Tidal flat macrobenthos resistance to medium-term emersion: The case of
the Tricolor oil pollution prevention in the Zwin nature reserve (Belgium)
CM 2005/ S:41
Carl Van Colena*°, Steven Degraera, Magda Vincxa
a
Marine Biology Section, Department of Biology, Ghent University Krijgslaan 281/S8, B-9000 Gent, Belgium
* Carl.VanColen@Ugent.be; °
Not to be cited without prior reference to the author
1. Introduction
On the 14th of December 2002, the car carrier Tricolor collided with the containership Kariba in the English Channel and sank in French waters nearby the Belgian border. Five weeks later, on the 22nd of
January 2003, approximately 170 tons of fuel leaked from the wreck of the Tricolor during salvage operations. Due to the meteorological conditions, with strong onshore winds, the oil washed ashore on
Belgian, French and Dutch beaches and threatened some coastal nature reserves, among which the saltmarshes of the Zwin nature reserve. To keep out the oil from the Zwin nature reserve both
entrance channels were blocked by use of a sandbarrier.
2. Objectives
Catching up a dam prevents the tidal regime within the area. It is generally accepted that biotic and abiotic aspects
of saltmarsh ecosystems are strongly determined by the frequency and duration of emersion by the tidal waters.
(1)
(2)
Closure of intertidal areas with the ambient sea may therefore result in minor to irreversible effects on organisms
(3)
and ecosystems. This method of protection therefore led to a lot of discussion: the choice between keeping out
chronic pollution versus acute mortality due to emersion. The damming up was taken as the ideal
(1) Oil spill of the Tricolor wreck on the 22nd of January 2003 (picture:BMM)
(2) Due to meteorological conditions, with strong onshore winds, the oil washed ashore on
Belgian, French and Dutch beaches and threatened some coastal nature reserves, among
which the saltmarshes of the Zwin nature reserve.
(3) Different methods of protection were used. Finally, both entrance channels were blocked by
use of a sandbarrier.
opportunity to study the effects of a medium-term emersion on macrobenthic species of a norhwestern European
intertidal habitat in winter, with a view of making better estimations in the future whenever this measure of
protection could be needed.
3. Materials & Methods
Study area, with indication of the
sampling stations and the main habitat
characteristics
51°21’ N
3°22’ E
• Sampling of a small side-creek of the Dutch entrance creek and the flanking intertidal mud –and sandflats, which
were blocked during 27 days. A total of 12 sampling stations were localized in mud –and sandflats in order to
Study area
Mudflat
Initial stage
Sandflat
Marsh vegetation
N 10 m
¿
encompass a maximal diversity of benthic habitats and species.
• Samples were collected starting just before, two times during (after 12 and 21 days of emersion) and frequently (one
S12
to two monthly) after the damming up during one year after the construction of the sandbarrier.
S7
S9
• Macrobenthic samples were taken to a depth of 15 cm and sieved alive over a 500 µm mesh sized sieve.
S11
S3
S6
• To characterize the sampling stations and to correlate possible effects (Spearman rank test; Sokal & Rohlf,1981),
S8
S4
sediment characteristics (mud content and median particle size), relative intertidal elevation and submersion time were
measured.
Sandbarriers in the
Belgian (red) and Dutch
(yellow) entrance creek.
Both are connected to
protect the marsh
vegetation (blue)
species after 12 and 21 days of emersion per sampling station and to examine seasonal variation in species densities in
order to detect possible recovery. When significant differences were observed, multiple comparisons were made
between groups, following Connover (1971).
5
RECRUITMENT
20000
density (ind./m²)
6000
S2
S4
S7
S8
S9
S10
S12
15000
10000
2000
• Two ecological patterns could be distinquised during the
emersion: (1) Immigration into the intertidal zone of Talitrus
5000
10000
before the construction of the sandbarrier. However, only for N.
0
0
0
M
J
J
A
S
O
N
D
J
F
F
M
A
Nereis diversicolor
M
J
J
A
S
O
N
D
J
F
F
M
A
M
Heteromastus filiformis
J
J
A
S
O
N
D
J
diversicolor and only in one station (S11) the latter pattern was
significant (p<0.05). Pygospio elegans and
Aphelochaeta marioni declining in all sampling stations were
statiscally
F
Pygospio elegans
these species were present. Both species are known to be very
6000
12000
2500
sensitive for periods of emersion, even during winter (Fortuyn
2000
et al., 1989). Even more, A. marioni declined to 0. However
1500
additional samples taken nearby the study area after the
5000
10000
4000
8000
3000
6000
2000
4000
1000
2000
B
12 E
21 E
damming up show the presence of A. marioni in the Zwin
1000
nature reserve.
