Ecological Studies in the Coastal Waters of Mauritania: Proceedings of a Symposium held at Leiden, The Netherlands 25–27 March 1991

223 Pages·1993·7.859 MB·English

by  J. Sevrin-Reyssac (auth.), W. J. Wolff, J. van der Land, P. H. Nienhuis, P. A. W. J. de Wilde (eds.)

Ecological Studies in the
Coastal Waters of Mauritania
Developments in Hydrobiology 86
Series editor
H. J. Dumont
Ecological 8tudies in the
Coastal Waters of Mauritania
Proceedings of a Symposium held at Leiden, The Netherlands,
25-27 March 1991
Edited by
W.J. Wolff, J. van der Land, P.H. Nienhuis & P.A.W.J. de Wilde
Reprinted from Hydrobiologia, voI. 258 (1993)
Springer Science+Business Media, B.V.
Library of Congress Cataloging-in-Publication Data
Ecologlcal studles In the coastal waters of Maurltanla ! edlted by
W.J. Wolff ... [et al. 1
p. cm. -- IDevelopments in hydrobiology ; 861
·Proceedlngs of a symposium held at Leiden, The Netherlands, 25 -
27 March 1991."
Inc I udes b i b li ograph i ca 1 references.
ISBN 978-94-010-4877-4 ISBN 978-94-011-1986-3 (eBook)
DOI 10.1007/978-94-011-1986-3
1. Marine ecology--Maurltania--Congresses. 2. Coastal ecology-
-Maurltanla--Congresses. 1. Series.
QH195.M479E25 1993
574.5·2636'09661--dc20 93-19531
ISBN 978-94-010-4877-4
Printed on acid-free paper
AII Rights Reserved
© 1993 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1993
Softcover reprint of the hardcover 1s t edition 1993
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical
including photocopying, recording or by any information storage and
retrieval system, without written permis sion from the copyright owner.
v
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. VB
Hydrology and underwater climate of the Banc d'Arguin, Mauritania: a review
by J. Sevrin-Reyssac .......................................................... 1
Wind, surface water temperature, surface salinity and pollution in the area of the Banc d'Arguin,
Mauritania
by Sidina ould Dedah ......................................................... 9
Hydrographical observations west of the Banc d'Arguin, Mauritania, in May 1988
by Y. Loktionov .............................................................. 21
Remote sensing of sea surface and coastal features in the area of the Golfe d'Arguin, Mauritania
by F. Cuq ................................................................... 33
Heavy metals (Cu, Zn, Pb, Cd) in sediment, zooplankton and epibenthic invertebrates from the area
of the continental slope of the Banc d'Arguin (Mauritania)
by J. M. Everaarts, R. Heesters & C. V. Fischer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41
Leaf dynamics and standing stocks of intertidal Zostera noltii Hornem. and Cymodocea nodosa
(Ucria) Ascherson on the Banc d'Arguin (Mauritania)
by J. E. Vermaat, J. A. J. Beijer, R. Gijlstra, M. J. M. Hootsmans, C. J. M. Philipp art, N. W.
van den Brink & W. van Vierssen ............................................... 59
Periphyton density and shading in relation to tidal depth and fiddler crab activity in intertidal
seagrass beds of the Banc d'Arguin (Mauritania)
by M. J. M. Hootsmans, J. E. Vermaat & J. A. J. Beijer ............................ 73
Primary production and distribution of phytopigments in the water column and sediments on the
upwelling shelf off the Mauritanian coast (Northwest Africa)
by E. M. Berghuis, G. C. A. Duineveld & J. Hegeman. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Distribution of sponges on the Mauritanian continental shelf
by R. W. M. van Soest ........................................................ 95
The benthic infauna and benthic respiration off the Banc d'Arguin (Mauritania, Northwest Africa)
by G. C. A. Duineveld, P. A. W. J. de Wilde, E. M. Berghuis & A. Kok .. . . . . . . . . . . . .. 107
Patterns in pelagic and benthic nanoflagellate densities in the coastal upwelling system along the
Banc d' Arguin, Mauritania
by R. P. M. Bak & G. Nieuwland ............................................... 119
Zooplankton distribution in the coastal upwelling system along the Banc d'Arguin, Mauritania
by B. R. Kuipers, H. J. Witte & S. R. Gonzalez ................................... 133
Biomass of macro benthic tidal flat fauna of the Banc d' Arguin, Mauritania
by W. J. Wolff, A. G. Duiven, P. Duiven, P. Esselink, Abou Gueye, A. Meijboom, G.
Moerland & J. Zegers ......................................................... 151
The trawlfauna of the Mauritanian shelf (Northwest Africa): density, species composition, and
biomass
by G. C. A. Duineveld, M. S. S. Lavaleye & G. J. van Noort ........................ 165
Food items of the grey mullet Mugil cephalus in the Bane d'Arguin area (Mauritania)
by H. Michaelis .............................................................. 175
VI
The distribution and abundance of young fish on the Banc d'Arguin, Mauritania
by Z. Jager .................................................................. 185
Seabirds in the shelf edge waters bordering the Banc d'Arguin, Mauritania, in May
by M. F. Leopold. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 197
The functioning of the ecosystem of the Banc d'Arguin, Mauritania: a review
by W. J. Wolff, J. van der Land, P. H. Nienhuis & P. A. W. J. de Wilde .............. 211
Hydrobiologia 258: vii-ix, 1993.
