Ceramium rubrum and Delesseria sanguinea), brown algae (dominant species:
Laminaria hyflerborea) and tubicolous organisms. These tubicolous organisms belong to
different taxa of Crustacea (Amphipoda, for instance Jassa falcata and corophiids) and
Polychaeta (Spionidae, for instance Polydora cfliata}. The red alga Membranoptera alata
is characteristic of this community. The bryozoans Membranipora membranacea and
Electra pflosa are often epiphytic on Laminaria hyperborea and on red algae, respectively. The encrusting layer is dominated by the red algae Phymatolithon sp. and
Hildenbrandia rubra. This community is established on the abrasion terraces around
Helgoland and D~ne, ranging from 4.7 to 10.8 m. The community is found on sloping
substrates (5-30~ composed of red sandstone, hmestone and concrete. The exposure to
water movement strongly varies with the topographic position in relation to the prevailing winds. Sediments available on the substrates belong to the types II, IV a n d V. On the
west side of I-Ielgoland mainly type II is found, while on the localities b e t w e e n the islands
Helgoland and Dfine only types IV and V are found. The stations with a well developed
top layer extend on the east side of the islands to a depth at which I7 % of the surface
light intensity is available and on the west side to a depth at which 13.5 % is available.
The station at Skittgatt, lacking a top layer, receives only 5.5 % of the surface light
intensity. The amount of dayhght received by the middle layer is strongly influenced by
the development of the top layer and the slope of the substrate. The station coefficient in
this layer varies between 4 and 87.5 %.
Community B is found at the locahties Kringel and H a m b u r g e r Loch. A top layer is
lacking. The middle layer is mainly formed by tubicolous organisms, the red alga
Phyllophora trail11, the hydrozoan Sertularia cupressina and the tunicate Sidnyum turbinatum. The bryozoan F.lectra pflosa is found epiphytic and epizoic on the other
organisms. The encrusting layer is dominated by bryozoans (dominan t species: A1cyonidium myti11). There is hardly any bare substrate left. The community occurs at the top of
sublittoral cliffs on the exposed west side of Helgoland at the lower limit of the photic
zone, between 9.2 and 10.0 m. The lack of a canopy of Laminaria hyperborea in this
community is caused by the diminished hght intensity at this depth (see also Liining,
1970, 1985}. Because of its greater depth, the influence of wave-induced w a t e r movement
is of less importance. The sediments found in this community belong to the coarse types I,
II and III, indicating a stronger tidal current than at the stations of community A. The
substrate is composed of red sandstone and limestone. The amount of daylight received
by the middle layer varies between 16 and 20 %, depending on the angle of inclination of
the substrates (10-70~
Community C is sampled at the location Dfine-Wittkliffbrunn, b e t w e e n 2.1 and
3.7 m. This community possesses a well developed canopy of the brown a l g a Laminaria
hyperborea. The middle layer is hardly developed; only Laminaria hyperborea and the
epiphytic growth form of Electra pilosa occur in substantial quantities. A characteristic
species of this community is the sponge Esperiopsis fucorum. The encrusting structural
layer is, hke the middle layer, hardly developed. This is probably caused b y the nature of
the substrate, which is composed of the erosive muschelkalk. The angle of inclination of
the substrates varies between 5 and 25~ The sediments belong to type II. The amount of
daylight received by the top layer varies between 37 and 57 % of the surface hght
intensity. The middle structural layer only receives i0 % of this irradiance.
Subhttoral communities off H e l g o l a n d
333
C o m m u n i t i e s restricted to the aphotic zone
The s e c o n d m a i n cluster (D, E a n d F) is also c o m p o s e d of three sublittoral communities (cf. d i a g r a m in Table 6). D o m i n a n t collective species of all t h r e e c o m m u n i t i e s
are tubicolous organisms, the p o l y c h a e t e Pomatoceros triqueter, the a n t h o z o a n Alcyon i u m digitatum a n d the encrusting a l g a Phymatofithon sp.