500
0
0
0
F 04
B
12 E
21 E
F 04
B
12 E
21 E
F 04
3500
7000
8000
3000
density (ind./m²)
7000
organisms need only a few food and oxygen (Zwarts & Wanink,
5000
1991).
•The high abundance of T. saltator and O. gammarellus during
2500
5000
2000
4000
1500
3000
1000
2000
500
1000
4000
3000
the emersion and their low abundance afterwards can be
2000
1000
F
M
A
M
J
J
A
S
O
N
D
J
F
F
explained by the natural distribution of this species. Both
0
0
0
M
A
M
J
J
A
S
O
N
D
J
F
emersion is presumptively associated with the season of
6000
6000
RECRUITMENT
•The high resistance of the tidal flat macrobenthos to the
emersion: the winter. During winter, intertidal macrobenthic
8000
9000
Decreasing
densities of polychaete species which were very abundant
5000
A
saltator and Orchestia gammarellus and (2)
15000
1000
M
5. Discussion and Conclusions
30000
20000
4000
3000
Dutch
entrance
creek
35000
25000
5000
S2
to a medium-term emersion during winter.
0 0
0
7000
S1
Tidal creek
• This study shows a high resistance of all macrobenthic species
4. Results
F
S5
S10
• Kruskal-Wallis rank sum test (Kruskal & Wallis, 1952) was used to examine the variance between the densities of
F
M
A
M
J
J
A
S
O
N
D
J
F
species are found most frequently nearby the high-water mark
at the supralittoral, semi-terrestrial habitats (Jones & Wigham,
Aphelochaeta marioni
Orchestia gammarellus
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
3500
8000
3000
7000
2500
6000
F 04
variables and the density effect during the damming up
(Spearman rank test, p>0,05).
3000
1000
2000
500
1000
0
21 E
•There was no significant correlation between the physical
4000
1500
12 E
from these habitats during emersion seems likely.
5000
2000
B
1993). An immigration into the intertidal zone of both species
Talitrus saltator
• In general this study shows a high resistance of all
0
B
12 E
21 E
F 04
B
12 E
21 E
F 04
Temporal variation (upper graphs) and the effect of the medium-term emersion on some dominant intertidal macrobenthic species (detail graphs).
Macrobenthic densitie values (B) before, after 12 days (12 E) and 21 days (21 E) of emersion, as these one year after the construction of the sandbarrier
(F 04, February 2004) are given. Station labels are given on top of the graphs.
Acknowledgments. The authors want to thank the people of the Marine Biology Section who assisted during the fieldwork and in analysing the macrobenthic and sedimentological samples. We also want to thank Kris Struyf for his logistic support of this study.
References.
Connover, W.J.,1971. Practical Non Parametric Statistics. John Wiley and Sons, New York, pp. 462
Sokal, R.R., Rohlf, F..J., 1981. Biometry, the principles practice of statistics in biological research. 2nd ed. San Fransisco: WH Freeman and Compagnie.
Kruskal, W.H., Wallis, W.A., 1952. Use of ranks in one-criterion variance analysis. J. American Statistics Association (47), 583 – 621.
Jones, M.B., Wigham, G.D., 1993. Reproductive-biology of Orchestia-gammarellus (Crustacea, Amphipoda) living in a sewage-treatmatn works. Journal of the marine biological association of the United Kingdom. 73 (2), 405 – 416.
Fortuin, A.W., Meijboom, A., de Wolf, L., 1989. Het gebruik van de stormvloedkering bij de afbouwwerkzaamheden in de Oosterschelde: effecten van een aantal sluitingsscenario’ s op bodemdieren. Rapporten en verslagen 1989 – 2, pp. 79.
Zwarts, L., Wanink, J.H., 1991. The macrobenthos fraction accessible to waders may represent marginal prey. Oecologia (87), 581-587.
macrobenthic species in the Zwin nature reserve to a mediumterm emersion during winter. In view of the high survival and
the fact that an oil pollution in the nature reserve was inhibited,
the choice to protect the reserve from the empending oil
pollution
by
use
positively evaluated.
of
a
sandbarrier
may
be