ArticlePDF Available

Scientific elements for a Yemeni wetland conservation strategy: overview of the main factors explaining the diversity and characteristics of wetlands

Authors:
  • Mohammed V University in Rabat - Institut Scientifique

Abstract and Figures

Day after day, the wetlands of arid regions reveal new secrets about their importance, in terms of biodiversity as well as functions and services. Yemen, a mountainous country surrounded by seas and a desert, has a flora and fauna heritage shaped by both African, Asian and Palearctic influences, and by a pronounced insularity that has enriched it with endemic forms of world interest. However, this biodiversity has still not received the attention it deserves, in terms of conservation. This lack prompted us to carry out a general diagnosis of the Yemeni wetlands, providing the essential scientific elements allowing to initiate a sustainable use strategy of these ecosystems. This diagnosis focuses first on the main factors that control the functioning of these wetlands, then on the characteristics of these, presented for each type, according to a usual classification scheme. While relating the richness already discovered in the seas and islands, this article provides arguments in favor of the originality of the estuarine and fluvial ecosystems. The creation of a geodatabase, using satellite data (digital elevation model, precipitation, thematic images) has made it possible to illustrate the high density of the river network in Yemen, which is justified by the census of some 450 estuaries, identified along a 2,500 km long coast. This base was enriched by cartographic inventories (in particular those of hydraulic dams and towns and villages), reconstructed from bibliographic and unpublished information, which also gives often non-cartographic information on the distribution of habitat types (especially marine). The striking features of these ecosystems are highlighted through arguments borrowed especially from orography, climate and human pressures. These are very old, but their recent increase is alarming, due to the rapid growth of the population and of its needs in agricultural and urban, even industrial, water and space. Urgent solutions are essential to improve and protect wetlands in Yemen, starting with research likely to lead to a complete classification and inventory of these ecosystems, but also to a better characterization of their originalities and their functioning and of the pressures they undergo. Résumé. Jour après jour, les zones humides des régions arides révèlent de nouveaux secrets sur leur importance, tant au niveau de leur biodiversité que de leurs fonctions et services. Le Yémen, pays montagneux encerclé par des mers et un désert, possède un héritage floristique et faunistique façonné par des influences à la fois africaines, asiatiques et paléarctiques, et par une insularité prononcée qui l'a enrichi de formes endémiques d'intérêt mondial. Pourtant, cette biodiversité n'a toujours pas reçu l'attention qu'elle mérite, en termes de conservation. Ce manque nous a incités à réaliser un diagnostic général des zones humides de ce pays, qui fournit les éléments scientifiques essentiels permettant d'initier une stratégie d'utilisation durable de ces écosystèmes. Ce diagnostic porte dans un premier temps sur les principaux facteurs qui contrôlent le fonctionnement de ces zones humides, puis sur les caractéristiques de celles-ci, présentées pour chaque type, selon un schéma de classification usuel. Tout en relatant les richesses déjà découvertes dans les mers et les îles, cet article donne les arguments en faveur de l'originalité des écosystèmes estuariens et fluviaux. La constitution d'une base de données géospatiale, à partir de données satellitaires (modèle numérique de terrain, précipitations, images thématiques) a permis d'illustrer la forte densité du réseau fluvial du Yémen, laquelle est justifiée par le recensement de quelque 450 estuaires, identifiés le long d'une côte longue de 2500 km. Cette base a été enrichie par des inventaires cartographiques (notamment ceux des barrages hydrauliques et des villes et villages), reconstitués à partir de sources bibliographiques et inédites, lesquelles donnent aussi des informations souvent non cartographiques sur la distribution des types d'habitats (surtout marins). Les traits marquants de ces écosystèmes sont mis en exergue via des arguments empruntés surtout à l'orographie, au climat et aux pressions humaines. Celles-ci sont très anciennes, mais leur augmentation récente est alarmante, en raison de la croissance rapide de la population et de ses besoins en eau et en espace agricole et urbain, voire industriel. Des solutions urgentes pour améliorer et protéger les zones humides au Yémen sont indispensables, à commencer par les recherches susceptibles d'aboutir à une classification et un inventaire complets de ces milieux, mais aussi à une meilleure caractérisation de leurs originalités et leur fonctionnement et des pressions qu'elles subissent.
Content may be subject to copyright.
Afrah Saad Al-MAhfAdi & Mohamed dAkki
Research Team on the Management of Wetlands, Zoology Department, Scientic Initute, Mohammed V University of Rabat, Ibn Battota
Street, BP 703, Rabat, Morocco. *(afrahalmahfadi@gmail.com)
Abract. Day after day, the wetlands of arid regions reveal new secrets about their importance, in terms of biodiversity as well as functions
and services. Yemen, a mountainous country surrounded by seas and a desert, has a ora and fauna heritage shaped by both African, Asian
and Palearctic inuences, and by a pronounced insularity that has enriched it with endemic forms of world intere. However, this biodiversity
has ill not received the attention it deserves, in terms of conservation. This lack prompted us to carry out a general diagnosis of the Yemeni
wetlands, providing the essential scientic elements allowing to initiate a suainable use rategy of these ecosyems. This diagnosis focuses
r on the main factors that control the functioning of these wetlands, then on the characteriics of these, presented for each type, according to
a usual classication scheme. While relating the richness already discovered in the seas and islands, this article provides arguments in favor of
the originality of the euarine and uvial ecosyems. The creation of a geodatabase, using satellite data (digital elevation model, precipitation,
thematic images) has made it possible to illurate the high density of the river network in Yemen, which is juied by the census of some 450
euaries, identied along a 2,500 km long coa. This base was enriched by cartographic inventories (in particular those of hydraulic dams
and towns and villages), reconructed from bibliographic and unpublished information, which also gives often non-cartographic information
on the diribution of habitat types (especially marine). The riking features of these ecosyems are highlighted through arguments borrowed
especially from orography, climate and human pressures. These are very old, but their recent increase is alarming, due to the rapid growth of
the population and of its needs in agricultural and urban, even indurial, water and space. Urgent solutions are essential to improve and protect
wetlands in Yemen, arting with research likely to lead to a complete classication and inventory of these ecosyems, but also to a better
characterization of their originalities and their functioning and of the pressures they undergo.
Key words: wetland, ecology, human pressures, conservation, GIS, Yemen.