C o m m u n i t y D is found at the localities West Seite, Kringel, R e p u l s e g r u n d , Nordmole,
Sellebrunnknoll, Nordhafenknoll, H a m b u r g e r Loch and Dfine-Sfid b e t w e e n 6.3 a n d
Table 6. Ordered diagram resulting from the inverse analysis for species restricted to the apho~c
zone in the natural environment, For an explanation of the abbreviations and symbols see Table 3
Community:
Metfidium senile (An)
Tubulipora liliacea (Br)
EL-Escharella immersa (Br)
Disporetla hispida (Br)
Tubularia indivisa (Hy)
Kirchenpaueria pinnata (Hy)
C1iona celata (S)
Pleraplysilla m/nc/u" (S)
Dendrodoa grossularia (T)
EL-Electra monostachys (Br)
EL-Escharella variolosa (Br)
EL-Membraniporella nitida (Br)
EL-A1cyonidium mamillatum (Br)
Cladophora sericea (GA)
Nolella sp. [Br)
Bicellariella ciliata (Br)
Bugula flabellata (Br)
Crisia aculeata (Br)
Cellepora pumicosa (Br)
Polymastia mamillaris (S)
Mycale macilenta (S)
Haliclona urceolus (S)
Halidona oculata (S)
Oscarella lobularis [S)
Opercularella lacerata (Hy)
Halecium halecinum (Hy)
Zirfaea crispata (Bi)
Ascidiella scabra (T)
EL-Cellepora pumicosa (Br)
Pomatoceros triqueter (P)
Abietinaria abietina (Hy)
Biemna variantia (S)
EL-Smittina landsborovi (Br)
Cerianthus lloydii (An)
Lomentaria orcadensis (RA)
A
B
C
D
E
~ms
F
~ t
G
H
334
M . J . de Kluijver
Fig. 8. The variant of community D at West Seite, dominated by Metn'dium senile. On the left hand
side, two contracted colonies of the octocoral Alcyonium digitatum are present (photograph: Marcel
Carpay)
17.3 m. The c o m m u n i t y l a c k s a top l a y e r of b r o w n algae. T h e m i d d l e l a y e r is d o m i n a t e d
b y the a n t h o z o a n Metridium senile, the b r y o z o a n Flustra foliacea or tubicolous organisms. The e n c r u s t i n g layer is formed b y b r y o z o a n s a n d e n c r u s t i n g r e d a l g a e . S e d i m e n t s
found in this c o m m u n i t y b e l o n g to the t y p e s I, II, III a n d V. The c o m m u n i t y is e s t a b h s h e d
at relatively s h a l l o w depths (6.3-7.3 m) on vertical cliffs formed b y gullies in the a b r a s i o n
terraces a n d at g r e a t e r d e p t h s (9.9-17.3 m). T h e substrates consist of r e d s a n d s t o n e a n d
hmestone, sloping b e t w e e n 5 a n d 100 ~ The a m o u n t of d a y l i g h t r e c e i v e d b y this c o m m u nity in the g u l h e s amounts to 5.5 % a n d varies b e t w e e n 2 a n d 20.5 % at g r e a t e r depths.
Sublittoral communities off Helgoland
335
Fig. 9. The variant of community D at West Seite, dominated by Flustra fohacea. In the centre, an
expanded colony of the octocoral Alcyonium digitatum is present (photograph'. Marcel Carpay)
There are no characteristic species of this community. O n account of species a b u n d a n c e ,
this h e t e r o g e n e o u s c o m m u n i t y can b e divided into three physiognomic variants:
T h e first variant is d o m i n a t e d by the a n t h o z o a n ?r
senile {Pig. 8). This
variant is established b e t w e e n 6.3 a n d 15.1 m on sand- a n d limestone vertical cliffs. On
horizontal a n d sloping 5mestone substrates {5-45~ b e t w e e n 11.2 a n d 15.1 m, a second
variant is [ound, in which tubicolous organisms b e c o m e more a b u n d a n t .
O n nearly horizontal sandstone substrates {5-10~ b e t w e e n 11.6 a n d 17.3 m, the third
variant is estabhshed. This variant is dominated by the bryozoan F1ustra foliacea (Pig. 9).
The bryozoan Bugula flabellata is restricted to this variant, always epizoic on P1ustra
foliacea.
C o m m u n i t y E is found at the localities Nordmole, Dfine-Sfid, Nordreede-West, West
Seite, Repulsegrund a n d Steingrund, b e t w e e n 10.2 a n d 22.9 m. A top layer is not
developed in this community. The middle layer is dominated by the polychaete
Pomatoceros triqueter. Other d o m i n a n t species are the octocoral Alcyonium digitatum
a n d the anthozoan Metrich'um senile. The encrusting layer is formed by the red alga
Phymatoh'thon sp. b u t also m a n y bryozoan species are found in this layer. The sediments
b e l o n g to the types II, III and V. The substrate is composed of red s a n d s t o n e a n d
limestone. The stations are sampled on nearly horizontal substrates (0-30 ~ a n d on
vertical sides of boulders (60~ The a m o u n t of d a y h g h t received by the c o m m u n i t y varies
b e t w e e n 0.5 a n d 16 % of the surface intensity.
336
M . J . d e Kluijver
Table 7. Ordered diagram resulting from the inverse analysis for species restricted to the artificially
created harbours, For an explanation of the abbreviations and symbols see Table 3
Community:
A
B
C
D
E
F
G
H
Barnacles (Cr)
Botryllus schlosseri (T)
Bryopsis hypnoides (GA)
Clavelina lepadfformis (T)
Trailh'ella intricata {RA)
Halichondfia bow~rbanki (S)
Leuconia johnstoni (S)
Plumaria elegans (RA)
Antithamnion plumula (RA)
Callopora lineata (Br)
Conopeum reticulum (Br)
Sagartiogeton undatus (An)
Asddiella aspersa (T)
Ciona intestinalis (T)
Codium fragile (tenuous form) (GA)
Cryptosula paflasiana (Br)
Coryne sarsii (Hy)
Suberites ficus (S)
**Q
Fig. 10. Community H in the S/idhafen, dominated by the anthozoan Sagartiogeton undatus and the
tunicates Ascidiella aspersa, Ciona intestinahs and Botryllus schlosseri (photograph: Marcel Carpay)
Sublittoral communities
Community
Nordreede
F is f o u n d b e t w e e n
(Ost and West), between
community.
