Red Sea

444 Pages·1987·13.17 MB·English

by  Alasdair J. Edwards (Eds.)

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KEY ENVIRONMENTS
RED SEA
Edited by
ALASDAIR J. EDWARDS
University of Newcastle upon Tyne, UK
and
STEPHEN M. HEAD
University of the West Indies, Jamaica
Foreword by
HRH THE DUKE OF EDINBURGH
Published in collaboration with the
INTERNATIONAL UNION FOR CONSERVATION OF
NATURE AND NATURAL RESOURCES
by
PERGAMON PRESS
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First edition 1987
Library of Congress Cataloging in Publication Data
Red Sea.
(Key environments)
I. Marine ecology — Red Sea. 2. Marine resources
conservation — Red Sea. I. Edwards, Alasdair J.
II. Head, Stephen M. III. International Union for
Conservation of Nature and Natural Resources. IV. Series.
QH93.5.R43R43 1986 333.91 '6416 '0916533 86-16974
British Library Cataloguing in Publication Data
Red Sea. — (Key environments)
1. Natural history — Red Sea
I. Edwards, Alasdair J. II. Head, Stephen M.
III. International Union for Conservation of Nature and Natural
Resources IV. Series
508.3165'33 QQ H94.3
ISBN 0 08 028873 1
Printed in Great Britain by A. Wlieaton & Co. Ltd., Exeter
BUCKINGHAM PALACE.
The general problems of conservation are understood
by most people who take an intelligent interest in the state
of the natural environment. But if adequate measures are to
be taken, there is an urgent need for the problems to be
spelled out in accurate detail.
This series of volumes on "Key Environments" concentrates
attention on those areas of the world of nature that are under
the most severe threat of disturbance and destruction. The
authors expose the stark reality of the situation without
rhetoric or prejudice.
The value of this project is that it provides specialists
as well as those who have an interest in the conservation of
nature as a whole, with the essential facts without which it i
quite impossible to develop any practical and effective
conservation action.
1984
General Preface
The increasing rates of exploitation and pollution are producing unprecedented environmental changes
in all parts of the world. In many cases it is not possible to predict the ultimate consequences of such
changes, while in some, environmental destruction has already resulted in ecological disasters.
A major obstacle, which hinders the formulation of rational strategies of conservation and management,
is the difficulty in obtaining reliable information. At the present time the results of scientific research
in many threatened environments are scattered in various specialist journals, in the reports of expeditions
and scientific commissions and in a variety of conference proceedings. It is, thus, frequently difficult
even for professional biologists to locate important information. There is consequently an urgent need
for scientifically accurate, concise and well-illustrated accounts of major environments which are now
or soon will be, under threat. It is this need which these volumes attempt to meet.
The series is produced in collaboration with the International Union for the Conservation of Nature.
It aims to identify environments of international ecological importance, to summarize the present knowledge
of the flora and fauna, to relate this to recent environmental changes and to suggest where possible,
effective management and conservation strategies for the future. The selected environments will be re-
examined in subsequent editions to indicate the extent and characteristics of significant changes.
The volume editors and authors are all acknowledged experts who have contributed significantly to
the knowledge of their particular environments.
The volumes are aimed at a wide readership, including: academic biologists, environmentalists,
conservationists, professional ecologists, some geographers as well as graduate students and informed
lay people.
John Treherne
Vll
CHAPTER 1
Introduction
STEPHEN M. HEAD
Department of Zoology, University of The West Indies, Kingston, Jamaica
CONTENTS
1.1. Geographical setting 1
1.2. Dimensions, structure and geological history of the Red Sea 3
1.3. Introduction to the ecology and inhabitants of the Red Sea 7
1.4. Biogeography of the Red Sea 12
1.4.1. Faunal affinities 12
1.4.2. Endemism 13
1.4.3. Lessepsian migration 14
1.5. History of exploration and research 14
1.6. The Red Sea as a key environment 20
1.1 .GEOGRAPHICAL SETTING
The Red Sea is a long, narrow body of water separating north-east Africa from the Arabian Peninsula.
Its nearly 2000 km of navigable waters connect at the south with the Indian Ocean, and very nearly join
the Mediterranean Sea at the north of the Gulf of Suez. The Red Sea has been an important trade route
throughout human recorded history, linking the trade goods of India and the Far East with the
historical markets of Egypt, the classical world, and Europe. When Ferdinand de Lesseps completed the
Suez Canal in 1869, the connection became direct, and now the Red Sea is one of the most important
shipping routes in the world.
Seven countries have shorelines on the Red Sea (Fig. 1.1), and they include some of the richest and
poorest nations in the world. Some basic statistics about these countries are summarised in Table 1.1.
On the western shore lies Egypt to the north, the Sudan borders the central section, and Ethiopia lies to
the south. On the eastern shore, the Kingdom of Saudi Arabia occupies the northern and central
sections, while the Yemen Arab Republic (North Yemen) borders the southern section. Two other
countries, Israel and Jordan, have tiny but strategically important footholds on the Red Sea at the
northern tip of the Gulf of Aqaba.