Résumé. Jour après jour, les zones humides des régions arides révèlent de nouveaux secrets sur leur importance, tant au niveau de leur
biodiversité que de leurs fonctions et services. Le Yémen, pays montagneux encerclé par des mers et un désert, possède un héritage oriique
et fauniique façonné par des inuences à la fois africaines, asiatiques et paléarctiques, et par une insularité prononcée qui l’a enrichi de
formes endémiques d’intérêt mondial. Pourtant, cette biodiversité n’a toujours pas reçu l’attention qu’elle mérite, en termes de conservation. Ce
manque nous a incités à réaliser un diagnoic général des zones humides de ce pays, qui fournit les éléments scientiques essentiels permettant
d’initier une ratégie d’utilisation durable de ces écosyèmes. Ce diagnoic porte dans un premier temps sur les principaux facteurs qui
contrôlent le fonctionnement de ces zones humides, puis sur les caractériiques de celles-ci, présentées pour chaque type, selon un schéma
de classication usuel. Tout en relatant les richesses déjà découvertes dans les mers et les îles, cet article donne les arguments en faveur de
l’originalité des écosyèmes euariens et uviaux. La conitution d’une base de données géospatiale, à partir de données satellitaires (modèle
numérique de terrain, précipitations, images thématiques) a permis d’illurer la forte densité du réseau uvial du Yémen, laquelle e juiée
par le recensement de quelque 450 euaires, identiés le long d’une côte longue de 2500 km. Cette base a été enrichie par des inventaires
cartographiques (notamment ceux des barrages hydrauliques et des villes et villages), reconitués à partir de sources bibliographiques et
inédites, lesquelles donnent aussi des informations souvent non cartographiques sur la diribution des types d’habitats (surtout marins).
Les traits marquants de ces écosyèmes sont mis en exergue via des arguments empruntés surtout à l’orographie, au climat et aux pressions
humaines. Celles-ci sont très anciennes, mais leur augmentation récente e alarmante, en raison de la croissance rapide de la population et
de ses besoins en eau et en espace agricole et urbain, voire induriel. Des solutions urgentes pour améliorer et protéger les zones humides au
Yémen sont indispensables, à commencer par les recherches susceptibles d’aboutir à une classication et un inventaire complets de ces milieux,
mais aussi à une meilleure caractérisation de leurs originalités et leur fonctionnement et des pressions qu’elles subissent.
Mots clés: zones humides, écologie, pressions humaines, conservation, SIG, Yémen.
INTRODUCTION
Wetlands are well known as rich reservoirs of biodiversity
and as sources of socioeconomic services and of knowledge
(Stuip et al. 2002, MEA 2005, Bruland 2008, Erwin 2008
and McCartney et al. 2010). However, these ecosyems are
exposed to continuous loss, mainly in arid regions (Sheppard
et al. 1992, O’Connor & Crowe 2005 and Duy 2006), due
to human expansion, whose needs in terms of land and water
are continuously growing. These losses are eimated at 50%
since 1900 (Davidson 2014), and have been amplied by
climate change and recurrent droughts (Barnard & Thuiller
2008, Elasha 2010 and Crooks et al. 2011). Therefore, wetland
protection and reoration become highly prior in national
policies (Hushulong 2012, Parry et al. 2007 and Erwin 2008),
more especially in arid countries. These rategies mu
be based on a solid knowledge of these ecosyems, more
especially of their main functional characteriics.
In Yemen, a mountainous country extending on 527,970
km², wetlands are supposed to hold a rich biodiversity due to
their high variety and to the original context of their genesis
e-ISSN : 1114-6834
Bulletin de l’Institut Scientique, Rabat, Section Science de la vie , 2020, n° 42, 31-42
Scientic elements for a Yemeni wetland conservation rategy:
overview of the main factors explaining the diversity and characteriics of wetlands
Éléments scientiques pour une ratégie de conservation des zones humides du Yémen:
aperçu des principaux facteurs expliquant la diversité et les caractériiques des zones humides
32 Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
and evolution (variable orographic and climate situations,
long coaline overlapping three dierent seas, high number of
islands, etc.). This richness is well marked by the biogeographic
situation of this country at the transition zone between three
major domains (Afrotropical, Oriental and Palearctic) and on
major routes of waterbird migrations. Besides these aspects,
the Yemeni wetlands evolved in an insular context, since they
belong to a mountainous area surrounded by seas and desert
and to a high number of islands dispersed in a semi-closed sea.
This evolution explains the high rate of endemism highlighted
in dierent Yemeni wetlands.
In Yemen, wetlands are endorsing heavy and rapid
degradations (EPA 2009, Al-Mahfadi & Dakki 2019),
whereas they provide mo of the survival resources to the
population. In order to design a good conservation rategy for
these wetlands, we gather in this article the mo signicant
information necessary to provide a good underanding of the
conguration and the sensitivity of these ecosyems.
MATERIAL AND METHODS
This article was essentially based on satellite and
published data, supported by our unpublished eld knowledge
of the Yemeni wetlands and by interviewing research and
adminirative competencies.
Mapping
Mapping of the natural context concerns essentially
orography, hydrography, geology and rainfall, which play
a decisive role in wetland conguration. This work was
accomplished, using GIS tools (ArcGIS) and Remote Data,
mainly the Digital Elevation Model (DEM) of the country,
extracted from ASTER GDEMV2 (Advanced Spaceborne
Thermal Emission and Reection Radiometer) and the
rainfall satellite data for the period 1981-2014 extracted from
CHIRPSV2 (Climate Hazards Group InfraRed Precipitation
with Station data). Data were compiled and assembled by
watersheds, with the knowledge that wetlands conguration is
mainly dened by their watershed characteriics. In addition
to natural factors, major human activities (e.g. damming and
agriculture) are evocated and discussed, in a way to and out
their hiorical and actual impacts on wetland characteriics.
Field knowledge and interviews
Although unnoticed in the article, intensive work on
wetland identication and location allowed an overview of
exiing wetland types in the country and an eimate of their
representativity. This inventory was mainly focused on coaal
and marine wetlands but also on articial reservoirs, knowing
that lacurine wetlands are quite absent in the country.
Considering our eld knowledge and observations, they
concern more than fourteen wetlands, which are moly on the
coa, in addition to some mountainous rivers. Moreover, the
remote and eld data were reinforced through interviews with
academicians in the Faculty of Agriculture (Environmental
Department) and adminirators in dierent initutions:
Directorate of Irrigation and Dams (DID), Environmental
Protection Authority (EPA), Regional Organization for the
Conservation of the Environment of the Red Sea and Gulf of
Aden (PERSGA), Food and Agricultural Organization (FAO),
the Ramsar Convention, etc.
RESULTS
Main factors conguring Yemeni wetlands
Using GIS tools and satellite resources, we provide
the mo useful information for a good underanding of
the abundance, the diversity and the classication of the
Yemeni wetlands. In addition to some classical results, this
analysis highlighted some originalities that should be taken
in account in designing an eventual conservation rategy of
these ecosyems or in planning researches or inventories or
monitoring programs on wetlands.
Oro-hydrographic context: a mountainous country with a
dense river network
The simplied oro-hydrographic map of Yemen (Fig. 1),
generated from a DEM, shows a mountainous country, with
highe altitudes (over 2,000 meters) in its weern and
South-weern sides, including the highe mountain of the
Arabian Peninsula (Jabal Al-Nabi Shu’ayb, at 3,666 meters).
Further ea, the mountains fall away in progressive eps
to the North-Ea (Rub’a Al-Khali) and the Ea, through a
large plateau, where altitudes are around 700-1,000 meters.