the islands Helgoland
The middle structural layer is dominated
and the polychaete
337
and Dfine, at the location
8 . 0 a n d 10.5 m . A t o p l a y e r is n o t d e v e l o p e d
by the anthozoan
in this
Met ri d i u m senile
Pomatoceros triqueter. T h e e n c r u s t i n g l a y e r is m a i n l y f o r m e d b y t h e
r e d a l g a Phymatolithon s p . T h e s e d i m e n t s
is composed
off H e l g o l a n d
of r e d s a n d s t o n e .
b e l o n g to t h e t y p e s II, V a n d VI. T h e s u b s t r a t e
The stations are sampled
on nearly horizontal substrates
T a b l e 8. O r d e r e d d i a g r a m of t h e distribution of t h e v a g i l e o r g a n i s m s over t h e different c o m m u n i t i e s .
T h e a b u n d a n c e is e x p r e s s e d as p e r c e n t a g e p r e s e n c e over t h e stations of a c o m m u n i t y . A b b r e v i a tions: Cr - C r u s t a c e a n , C h - Chelicerate, Ech - E c h i n o d e r m a t e , M - Mollusc, Pi - Pisces, P Polychaete
Community:
Archidoris pseudoargus (M)
Ctenolabrus rupestris (Pi)
Carcinus maenas (Cr)
Asterias rubens (Ech)
Ectn'nus esculentus (Ech)
Rissoa parva (M)
Gibbula cineraria (M)
Cancer pagurus (Cr)
Acanthodoris pflosa (M)
Myoxocephalus scorpius (Pi)
Nymphon rubrum (Ch)
A
B
C
23
31
15
85
77
100
46
23
20
40
.
100
100
20
-
50
-
D
31
60
.
.
.
50
100
71
50
80
50
29
50
60
E
F
G
H
10
10
17
33
17
83
17
83
50
67
17
33
17
17
17
67
67
100
-
.
100
100
40
60
70
15
38
I00
50
-
11
57
10
30
83
100
33
100
67
33
17
17
Caprella sp. (Cr)
Macropodia rostrata (Cr)
Hyas araneus (Cr)
Homarus gammarus (Cr)
Pholis gunnellus (Pi)
92
100
50
91
70
33
-
3
-
50
Enophrys bubalis (Pi)
Amphipholis squamata (Ech)
Ophiotrix fragilis(Ech)
Lepidochitona cinerea (M)
Polycera quadrilineata(M)
Galathea strigosa (Cr)
Pagurus bernhardus (Cr)
Pycnogonum littorale (Ch)
Dendronotus frondosus (M)
Janolus cristatus (M)
Coryphella pellucida (M)
Lepidonotus squamatus (P)
Gadus morhua (Pi)
8
8
-
-
3
40
-
-
-
23
20
8
-
-
3
-
-
15
20
-
-
6
6
2O
8
-
-
6
-
17
33
17
8
-
-
3
-
8
.
15
15
-
40
.
.
-
.
33
9
20
-
-
--
--
6
--
--
3
-
-
30
10
33
33
S y n g n a t h i d a e (Pi)
Pleuronectes platessa (Pi)
Zoarces viviparus (Pi)
Crossaster papposus (Ech)
10
-
17
-
17
-
-
338
M . J . de Kluijver
(10-20 ~ a n d vertical sides of b o u l d e r s (65~ The amount of d a y h g h t varies b e t w e e n 6 a n d
11.5 % of the surface intensity.
Communities restricted to artificially constructed harbours
The last m a i n cluster (G a n d H) consists of two communities s a m p l e d in s h e l t e r e d
h a r b o u r s in the s o u t h - e a s t of H e l g o l a n d . Table 7 shows the o r d e r e d d i a g r a m for this
cluster. Characteristic species of both communities a r e b a r n a c l e s a n d the tunicate
Botzyflus schlosseri.
Community G is restricted to the Vorhafen. Most stations are sampled on vertical
concrete quay-walls between 6.1 and 7.4 m. One station is sampled at red sandstone on
the bottom, with an angle of inclinationof 5~ The community does not possess a top layer.
The middle layer is dominated by tubicolous organisms and the tunicate Ascidiella
aspersa. Characteristic species are the tunicate Clavelina lepada'formis, the red alga
Trailh'ella intricata a n d the s p o n g e Hafichondria bowerbanki. The e n c r u s t i n g l a y e r is
d o m i n a t e d b y the r e d a l g a e Phyrnatolithon sp. a n d Hildenbrandia rubra. T h e a m o u n t of
d a y l i g h t r e c e i v e d b y the c o m m u n i t y varies b e t w e e n 6.5 a n d 10 % of the s u r f a c e intensity.
S e d i m e n t s on the b o t t o m of the h a r b o u r b e l o n g to the types III, V a n d VI.
