Commemorative volume for the 80th birthday of Willem Vervoort in 1997
The occurrence of Sagartia elegans (Dalyell, 1848)
(Anthozoa: Actiniaria) in the Netherlands
R . M . L . A t e s , R . D e k k e r , M . A . Faasse & J . C . d e n H a r t o g
Ates, R.M.L., R. Dekker, M . A . Faasse & J . C . den Hartog. The occurrence of Sagartia elegans (Dalyell,
1848) (Anthozoa: Actiniaria) in the Netherlands.
Zool. Verh. Leiden 323, 31.xii.1998: 263-276, figs 1-3, tabs 1-5.— ISSN 0024-1652/ISBN 90-73239-68-0.
R.M.L. Ates, Govert Flinckstraat 19,1506 L L Zaandam, The Netherlands, e-mail: [email protected].
R. Dekker, Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 A B Den Burg, Texel, The
Netherlands, e-mail: [email protected].
M . A . Faasse, Schorerstraat 14, 4341 G N Arnemuiden, The Netherlands.
J.C. den Hartog, National Museum of Natural History (NNM), P.O. Box 9517, 2300 R A Leiden, The
Netherlands, e-mail: [email protected]. [Address for reprint requests].
Key words: Actiniaria; Sagartia elegans; Dutch coast; distribution; winter temperatures; larval dispersal.
The occurrence of the sea anemone Sagartia elegans var. miniata, var. nivea and var. venusta in considerable numbers at three localities in the Netherlands is reported upon. Previous records of the species in
Dutch coastal waters are reviewed. Most of these are considered as doubtful. Characters to distinguish S. elegans from S. troglodytes are discussed. Attempts are made to relate local occurrence of S.
elegans with temperature data. Sagartia elegans is an autochthonous species in the Netherlands but its
numbers vary considerably, and populations probably have no permanent character. In the past, populations presumably have been reduced and sometimes wiped out during relatively severe winters.
Reinforcement of rest populations or recolonization is likely to happen through planktonic larvae
from the Channel area and from off-shore populations. Recovery of populations in Dutch coastal
waters apparently takes place after consecutive mild winters.
Introduction
D u r i n g 1990 a n d subsequent years extensive p o p u l a t i o n s o f the a c o n t i a r i a n sea
a n e m o n e Sagartia elegans ( D a l y e l l , 1848) w e r e f o u n d at different sites a l o n g the D u t c h
coast. T h i s is r e m a r k a b l e , as the species w a s c o n s i d e r e d to b e rare i n the N e t h e r l a n d s .
A l t h o u g h its occurrence i n D u t c h w a t e r s w a s r e p o r t e d u p o n f r o m 1897 o n w a r d s , a l l
records u n t i l 1950 w e r e c o n s i d e r e d d o u b t f u l b y V a n U r k (1952). I n the present p a p e r
the records of S. elegans i n the N e t h e r l a n d s since 1950 are r e v i e w e d , a n d recent observations added.
I n a p a p e r o n the d i s t r i b u t i o n of A n t h o z o a i n the s o u t h - w e s t of the N e t h e r l a n d s
B r a b e r & B o r g h o u t s (1977) s u g g e s t e d that Sagartia elegans is sensitive to c o l d w i n t e r s .
A f t e r h a v i n g b e e n o b s e r v e d i n 1962, the species d i s a p p e a r e d d u r i n g the severe w i n t e r
of 1962/ 63. T h e observations of S. elegans f r o m 1990 o n w a r d s w e r e m a d e after a series
of m i l d w i n t e r s . Therefore i t w a s d e c i d e d to relate a l l reliable a u t o c h t h o n o u s
records
of the species to the m i n i m u m seawater t e m p e r a t u r e s i n the w i n t e r p r e v i o u s to each
o b s e r v a t i o n . F o r that p u r p o s e a l l post-1950 literature w a s s c a n n e d , as w e l l as the soc a l l e d C e n t r a l S y s t e m (C.S.), a c o l l e c t i o n of r e c o r d files of the S t r a n d w e r k g e m e e n schap (a D u t c h society of m a r i n e naturalists) k e p t i n the N a t i o n a a l N a t u u r h i s t o r i s c h
M u s e u m at L e i d e n .
264
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
Records of Sagartia elegans in the Netherlands prior to 1990
Records of Sagartia elegans d a t i n g f r o m before 1950 w e r e r e v i e w e d a n d discussed
b y V a n U r k (1952), w h o c o n c l u d e d that a l l records u n t i l then s h o u l d be r e g a r d e d as
d o u b t f u l ( i n c l u d i n g h i s o w n ) a n d that the species c o u l d h a r d l y be considered
autochthonous i n the N e t h e r l a n d s . A n d i n d e e d , records available f r o m this p e r i o d are
v a g u e o r altogether l a c k i n g descriptive notes, a n d n o t s u p p o r t e d b y v o u c h e r speci­
mens.