In the Mountain Massif, slightly parallel to the Red Sea,
landscapes are marked by eep slopes and deep valleys, with
relatively frequent volcanic craters. This topography plays
in favor or a dense riverine network, mainly permanent and
semi-temporary, whereas these ecosyems are intermittent
or ephemeral in the large eaern Plateau and Desert areas.
Plains are diributed along the weern and Southern coas
of the country and along its northern boundary with Oman.
They are relatively narrow (less than 30 km wide), slightly
sloppy, with highe altitudes around 200 meters. They are
also dominated by alluvial landscapes (EPA 2004b) with
several large and dry valleys.
Marine context: high representativity of coaal and island
ecosyems
The 2,500-km coaline of Yemen belongs to three dierent
seas (Red Sea, Golf of Aden and Arabian Sea) with dierent
hydrological and ecological conditions. The use of satellite
images with some exiing maps revealed a coaal landscape
dominated by long rocky clis with variable height, and a
minimum of 450 euaries, which corroborates with the high
number of watersheds. The weern and south-weern margins
of the country, overlooked by high mountains, show several
large euaries, mo of them being often separated from the
sea by natural sediment dams. Between these euaries exi
also many small river mouths, with coaal small watersheds
that occasionally ow, whereas these rivers mouths are often
separated from the sea with sediment thresholds. These two
kinds of euaries exi also on the Arabian Sea side, but this
coa has the particularity to receive the large euary in the
country, generated by Wadi Hadramawt, which drains the
large watershed of the Arabian Peninsula.
Yemen is also well known for its numerous islands
(more than 186), mo of which (more than 112 volcanic
islands) being in the Red Sea. These reliefs enrich the marine
environment in shallow rocky habitats occupied by very rich
communities, whereas their terrerial biodiversity is highly
marked by endemism, which has been clearly demonrated in
the bigge islands (Tardelli & Baldini 2000 and RAP 2004),
as Socotra (3625 km²) in the Arabian Sea and Kamran (108
km²) in the Red Sea.
Geological context: basic data explaining ecological
diversity and endemism
Geology can aect wetland diversity and abundance through
dierent aspects (petrography, permeability, hiory, etc.),
besides its determinism of the orography and the hydrology.
A simplied geological map of Yemen (Fig. 2) drawn
according to an exiing scheme (Van der Gun & Ahmed
1995), shows a relatively high petrographic diversity. The
main rocky outcrops date from the Mesozoic and continues
33
Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
until now (Geukens 1966); the basement of this cover, which
ushes in limited mountainous areas, consis of Precambrian
impermeable cryalline rocks (amphibolite’s, migmatites,
gneiss and granite), Cambrian sandones and Permian shale.
Until the middle of the Mesozoic, Yemen remained attached
to the African continent, before being immersed from Jurassic
to Cretaceous, when great limeone series were generated,
conituting a large part of the high mountainous outcrops.
In the middle of the Tertiary, tectonic movements led to
the opening of the Red Sea and the Gulf of Aden and to the
overelevation of the Yemeni mountains, simultaneously to
an intense volcanic activity (basaltic deposits), that marked
a large part of the weern mountain relief. The exiing
limeone series were surmounted by Tertiary widespread
river deposits (sandone) and by Paleocene deposits (thick
layer of limeone) that form the Jawl plateau in the eaern
half of the country.
During the Quaternary, the volcanic activity resumed locally
in the weern half of the country. During the wet quaternary
periods (e.g. la glaciation), an intensive erosion happened
in mountains, creating remarkable deep valleys and abundant
alluvial sediments that conructed the main coaal plains
and the platforms of Rub-Al-Khali and Hadramawt valley
(Mohammed et al. 2018).
From this hiory, it could be concluded that both mountainous
and coaal wetlands exied in Yemen since the Tertiary
and their actual biodiversity survived under the Quaternary
climate oscillations. The impermeable cryalline subratum
is generally favorable to groundwater oring, mainly
during the Quaternary wet periods, and to springs and rivers
abundance. During the Cenozoic, the inland wetlands have
evolved in insular environment (country between seas and
desert), which generates numerous endemic forms among
aquatic biodiversity, as well as in islands.
Climate: a determinant factor of the hydrology ress in
wetlands
Yemen lies within the sub-tropical climatic and the
northern retches of the tropical zone (Elasha 2010). It is
submitted to the monsoon regime, with two rainfall seasons
(March-May and July-September), separated by a dry season
(October to February), with some irregular precipitations in
the weern mountains (Fig. 3).
Annual rainfall, calculated using satellite data for
the period 1981-2014, varies from We to Ea between
1500 mm/year, mainly recorded in the high mountainous
dirict of Ibb, and less than 100 mm/year in the eaern and
northern deserts (Fig. 4). Mo of the country, including
medium altitude slopes, is under more or less dry climate (Van
der Gun & Ahmed 1995). The rainfall trend, as illurated by
four watershed examples chosen in dierent regions (Fig. 5),
is slightly negative, characterized by high interannual
uctuations and frequent droughts.
In concordance with the sunshine duration (6-9 hours/
day), the evapotranspiration rate is regularly high, with large
spatial variation (NBSAPY 2005): 1500-2500 mm/year in the
weern mountains and 1800-2700 mm/year in the coaal
zones and foothills, whereas higher values (2000-3500 mm/
year) are recorded in inland arid areas.
Given this climate, inland wetlands should be frequently
submitted to hydrologic ress during a large part of the year
(EPA 2004b). Therefore, intermittent wadis and ponds are
predominant and very few and small lakes are known in the
volcanic crater of Bir Ali in Balhaf area of the Arabian Sea
as well as on Al Zubair Group in the Red Sea. Due to the
recent droughts and the high number of articial dams, the
river waters generally do not reach the sea, in the sense that
their low courses are ooded only after violent rain showers.
Therefore, mo of the euarine ecosyems are intermittently
open/closed (sensu Whiteld 1992), due to sediment barriers
Figure 1. Oro-hydrography and main geographical regions of Yemen.
34 Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
Figure 2. Simplied geological Map of Yemen (Van der Gun & Ahmed 1995).
Figure 3. Monthly variation of precipitations in Yemen (Hadramawt watershed).
35
Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
Figure 5. Rainfall trend in Yemen: annual average precipitations (1981-2014) in four rivers.
Figure 4. Spatial diribution of the annual rainfall in Yemen.
36 Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
mainly built by sea and wing dynamics, and behave like North-
African euarine gueltas (Dakki et al. 2020), as brackish to
hypersaline agnant water.
Human context: heavy pressures on wetlands, amplied by
frequent droughts
Human activities conitute a key issue in conservation
rategies, since they play a decisive role in wetland loss,
more especially in arid emerging countries that know a rapid
increase of their population, while recurrent droughts deplete
their water resources. In Yemen, the population increased
ve-times between 1955 and 2019 (Fig. 6); its growth rate
regiered between 2014 (CSO 2014) and 2016 (Worldmeters
2019) is 3.2% (i.e. 26.25 to 27.58 million), with alarming
values in major cities, which have absorbed large numbers of
rural emigrants. The average population density is about 55.6
people/km² (CSO 2014), with large spatial variation (e.g. 1.1
and 388 people/km2 respectively in Almahra and Ibb regions).