C o m m u n i t y H is restricted to the s h e l t e r e d Sfidhafen. The stations w e r e s a m p l e d on
vertical surfaces of iron poles, b e t w e e n 4.2 a n d 5.1 m. A top l a y e r is missing. T h e m i d d l e
structural l a y e r is d o m i n a t e d b y tubicolous organisms, barnacles, the t u n i c a t e Botryllus
schlosseri a n d the characteristic tunicates Ascidiefla aspersa a n d Ciona intestinalis
(Fig. 10). O t h e r characteristic species are the ctenostome b r y o z o a n Bowerbankia sp. a n d
the a n t h o z o a n Sagartiogeton undatus. T h e s e d i m e n t on the b o t t o m of the h a r b o u r
b e l o n g s to the fine t y p e s VI a n d VII.
T a b l e 8 shows the distribution of the vagile organisms over t h e different communities. In the c o m m u n i t i e s with the h i g h e s t n u m b e r of sessile o r g a n i s m s (the w i d e s p r e a d algal d o m i n a t e d c o m m u n i t y A a n d the h e t e r o g e n e o u s c o m m u n i t y D, see T a b l e 9),
the h i g h e s t n u m b e r of v a g i l e o r g a n i s m s w e r e found. C o m m u n i t i e s w h i c h a c c o m o d a t e
only small n u m b e r s of v a g i l e o r g a n i s m s w e r e the other algal d o m i n a t e d c o m m u n i t i e s (B
a n d C) a n d the c o m m u n i t i e s restricted to the artificially constructed h a r b o u r s (G a n d H).
Especially c o m m u n i t y H, in the s h e l t e r e d Sfidhafen, houses very few v a g i l e animals. It
should b e k e p t in m i n d that t h e s e v a g i l e animals w e r e only r e c o r d e d w i t h i n t h e q u a d r a t s
of the stations. As t h e s e animals are vagile, only a faint i d e a of the r e a l a b u n d a n c e of
these organisms is g i v e n b y t h e s e records.
DISCUSSION
The first division in the d e n d r o g r a m (Fig. 4) divides the c o m m u n i t i e s into two groups,
viz.: c o m m u n i t i e s in t h e n a t u r a l e n v i r o n m e n t a n d in an artificially c o n s t r u c t e d environment. The m a i n difference b e t w e e n b o t h is c a u s e d b y the e x p o s u r e to w a t e r m o v e m e n t
a n d s u b s e q u e n t l y b y differences in sedimentation.
In the n a t u r a l e n v i r o n m e n t the sublittoral h a r d substrate c o m m u n i t i e s of H e l g o l a n d
are d e t e r m i n e d b y two major abiotic p a r a m e t e r s a n d two modifying ones. T h e a v a i l a b l e
a m o u n t of d a y h g h t restricts the d e p t h of the photic zone. In this zone the c o m m u n i t i e s a r e
d o m i n a t e d b y a l g a e in the top a n d m i d d l e layer. As stated b y Liining & D r i n g (1979), t h e
turbidity of the w a t e r s a n d thus h g h t conditions in the H e l g o l a n d r e g i o n a r e e x t r e m e l y
Sublittoral communities off H e l g o l a n d
339
Table 9. The contribution in % of different taxa to the community composition
Community:
A
B:
C.
D
E
F
G
H
Top layer
Brown algae
60.0
0.0
Middle layer
Red algae
Brown algae
Green algae
Anthozoans
Tunicates
Bryozoans
Hydrozoans
Sponges
Bivalves
Crustaceans
Polychaetes
Tubicolous organisms
80.0
0.1
0.0
0.0
0.0
0.0
28.6
14.7
1.1
3.2
1.5
13.3
7.8
1.7
0.1
0.2
0.5
13.3
24.8
2.0
1.2
4.3
5.2
16.6
11.9
1.5
0.1
0.2
0.0
30.9
4.2
12.4
0.1
0.3
0.2
9.7
3.8
3.3
0.3
0.0
0.0
0.3
1.9
0.5
0.0
23.8
0.9
34.3
7.2
4.5
0.2
0.2
0.9
15.9
0.0
0.0
0.0
20.9
0.0
1.4
3.3
0.5
0.0
0.4
46.2
2.4
1.0
0.2
0.1
48.2
0.3
0.7
1.1
0.1
0.0
0.3
6.6
0.9
22.2
0.0
0.3
2.0
22.4
1.9
2.8
10.6
0.0
2.0
0.9
11.0
1.8
0.1
0.7
1.9
68.1
0.8
5.5
4.6
0.0
26.1
0.1
12.7
Encrusting
layer
Red algae
Brown algae
Bryozoans
Bare substrate/sediment
18.4
0.1
3.1
27.7
3.2
0.0
12.1
8.8
2.9
0.0
0.8
82.0
4.9
0.0
7.3
14.6
16.5
0.0
7.7
7.7
38.5
0.0
2.3
5.3
29.0
0.0
0.0
7.6
0.0
0.0
0.2
12.5
Number of species
93
72
25
49
51
53
33
105
variable during different seasons. A l g a e d o m i n a t e d communities w e r e f o u n d d o w n to
depths at wh i c h 10 % of the surface h g h t intensity was available (De Kluijver, 1989; De
Kluijver et al., in prep.). As the exposure to w at er m o v e m e n t strongly v a r i e s with the
topographic position in relation to the p r e v a i h n g winds, this p a r a m e t e r cannot be
considered as a r e g u la to r in the photic zone. The nature of the substrate is, h o w e v e r , a
modifying parameter. Erosive substrates lead to poor d e v e l o p m e n t of the m i d d l e an d
encrusting structural layers.