A m o n g the records discussed b y V a n U r k w a s a n u n p u b l i s h e d allochthonous one
b y D . v a n N i e v e l t f r o m the files of the former Z o o l o g i c a l Station of the D u t c h Z o o l o g ­
ical Society. V a n N i e v e l t (1953), i n a w r i t t e n defence, questioned V a n U r k ' s c o n c l u ­
s i o n as to this record, a n d , a l t h o u g h n o t c l a i m i n g V a n U r k to be definitely w r o n g ,
suggested it to have borne p o s i t i v e l y u p o n S. elegans. The record concerned t w o i n d i ­
v i d u a l s , 13 a n d 2 m m i n diameter, w a s h e d ashore o n the beach of D o m b u r g , p r o v i n c e
of Z e e l a n d , a m o n g a cluster of egg-capsules of the C o m m o n W h e l k Buccinum undatum L i n n a e u s , 1758. A f t e r they h a d been transferred to a n a q u a r i u m , the largest
anemone " p r o d u c e d a second j u v e n i l e " . The large s p e c i m e n h a d a b r i g h t l y orangeb r o w n c o l u m n w i t h w h i t e dots. W h e n offered f o o d it repeatedly emitted acontia
t h r o u g h the c o l u m n a n d sometimes t h r o u g h the m o u t h . These descriptive notes are
i n d e e d most suggestive of S. elegans except for the c l a i m that the a n i m a l " p r o d u c e d a
second j u v e n i l e " . T h i s suggests that V a n N i e v e l t actually observed v i v i p a r i t y , w h i c h
w o u l d not p o i n t at S. elegans. [It is true that v i v i p a r i t y has occasionally been suggest­
e d for this species, even quite recently (Ates, 1989: 25, e x p l i c i t l y for the var. venusta),
but never b e y o n d doubt]. O n the other h a n d V a n N i e v e l f s d e s c r i p t i o n does n o t
m a t c h any of the manifestly v i v i p a r o u s acontiate species k n o w n f r o m the D u t c h coast
a n d adjacent areas, v i z . : Sagartia ornata ( H o l d s w o r t h , 1858), Cereus pedunculatus (Pen­
nant, 1777), a n d Hormathia coronata (Gosse, 1858). It therefore seems that the s p e c i m e n
w a s i n d e e d S. elegans, a n d that V a n N i e v e l f s statement that it " p r o d u c e d a l i v i n g
j u v e n i l e " w a s a n interpretation rather than a n actual observation, the juvenile con­
cerned i n i t i a l l y h a v i n g been o v e r l o o k e d (cf. e.g. Stephenson, 1935: 323).
A l l records of Sagartia elegans f r o m between 1950 a n d 1990 traced i n the literature
a n d the " C e n t r a l S y s t e m " are listed i n table 1.
Table 1 (cf. fig. 1). Synopsis of the records of Sagartia elegans along the Dutch coast for the period 19501990. Reliable autochthonous records are marked with an asterisk (*). Autochthonous (Aut.) and
allochthonous (All.) records are indicated. C.S. = Central System, the collection of record files of the
Strandwerkgemeenschap; R M N H Coel. = Coelenterate collection of the former Rijksmuseum van
Natuurlijke Historie, now National Museum of Natural History (NNM), at Leiden; Vlissingen =
Flushing.
Date
Locality
Status
Ν
viii.1950
Schouwen
Aut.
?
Source
Remarks
C. den Hartog
Undocumented record
et al., 1951:100
ll.iv.1953
't Horntje, Texel
Aut.
2
C.S. (Stock & Swennen)
Undocumented record;
17.iv.1954
Terschelling
All.
2
C.S. (Swennen)
R M N H Coel. 4869
specimens mislaid
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
8.X.1955
Noord wijk/
All.
3
Noordwijkerhout
C.S. (A.W.Lacourt);
R M N H Coel. 17712 (3
Spaink, 1957:11
specimens); Sagartiogeton
Undocumented record;
265
undatus
26.iv.1958
Terschelling
Aut.
1
C.S. (Swennen)
18.X.1958
Huisduinen
All.
3-4
Den Hartog, 1959: 6
eastern mole of harbour.
Misidentification;
Actinothoe sphyrodeta
2.viii.l960
Den Helder
All.
3
Den Hartog, 1962a: 11
Idem.
24.viii.1960
Den Helder
All.
2
Den Hartog, 1962a: 11
Idem.
26.viii.1960
Den Helder
All.
4
Den Hartog, 1962a: 11
Idem.
*18.i.l961
Huisduinen
Aut.
1
Den Hartog, 1962b
Documented record.
23.iii.1961
Scheveningen
All.
1
C.S. (Swennen)
Undocumented record;
from egg-capsules of
Common Whelk.
Early 1962
Schouwen
Aut.
?
Braber & Borghouts,
Early 1962
Vlissingen
Aut.
?
Braber & Borghouts,
Undocumented record.
1977:19-20
Idem.
1977:19-20
*12.xi.l962.
Mole Ν of
Aut
ca 10
Den Hartog, unpubl.
Conclusive field notes; near
Aut.
50-60
Den Hartog, unpubl.
Idem.
Aut.
1
Adema, 1978: 111
Undocumented record;
Beach-marker 3
*16.xi.l962
Nollepier,
low water mark.
Vlissingen
18.X.1977
Gorishoek/
Tholen
probably S. troglodytes.
26.xii.1977
Flauwers
Aut.
5
Adema, 1978: 111.
Idem.
25.vii.1978
Noord-Beveland
Aut
many
W. Dekker: 114
Idem.
21.Χ.1978
Flauwers
Aut.
1
Adema, 1979: 99
Idem.
l.viii.1981
Kats
Aut.
1
Slager, 1982:16-17
Idem.
l.viii.1981
Sas van Goes
Aut.
C.S. (Huysman).
Idem.
X.1981
Gorishoek
Aut.
1
?
Huysman, 1982: 33
Idem; purple variety.
X.1982
Terschelling
Aut.
?
Huysman, 1983:19
Undocumented record of
var. aurantiaca?; presumably
S. troglodytes.
19.X.1982
West-Terschelling Aut.
2
Slager, 1983:150
Undocumented record.
*8.x.l983
Burghsluis
Aut.
3
Ates, 1989
Documented record.
17.ii.1988
Zoutelande
All.
2
Rappé, 1988:129
In boring holes of Barnea
candida (Linnaeus, 1758) in
lump of peat; hence more
likely to refer to S. troglodytes
or Sagartiogeton undatus.
M o s t records l i s t e d w e r e p r o v i d e d b y non­specialists, a n d are i n s u f f i c i e n t l y d o c u ­
m e n t e d to a l l o w i d e n t i f i c a t i o n a f t e r w a r d s
(no v o u c h e r s p e c i m e n s a n d n o relevant
d e s c r i p t i v e i n d i c a t i o n s b e i n g available) a n d bear p r e s u m a b l y u p o n b r i g h t l y c o l o u r e d
s p e c i m e n s of Sagartia troglodytes (Price, 1847).