This explosive growth means a high increase of both water
demand and pollution; however, the decit between available
resources and consumption is continuously increasing, i.e.
400,000 m3 in 1990 and 900,000 m3 in 2000 (Ward et al. 2000).
In this arid agricultural country, thousands of water
derivations have been managed for millennia along the
riverbanks and from springs; their increasing number often
dry up the riverbeds on long diances. Damming was also a
traditional approach in this country, as illurated by the old
Ma’rib dam, but the increased water demand has forced the
government to adopt and intensied damming politics. The
number of dams has increased concomitantly to recurrent
droughts, from 60 in 1970 to 240 in 1990 (Charbonnier 2009),
exceeding now more than 600 dams (MAI 2016), mainly
concentrated in the weern highlands of the country.
Similarly, the groundwater exploitation has led to their
rapid depletion, mainly in the weern part of the country
where the great majority of the population resides (NWRA
2005). The decrease of the water table level was eimated
between 1.0 and 3.0 meters/year in Al-Hodidah, Ta’iz and
Amran regions, but in Sana’a region, it reached 6-8 m/year.
Recently, the water extraction was extended to fossil deep
aquifers, which have been also depleted in some zones, such
as Amran and Ta’iz basins, after what agriculture has been
opped.
This evolution is ecologically translated into a recurrent
hydrologic ress in all wetlands depending from riverine
waters, mo of them being frequently dried, sometime for
several years. As mo of the human agglomerations are
close to rivers (Fig. 7), water pollution is ill increasing due
to continuous growing of urban euents and to dierent
development poles. Being the nal recipient of watersheds,
euarine wetlands are certainly suering from all these
impacts.
Status of the major wetland types present in Yemen
Considering the former description, we mu conclude
that wetlands are relatively diversied in Yemen, despite the
aridity of this country. This diversity is presented hereafter,
through a simplied classication borrowed from the
Ramsar Convention scheme (Navid 1989), where all factors
described above are reected. However, this presentation is
moly focused on their characteriics, representativity and
diribution in the country.
Coaal and marine wetlands
As formerly explained, Yemen coaline is 2,500 km long
and belongs to three dierent seas, with dierent sizes, hydro-
sedimentary dynamics and ecological factors: (1) the Arabian
Sea, which is largely open on the Pacic Ocean and its coaal
wetlands are submitted to its high hydrodynamics; (2) the
Gulf of Aden, where salinity increases from Ea (35.5 mg/l)
to We (37.5 mg/l) and the coaal wetlands are inuenced
by upwellings (surface waters relatively cold); and (3) the
Southern Red Sea, which width decreases from the North
(270 Km) to the Bab Al-Mandeb retch (20 Km). This latter
regulates the water exchange between this sea and Gulf of
Aden, isolating the Red Sea ora and fauna from the other
marine communities and enriching them in endemic forms
(EPA 2009).
Figure 6. Yemen population growth during 1955-2020 period (Worldmeters 2019).
37
Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
Figure 7. Superposition between human habitat and hydrographic network, an illuration of human pressures on wetlands
(e.g. Wadi Al Mahiam).
Coaal open waters
Considering the former introduction, tidal and subtidal
shallow waters in the three seas dier by their hydrodynamics,
with clear decrease of the tide amplitude, depth and bottom
slope from the Arabian Sea to the Red Sea.
Coaal beaches
These ecosyems include sediment coaal lands, at
or slightly sloping, submitted to sea tides and waves; they
slightly vary in pace, mainly in relation with the coa slope
the tide amplitude and the orm waves. In the weern half
of the country and Socotra, mo of the coaline is close to
foothills and its beaches are more or less narrow and sloping,
frequently enriched with coarse sediments (gravel, pebbles
and blocks), mainly when they are close to river mouths. Pure
sandy beaches are relatively rare, but more frequent on the
Arabian Sea coa.
Sea clis
These habitats correspond to vertical or sub vertical coaal
lands, beaten by sea waves and spray. These landscapes,
with variable height (generally exceeding 20 meters), have
remarkable length, although they are frequently interrupted
by euaries. High sea clis play an important ecological role,
mainly as refuges for particular forms of ora and fauna; this
importance is amplied in Yemen by the high rate of endemic
species (Sheppard et al. 1992).
Euarine syems
These habitats correspond to sea inlets (lagoons and river
mouths), relatively sheltered from marine hydrodynamics and
more or less fed with inland waters. As the country is mainly
mountainous, it holds a dense river network that generated
more than 450 euaries. Considering their extension, 89 %
of them have an area of less than 50 ha; the remaining 47
euaries that exceeds 50 ha are mainly in the Red Sea (43%)
and the Gulf of Aden (36%). Sixteen euaries exceed 200 ha
and are also on the Red Sea side, and only three of them are on
the Gulf of Aden or the Arabian Sea coas. This latter receives
the large euary (555 ha) in the country, Wadi Hadramawt
(or Almasilah). The morphology of euaries reects the
impact of large oods that happened during pa wet periods,
including the Holocene. Actually, the riverbeds are frequently
dried up for several weeks or months, even for several years,
and mo of the river mouths took the form of a anding water
pond. Therefore, they can be classied as intermittently open/
closed euaries (Whiteld 1992), due to sediment obacles
built between the sea and the river by marine hydrodynamics,
sometime supplied by wind. However, the river oods
transport coarse materials, enriching the euarine subrate
with gravels and pebbles, even in blocks, which contribute to
consolidating the sediment dam. Outside of these oods, the
ponds will be enriched with ne materials, including organic
matter produced by biological processes, more especially in
Red Sea inlets. Sandy habitats seem to be more abundant
in the eaern half of the country (about 115 euaries of the
Arabian Sea).
This functioning scheme was well described in similar arid
zones, as in North Africa (Dakki et al. 2020), where they are
named ‘euarine gueltas’, in Southern Asia (Ranasinghe &
Pattiaratchi 2003), Auralia (Roy et al. 2001), New Zealand
(Lill et al. 2012) and more especially in South Africa, where
they conitute more than 70% of the euaries (Perissinotto et
al. 2010, etc.) and beneted from abundant udied (Nozais et
al. 2005, James et al. 2007, Snow & Taljaard 2007, Taljaard
et al. 2009, Whiteld et al. 2012, Tweddle & Froneman 2015,
Scharler et al. 2020, etc.).