Th e other c o m m u n i ti e s in the natural e n v i r o n m e n t are restricted to the aphotic zone.
Encrusting al g a e m a y b e present, but a l g a e in the middle layer are of m i n o r importance.
C o m m u n i t y E, d o m i n a t e d by the p o l y c h a e t e Pomatoceros triqueter, is p r o b a b l y the most
w i d e s p r e a d c o m m u n i t y in d e e p e r waters in the H e l g o l a n d region (K15ckner, 1976;
Anger, pers. comm.). U n d e r more e x p o s e d conditions on the west side of H e l g o l a n d , the
h e t e r o g e n o u s c o m m u n i t y D is found. T h e three variants display different p r e f e r e n c e s
r e g a r d i n g the a n g l e of inchnation and nature of the substrates. In the direction Nordreede, b e t w e e n H e l g o l a n d and Dfine, c o m m u n i t y E g r a d e s into c o m m u n i t y F. Th e
distribution of the s e d i m e n ts indicates a d e c r e a s e in current velocity, a n d the tidal
currents s e e m to b e forced around the west side of the collective b a s e of the islands,
instead of passing t h r o u g h the shallow p a s s a g e b e t w e e n the islands. T h e m a i n difference
b e t w e e n co m m u n it ie s E and F is the composition of the encrusting l ay er an d the
a b u n d a n c e of the p o l y c h a e t e Pomatoceros triqueter in the middle structural layer.
340
M . J . de Kluijver
The last two communities are located in the sheltered Vor- a n d Stidhafen, an
e n v i r o n m e n t w h e r e s e d i m e n t a t i o n e x c e e d s erosion. The community in the V o r h a f e n (G)
also contains faunal a n d floral e l e m e n t s that are common outside the q u a y - w a l l s in the
n a t u r a l environment. Some of the d o m i n a n t a n d characteristic s p e c i e s of c o m m u n i t y H
inside the e x t r e m e l y s h e l t e r e d Sfidhafen (for instance the a n t h o z o a n Sagartiogeton
undatus a n d the tunicates Botryllus schlosseri, Ciona intestinalis a n d Ascidiefla aspersa)
h a v e b e e n d e s c r i b e d as characteristic of the tideless salt w a t e r l a k e G r e v e l i n g e n in the
s o u t h - w e s t N e t h e r l a n d s (De Kluijver, 1989). The tunicates, characteristic of s h e l t e r e d
environments, are able to c r e a t e their own w a t e r movement, n e c e s s a r y for their food
s u p p l y (Hiscock, 1983). Moreover, these species are able to survive at l o w levels of
dissolved o x y g e n (Buizer, 1983). Suspension feeders (e.g. Metridium senile, Pomatoceros
triqueter a n d Flustra foliacea), d o m i n a n t in the e x p o s e d communities, are d e p e n d e n t on
tidal currents for their food s u p p l y (Hiscock, 1983). This distribution is c l e a r l y s e e n in
T a b l e 9. A c o m m u n i t y d o m i n a t e d b y Metridium senile has b e e n found in the e x p o s e d
m o u t h of the O o s t e r s c h e l d e estuary, south-west N e t h e r l a n d s (De Kluijver, 1989).
A l t h o u g h the communities are g o v e r n e d b y the environmental p a r a m e t e r s , m a n y
biotic interactions within the communities are also e x p e c t e d to b e of i m p o r t a n c e . T h e first
e x a m p l e of t h e s e biotic interactions are competitive interactions. A l t h o u g h definite proof
is lacking, competitive interactions are h k e l y to occur in the different structural layers of
all c o m m u n i t i e s (e.g. competition for s p a c e b e t w e e n Phymatoh'thon sp. a n d Hildenbrandia rubra, encrusting r e d a l g a e a n d bryozoans; the overgrowth of Pomatoceros triqueter
b y bryozoans, especially in c o m m u n i t y E [see also Rubin, 1985]; a n d c o m p e t i t i o n for
food). M o r e e x a m p l e s are given b y Moore (1983). All these interactions, h o w e v e r , t a k e
p l a c e u n d e r conditions c r e a t e d b y the e n v i r o n m e n t a l p a r a m e t e r s . For e x a m p l e , an
e n c r u s t i n g l a y e r only d e v e l o p s u n d e r conditions with low potential s e d i m e n t a t i o n . This
a g a i n d e p e n d s on the w a t e r m o v e m e n t a n d i n p u t of s u s p e n d e d matter. Light intensity
d e t e r m i n e s w h e t h e r a l g a e or b r y o z o a n s d o m i n a t e this layer. W h e n an e n c r u s t i n g l a y e r
d e v e l o p s u n d e r t h e s e conditions, it is irrelevant for the c o m m u n i t y s t r u c t u r e w h i c h
particular s p e c i e s occupies the substrates.