1
2 S. M. HEAD
USSR S *^-v USSR S
η \ νι
υ
\ Λ 1 ^—
Iran \ /
_ /y \ V τ Turkey / Iraq >
\ Mediterranean |
1 Libya Egypt \\ Saudi ®
Arabia
8
J
- ^7
Sudan
—-^C Chad J
/ 6^
// ®
Ethiopia
y
Fig. 1.1. General outline map to show the countries surrounding the Red Sea. Key to numbers: 1, Lebanon. 2, Israel. 3, Syria.
4, Jordan. 5, Yemen Arab Republic (North Yemen). 6, Djibouti. 7, Somalia. 8, People's Democratic Republic of Yemen
(South Yemen). 9, Oman. 10, United Arab Emirates. 11, Persian Gulf. 12, Gulf of Aden. 13, Gulf of Oman. 14, Arabian Sea.
15, Indian Ocean.
Through most of the Red Sea region, the spoken language is Arabic, often with major dialectical
variations, and so the names of towns and geographical features used in this book have been
transliterated into English spelling, following the versions given in The Times Atlas of the World (1980).
These places are shown on the map on the endpapers, and some of the spelling variants encountered are
shown in Table 1.2.
The narrow southern Straits of Bab al Mandab mark the boundary between the Red Sea and the Gulf
of Aden. Immediately outside the Red Sea proper, two other countries border the entrance. To the west
lies the tiny state of Djibouti, and to the east is the People's Democratic Republic of Yemen (South
TABLE 1.1. Geographical and economic statistics for countries bordering the Red Sea. Largely adapted from data in
Year Book (1985).
Approx.
Red Sea Per capita
2
Area shoreline Population Trade balance G.N.P. G.N.P.
km km millions million US$ million US$ us$
EGYPT 1,002,270 1,386 47.0 -$5,958 $28,160 $600
ETHIOPIA 1,222,896 800 32.0 -$383 $4,530 $141
ISRAEL 20,711 <10 4.2 -$3,455 $20,420 $4,861
JORDAN 97,821 27 3.5 -$2,451 $3,880 $1,108
SAUDI 22,,115511,,444433 11,,774400 10.8 ++ $$3388,,446644 $117,240 $10,855
ARABIA
SUDAN 2,507,857 750 21.1 -$730 $7,390 $$335500
NORTH 195,185 430 5.9 -$748 $910 $433
YF.MF.N
INTRODUCTION 3
Yemen), which occupies the southern portion of the Arabian peninsula coast. South Yemen has a small
foothold in the Red Sea proper, by occupying the island of Kamaran which lies just off the coast of
North Yemen.
The Red Sea lies between 30°N and 12°30'N, and in this considerable latitudinal range one might
expect to find a range of climatic conditions. As Frederick Edwards describes in Chapter 3, this is not
the case. There are naturally some seasonal wind and air temperature differences between the north and
the south, but the whole seaboards of both eastern and western margins are overwhelmingly arid.
Rainfall nowhere exceeds about 18 cm per year, and the coastal vegetation is semi-desert. This is not the
apparently lifeless sand waste of the Sahara, or the Rub al Khali of central Arabia, but its vegetation
cover and productivity are very sparse. Rainfall is very irregular, especially towards the north, where
years may intervene between showers. When rain at last falls, the grey-brown desert becomes a carpet of
green for a few weeks, but this temporary bounty provides no long-term help for the sparse animal
populations of rodents and small antelope which graze the coastal plain. The dearth of rain and
vegetation has been the principal reason for the low human population levels anywhere along the Red
Sea coast, which even now do not exceed about 20 to the square kilometre except in the vicinity of
major towns. Historically, the human population has subsisted by nomadic pastoralism of near-biblical
simplicity, artisanal fishing, and in a few favoured ports, by trade, transhipment and the pilgrim
business. Nowadays the situation has begun to change very rapidly, at least in those coastal areas where
oil-fed economies are investing heavily in plant and building in the coastal zone.
1.2. DIMENSIONS, STRUCTURE AND GEOLOGICAL HISTORY OF THE RED SEA
According to Morcos (1970), the Red Sea is 1932 km long, and averages 280 km in width. Even at its
widest, in the south near Massawa, it is only 354 km wide, and this narrows to 29 km at the shallow
Straits of Bab al Mandab, a figure which includes the island of Perim, which further restricts the
TABLE 1.2. Alternative place name spellings.