Lagoons are intended here as sea inlets that are not fully
open to the sea and receive few inland waters. The whole
information used in this udy is based on satellite images
and punctual eld visits, noting that the ecological udies
dedicated to these ecosyems (EPA 2009) concern mainly
Kalnsia and Ditwah lagoons on Socotra coa and the Mocha
Lagoon in Ta’iz region (Red Sea). These ecosyems are
38 Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
mainly represented on the Red Sea coa, where 26 inlets
could be identied as lagoons, the two other seas show only
six small inlets, the large one (Almahra-Arwet) having a
maximum surface of 65 ha. Some large shores, developed in
the Gulf of Aden and the Arabian Sea coas, show on their
inland side a sebkha like landscape, which dries out seasonally
and form va salty ats, with scattered halophytic plants or
blue-green algal crus (EPA 2013).
Islands
These small lands entirely surrounded by sea waters, are
particularly numerous along the Yemen coas, about 186
islands (Al-Najar et al. 2008). The bigge Islands in the
Red Sea are Zugur groups (120 km²), Kamaran (108 km²)
and Big Hanish (65 km²), Socotra is however the large
Yemeni island on the southern margin of Arabian Sea (3,549
km²). It holds diverse ecosyems, including terrerial
habitats, and a rich ora and fauna, with high endemism rate
(Tardelli & Baldini 2000, Al-Saghier 2002b …). Islands are
ecologically remarkable by their coaal and marine habitats
(clis, beaches, mangroves and coral beds), which are treated
separately in this article.
Mangroves and Seagrass
These tropical sea-coa formations are common in the Red
Sea, where they were identied in more than 130 km of coas;
they are organized in discontinuous belts, with some large
formations in the north-weern coa of Yemen (e. g. Midi
to Alluhayah). More to the South (e.g. Al-Urj to Al-Hodidah
or Bab Al-Mandab areas), these habitats are organized in
well conserved thin belts around islets, but sometimes highly
fragmented into small patches. Furthermore, the seagrass
diribution is quite-continuous along the Red Sea coa
(Barratt et al. 1987), while they are rare in the Gulf of Aden
and the Arabian Sea.
Coral reefs/beds
These habitats make the Red Sea among the mo famous
coral areas in the world, both by their diversity, in terms of
number of species and communities, and by their extension.
This sea contains about 260 species of hermatypic corals,
organized in large but discontinuous patches (Kemp 2000
and Sheppard et al. 1992). In Socotra Island, coral reefs are
remarkable, while they are relatively rare in the Gulf of Aden.
In addition to its high richness, the Yemeni Coral fauna is
mainly remarkable with its high rate of endemism both in
Socotra and the Red Sea (Sheppard et al. 1992).
Inland wetlands
River (Wadi) syems
This category includes all types of running waters,
the local term Wadi refers to ‘surface drainage channels
essentially characterized by intermittent ow (Hall et al.
2008). These ecosyems are very widespread in Yemen, due
to its mountainous reliefs (more than 450 watersheds). Mo
of them belong to nine wide watersheds, draining the weern
mountains and southern slopes. The appreciable rainfall at
these highlands ensures some regular ow to the mountainous
wadis, but these acquire intermittent regime when moving
downream, taking then the form of a chain of separate ponds.
Their waters arrive to the sea or to the desert only during high
oods (NBSAPY 2005), which oods carry a great quantity
of alluvial deposits, with variable sizes, allowing agriculture
on hillside terraces and riparian farms, even in high altitudes.
Surface water temperature, as a highly determinant
ecological factor in the longitudinal organization of river
communities, have been poorly udied, but punctual
measures show high values: i.e. 27 to 35°C (exceptionally
40°C) at dry season between elevations of 230 m and 1254 m
(Minissale et al. 2007). These values translate a determinant
role of insolation combined to ow lowering in warm running
waters. Consequently, as demonrated in other dry lands
(e.g. Dakki 1987), the Yemeni river communities are exposed
during dry seasons to extreme thermal conditions in addition
to the severe hydrologic ress.
The global warming, expressed in Yemen by frequent
droughts, generates heavy loss in running water’s
biodiversity. On another hand, the riverine natural vegetation
was dramatically deroyed in medium altitudes, due to the
excessive occupation of the riverbanks. In the mountains, as
well as in the plains, dams contribute to this regression by
drying these riverbanks for long periods. However, vegetation
is ill relatively abundant at several canyons, that have been
dug during the Quaternary pluvial periods (i.e. Hadramawt,
Ayhaft, Dirhur, Al-Guedam north of Sana’a) and continue to
deepen with violent oods. Because of their inaccessibility,
canyons therefore play a signicant role as reservoirs for
aquatic biodiversity (Scholte 1992).
Springs
These small habitats correspond generally to groundwater
emergencies, characterized by a low thermal amplitude and
low concentration of organic matter. They are abundant in
the weern highlands and are responsible for the permanent
and semi-permanent ow of some torrents. Mo of these
habitats have been transformed in a way to facilitate their
use for drinking and irrigation. Thermal springs are relatively
widespread in the weern mountains and the southern
littoral; at lea 65 sites are known, moly in the Tertiary
and Quaternary volcanic areas (Kamra 2006 and Al Kubati
et al. 2017). Their water temperature ranges between 40°C
and 96°C (Minissale et al. 2007), giving them low chance
to hold living communities, except some endemic phreatic
invertebrates. The other springs, considered in geological
literature as cold, have hot waters (30-35°C), in the sense
that they are very selective of living communities. The lowe
temperatures measured in springs and wells (21-27°C) are
favorable to subtropical thermophilic fauna rather than to the
Palearctic one (Dakki 1987 and Abd El-Mageed et al. 2013).
Lakes and ponds
In Yemen, freshwater lakes are practically absent, mainly
because of the scarcity of large natural depressions and the
dominance of the arid climate. However, intermittent pools
are signicantly frequent, as a consequence of the dry climate
and intensive evaporation. The crater lake of Bir Ali near the
coaal village of Bir Ali, is the only natural permanent lake;
its brackish water reaches 28°C in dry season, indicating no
volcanic inuence (Mohammed et al. 2018).
Articial wetlands
Throughout hiory, wetlands of Yemen as well as in
other arid countries, have provided essential services to the
local populations, thus their management and transformation
date back to thousands of years. The traditional uses of these
ecosyems were moly suainable, in the sense that they
generate soft modications. However, the recent exponential
increase of the population intensies the use of ecosyems
with modern techniques that led to their deep transformation.
39
Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
Articial reservoirs
It includes large articial reservoirs and small ponds, mainly
created for agriculture, domeic use and aquifer recharge.
According to the Miniry of Agriculture and Irrigation, 615
dams have been conructed in the upper lands until 2015,
with dierent sizes and objectives. Mo of the dams are in the
weern and central parts of the country, where more than 77%
of the population lives. It should be reminded that Yemen has
a long hiory in river damming and its ancient civilizations
(like Ma’in, Saba and Himyar, which exied before the 12th
century BCE) were mainly dependent of the great dam of
Ma’rib, in such a way that their civilization disappeared when
this dam collapsed. The new Ma’rib reservoir has a capacity
of 400 million m3, while the others reservoirs have a total
capacity of 62.5 million m3 (MAI 2013). This means a very
high domination of small reservoirs that are relatively benec
at lea in terms of recharging supercial aquifers (FAO
1997). Mo of these reservoirs have small extension and are
in deep valleys; therefore, their capacity to hold waterbirds is
supposed to be relatively low (Al-Safadi 1995); many other
reservoirs are exposed to intense insolation, which is highly
favorable to evaporation and to eutrophication with frequent
algae blooms (Charbonnier 2009).