The s e c o n d e x a m p l e of biotic interactions is the effect of v a g i l e p r e d a t o r s , i n c l u d i n g
grazers, on c o m m u n i t y structure. O n e of the effects of p r e d a t i o n is the r e d u c e d p r e y
density. This m a y influence species richness a n d stability properties of t h e c o m m u n i t y
(Hughes, 1980, 1985). The distribution of vagile organisms (Table 8), w h i c h i n c l u d e s
s e v e r a l p r e d a t o r s (such as the N u d i b r a n c h i a Archidoris pseudoargus a n d Acanthodoris
pilosa a n d the E c h i n o d e r m a t a Asterias rubens a n d Echinus esculentus), d o e s n o t i n d i c a t e
a n y relation to a particular community. Especially d o m i n a n t p r e d a t o r s (Asterias rubens,
Table I0. Comparison between the erosion values of the gypsum blocks and the sediment characteristics
Erosion value
O.16
O.14
I
Station
Sediment type
I
I
2
3
II
O.10
[
1
6
i
I
1
V
t
I
~
1
5
IV
4
I [__J
VI
Sublittoral communities off H e l g o l a n d
341
Ecln'nus esculentus a n d the goldsinny Ctenolabrus rupestris) are distributed over a wide
variety of communities. The occurrence of the same p r e d a t o r s in the photic a n d aphotic
zone indicates a w i d e dietary preference. In the sheltered Sfidhafen, c o m m u n i t y H, the
low richness of sessile organisms (number of species = 33) is p r o b a b l y not c a u s e d b y a
low p r e d a t o r intensity (n = 3). C o m p a r i n g this community with other regions, the s a m e
community is found in the tideless l a k e G r e v e h n g e n in the south-west N e t h e r l a n d s (De
Kluijver, 1989). In the Dutch situation, 22 vagile organisms w e r e r e c o r d e d within this
community. The only species found at both locahties is the shore crab Carcinus maenas, a
real opportunist with a p r e f e r e n c e for the mussel Mytilus edulis (Hughes, 1980). However, M y t f l u s edulis is not found in c o m m u n i t y H.
All these aspects indicate that i n s t e a d of r e g u l a t i n g the subhttoral communities, the
vagile organisms in the s t u d i e d locahties d e p e n d t h e m s e l v e s on the distribution of their
p r e y organisms a n d on the e n v i r o n m e n t a l parameters.
E v a l u a t i o n of m e t h o d s
The q u a d r a t s a m p l i n g techniques a n d cluster analysis l e d to r e p r o d u c i b l e results. On
the basis of the results of 1987, seven subhttoral communities w e r e described. A c c o r d i n g
to the c o m p l e t e d d a t a - s e t covering the stations s a m p l e d in 1988 a n d 1989, t h e s e
communities did not c h a n g e a n d w e r e found to occur furthermore at the n e w stations (cf.
Table 1). A n e w c o m m u n i t y in the S/idhafen was sampled.
Similarly, the s e d i m e n t characteristics did not c h a n g e d u r i n g t h e s e years. The u s e of
these characteristics as an indicator of the tidal current velocity delivers the s a m e results
as those g a i n e d from the e x p e r i m e n t s using the g y p s u m blocks (Table 10). Both m e t h o d s
provide a relative scale w h i c h m a k e s it possible to c o m p a r e the total a m o u n t of w a t e r
m o v e m e n t at the different stations. In this study, the s e d i m e n t characteristics p r o v i d e a
more accurate scale, b u t for comparison of these communities with those in other
environments, for i n s t a n c e in estuaries w h e r e s e d i m e n t a t i o n e x c e e d s erosion, the use of
g y p s u m blocks (or a n o t h e r method) is necessary.
The d a t a analysis using the computer p r o g r a m T W I N S P A N y i e l d e d the d e n d r o g r a m
of Figure 11. C o m m u n i t i e s E, F, G a n d H are not affected by the other cluster m e t h o d . The
I
I
F
E
100%
100%
D
34%
I
D
40%
I
I
D+B
26+20%
I
B+A
A+C
G
80+8%
92+100%
100%
H
100%
Fig. 11. Dendrogram resulting from cluster analysis using TWINSPAN. A comparison of the
communities is made with CLUSTAN
342
M.J. de Klu~ver
m a i n d i f f e r e n c e i n t h e p h o t i c z o n e is t h a t T W I N S P A N d o e s n o t d i s c r i m i n a t e b e t w e e n
c o m m u n i t i e s A a n d C ( b o t h c o m m u n i t i e s w i t h a w e l l d e v e l o p e d c a n o p y of L a m i n a r / a
hyperborea). T h e o n l y s t a t i o n of c o m m u n i t y A w i t h o u t t h i s t o p l a y e r is a d d e d to t h e
e x p o s e d c o m m u n i t y B T h e h e t e r o g e n e o u s c o m m u n i t y D is d i v i d e d i n t o t h r e e g r o u p s as
well. T h e v a r i a n t d o m i n a t e d b y Metridium senile d u s t e r s w i t h c o m m u n i t i e s E a n d F ( b o t h
d o m i n a t e d b y Metridiurn senile). A n o t h e r d i v i s i o n is m a d e b e t w e e n t h e v a r i a n t d o m i n a t e d b y Flustra foliacea a n d t h e v a r i a n t d o m i n a t e d b y t u b i c o l o u s o r g a n i s m s .