S o m e of these records m a y here b e f u r t h e r e l u c i d a t e d a n d d i s c u s s e d :
—
The allochthonous
record b y Swennen,
RMN H
C o e l . 4869, concerns t w o v e r y
s m a l l rather p o o r l y p r e s e r v e d s p e c i m e n s w h i c h are p o s i t i v e l y S. elegans [ a n a t o m y
s l i g h t l y a s y m m e t r i c a l ; nematocysts i n acontia: p e n i c i l l i ca 49­57 χ 5.3­5.8 μιη; s p i r u ­
lae ca. 14­16 χ 1.8 μ ι η a n d 28.5­33 χ 3.1­3.6 μ ι η (cf. table 3)].
266
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
Fig. 1. Map of the coast of the Netherlands indicating all localities with reliable records of autochthonous Sagartia elegans. Open circles = pre-1990 records; black dots = post-1990-records.
1. West-Terschelling; 2. 't Horntje; 3. Huisduinen; 4. Beach-marker 3, near Den Helder; 5. Burghsluis; 6
Westbout; 7. Northern end of storm surge barrier, Schouwen; 8. Borrendamme; 9. Lokkersnol (near
Cauwers-inlaag); 10. Weldamseweg; 11. Neeltje Jans; 12. Southern end of storm surge barrier, NoordBeveland; 13. Jacobahaven; 14. Anna Friso; 15. Westkapelle; 16. Zoutelande; 17. Nollepier, Vlissingen;
18. Ritthem.
For topographic details and exact co-ordinates of these localities, see Topografische Dienst Nederland
(TDN), 1995.
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
—
267
T h e record p u b l i s h e d b y S p a i n k (1957: 11; c o m m u n i c a t e d b y A . W . Lacourt) of
thousands of sea anemones, m o s t l y S. elegans a n d S. troglodytes, f o u n d w a s h e d u p
o n the beach at No o r d w i j k ­ No o r d w i j k e r h o u t o n 8.x.1955, represents a m i s i d e n t i f i ­
cation as far as S. elegans is concerned. A s a m p l e f r o m the collection of the late M r
A . W . Lacourt, labelled Sagartia elegans, N o o r d w i j k e r h o u t , 8.X.1955, A . W . Lacourt,
V I I C 6 , n o w i n the R M N H collection ( R M N H C o e l . 17712), actually contains 3
specimens of Sagartiogeton undatus (re­identification J.C. d e n H a r t o g , 1987).
T h i s p h e n o m e n o n of massive strandings of sea anemones,
p r e d o m i n a n t l y S.
troglodytes, u s u a l l y m i x e d w i t h m u c h smaller n u m b e r s of Metridium
senile ( L i n ­
naeus, 1761) a n d Sagartiogeton undatus (O.F. Müller, 1788), has been k n o w n f o r a
l o n g time f r o m the s a n d y beaches of the p r o v i n c e s of N o r t h a n d S o u t h H o l l a n d
a n d still occurs r e g u l a r l y . So far these strandings have never y i e l d e d a n y S.
elegans.
—
F o u r records of allochthonous specimens b y J.C. d e n H a r t o g (1959: 6; 1962a: 11­
12), c l a i m e d to b e l o n g to Sagartia elegans var. venusta, w e r e based o n m i s i d e n t i f i c a ­
tions a n d actually bore u p o n Actinothoe sphyrodeta (Gosse, 1858). T h e y constitute
the first records of that species i n the N e t h e r l a n d s .
—
The record b y J.C. d e n H a r t o g (1962b) of a n autochthonous i n d i v i d u a l of S. elegans
var. miniata f o u n d just b e l o w l o w water m a r k o n the sea­dike at H u i s d u i n e n near
D e n H e l d e r o n 18.L1961, is p r o v i d e d w i t h clear descriptive notes a n d leaves n o
d o u b t about the i d e n t i t y of the specimen. It is the first authentic
autochthonous
record of Sagartia elegans i n the N e t h e r l a n d s .
—
U n p u b l i s h e d finds b y J.C. d e n H a r t o g of ca 10 specimens o n a jetty near beach­
marker 3 (close to D e n H e l d e r ) o n 12.xi.1962, a n d of 50­60 large specimens (measur­
i n g u p to at least 3 c m across the base) o n the N o l l e p i e r at V l i s s i n g e n o n 16.xi.1962,
leave no doubt either.
—
The records b y Braber & Borghouts (1977) are unfortunately u n d o c u m e n t e d . Their
sea anemone collection, donated b y the D e l t a Institute, Yerseke, to the Na t i o n a a l
N a t u u r h i s t o r i s c h M u s e u m , L e i d e n , contained n o samples of Sagartia elegans.
Records of Sagartia elegans in the Netherlands since 1990
In 1990, p o p u l a t i o n s of Sagartia elegans w e r e d i s c o v e r e d at three localities a l o n g
the D u t c h coast, v i z . near Z o u t e l a n d e a n d W e s t k a p e l l e i n the p r o v i n c e of Z e e l a n d ,
a n d n e a r ' t Horntje o n the Island of Texel (fig. 1). The records of the species since 1990
are s u m m a r i z e d i n table 2.
Table 2 (cf. fig. 1). Synopsis of autochthonous records of Sagartia elegans along the Dutch coast since
1990. A l l records refer to the var. miniata, unless stated otherwise.
Date
Locality
Ν
Observer/
collector
Remarks
30.iii.1990
Zoutelande
100s
Faasse
Attached to stones at MLWS-level. Bases
of some anemones surrounded by freshly
accumulated sand. Some anemones with
shell debris attached to column. A few
268
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
specimens of the varieties nivea and
venusta among predominating var. miniata.
29.iv.1990
Zoutelande
100s
Faasse
Intertidal, among stones of breakwater
near low water mark. Including specimens of var. nivea and var. venusta; 10
specimens collected ( R M N H Coel. 18794).