Oases
These ecosyems, highly important in dierent
international conventions, are considered as articial because
of their absolute domination by human habitats and activities.
In Yemen, as in other dry and desert countries, oases take
place on large river banks that benet from renewable
fertile soils (provided by the river) and from both surface
and underground waters, making them as key agricultural
lands. Oases have been managed for millennia; however,
their vegetation and hydrological regime have recently been
deroyed and depleted. In Yemen, mo of the cities were
originally in oases, as well as numerous villages that are
actually growing up. However, the luxurious vegetation of
oases, generally articial and dominated by palm trees, oers
very attractive habitats to breeding and migrating birds. The
presence of large oases in Yemen, both at foothills and in
mountains, amplies this role (Almhab & Busu 2011).
Sewage wetlands
Waewater treatment arted only recently in Yemen,
and less than twenty sewage ations have been created, but
this number is expected to increase. Some famous treatment
areas (as Ta’iz, Aden, Dhamar …) created large mud pans
and marshes where several species of ora and fauna exi,
including waterbirds. For example, sewage ponds in Aden
including inter-tidal mudats and a retch of sandy beach and
salt pans, are considered as important wetlands especially for
migrant birds (e.g. Shobrak et al. 2003).
Channels
These articial wetlands are very abundant, but small
and traditionally concentrated in mountainous valleys, where
they ensure domeic waters and more especially irrigation
water for small agricultural terraces (Mohammed et al. 2018).
Nevertheless, some large channels exi, mainly located in
Coaal areas, the mo popular one being in Mukalla city.
Salt pans
In Yemen, salt exploitation played an appreciable role in
improving local people income, particularly on sea borders.
Several salt pans were managed on the coas of the Red Sea
and the Gulf of Aden, the mo famous salt production being
in the Al-Hodidah region (mainly Alsaleif coa). However,
salt pans are progressively abandoned since the 1990s and
their number is decreasing in the whole country (Al-Najar
et al. 2008), reducing their function as habitats for migrant,
wintering and breeding waterbirds.
Several euarine habitats were transformed, at lea
partly, in saltpans that are treated here as articial ecosyems,
although their area has been accounted in the euaries.
DISCUSSION: MAJOR ORIGINALITIES OF
YEMEN WETLANDS
The r major output of this overview concerns the high
diversity and abundance of the Yemen wetlands, which have
been demonrated and juied. This result, unexpected in an
arid country that evolves as a large island, is mainly explained
by the diversity of orographic and marine situations and by
the country’s position at the crossroads of three biogeographic
regions. Indeed, hundreds of wetlands have been identied,
dominantly in riverine, marine and coaal domains, while
lacurine syems are quasi-absent.
Rivers hold, as well as in other arid zones, a high number
of permanent puddles, named gueltas in North-Africa (Dakki
et al. 2020), which hydrology is rongly linked to large oods
that alternate with long droughts. These habitats extend to the
river mouths, as these are in majority intermittently open/
closed euaries (Whiteld 1992, Whiteld et al. 2012).
This udy focused also on the remarkable endemism that
gives a high patrimonial importance to the ora and fauna of
the country. Several udies focused on endemism in islands
and in the Red Sea, but this aspect remains unudied in
running waters and springs, habitats as endemism hotbeds in
arid zones (e.g. Dakki 1987). Indeed, the country evolves at
lea since the early Quaternary in insular context, amplied
since the Arabian Desert appears.
In addition, Yemen is located in a major crossroads of
bird migration between Eaern Europe and Weern Asia to
the North and Eaern Africa to the South. The data on this
aspect are ill relatively poor (Porter 1993, Shobrak 2003, Al-
Obaid et al. 2017), but the habitat composition of the coaal
wetlands and articial reservoirs permit to suppose that they
conitute determinant aging habitats for a high number of
waterbirds.
Despite this importance, the Yemen wetlands undergo
heavy human impacts. In fact, this country hiorically
conituted a land of agriculture and shing, mainly thanks
to its river waters and seas. These were widely used since
millennia, but this use became recently unsuainable because
of an exponential population growth, combined with frequent
droughts, political inabilities and a conservation policy
context very lacunar.
The precipitation trend is until now clearly negative and
don’t seem improving in the near future; this means that the
water scarcity is the major challenge that will face an eventual
conservation rategy for wetlands. Actually, river damming
and derivation and groundwater pumping are highly prior in
facing this scarcity, but they transformed hundreds of river
sectors, including euaries, and impoverished their aquatic
biodiversity.
CONCLUSION
The present article oers a large overview of the wetland
diversity and characteriics in Yemen, and describes the
natural and human factors that determine these characteriics,
including dysfunctions. Facing the great rarity of academic
udies, this work was achieved mainly thanks to satellite
data, technical reports and unpublished information.
40 Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
With this overview, it becomes easy to launch a national
wetlands’ inventory, as a major ep in the assessment of
their patrimonial values, their services and their dysfunctions
and in planning their management, whether for conservation
purposes or for suainable use.
Compared to the whole Arabian Peninsula, Yemen shows
the highe richness in wetlands and should therefore play a
major role in conserving the regional aquatic biodiversity.
This role is essential especially because of the originality
(in terms of richness in endemics) of its ora and fauna. It is
therefore clear that a high priority should be given to wetland
conservation in this country. Indeed, despite their great value,
these ecosyems beneted from poor conservation eorts
(Harvey 1999, Shobrak et al. 2003, Al-Sagheir 2002b …) and
few biological udies (i.e. Almhab & Busu 2011, Al-Safadi
1991, 1992, 1995), meanwhile they remain under heavy
human and natural pressures.
In the actual political context, marked by inabilities
that amplify poverty and juify more water use, a wetland
conservation rategy has few chances to emerge, and even
less for being implemented, only with national initiatives.
It is to say that international organizations are called to give
more attention to these wetlands and to help in gathering and
publishing scientic data and in conserving habitats.
The poverty of the ecological knowledge on Yemen
wetlands is another challenge that the country has to meet, for
improving the conservation processes, mainly in inland water
ecosyems. We are convinced that their aquatic communities
will reveal many great surprises, mainly their relationships
with European, African and Asian communities.
Abbreviations
GIS: Geological Information Syem, MEA: Millennium
Ecosyem Assessment, EPA: Environmental Protection Authority,
DEM: Digital Elevation Model, DID: Directorate of Irrigation and
Dams, MAI: Miniry of Agricultural and Irrigation, NWRA: National
Water Resources Authority, PERSGA: Regional Organization for the
Conservation of the Environment of the Red Sea and Gulf of Aden,
FAO: Food and Agricultural Organization, CSO: Central Statiical
Organization.
