leES C.M. 1991
E 19
BENTHIC HISTORY OF TIIE WADDEN SEA
by
Karsten Reise
Biologi che Anstalt Helgoland, Wattenmeer tation Sylt, 2282 List, Germany
Aß TRACT
o
er the la t hundred car, conspicuou change. occurred in the benthos of lhe Wadden Sea.
Direct exploitalion and di.lurb nee. b the f'ishery, and enhanced eutrophication of the
coastal wat rs eem lO leIh primar agents of change. Oy ter beds were overexploited and
vanished togelher with asso iated species. e sile epib nlhos declined. More recently, natural
mu el bed are aff-cted 11 ' c ploitation. Red algae retreated from the deeper part of their
vertical rang, and grccn (11 fle ho\ cd unpreccdented ma s dcvelopments on tidal f1als in
reeenl car. Benlhie infilllna beeame more numerou , and musseI beds showed an
inlermittent expan ion. 11 inerea d uppl of nutrient and food may explain these changes.
S agra declined in the 19 0 . A com back wa re trieted to the intertidal zone. ow it is
declining again. The eau
i. unknown. Th re is a necd for eomprehensive, regional surveys
of the entire bentho in order to deteet ehanges in the biota.
INTRODUCTIO
A summary of benthic ehangcs in the Wadden Sea over the past 100 years is presented.
Report on the benthos started with Möbius (1893) Dahl (1893) and Warming (1904) at the
turn of the eentury. Evid nee i taken from these and later publications to reeonstrucl
hi torical change. Thi
ndeavour may help to judge upon the ongoing changes, and to
evaluate present ceologi al conditions.
SEAGRA S
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Populations of ZosleJ'a l1IaJ'ina era hed in the 1930s throughout the northern Atlantic (den
Hartog 1987). In the Wadden Sea, ubtidal eagras beds did not recover. On the intertidal
f1ats Z. marina came bilck wh r Z. nollii was not or on1y very little affeeted. However, in
recent Cflr., the
intcnidfll sagras bcd ecm to decline from south to nonh in the Wadden
Sea. Aceording to an a rial !-url' y in 1991 (Rci. c, in prcp.) thcre is almost no eagrass left
in thc Dutch \. addcn, a. fcw I cd occur in thc Jerman Wadden Sea, exeept in the most
nonh rn pan and in lh 0 ni. h Wadden .. fl, wh r~ both eagras e arc still thriving. A
limemold-like proti I (LaI 'rintllllla P), a di ae agent affeeting Z. l1Iarina in the 19305, is
back again, but doe not 'ct altain epidemie proponion (Vergeer & den Hartog 1991). The
eau e of the pr ent sen ras. dcc.line i still ariddie.
MACROAL ,A .
Red algae onee abundanl on lh formcr oyster beds of the North Frisian Wadden Sea, are
rare toda on ultidal hOl10ms but are .till eommon in the 100ver inlertidal (Reise el al.
19 9). This pattern ugg '. l. that I s light penetrat(' thc muddy waters of the present
Wadden ea. Grcen al a , on the other hand, regular! 'howed mass developments during the
last decade \ovhile bein of marginal occurrence in the earlier Wadden Sea (Rei e 1983, Reise
et al. 199). Aerial ,ur y conducted in 199 to 1')91 revealed e ten ive algal mats covering
sand tidal rlat along thc hell r d idc of the island (Rci c in prcp.). Underneath these
green algaI mat ,mainl eompo cd of Enterolllorp!Jn spp., anoxie eonditions develop which
kill thc endobenthic fauna. It also cau es nutricl1t to be released from the sediment which
further enhance algaJ growth.
BE. THIC EplJ-'AUNA
Natural beds of 0 ster (0. trea eduli ) have been 0 erexploited in the Wadden Sea since the
middle of the 19th ccnlur ( öbiu 1(77). In 192:- economic use came to an end, and the
last li ing 0 ster \ erc caught in 1940 (Hagmeier & Kändler 1927, Hagmeier 1941). Several
associated pecie. ani hed togelhcr with the oy ter bed (Reise 1982, 1990a). Comparative
dredging in the subtidal channel revealed that ses. ile and slow moving epifauna were more
common in the period 1924 to 1940 lhan in the 19 'Os, while mobile species showed liule
change (Reise et al. 19 9 Reise 1990b). Bottom trawling of the fishery is a likely cause.