1.V.1990
Zoutelande
100s
Den Hartog
Idem. Including 1 specimen of var. nivea;
& Faasse
8 specimens collected (RMNH Coel. 18501).
16.ix.1990
W-Terschelling
1
Dekker
Depth 10 m ( R M N H Coel. 18508).
15.X.1990
't Horntje
1
Dekker
MLWS-level ( R M N H Coel. 18507).
19.X.1990
21.xi.1990
't Horntje
1
Dekker
MLWS-level.
't Horntje
6
Dekker
MLWS-level.
14.xii.1990
't Horntje
2
Dekker
Intertidal? One specimen of var. nivea.
19.xii.1990
't Horntje
18
Dekker &
Var. miniata and var. nivea.
15.Í.1991
't Horntje
30-40
Ates
Dekker &
MLWS-level. Including var. nivea;
Ates
var. miniata predominating.
29.Í.1991
't Horntje
5
Dekker
MLWS-level. Including var. nivea.
2.iii.l991
Vlissingen
5
Faasse
—
25.Í.1992
Zoutelande
100s
Faasse
Especially below low water mark.
22.ii.1992
Schouwen
10
Faasse
Near northern end of storm surge barrier
7.iii.l992
Ritthem
1
Faasse
in Oosterschelde.
—
l.x.1992
Zoutelande
30
Ates&
Subtidal (SCUBA dive). Dramatic decline
Faasse
of population in this locality caused by
supply of sand for coastal protection.
Including var. nivea.
10.X.1992
Neeltje Jans
1
Faasse
On a pontoon.
ll.iii.1993
't Horntje
2
Dekker
MLWS-level.
29.vi.1993
Neeltje Jans
15
Faasse
On a pontoon, var. venusta.
20.xi.1993
Westkapelle
10s
Faasse
—
29.xi.1993
't Horntje
2
Dekker
Under stones, 0.5 m below low water
12.ii.1994
Westkapelle
10s
Faasse
mark ( R M N H Coel. 18795).
—
ll.vi.1994
Borrendamme
1
Faasse
Subtidal (SCUBA dive).
6.VÜÏ.1994
Lokkersnol
1
Faasse
Idem.
3.ÍX.1994
Wissenkerke
1
Faasse
Idem. Depth 35 m.
15.X.1994
Zoutelande
10s
Faasse
Subtidal (SCUBA dive). Varieties miniata,
5.XÍ.1994
Weldamseweg
1
Ates&
Subtidal (SCUBA dive).
12.xi.1994
Westbout
28
Faasse
Idem; including 8 specimens var. nivea
3.Ü.1995
Jacobahaven
ca 20
Faasse
Intertidal.
3.Ü.1995
Noord-Beveland
100s
Faasse
Including 6 specimens of var. nivea. Near
nivea, and venusta.
Faasse
and 1 specimen var. venusta.
southern end of storm surge barrier in
Oosterschelde.
3.V.1995
Westbout
ca 40
Faasse
incl. var. nivea.
5.V.1995
Weldamseweg
2
Ates&
Subtidal (SCUBA dive). Including 1 sp. of
Faasse
var. nivea and 1 var. rosea.
20.V.1995
Weldamseweg
22
Faasse
Subtidal (SCUBA dive). Including 20
l.vii.1995
Neeltje Jans
10s
Faasse
On a pontoon. Including ca 5 specimens of
specimens of var. nivea.
var. venusta
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
269
12.vii.1995
Westkapelle
10s
Faasse
Subtidal (SCUBA dive).
16.ix.1995
Weldamseweg
2
Ates &
Subtidal (SCUBA dive).
29.xi.1995
Burghsluis
11
Faasse
Intertidal.
29.xi.1995
Schouwen
ca 30
Faasse
Near northern end of storm surge barrier
Faasse
in Oosterschelde. Including 1 specimen
var. nivea.
9.iii.l996
Neelrjejans
ca20
Faasse
Intertidal.
26.vi.1996
Westbout
4
Faasse
Subtidal (SCUBA dive).
26.vii.1996
Anna Friso
10
Faasse
Including 6 specimens of var. venusta.
14.xii.1996
Westbout
6
Faasse
Intertidal.
ll.iii.1997
Westkapelle
ca 30
Faasse
Intertidal.
The locality near Z o u t e l a n d e w a s v i s i t e d n u m e r o u s times. Therefore o n l y some
k e y data are listed i n the table. A l t h o u g h the p o p u l a t i o n at this locality seemed o n the
decline ever since it w a s d i s c o v e r e d o n 30 M a r c h 1990, considerable n u m b e r s ( h u n dreds) w e r e still present u n t i l at least January 1992, especially concentrated s u b t i d a l l y . H o w e v e r , i n the s u m m e r of 1992 a t h i c k layer of s a n d w a s s u p p l i e d to the beach of
this locality for coastal protection. T h i s h a d a devastating effect o n the p o p u l a t i o n as
revealed b y a S C U B A d i v e o n 1 October, w h e n n o m o r e t h a n a p p r o x i m a t e l y 30 surv i v i n g specimens w e r e f o u n d . Since, the p o p u l a t i o n s u r v i v e d u p to at least 15 A p r i l
1995 ( w h e n t w e n t y specimens w e r e observed s u b t i d a l l y (Faasse; S C U B A d i v e ) .
A t the locality near 't Horntje, Texel, the species w a s frequently o b s e r v e d u p to 29
January 1991. F o l l o w i n g a n icy s p e l l i n F e b r u a r y 1991, n o specimens w e r e f o u n d
despite intensive search, b o t h i n t e r t i d a l l y a n d s u b t i d a l l y . A f t e r a n absence of m o r e
than t w o years the species re-appeared i n M a r c h 1993.