ACKNOWLEDGMENT
The authors are grateful to all Yemen’s experts in the Miniry
of Environment, the Miniry of Agriculture, the Faculty of
Engineering, the Environmental and Water Centre and the Research
Authority for providing precious Available at data. We would like
to thank also for their help the members of the Research Unit for
Wetlands Management at the Scientic Initute.
REFERENCES
Abd El-Mageed A, El-Kamel A., Abbady A. et al., 2013. Natural
radioactivity of ground and hot spring water in some areas in
Yemen. Desalination, 321, 28-31. https://doi.org/10.1016/j.
desal.2011.11.022
Al Kubati M. Al Qraa Fahd, Mattash M. et al., 2017. Geothermic
characters of the mo promising geothermal led for power
generation in republic of Yemen. International Journal of
Scientic & Technology Research, 6, 55-63.
Almhab A. & Busu I. 2011. The approaches for oasis desert
vegetation information abraction based on medium-resolution
Landsat TM image: A case udy in desert wadi Hadramut,
Yemen. Faculty of Geoinformation Science and Engineering,
University of Technology, Malaysia, 1-5.
Al-Najar A., Aldeeb A. & Ahmed A., 2008. Geological and Tourism
Study for Coaal Areas in Yemen. PHD Thesis, Aswan
University, Egypt, 1-427. [Original version in Arabic].
Al-Obaid S., Samraoui B., Thomas J., El-Serehy H.A., Alfarhan
A.H., Schneider W., O’Connell M., 2017. An overview of
wetlands of Saudi Arabia: Values, threats, and perspectives.
Ambio, 46, 98–108.
Al-Safadi M.M., 1991. Freshwater macrofauna of agnant waters in
Yemen Arab Republic. Hydrobiologia, 210, 203-208.
Al-Safadi M.M., 1992. Freshwater shes of Yemen. Proceedings of
the Egyptian Academy of Sciences, 42, 265-271.
Al-Safadi M.M., 1995. A pilot udy of lake Ma’rib, Yemen.
Hydrobiologia, 315, 203-209.
Al-Saghier O. 2002b. Survey for the Breeding Seabirds in Red Sea
of the Republic of Yemen. PERSGA Report. Jeddah, 1-35.
Barnard P. & Thuiller W., 2008. Introduction Global change and
biodiversity: Future challenges. Biology Letters 4, 553-555.
Barratt L., Dawson-Shepherd A., Ormand, R. et al. 1987. Yemen
Arab Republic Marine Conservation Survey. Volume 1,
Diribution of habitats and species along the YAR coaline,
IUCN, Red Sea and Gulf of Aden Environmental Programme/
TMRU, UK, 1-23.
Bruland G.L., 2008. Coaal wetlands: function and role in reducing
impact of land-based management. Natural Resources and
Environmental Management Department, University of Hawaii
Manoa, USA. 1-39. Available at: http://www.ctahr.hawaii.
edu/brulandg/publications/CWM_Chapter04.pdf [Accessed:
February 7th2016].
Charbonnier J., 2009. Dams in the weern mountains of Yemen:
a Himyarite model of water management. Proceedings of the
Seminar for Arabian Studies, 39, 81-94.
CHIRPS. 2015. Climate Hazards Group. UC Santa Barbara.
Available at: http://chg.geog.Uc sb.edu/data/chirps/ [Accessed
April 21th 2016].
Crooks S., Herr, D., Tamelander J. et al. 2011. Mitigating Climate
Change through Reoration and Management of Coaal
Wetlands and Near-shore Marine Ecosyems: Challenges
and Opportunities. Environment Department Paper 121,
World Bank, Washington DC, 1-47. Available at: http://
siteresources.worldbank.org/ENVIRONMENT/Resources/
MtgtnCCthruMgtofCoaalWetlands.pdf [Accessed: June 14th
2015].
CSO (Central Statiical Organization), 2014. Central Statiical
Organization Yearbook 2014. Miniry of Planning, Yemen,
1-127. [Original version in Arabic].
Dakki M., 1987. Ecosyèmes deau courante du haut Sebou
(Moyen Atlas): études typologiques et analyses écologique et
biogéographique des principaux peuplements entomologiques.
Travaux de l’Initut Scientique, Rabat, Série Zoologie, 42,
1-99.
Dakki M., El Fellah B. & Qninba A. 2020. Rivers natural
reservoirs: new inputs to the classication of Mediterranean
and Saharan wetlands. Bulletin de l’Initut Scientique, Rabat,
Série Sciences de la Vie , 1-14.
Davidson N.C., 2014. How much wetland has the world lo?
Long-term and recent trends in global wetland area. CSIRO
Publishing. Marine and Freshwater Research, 65, 10, 936-941.
Available at: http://dx. doi.org/10. 1071/MF14173 [Accessed:
September 18th 2018].
Duy, J.E., 2006. Biodiversity and the functioning of seagrass
ecosyems. Marine Ecology Progress Series, 311, 233-250.
41
Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
Elasha B.O. 2010. Mapping of Climate Change Threats and Human
Development Impacts in the Arab Region. UNDP, Regional
Bureau for Arab States, Arab Human Development Report,
Research Paper Series, 1-49.
EPA (Environmental Protection Authority), 2004. Fir National
Report to the Convention on Biological Diversity. Miniry of
Water and Environment, Yemen, 1-88.
EPA (Environmental Protection Authority), 2009. The 4th National
Report: Assessing Progress towards the 2010 Target - The 4th
National CBD Report. Miniry of Water and Environment,
Yemen, 1-100.
EPA (Environmental Protection Authority), 2013. Yemens Second
National Communication under the United Nations Framework
Convention on Climate Change. Environmental Protection
Authority, Yemen, 1-68.
Erwin K., 2008. Wetlands and global climate change: the role of
wetland reoration in a changing world. Wetlands Ecology
Management, 17, 71-84. Available at: https://www.wetlands.
org/wp-content/uploads/2015/11/Wetlands-and-Global-
Climate-Change. pdf. [Accessed: October23th 2015].
FAO (Food Agricultural Organization), 1997. Irrigation in the Near
Ea Region in Figures, FAO , Rome, 1-320. Available at: http://
www.fao.org/documents/show_cdr.asp?url_le=/ docrep/
W4356E/w4356e0z.htm [Accessed October 24th 2015].
Geukens, F., 1966. Geology of the Arabian Peninsula, Yemen: U.
S. Department of the interior ewartl. UDALL, Secretary
Geological survey. B1-B22. Available at: https://pubs.usgs.gov/
pp/0560b/report.pdf [Accessed September 13th 2018].
Hall M, Al-Khulaidi A.W. & Miller A.G. et al. 2008. Arabia’s La
Fores under Threat. Plant Biodiversity and Conservation in
the Valley Fore of Jabal Bura’a (Yemen). Edinburgh Journal
of Botany, 65, 113–135.
