3
.
S
ocul
<oS~
U
/Z a L j< x £ e
A ) ; /fe ?
S' i —
oC>_
o ^£ fe JVhC
5
3
THE HYPERBENTHIC FAUNA OF THE
BELGIAN CONTINENTAL SHELF:
SPATIAL VARIABILITY
IN COMMUNITY STRUCTURE
I
7 2 8 0
Ann DEWICKE and Jan MEES
I
Vlaams Instituut voor dB Zee
Flanders Marine Institute
$
T he hyperbenthos o f the Belgian coastal w aters, the W esterschelde estuary and part
f th e D utch delta w as sampled within a 2-w eek period at 4 1 locations in the sum m er o f
993 (figure l). At each location sampling w as done at tw o depth strata, covering all m ajor
andbanks in the area, and the gullies separating them. Sampling depth ranged from 6 to
leter.
!
&
to
i
r<
&
I
I
‘if;
i
•V
K eyw ords: hyperbenthos, com m u nity structure, N o r t h Sea
55
F ig u re 2: The hyperbenthic sledge (modified sledge described by Sorbe J .- C ., 1983)
T he samples w ere taken with a hyperbenthic sledge (figure 2) equipped with four
nets (1 mm and 0.5 mm mesh size), covering tw o low er strata ° f ■
t he w atercolum n.
0 •
m eter and 0.5 to 1 m eter above the bottom . Trawling (5 m inutes at 1.5 knots, approx. 2
m eter per traw l) w as always done during daylight and against the tide. The sledge wa
equipped w ith an autom atic opening-closing device, an odom eter and a current m e te r n
addition, sediment and w ater samples w ere taken at each station for grain fract.on analysis
and pigm ent analysis.
In the laboratory all animals w ere identified, if possible to species level, counted and
m easured. D ensity w as calculated and biom asses w ere derived from ash-free-dry-weight
regressions. D ensity and biomass data w ere subjected to m ultivariate statistical an^ * - »
classification (clustering based on the Bray-Curtis similarity
S orting), an ordination (Canonical Correspondance Analysis) and a hybnd technique (
way Indicator Species Analysis).
A total o f 135 species w ere recorded in the hyperbenthic fauna o f the Belgian
continental shelf. The m ost abundant faunistic taxa include M ysidacea
B rachyura (20 species), Amphipoda (33 species) and C an d ea (14 species). Chaetognat a,
Pisces, A nom ura, Polychaeta, Isopoda, C opepoda and C um acea w ere caught to a lesser
extent T h e hyperbenthos o f the Belgian coastal area can be divided into 6 geographical^
defined com m unities (figure 3), characterised by their species com pos.t.on diversity
density and biomass. In the eastern part o f the W esterschelde, a typical brackish w ater
com m unity w as found ( W ) . Tw o com munities w ere found onshore: onshore east is
located on the east co ast (from O ostende to Z eebrugge) including the m anne part o f
56
F igure 3: Geographical location o f the hyperbenthic com m unities on the Belgian continental shell
> 32000 N /100m‘.
8000
6000
4000
2000
ws
□
onshore w est
o n sh o re east
M ysidacca B A m phipo d a □ C arid ea
13 A nnelida
W C u m acea
® P isces
m id bkp
m id v d
o flshore
B C haeto g n ath a H B rach y u ra ■ C o p ep o d a
■ A n o m u ra @ M o llu sca ^
Thalassim dea ■ o th ers__________________
F igure 4: Average density and taxonomic com position o f the hyperbenthic communities
W esterschelde; on the w est coast (from O ostende to D e Panne) the
w est’ w as found. ’M id bkp' and 'mid vd' are the tw o transition com m unities between
onshore and m ore offshore area. T he 'offshore' community occurs tow ards the open sea.
The com m unity structure changes sharply along a gradient perpendicular to the
coastline- highest densities and biom asses w ere recorded onshore (figure 4). T he onshore
com m unities (and the 'ws' community) w ere characterised by a low diversity and^consisi
mainly o f M ysidacea. Diversity increased offshore and the species com position o f the hyp
benthic fauna is changed: m ore faunistic groups becam e alm ost equally represented,
especially the B rachyura being dominant.
A c k n o w le d g e m e n ts
T his research w as partly supported by the GOA 92/98-08 project from the U niversity o f Gent (Flemish
Advancement o f Scientific-Technological research in Industry (1WT).
R e fe re n c e s
S orbe, J.-C. (1983). D escription d'un traîneau destiné à l'échantillonage quantitatif étagé de la faune
suprabenthigue néritique. Ann. Inst. Océanogr. 59'. 117-126.
U niversity o f Gent, M arine B iology Section, Institute o f Zoology
K.L. L edeganckstraat 35, B -9000 Gent, B elgium
E-m ail: Ann.D ew icke@ rug.ac.be / Jan.M ees@ rug.ac.be
58