It is w o r t h m e n t i o n i n g that the var. nivea (oral disc a n d tentacles w h i t e ; Z o u t e lande, Westbout, 't Horntje) a n d the var. venusta (oral disc p l a i n orange, tentacles
w h i t e ; Z o u t e l a n d e , Westbout) w e r e not p r e v i o u s l y r e c o r d e d i n the N e t h e r l a n d s .
Characters distinguishing Sagartia elegans and S. troglodytes
Sagartia elegans a n d S. troglodytes are h a r d to confuse b y specialists a n d b y those
w h o b y experience h a v e learned to d i s t i n g u i s h b e t w e e n b o t h species i n the f i e l d . In
spite of this, most of the autochthonous D u t c h records of S. elegans u n d o u b t e d l y bear
u p o n S. troglodytes. T h i s is d u e to the fact that these records w e r e p r o v i d e d b y n o n specialists a n d amateur naturalists of the ' S t r a n d w e r k g e m e e n s c h a p ' w h o p o s s i b l y
h a d never seen the species, b u t w h o a p p a r e n t l y k n e w f r o m the literature or b y
hearsay that b o t h species occur i n the N o r t h Sea a n d w e r e to be expected o n the
D u t c h coast. T h u s , l a c k i n g b o t h sufficient f i e l d experience a n d k n o w l e d g e (and
equipment!) to take into account relevant a n a t o m i c a l a n d m i c r o s c o p i c a l characters,
they generally seem to have based their identifications o n a c o m b i n a t i o n of v a g u e
indications a n d w i s h f u l t h i n k i n g .
N o t a b l y for this reason it m a y here be u s e f u l to present a n d discuss once m o r e the
differences b e t w e e n the t w o species (table 3). These w e r e p r e v i o u s l y s u m m a r i z e d , b u t
not f u l l y so, b y Stephenson (1935: 338-340) a n d M a n u e l (1981:142, table 1).
270
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Table 3. Differences between Sagartia elegans and S. troglodytes.
Sagartia elegans
Sagartia troglodytes
1. Habitat
Often in mud or sand, the base fixed to
Usually on hard substrata in localities
without, or with only little sedimentation. submerged solid substrata such as
2. Columnar
Suckers usually conspicuous, visible as
Suckers rather inconspicuous, strongly
suckers
distinct pale dots, very weakly adherent
adherent, often attaching course shell
and only rarely with attached fine debris
gravel, etc.
stones, shells, etc.
or shellfragments.
3. Colour and
pattern
Pattern of the oral disc and tentacles in
Pattern and colour of oral disc and
bright tints and relatively uniform.
tentacles extremely variable, often in
Insertions of mesenteries usually obscure.
dull colours, but specimens with a
predominantly brightly orange, purple
or opaquely white oral discs are not
uncommon. Insertions of mesenteries
usually distinct in at least the lowest
part of the column.
4. Asexual
reproduction
Frequent pedal laceration, often giving
Absent. Never occurring in groups of
rise to smaller or larger groups of
identically coloured specimens.
identically coloured individuals.
5. Symmetry
Often somewhat irregular due to asexual
Hexamerous.
reproduction.
6. Texture
7. Acontia
8. Cnidom of
Relatively soft and easily damaged when
Relatively tough and less vulnerable to
detached from its substratum.
damage.
Relatively thick, usually present in
Very thin and relatively inconspicuous.
profusion and emitted freely upon
Only emitted by highly stressed or
irritation.
damaged specimens.
Spirulae: 34.9(32.0-37.8) x 3.6(3.6-4.0)
Spirulae: 15.4(13.4-16.5) x 2.6(2.4-2.7)
acontia (cf.
[Spirulae: 15.8(14.2-17.8) x 2.0(1.8-2.2)]
[Spirulae: 15.1(13.4-16.0) χ 1.4(1.3-1.6)]
fig-2)
Penicilli: 60.2(56.1-65.8) χ 5.8(5.3-6.2)
Penicilli: 24.9(22.7-26.7) χ 3.8(3.6-4.0)
A d . 1 a n d 2. H a b i t a t a n d c o l o u r . — T h e r e are n o absolute differences i n the habitat
of the t w o species. Sagartia troglodytes is m o s t f r e q u e n t l y f o u n d b u r i e d i n m u d o r
s a n d , the base f i x e d to s u b m e r g e d h a r d substrata s u c h as stones a n d e m p t y b i v a l v e
shells, b o t h i n t e r t i d a l l y a n d s u b t i d a l l y . S u c h f o r m s u s u a l l y h a v e o p a q u e , g r e y i s h t o
f l e s h - c o l o u r e d c o l u m n s . H o w e v e r , the species m a y also o c c u r i n cleaner habitats, e.g.
a m o n g e x p o s e d b e d s of j u v e n i l e m u s s e l s
(Mytilus
edulis L i n n a e u s , 1758) b e t w e e n
g r a n i t i c b o u l d e r s h i g h i n the t i d a l z o n e . H e r e o n e often f i n d s i n d i v i d u a l s w i t h m o r e
b r i g h t l y c o l o u r e d , often s t r i p e d c o l u m n s .
A d . 2. A d h e r e n c e of g r a v e l to the c o l u m n . — T h e u p p e r p a r t of the c o l u m n of S.
troglodytes is often c o v e r e d w i t h attached coarse s h e l l g r a v e l . Sagartia elegans i s d e f i ­
n i t e l y m u c h less i n c l i n e d to cover its c o l u m n w i t h f o r e i g n m a t e r i a l , b u t m o d e s t cover
w i t h fine g r a v e l h a s o c c a s i o n a l l y b e e n o b s e r v e d b y u s i n the v a r . miniata, b o t h i n s i t u
and under aquarium conditions.
A d 4. A s e x u a l r e p r o d u c t i o n . — Sagartia elegans v a r . miniata f r e q u e n t l y r e p r o d u c e s
a s e x u a l l y b y p e d a l laceration, w h i c h g i v e s rise to the f o r m a t i o n of clones o f i d e n t i c a l ­
l y c o l o u r e d specimens. T h i s p h e n o m e n o n i s n o t f o u n d i n S. troglodytes, w h e r e i t i s
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
271
u s u a l l y h a r d to f i n d e v e n t w o specimens w i t h i d e n t i c a l coloration close together.