D e s p i t e all t h e a d v a n t a g e s of T W I N S P A N (Hill, 1979), t h e o l d e r C L U S T A N p r o g r a m
is to b e p r e f e r r e d , b e c a u s e t h e s i m i l a r i t y b e t w e e n t h e s t a t i o n s is a f i x e d v a l u e , i n d e p e n d e n t of n e w d a t a i n p u t . T h i s g i v e s a m o r e s t a b l e r e s u l t w h e n n e w d a t a a r e a d d e d .
M o r e o v e r , T W I N S P A N d o e s n o t g i v e l e v e l s for n e w d i v i s i o n s . A s s i m i l a r i t y l e v e l s w i t h i n
d i f f e r e n t c o m m u n i t i e s a r e n o t t h e s a m e (e.g. c o m p a r e c o m m u n i t y D [ s i m i l a r i t y l e v e l 0,45]
a n d c o m m u n i t y H [ s i m i l a r i t y l e v e l 0.69]), it is difficult to d e c i d e w h e r e to s t o p n e w
divisions.
Acknowledgements. I wish to express my sincere thanks to the Biologische Anstalt Helgoland for the
hospitality and the use of laboratory and diving facilities during my stays; to G u n t h e r Tadday
(Arbeitsgruppe Gastforschung) for helping to solve all kinds of practical problems; to Udo Schilling,
Andreas a n d Thorsten K6hn, Dieter Klings, H. E. Lorenzen, Walter R6w and Hans H e r m a n L6sche
for their enthusiastic support during the sampling-trips with the "Diker" a n d "Aade"; to Dr Marcel
Carpay, Dr Bea Steiff, Andreas Krfiss M.Sc., Tatiana Eggert M.Sc., a n d Hans R e i c h e n b e r g e r for their
assistance during the diving work; Dr Marcel Carpay is also thanked for providing the photographs.
I a m most grateful to U d o Schilling and Juliane Schorn for their hospitality,Thanks are also due to Dr
Rob van Soest, Dr Wallie de Weerdt for the identification of the sponges; to Dr Bert Buizer for
checking the tunicates; to Dr J. C. den Hartog for checking some anthozoans; to Dr Jaap Kaandorp
and Prof. Dr S. van der Spoel for their criticalremarks; Jan Vermeulen is thanked for his practical
help in the Netherlands; Prof. Dr J. H. Stock and Dr R. W. M, van Soest of the Institute of Taxonomic
Zoology (Amsterdam) reviewed the firstdrafts of the manuscript. The "Wetterstation Helgoland"
and the "Wasser- und Schiffahrtsamt", T6nning provided essential data for, respectively, the
weather conditions and the water-levels. In 1987 thisinvestigation was supported by the Koninklijke
Nederlandse Akademie van Wetenschappen.
LITERATURE CITED
Anger, K., 1978. Development of a subtidal epifaunal community at the island of Helgoland. Helgol~inder wiss. Meeresunters. 31, 457--470.
Bloesch, J. & Burns, N. M , 1980. A critical review of sedimentation trap technique. - Schweiz. Z.
Hydrol. 42, 15-55.
Buizer, D. A. G., 1983. De Nederlandse zakpijpen (Manteldieren} en Mantelvisjes. Tunicata,
Ascidiacea e n Appendicularia. - Wet. Meded. K. n e d natuurh. Veren. 158, 1-42.
Caspers, H., 1938. Die Bodenfauna der Helgol~nder Tiefen Rinne. - HeIgol~inder wiss. Meeres~
unters. 2, 1-112.
Caspers, H., 1950. Die Lebensgemeinschaft der Helgol~inder Austerubank. - Helgol~inder wiss.
Meeresunters. 3, 120-169.
Caspers, H., 1952. Der tierische Bewuchs an Helgol~inder Seetonnen. - Helgol~inder wiss.
Meeresunters. 4, 138-160.
Gillandt, L, 1979a. Zur Oko[ogie der Polychaeten des He[gol~inder Felslitorals. - Helgol~inder wiss.
Meeresunters. 32, 1-35.
Gfllandt, L., 1979b. Zur Systematik, Biologie und Aut6kologie der Polychaeten des Helgol~nder
Felslitorals. - Mitt. hamb. zooL Mus. Inst. 76, 19-73.
S u b l i t t o r a l c o m m u n i t i e s off H e l g o l a n d
343
Gillbricht, M., 1987: Hydrographie, N~ihrstoffe u n d Phytoplankton bei Helgoland. - Jber. Biol. Anst.
Helgoland, 1986, 29-32.
Gislen, T., 1930. Epibioses of the Gullmar Fjord II. (Kristinebergs Zoologiska Station 1877-1927), SkrSer. K. svenska Vetensk Akad. I930 (4 i, 1-380.'
Hagmeier, A., 1930. Die Besiedelung des Felsstrandes und der Klippen von Helgoland. Teil 1. Der
L e b e n s r a u m . - Wiss. Meeresunters. (Helgoland) 15, 1-35.
Harms, J. & Anger, K., 1983. Seasonal, annual, and spatial variation in the development of hard
bottom communities. - Helgoliinder Meeresunters. 36, 137-150.
Hi]/, M. O., 1979. TWINSPAN - A FORTRAN program for arranging multivariate data in an ordered
two-way table by classification of individuals and attributes. Cornel/Univ., Ithaca, N. Y., 90 pp.