Place Alternative spelling
Al Hudaydah Hodeidah
Al Mukha Mocha
Al Wajh Wejh
Aqaba Akaba
Assab Aseb
Bab al Mandab Bab el Mandeb
Dahlak Archipelago Dahlac Archipelago
Dungunab Bay Dongonab Bay
Elat Eilat, Eilath
El Kharga El Karija
Hurghada Al Ghardaqa, Ghardaqa
Jiddah Djidda, Jedda, Jeddah, Jidda
Massawa Mits'iwa
Mecca Makkah, Meccah
Muhammad Qol Mohammad Qol
Port Sudan Bur Sudan
Quseir Koseir
Riyadh Ar Riyad
Rub al Khali Ar Rab'al Khali
Safaga Bur Safaga
Sinai Es Sina
Suez El Suweis
Yanbu al Bahr Yenbo, Yenbu
4 S. M. HEAD
Fig. 1.2. Bathymétrie map of the Red Sea, based on the chart in Morcos (1970), considerabl y simplified.
opening to the Gulf of Aden. The total surface area of the Red Sea is variously estimated between 438
and 450 thousand square kilometres, while the volume is between 215 and 251 thousand cubic
kilometres. Morcos considers the average depth to be 491 m, although some other estimates are a little
deeper. This compares to an average depth of 3700 m for the World's oceans.
The bathymetry of the Red Sea is shown in Fig. 1.2, and Table 1.3 shows the approximate
proportional distribution of depth. The maximum depth recorded in the Red Sea is 2850 m, which is
small compared with the great oceans, but large for a body of water of its size. The Red Sea is for
example much deeper than the Arabian Gulf. Although in the southern Red Sea the shallow coastal shelf
is extensive, in the northern and central Red Sea it may only extend a few kilometre s offshore. Morcos
(1970) refers to this region as the 'coral reef zone', because over much of the length of the Red Sea, this
shelf is covered with actively growing reefs. From the coral reef zone, the sea bottom drops away
rapidly in a series of stepped cliffs to the main trough at about 500m depth. The trough gradually
INTRODUCTION 5
TABLE 1.3. Approximate distribution of surface area by depth for the Red Sea (including northern gulfs).
Original, calculated from the bathymétrie map in Morcos (1970).
Depth range Area as proportion of total
0- 50m 23.86%
50- 100m 17.27%
100- 500m 15.71%
500-1000m 29.06%
1000-1500m 11.64%
1500-2000m 2.04%
2000m 0.42%
deepens to about 1000 m near the central axis of the Red Sea, where there may be a further change in
topography as the bottom slopes steeply down in the central rift. This central rift or axial trough is
about 1500 m deep along much of its length, and contains pits or 'Deeps' where depths may reach over
2500m.
Figure 1.3 shows three representative profiles through the northern (26°N), central (20°N) and
southern (14°N) Red Sea. The central region shows the most dramatic topography, with a steep
western profile, a well developed main trough or platform at ca. 500 m and a plunge to over 2000 m
depth in the central rift. To the north the 500 m platform is less well developed and the central rift less
prominent. In the south, the shelf is very wide to east and west, and the profile descends steeply to the
maximum depth of some 1600 m.
The northern gulfs of Suez and Aqaba present great contrasts in bathymetry. The Gulf of Suez is
shallow and flat bottomed basin, with a depth of 55 to 73 m, deepening at the entrance to the Red Sea
proper. The Gulf of Aqaba is very steep-sided and deep, reaching maximum depths of over 1800 m near
the east coast, although the Gulf is only some 30 km wide. Just as the Red Sea is cut off from the Gulf of
Aden by a 100—130 m deep sill about 140 km north of the Straits of Bab al Mandab, the Gulf of Aqaba
is separated from the rest of the Red Sea by a sill (the sill of Tiran) at its entrance, about 250—300 m
deep (discussed in Chapter 3). The Gulf of Aqaba is in these respects a model, on a very small scale, of
the Red Sea itself.
Figure 1.4 shows a hypsometric curve for the Red Sea, including the northern gulfs calculated from
the bathymétrie chart in Morcos (1970). This curve is obtained by measuring the total area occupied by
successive depth bands, and then plotting the cumulative areas against depth. This results in an averaged
profile for the Red Sea. The various breaks in topography mentioned above are well demonstrated and it
can be seen that about a quarter of the surface area is of 50 m or less depth, thus capable of supporting
active coral growth. As Figure 1.2 showed, much of this area is concentrated to the south of the Red
Sea. About 14% of the area is deeper than 1000 m and forms part of the axial rift.
The structure and history of the Red Sea are described in Chapter 2 by Colin Braithwaite. By way of
introduction a much simplified summary follows here. The Red Sea is part of a system of crust al
expansion in which Africa and the Arabian Peninsula are drifting slowly apart, by the same mechanism
that created the Atlantic Ocean. The deep axial trough of the Red Sea forms part of a much larger
system extending from the Dead Sea to the African Rift Valley, and from Aden eastwards into the
Indian Ocean. Associated with this rift system is the uplift of mountain ranges which lie along the
length of the Red Sea behind the narrow coastal plain. As the continental masses of Africa and Arabia
separate, the deep rift described above is formed, and new crust is continually being injected into this
region. The injection of hot magma into the depths of the Red Sea accounts in part for the high
temperatures at the bottom of the Red Sea, assisted by the isolation of its deep water from the rest of the
Indian Ocean by the sill to the south. It is also responsible for the hot brine pools and valuable metal-rich
sediments described in Chapter 4 by Ludwig Karbe.