B o t h Stephenson (1935: 338) a n d M a n u e l (1981: 148) c l a i m e d that S. troglodytes
m a y r e p r o d u c e b y v i v i p a r i t y . H o w e v e r , records of v i v i p a r i t y , also i n the N e t h e r l a n d s ,
relate e x c l u s i v e l y to Sagartia ornata ( H o l d s w o r t h 1855) (cf. D e n H a r t o g , 1970: 96-97;
Faasse, 1991), f o r m e r l y r e g a r d e d as a variety of S. troglodytes b u t suggested to be at
least a different subspecies b y D e n H a r t o g (1970) a n d currently s h o w n to be a sepa­
rate species (Shaw et al., 1987).
A d . 7. A c o n t i a . — I n S. elegans the acontia are longer, thicker a n d m o r e c o n s p i c u ­
ous t h a n i n S. troglodytes. U p o n irritation, e.g. b y d e t a c h i n g a s p e c i m e n f r o m its sub­
stratum or b y s i m p l y t o u c h i n g it, S. elegans generally r e a d i l y emits acontia t h r o u g h its
m o u t h a n d / o r t h r o u g h cinclides i n the c o l u m n w a l l , often i n p r o f u s i o n . Sagartia
troglodytes has a tougher texture a n d is far less i n c l i n e d to e m i t its thinner, less d e v e l ­
o p e d acontia, unless the internal structures are forced o u t of the gastric c a v i t y b y
severe damage. If it p r o v e s d i f f i c u l t to trace a n y acontia, the species concerned is d e f i ­
nitely n o t S. elegans.
A d . 8. C n i d o m of a c o n t i a . — A c o n t i a of members of the genus Sagartia a n d of the
family Sagartiidae are h e a v i l y l a d e n w i t h nematocysts of t w o k i n d s , here referred to as
spirulae (= basitrichs) a n d penicilli (= p-mastigophores or p-rhabdoids). A s s h o w n i n the
table a n d i n fig. 2, the dimensions of b o t h
types differ p r o f o u n d l y i n S. elegans a n d
S. troglodytes.
The means a n d ranges presented i n
the table are i n μιη, based o n 20 measure­
ments each. They were taken f r o m a w e l l
developed specimen of S. elegans f r o m
Westkapelle ( R M N H C o e l . 18794) a n d a n
about
equally
large
specimen
troglodytes f r o m K a t w i j k ( R M N H
of S.
Coel.
11549). The second size-class of spirulae is
generally relatively u n c o m m o n a n d incon­
spicuous, a n d therefore easily overlooked;
hence being of n o practical importance for
identification this category is placed i n
brackets a n d not depicted i n fig. 2.
The dimensions g i v e n here for S. ele­
gans are i n accordance w i t h those f o u n d
i n specimens f r o m the British Isles, the
Faroes a n d the A t l a n t i c coasts of France
a n d Spain, a n d those presented for S.
troglodytes are i n accordance w i t h British
specimens
(unpublished data J . C . d e n
Hartog). T h e considerably w i d e r ranges
g i v e n for b o t h species
b y Stephenson
(1935: 337, 339) a n d especially M a n u e l
Fig. 2. (cf. table 3.8). Nematocysts of acontia of
Sagartia elegans ( R M N H
Coel.
18794; West-
kapelle) and S. troglodytes ( R M N H Coel. 11549;
(1981: 144, 148) are m i s l e a d i n g , a n d
Katwijk aan Zee); a = spirulae, b = penicilli. Scale
a p p a r e n t l y based o n u n u s u a l extremes;
bar = 20 μιη.
272
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
these ranges further indicate that the authors d i d n o t d i s t i n g u i s h the i n c o n s p i c u o u s ,
s m a l l s p i r u l a e as a separate category.
T h e relatively s m a l l nematocysts f o u n d i n the acontia of the v e r y s m a l l allochthon o u s specimens f o u n d b y S w e n n e n (cf. p . 265) are i n accordance w i t h a c o m m o n ten­
d e n c y that nematocyst size i n species of A c t i n i a r i a correlates w i t h b o d y size (large
specimens u s u a l l y h a v i n g larger nematocysts t h a n smaller specimens).
The difference i n size of the acontian nematocysts p r o v i d e s a c o n c l u s i v e character
to d i s t i n g u i s h b e t w e e n S. elegans a n d S. troglodytes. H o w e v e r , u s i n g this character,
notably w h e n d e a l i n g w i t h p r e s e r v e d material, care s h o u l d b e t a k e n n o t to confuse
s m a l l S. elegans w i t h Sagartiogeton undatus (cf. table 4). It s h o u l d further be e m p h a ­
s i z e d that the c n i d o m s of S. troglodytes a n d S. ornata cannot be differentiated b y light
microscopy.
Table 4. Sagartiogeton undatus, survey of the cnidom of acontia of two well developed Dutch speci­
mens from Katse Hoek, Noord-Beveland ( R M N H Coel. 11227) and from Noordwijkerhout ( R M N H
Coel. 17712). For comparison with Sagartia elegans and S. troglodytes, see table 3.