W. J. WoljJ. J. van der Land, P. H. Nienhuis & P. A. W. J. de Wilde (eds), Vll
Ecological Studies in the Coastal Waters oj Mauritania.
Preface
Ultimately this volume on the ecology of Mauritanian coastal waters and in particular the Banc d' Arguin
has its origin in a number of earlier Dutch projects. The pelagic system off the Mauritanian coast was
studied during the NECTA R-77 and NECTA R-78 cruises. Benthic studies of the shelf, including the edge
of the Banc d'Arguin and the Baie du Levrier, were made during the CAN CAP-III cruise in 1978. A visit
of the Banc d'Arguin proper by four Dutch biology students followed in 1980. Their account (Altenburg
et al., 1982) of the millions of birds wintering in that tidal flat area and their description of the ecology
of that area, provoked interest among other Dutch ornithologists and estuarine ecologists. This resulted
in a larger Dutch-Mauritanian research project at the Banc d'Arguin carried out in 1985 and 1986. The
ornithological studies of that project have been published in a special volume of Ardea (Ens et aI., 1990).
However, such projects normally result in more questions than answers and this project proved no
exception to that rule. At the same time the attention of some of the scientists involved shifted from purely
ornithological to more general ecological questions, particularly the functioning of the Banc d'Arguin
ecosystem. This led to a research project in which a large part of the Dutch oceanographic and ecological
scientific community participated: the project Banc d'Arguin 1988.
The Banc d'Arguin is an area of tidal flats and shallows situated between roughly 19° 20' and 20° 30'N
along the Saharan coast of Mauritania (Fig. 1). It is characterized by water temperature of about
20-250 C and salinities over 38. There are no rivers and rainfall is rare. Off the coast of Mauritania cold
water masses from the northern Atlantic and warm water from tropical areas meet. Hence flora and fauna
contain both temperate and tropical species. Examples are the temperate mudsnail Hydrobia ulvae and
the seagrass Zostera nollii, and the tropical mangrove A vicennia africana and the bivalve Anadara senilis.
Conspicuous features are extensive seagrass beds, relatively low biomasses of the zoobenthos and
extremely high densities of birds (Wolff & Smit, 1990).
The project Banc d'Arguin 1988 endeavoured to understand the functioning of this remarkable coastal
wetland. Major questions to be answered concerned the interaction between the Banc d'Arguin ecosystem
on the one hand, and the adjoining systems of the open ocean with its intensive upwelling phenomena,
and of the Sahara desert on the other. Is the Banc d'Arguin ecosystem relatively isolated from its
surroundings and does it function as a tropical pocket in a more temperate surrounding as suggested by
Sevrin-Reyssac (1983), or does it interact with both Sahara and Atlantic Ocean? It was decided
beforehand that the interaction between the Banc d' Arguin and the open ocean should get the major part
of the attention. However, at the Banc d'Arguin this is not an easy task, because the area between the
estuarine parts of the area and the open ocean is extremely shallow and largely uncharted. Large research
vessels cannot penetrate the shallows whereas small vessels are often unable to negotiate the outer part
of the shallow area due to rough weather conditions. Hence, seperate teams were organized for work at
the seaward side of this shallow sill and at the landward side. In addition other teams used the opportunity
to address other questions such as the productivity of the seagrass beds and the benthic fauna, the number
of birds spending the summer at the Banc d'Arguin, and the distribution of several taxonomic groups
of flora and fauna.
The project was organized in cooperation with Mauritanian institutions, viz. the Banc d'Arguin
National Park (,Parc National du Banc d'Arguin') and the National Centre of Oceanography and
Fisheries (,Centre National de Recherches Oceanographiques et de Peches'), both at Nouadhibou.
viii
z
,o.. ..
N
z
o
o
N
25km
Fig. 1. The Mauritanian coast between Nouadhibou and Cap Timiris.
The participants from The Netherlands originated from Amsterdam University, the DLO - Institute
for Forestry and Nature Research (formerly Research Institute for Nature Management), Groningen
University, Leiden University, National Museum of Natural History, Netherlands Institute for Ecological
Research (formerly Delta Institute for Hydrobiological Research), Netherlands Institute for Sea Research,
Wageningen University and Working Group for International Waterfowl Research. In addition colleagues
from Ghana and Germany took part.
To evaluate the results of the project Banc d'Arguin 1988 a symposium was held in the National
Museum of Natural History at Leiden, The Netherlands, from 25-27 March 1991. At this symposium
the results of the 1988 project have been placed in perspective by inviting a number of key scientists who
reported on research at the Banc d'A rguin by Mauritanian and French institutions.
The symposium was opened by the Director of the Parc National du Banc d'Arguin, Mr Kane Hadya,
and it was very appropiate that the first lecture could be given by the nestor of research at the Banc
d' Arguin, Prof. Theodore Monod.