MusseI bed (Mytilus edulis) increa ed (Riesen & Reise 1982, Rei e & Schubert 1987,
Michaelis 19 7). This ma J have rc ulled from culturing practices, and/or the mllssels were
augmented by an increa e in planktonic food. DlIrJng the 19 Os, exploitation of the wild beds
int nsified and the the former trend reversed (Obert & Michaelis 1991).
BENTJ-IIC I FAUNA
Benthic infauna inerea cd in abundance. This i re ealed by revisiting subtidal and intertidal
stalion , .ampled I efore in th 1920s and 1930s (Rie en & Reise 1982, Reise & Schuben
19 7, Rei.e 1990b) anel b' regular sampling over the past 20 years (Beukema & Cadee 1986,
Bellkema 19 ()). Polychael
b came more abundant, and infaunal bivalve gained in biomass.
Pre umably the endobenthic fauna take advantage from an increased food supply.
COl\CLU 10:'\
Over the past hundred ycar. gain. il. w 11 as 10 ses occllrred in the benthos of the Wadden
Sea. Thcre . c m to be two major agent.. One i. t hl d irect exploilat ion and d isturbance of the
bentho. b th fi. her. 0 ·.Icr I cd and a. sociated 'pecies vani hed, epibentho dcclined, and
more recently natural mus el beds are on the retreal. The other major cause of change eems
to be enhanced eutrophicalion. Thi i suggested b y ma de eIopments of green algae, an
increase in the infauna, (lnd an intermittent expan.lon of natural mussei beds. Even the
contraction of the verlical range of red algae, if cau ed by decreased light penetration, may
bc ultimatcly r lat d 10 cUlrophicalion. The recent .;Ieclinc of seagras. lilI presenls ariddie.
The inh rent spal ial and temporRI varial ilily in tl1(' 1 enthos of I he Wadden eR makes il
difficult (0 recognize long-t·rm change, b repealcd sall1pling at ome selected stations. The
historical change ummarized in thi article are oflen b tl.er identified by occa ional, largescale sur ey . Comprehcn. i c studies on the entire benthos of particlilar regions of the
Wadden Sea in the [ir t half of the eentllry, i.e. by Hagmeier & Kändler 1927, Thamdrup
1935, Wohlenberg 1937 and Linke 1939, are nowadays of great value to judge upon the
prcsent ecological conditions. Encollragell1ent hould be given to modern equivalents of such
studies, requiring ver atile naturalists.
LITERATURE
Beukema J J 1989 HeigoI Meeresunlers 43:405-415. Beukema J J, Cagee G 1986 Ophelia
26:55-64. Dahl F 1 93 Komm wis Unters dt ch M.:eres 6 (3): 1-185. Hagmeier A 1941 Z
Fisch 39: 105-165. Hagmeier A Kändler R 1927 \\'i . Meere unters (A bl. Helgoland) 16: 190. Hanog den
19 7 qual. Bol. 27:3-14. Linke () 1939 H Igol Wi . Jieeresllnters. 1: 20134 . Michaeli. H 19 7 Jber For'ch, Ki.i.le, orderlley"': 1-97. Möbiu K I 77 Die Auster
und di Au ternwirthschafl. Wiegandt Hempel ' "are, Berlin, 126 S. Möbiu K 1 93 Sber
preuss Akad
i s 7: 33- c. Obert B,
ichaelis H )')91 In: E luaric and coa ts: Spatial and
temporal inlercomparison . Ed .: Ellioll M DucrO[(l .I-P. Ol'on & Olson, Viborg, 185-194.
Reise K 1982 eth J ,ea Re.. 16: 9-36. Rei. e K I I 3 Heigoi Meere, unters 36: 15 J -162. Reise
K 1990a Dt hydrogI'. Z rg- H. B (22): 14<)-152. RCI;c K I C)C)Oh Rhcinisch-West nilischc kad.
Wi.s.
J,2: .,-:;n. R is' I , Hcrrc ,.lurm MI<),') He/Jol leere. unters 4 :417-43:1. R ise
K, Schuber! A I C) 7 Heigoi !leer. Unl r. 4 \:(9-( 2. Rie en W Rei e K 19 2 Helg 1
Meere. unler . .\ -:409-4 :'. Thall1drup H M 19 dd Dan Fisk Havunders 10 (2): 1-125.
Vergcer LHT, Hanog dcn C 1991
qual BOI 40:15:'-163. Warl1ling E 1904 Kgl Dan idensk
Selsk kr 7 (11)1:1-.-6. \ ohlenberg E 19 7 Heigoi \- iss Meere unters 1:1-92.
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