Specimen
Nematocyst type
Dimensions in μ m
Ν
R M N H Coel. 11227
Spirulae
23.8(20.5 - 26.6) χ 2.7(2.7 - 2.9)
13.2(11.6-14.2) χ 1.6(1.4-1.8)
20
40.8(35.6 - 43.6) χ 5.1(4.5 - 5.4)
20
26.6(24.0 - 28.5) χ 2.7
14.2(12.9-15.6) χ 1.9(1.8-2.2)
20
[Spirulae
Penicilli
47.0(42.7 - 50.7) χ 5.4(5.3 - 6.2)
20
[Spirulae
Penicilli
R M N H Coel. 17712
Spirulae
20]
20]
D u t c h a u t o c h t h o n o u s records o f Sagartia elegans i n r e l a t i o n
to sea-water temperatures
F o r a n analysis of the possible relation b e t w e e n autochthonous records of Sagartia
elegans i n the N e t h e r l a n d s a n d sea-water temperatures o n l y f u l l y reliable records
w e r e taken into account, i.e. those listed i n table 2 a n d those m a r k e d w i t h a n asterisk
i n table 1. Sea-water temperature data w e r e taken for this p u r p o s e f r o m a l o n g - t e r m
series of measurements f r o m ' t Horntje, Texel ( V a n d e r H o e v e n , 1982, a n d s u p p l e ­
m e n t a r y data u p to 1993 f r o m the files of the N e t h e r l a n d s Institute for Sea Research,
NIOZ).
It appears that most reliable observations of S. elegans w e r e m a d e i n p e r i o d s f o l ­
l o w i n g one o r m o r e m i l d w i n t e r s w i t h relatively h i g h m i n i m u m m o n t h l y m e a n sea­
water temperatures (fig. 3a).
It is interesting to note that the species d i s a p p e a r e d f r o m 't Horntje i n the w i n t e r
of 1991 (February), whereas the p o p u l a t i o n at Z o u t e l a n d e (near V l i s s i n g e n ) s u r v i v e d
this w i n t e r . F o r a c o m p a r i s o n of the m i n i m u m m o n t h l y m e a n temperatures at these
localities for the years 1988-1991, see table 5.
Temperatures d u r i n g the s u m m e r m o n t h s d o n o t seem to h a v e i n f l u e n c e d the
occurrence of Sagartia elegans (cf. f i g . 3b).
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
+
273
+
Year
Year
Fig. 3. Sea-water temperatures (in °C) at't Horntje, Texel; 3a, minimum monthly mean temperatures
from 1947 to 1994; 3b, mean summer temperatures (July, August, September) from 1947 to 1993. The
horizontal lines denote the long term means.
Years with reliable observations of Sagartia elegans indicated for the southwestern (*) and northern (+)
part of the Dutch coast.
274
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
Table 5. Comparison of the minimum monthly mean sea-water temperature at't Horntje (Wadden
Sea) and Vlissingen (Westerschelde) in the period 1988-1991. Data from't Horntje from files of NIOZ,
those from Vlissingen made available by Rijkswaterstaat.
Locality /Year
1988
1989
1990
1991
't Horntje
5.1°C
5.6°C
5.8°C
5.8°C
1.4°C
5.7°C
6.2°C
1.9°C
Vlissingen
Discussion
The D u t c h coast is characterized b y s a n d y shores a n d estuaries. O r i g i n a l l y , h a r d
substrata w e r e barely present, b u t since some centuries d i k e s have been reinforced
w i t h limestone, basalt cobbles, granite b o u l d e r s a n d m o r e recently concrete b l o c k s
a n d asphalt. A t several sites, m a i n l y at the entrances of the estuaries, these d i k e s f l a n k
deep t i d a l channels. A t three s u c h sites p o p u l a t i o n s of S. elegans have become establ i s h e d b e y o n d doubt, v i z . the n o r t h e r n part of the entrance of the Westerschelde, the
entrance of the Oosterschelde a n d the M a r s d i e p r e g i o n ( H u i s d u i n e n a n d Texel)
(tables 1, 2; f i g . 1). A t a l l locations the species w a s f o u n d at a n d b e l o w M L W S - l e v e l .
The species is u s u a l l y f o u n d o n h a r d substrata, a n d does not thrive i n estuarine c o n ditions w i t h sedimentation a n d r e d u c e d salinities.
Braber & B o r g h o u t s (1977) suggested a susceptibility of S. elegans to l o w w i n t e r
temperatures. A s m e n t i o n e d above, the species d i s a p p e a r e d d u r i n g the w i n t e r of
1991 f r o m 't Horntje, Texel ( m i n i m u m m o n t h l y m e a n sea-water temperature 1.4°C)
a n d not f r o m Z o u t e l a n d e . The m i n i m u m for V l i s s i n g e n (near Z o u t e l a n d e , cf. f i g . 1) i n
this w i n t e r w a s 0.5°C higher than at Texel (table 5). T r u e e n o u g h , this is not a s t r i k i n g
difference, b u t m o r e detailed data m i g h t have revealed m o r e extreme short-term differences b e t w e e n the m i n i m a for Texel a n d V l i s s i n g e n (note also that use of the ' m i n i m u m m o n t h l y m e a n ' implicates that a possible l o w e r m i n i m u m for a n y significant
p e r i o d r a n g i n g over e n d a n d b e g i n n i n g of t w o subsequent m o n t h s goes unnoticed).
U n f o r t u n a t e l y s u c h detailed data w e r e n o t available to u s . H o w e v e r , if w e assume
that a m i n i m u m m o n t h l y m e a n of s l i g h t l y b e l o w 2°C is u n f a v o u r a b l e for S. elegans, i t
s h o u l d be e m p h a s i z e d that this m i n i m u m w a s n o t reached i n the majority (28 out of
46) of D u t c h w i n t e r s between 1947 a n d 1993 (fig. 3a). N o t i n g this, considerably m o r e
records of the species i n this p e r i o d w o u l d be expected t h a n are actually available.