We are vere grateful to the Mauritanian authorities, in particular the Director of the Parc National du
Banc d'Arguin, Mr Kane Hadya, for their permission to carry out our research in the coastal waters of
Mauritania. We thank the Director of the Centre National de Recherches Oceanographiques et de Peches,
IX
Dr Moctar Ba, as well as the Director of the Parc National, Mr Kane Hadya, for their cooperation and
assistance, both by themselves and by their staff. We also want to acknowledge the help of Mr Tom van
Spanje and his friends in Mauritania. The participants of the expedition based in Iouik during the project
will not easily forget the kind help of the local population.
Financial support for either the work in Mauritania, or the symposium, or both was received from the
Netherlands Marine Science Foundation (SOZ), which funded the lion's share, the Directorate-General
for International Cooperation of the Netherlands Ministry of Foreign Affairs, UNESCO, the Netherlands
Natural History Museum, and the Netherlands DLO - Institute for Forestry and Nature Research.
W.J. WOLFF
J. VAN DER LAND
P. H. NIENHUIS
P. A. W. J. DE WILDE
References
Altenburg, W., M. Engelmoer, R. Mes & T. Piersma, 1982. Wintering waders on the Bane d'Arguin, Mauritania. Stiehting Veth
tot Steun aan Waddenonderzoek, Leiden, 283 pp.
Ens, B. J., T. Piersma, W. J. Wolff & L. Zwarts (eds), 1990. Homeward bound: problems waders face when migrating from the
Bane d'Arguin, Mauritania, to their northern breeding grounds in spring. Ardea 78: 1-364.
Sevrin-Reyssae, J., 1983. Affinite biogeographique de la region des iles de Bane d'Arguin (Pare National du Bane d'Arguin,
Mauritanie). Bull. Centre Natl Reeh. Oeeanogr. Peehes (Nouadhibou) 11: 53-56.
c.
Wolff, W. J. & J. Smit, 1990. The Bane d'Arguin, Mauritania, as an environment for coastal birds. Ardea 78: 17-38.
Hydrobiologia 258: 1-8, 1993.
W. J. Wolff, J. van der Land, P. H. Nienhuis & P. A. W. J. de Wilde (eds), 1
Ecological Studies in the Coastal Waters of Mauritania.
© 1993 Kluwer Academic Publishers.
Hydrology and underwater climate of the Bane d' Arguin, Mauritania:
a review
J. Sevrin-Reyssac
Laboratoire d'Ichtyologie generale et appliquee, Museum national d'Histoire naturelle, 43, Rue Cuvier,
75231 Paris, Cedex as, France
Key words: Banc d'Arguin, Mauritania, hydrology
Abstract
The northern coast of Mauritania between Cap Blanc and Cap Timiris is characterized by a large va
riety of hydrological situations. At the western slope of the Banc d'Arguin, at a depth of about 20 m,
the underwater climate is essentially of a temperate character. This is a highly unstable area due to the
occurrence of upwellings and the movements of the intertropical front. Close to the coast the isolation
of water masses by the very shallow Banc d'Arguin results in an increase of temperature and salinity.
These factors show a gradient towards the South from Cap. St. Anne to the islands. In this region the
underwater climate is tropical, a feature which is most Clearly expressed in land-locked bays such as the
Baie d'Arguin, the area around the island of Tidra, and the Baie de St. Jean. In the latter bay the
conditions are most extreme (salinity> 80%0)' Due to the coastal topography the area of the islands
around Tidra is highly isolated. This area receives no fertilization from the upwellings offshore.
Introduction The situation of the Mauritanian coast in a West
African framework
The Mauritanian coast between Cap Blanc and
Cap Timiris is a very interesting region because of The northern part of the Atlantic Ocean in front
its hydrological complexity and its climatological of the African coast belongs to the Atlantic
and biogeographical pecularities. The richness of Mediterranean province (Ekman, 1953) including
the upwelling system in the coastal zone beyond the Mediterranean and the adjoining parts of the
25 m is known worldwide and it has been the goal Atlantic. Within this area the Mrican coast be
of numerous international oceanographic expedi tween Gibraltar and Cap Blanc constitutes the
tions. Mauritanian subprovince (Fig. 1). In this area the
The littoral zone, however, and in particular waters are relatively cold. This is due to the pres
the Banc d' Arguin, has not been explored by the ence of the cold Canary Current penetrating
large expeditions because of its very shallow na South until the environs of Cap Blanc, and the
ture making it inaccessible for the large vessels. forming of upwellings between this current and
The small trawler 'Almoravide' of the Centre Na the coast. The frequency and intensity of these
tional de Recherches Oceanographiques et des phenomena increase from Cape Bojador towards
Peches at Nouadhibou has enabled the first stud the South. Maximum frequency occurs near Cap
ies of the shallow water area. In this paper the Blanc (Margalef, 1975; Schemainda et al., 1975;
major conclusions from this research will be re Bas & Cruzado, 1976).
viewed. Between Cap Blanc and Cape Verga in Guinea