Hiscock, K., 1983. Water movement. In: The ecology of the shallow subhttoral benthos. Ed. by R. Earl
& D. G. El-win. Clarendon Press, Oxford, 58-96.
Hiscock, K. & Hiscock, S., 1980. Subhttoral piant and animal communities in the area of Roaringwater Bay, South-West Ireland. - J. Sherkin Isl. I, 7-48.
Hughes, R. N., 1980. Predation and community structure. In: The shore environment. Ed. by J. H.
Price, D. E. G. Irvine & W. F. Farnham. Acad. Press, London, 2, 699-728.
Hughes, R. N., 1985. Rocky shore communities: catalysts to understanding predation. In: The
ecology of rocky coasts. Ed. by P. G. Moore & R. Seed. Hodder & Stoughton, London, 223-233.
Janke, K., 1986. Die Makrofauna und ihre Verteilung im Nordost-Felswatt yon Helgoland. Helgol~nder Meeresunters. 40, 1-55.
Kaandorp, J. A., 1986. Rocky substrate communities of the infralittoral fringe of the Boulonnais coast,
NW France: a quantitative survey. - Mar. Biol. 92, 255-265.
K16ckner, K., 1976. Zur Okologie von Pomatoceros triqueter (Iinn6 1758) (Serpuhdae, Polychaeta).
Diss. Univ. Tfibingen, 168 pp.
Kluijver, M. J. de, 1989. Sublittoral hard substrate communities of the southern Delta area, SW
Netherlands. - Bijdr. Dierk. 59, 141-158.
K6nnecker, G. & Keegan, B. F., 1983. Littoral and benthic investigations on the west coast of Ireland
- XVII. The epibenthic animal associations of Kilkieran Bay. - Proc. R. Ir. Acad. 83B, 309-324.
Kornmann, P. & Sahhng, P.-H., 1977. Meeresalgen von Helgoland. - Helgol~nder wiss. Meeresunters. 29, 1-289.
Korringa, P,, 1968. Biological consequences of marine pollution with special reference to the North
Sea fisheries. - Helgol~nder wiss. Meeresunters. 17, 126-140.
Lfining, K., 1970. Tauchuntersuchungen zur Vertikalverteilung der sublitoralen Helgol~inder Algenvegetation. - I-Ielgol~inder wiss. Meeresunters. 21,271-291.
Lfining, K., 1985. Meeresbotanik. Thieme, Stuttgart, 375 pp.
Lfining, K. & Dring, M. J., 1979. Continuous underwater fight measurement near Helgoland (North
Sea) and its significance for characteristic light bruits in the subhttoral region. - Helgol~inder
wiss. Meeresunters. 32, 403-424.
Markham, J. W. & Munda, I. M., 1980. Algal recolonization in the rocky eulittoral of Helgoland. Aquat. Bot. 9, 33-71.
Martens, P., 1978. Contribution to the hydrographical structure of the eastern German Bight. Helgol~inder wiss. Meeresunters. 3I, 414-424.
Moore, P. G., 1983. Biological interactions. In: The ecology of the shallow sublittoral benthos. Ed. by
R. Earl & D. G. Erwin. Clarendon Press, Oxford, 125-143.
Munda, I. M. & Markham, J. W., 1982. Seasonal variations of vegetation patterns and biomass
constituents in the rocky eulittoral of Helgoland. - Helgol~nder Meeresunters. 35, 131-151.
Rubin, J. A., 1985. Mortality and avoidance of competitive overgrowth in encrusting Bryozoa. - Mar.
Ecol. Prog. Ser. 23, 291-299.
Ruijter, W. P. M. de, Postma, L. & Kok, J. M. de, 1987, Transport atlas of the southern North Sea.
Rijkswaterstaat, The Hague, 33 pp.
Shin, P. K. S., 1982. Multiple discriminant analysis of macrobenthic infaunal assemblages. - J. exp.
mar. Biol. Ecol. 59, 39-50.
Soest, R. W. M. van & Weinberg, S., 1981. Preliminary quantitative assessment of the marine hard
substrate communities of Roaringwater Bay. - J. Sherkin IsL I (2), 10-26.
Sokal, R. R. & Michener, C. D., 1958. A statistical method for evaluating systematic relationships. Kansas Univ. Sci. Bull. 38, 1409-1438.
344
M.J. de Kluijver
Straaten, L. M. J. U. van, 1973. De zee I: Water e n waterbeweging. In: A l g e m e n e geologie. Ed. b y
A. J. Pannekoek. Tjeenk Willink, Groningen, 411-417.
Weinberg, S., 1978. The minimal area problem in invertebrate communities of M e d i t e r r a n e a n rocky
substrate. - Mar. Biol. 49, 33-40.
Weinberg, S., 1979. M e d i t e r r a n e a n shallow-water Octocorallia. I. Ecology. Diss. Univ. of Amsterdam, 168 pp.
Wills, L, J., 1968. Palaeogeographical atlas. Blackie, London, 64 pp.
Wishart, D., 1978. CLUSTAN user manual. Program Library Unit, Edinburgh Univ., Edinburgh,
175 pp.