There m a y be several reasons w h y the n u m b e r of reliable records is m u c h l o w e r t h a n
expected. F o r instance, the quantity a n d q u a l i t y of (potential) observers a n d their
m e t h o d s m a y be significant. T h u s , for p l a u s i b l e reasons, most of the o l d e r observations are f r o m the t i d a l z o n e o r just b e l o w it, whereas o u r o w n search f o r A n t h o z o a
f r o m the 1980s o n w a s also extended into the s u b t i d a l area, b y s n o r k e l i n g a n d S C U B A
diving
D u r i n g l o w tide, specimens i n the t i d a l zone face exposure to m o r e extreme a i r
temperatures. A s a consequence i n t e r t i d a l i n d i v i d u a l s o r p o p u l a t i o n s are l i k e l y to be
the first to disappear. A c t u a l l y , since the c o l d w i n t e r s of 1995/1996 a n d 1996/1997,
n u m b e r s of S. elegans h a v e decreased significantly, i n t e r t i d a l l y b u t also s u b t i d a l l y ,
a n d w e o n l y succeeded i n f i n d i n g the species at localities near the entrances of the
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
275
estuaries i n the southwestern part of the N e t h e r l a n d s (table 2, f i g . 1). I n c a p t i v i t y S.
elegans w a s f o u n d to tolerate i n c i d e n t a l temperature d r o p s to as l o w as 0 ° C (pers.
observ. R . M . L . Ates). Nevertheless, o u r f i n d i n g s , a l t h o u g h o f f e r i n g n o conclusive
proof, definitely suggest that Braber & B o r g h o u t s (1977) r i g h t l y a s s u m e d the d i s a p pearance of S. elegans to be d u e to the severe w i n t e r of 1962/1963. D u r i n g that w i n t e r
the m i n i m u m m o n t h l y m e a n sea-water temperature d r o p p e d some 3 ° C b e l o w the
m i n i m u m registered at Texel i n 1991 (see f i g . 3a), w h i c h c o i n c i d e d w i t h the d i s a p pearance of the species.
F r o m the data i n f i g . 3a it f o l l o w s that the D u t c h p o p u l a t i o n of S. elegans m a y h a v e
suffered d e c i m a t i o n d u e to l o w temperatures d u r i n g 18 out of 46 w i n t e r s since 1947.
In six w i n t e r s the m i n i m u m m o n t h l y m e a n d r o p p e d b e l o w 0°C ( w h i c h implicates the
incidence of e v e n l o w e r short t e r m m i n i m a ) . Therefore, e v e n i n the absence of m o r e
detailed data, it seems o b v i o u s that p o p u l a t i o n s of S. elegans i n the N e t h e r l a n d s have
n o p e r m a n e n t character, a n d that p e r i o d s of d e c i m a t i o n o r extinction alternate w i t h
p e r i o d s of r e c o l o n i z a t i o n a n d / or recovery.
H a v i n g d e t e r m i n e d w h e r e a n d i n w h i c h p e r i o d s S. elegans w a s d e f i n i t e l y present,
or is l i k e l y to have been present o n the D u t c h coast, some of the u n d o c u m e n t e d
records listed i n table 1 c o u l d refer to S. elegans after a l l , v i z . : l l . i v . 1 9 5 3 , T e x e l (Stock
& Swennen); 26.iv.1958, T e r s c h e l l i n g (Swennen); b e g i n n i n g of 1962, S c h o u w e n a n d
V l i s s i n g e n (Braber & Borghouts, 1977) (cf. table 1 a n d f i g 2a).
Sagartia elegans f o r m s stable, p e r m a n e n t p o p u l a t i o n s i n the C h a n n e l area, a n d the
species also occurs occasionally i n off-shore waters a l o n g the D u t c h coast, w h e r e i t
has been r e c o r d e d o n ship's w r e c k s , etc. ( V a n M o o r s e l et al., 1991; V a n M o o r s e l &
W a a r d e n b u r g , 1992), a n d i n t r a w l catches of a benthic s u r v e y b y N I O Z ( R M N H C o e l .
18648, 18649). Therefore, r e c o l o n i z a t i o n of the D u t c h coast after relatively extreme
w i n t e r s is l i k e l y to take place b y p l a n k t o n i c larvae f r o m these p o p u l a t i o n s . It m a y
take some time f o r settled larvae to g r o w u p a n d d e v e l o p significant p o p u l a t i o n s b y
subsequent sexual a n d asexual r e p r o d u c t i o n . O b v i o u s l y the d e v e l o p m e n t of s u c h
" s e l f - s u s t a i n i n g " p o p u l a t i o n s w i l l be f a v o u r e d b y a n u m b e r of consecutive m i l d w i n ters, a n d it m a y therefore be m o r e t h a n mere chance that the records of manifest n u m bers of the species coincide w i t h s u c h p e r i o d s (cf. table 1, 2 a n d f i g . 2a). It m a y further
be o b s e r v e d that, p r o v i d e d suitable temperatures a n d substrata, s u c h p o p u l a t i o n s
once established w i l l r e p r o d u c e sexually, thus increasing the n u m b e r s of p l a n k t o n i c
larvae a n d hence the chance of settlement i n less t y p i c a l habitats a n d deeper penetrat i o n into the sea arms of the D u t c h delta area.
Conclusion
There is n o c o n c l u s i v e evidence f o r the occurrence of Sagartia elegans i n the
N e t h e r l a n d s p r i o r to 1952 ( V a n U r k , 1952) b u t at present i t i s u n q u e s t i o n a b l y a n
autochthonous species. It is most l i k e l y to b e f o u n d o n d i k e s i n the most s e a w a r d
parts of the Westerschelde, Oosterschelde a n d W a d d e n Sea. A s the species appears to
be sensitive to relatively l o w w i n t e r temperatures, i t c a n o n l y d e v e l o p significant
p o p u l a t i o n s after several consecutive m i l d w i n t e r s . D u e to its estuarine character a n d
the frequency of relatively c o l d w i n t e r s , the D u t c h coast is a m a r g i n a l area f o rS.elegans.
276
Ates et al. The occurrence of Sagartia elegans in the Netherlands. Zool. Verh. Leiden 323 (1998)
Acknowledgements
Part of the temperature data w e r e k i n d l y m a d e available b y Rijkswaterstaat. W e
t h a n k D r E.J. v a n N i e u k e r k e n , N N M , for processing o u r d i s t r i b u t i o n records into the
m a p s h o w n i n fig. 1.
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