Harvey D. 1999. Wildlife conservation initiatives in Yemen. Al-
bab, Available at: https://al-bab.com/wildlife-conservation-
initiatives-yemen [Accessed: May 18th 2019].
Hushulong Q. 2012. The problems of wetlands in our country and
the researches. International Conference on Future Electrical
Power and Energy Syems. Energy Procedia, 17, 462-466.
James N.C., Cowley P.D., Whiteld A.K. & Lamberth S.J. 2007.
Fish communities in temporarily open/closed euaries from the
warm -and cool- temperate regions of South Africa: A review.
Reviews in Fish Biology & Fisheries, 17, 565-580.
Kamra A.A., 2006. Yemen Geothermal Resources. GRC Transactions,
30, 637-642. Available at: http://pubs.geothermal-library.org/
lib/grc/1025103.pdf [Accessed: June 11th 2017].
Kemp, J.M. 2000. Zoogeography of coral reef shes of the Gulf of
Aden. Fauna of Arabia, 18, 293-321.
Lill A.W.T., Closs G.P., Schallenberg M. & Savage C. (2012).
Impact of berm breaching on hyperbenthic macroinvertebrate
communities in intermittently closed euaries. Euaries and
Coas, 35, 155-168.
MAI (Miniry of Agricultural and Irrigation), 2013. Annual Report.
Yemen. 1-78. [Original version in Arabic].
MAI (Miniry of Agricultural and Irrigation), 2016. Annual Report.
Yemen. 1-56. [Original version in Arabic]
McCartney M., Rebelo L-M., Senaratna Sellamuttu S. et al., 2011.
Wetlands, agriculture and poverty reduction. IWMI Research
Report, International Water Management Initute, Colombo,
137, 26 pp. DOI: 10.5337/2010.230.
MEA (Millennium Ecosyem Assessment), 2005. Ecosyems and
Human Well-being: Wetlands and Water-Synthesis. World
Resources Initute, Washington DC, 67 pp. Available at: https://
www.Millennium-assessment. org/documents/document. 356.
aspx.pdf [Accessed: Augu 13th 2016].
Minissale A., Mattash M.A., Vaselli O., et al., 2007. Thermal springs,
fumaroles and gas vents of continental Yemen: Their relation
with active tectonics, regional hydrology and the countrys
geothermal potential. Applied Geochemiry, 22, 799–820.
Mohammed M., Frenzel P., Keyser D. et al., 2018. A humid
early Holocene in Yemen interpreted from palaeoecology
and taxonomy of freshwater oracods. Journal of
Micropalaeontology, 37, 167-180. Available at: https://doi.
org/10. 5194/jm-37-167-2018 [Accessed: September16th 2018].
Navid D., 1989. The international law of migratory species: The
Ramsar Convention. Natural Resources Journal, 29, 1001-1016,
Available at: http://digitalrepository.unm.edu/cgi/viewcontent.
cgi?article=2481&context=nrj [Accessed: March 23th 2015].
NBSAPY 2005. National Biodiversity Strategy and Action Plan for
Yemen. UNDP/GEF/IUCN YEM/96/G31, Miniry of Water and
Environment, Yemen, 70 pp. Available at: https://www.cbd.int/
doc/world/ye/ye-nbsap-01-en. pdf [Accessed June 14th 2015].
Nozais C., Perissinotto R. & Tita G. 2005. Seasonal dynamics of
meiofauna in a South African temporarily open/closed euary
(Mdloti Euary, Indian Ocean). Euarine, Coaal and Shelf
Science, 62, 325-338.
NWRA (National Water Resources Authority), 2005. Annual Report.
Miniry of Water and Environment. Yemen, 49 pp.
O’Connor N. & Crowe T., 2005. Biodiversity Loss and Ecosyem
Functioning: Diinguishing Between Number and Identity of
Species. Ecology, Ecological Society of America, 86, 7, 1783-
1796.
Parry M.L., Canziani O.F., Palutikof J.P., van der Linden
P.J. & Hanson C.E. (Eds.), 2007. Climate Change 2007:
Impacts, Adaptation and Vulnerability. Contribution of
Working Group II to the Fourth Assessment Report of
the IPCC, Cambridge University Press, 811 pp. Available
at: https://www.ipcc.ch/pdf/assessment-report/ar4/wg2/
ar4_wg2_full_report.pdf [Accessed: May 14th 2015].
Perissinotto R., Stretch D.D. & Whiteld A.K. et al. 2010.
Ecosyem functioning of temporary open/closed euaries in
South Africa. In Crane J.R. & Solomon A.E. (Eds). Euaries:
Types, movement patterns and climatical impacts. Nova Science
Publishers, New York, ISBN 978-1-60876-859-2. 69 pp.
Porter R. 1993. Birds of Yemen. Al-Bab, https://al-bab.com/birds-
yemen
Ranasinghe R. & Pattiaratchi C. 2003. The seasonal closure of tidal
inlets: causes and eects. Coaal Engineering Journal, 45, 4,
601-627.
RAP (Rural Access Program). 2004. Draft Sectoral Environmental
Assessment. SHEBA Engineering Services, Sana’a, 165 pp.
Roy P.S., Williams R.J. & Jones A.R. et al. 2001. Structure and
function of south-ea Auralian euaries. Euarine, Coaal
and Shelf Science, 53, 351-384.
Scharler U.M., Lechman K., Radebe T. et al. 2020. Eects of
prolonged mouth closure in a temporarily open/closed euary:
a summary of the responses of invertebrate communities in
the uMdloti Euary, South Africa. African Journal of Aquatic
Science, 45, 1, 1-10. DOI: 10.2989/16085914.2019.1689911.
Scholte P. 1992. The birds of Wadi Rima, a permanently owing
mountain wadi in weern Yemen. Sandgrouse, 14, 2, 93-108.
42 Al-Mahfadi & Dakki - Scientic elements for a Yemeni wetland conservation rategy
Sheppard C.R.C., Price A.R.G. & Roberts C.M. 1992.
Marine ecology of the Arabian Region: patterns and
processes in extreme tropical environments. Academic
Press, London, 359 pp.
Shobrak M., Alsuhaibany A. & Al-Saghier O. 2003. Regional atus
of breeding seabirds in the Red Sea and the Gulf of Aden.
PERSGA Report, 74 pp.
Snow G.C. & Taljaard S. 2007. Water quality in South African
temporarily open/closed euaries: a conceptual model. African
Journal of Aquatic Science, 32, 2, 99-111.
Stuip M.A., Baker C.J. & Ooerberg W. 2002. The Socio-economics
of Wetlands. Wetlands International and RIZA, The Netherlands,
28 pp.
Taljaard S., Van Niekerk L. & Joubert W. 2009. Extension of a
qualitative model on nutrient cycling and transformation
to include microtidal euaries on wave-dominated coas:
Southern hemisphere perspective. Euarine, Coaal and Shelf
Science, 85, 407-421.
Tardelli M. & Baldini R. 2000. Botanical Report on the Island of
Socotra (Yemen). Portugaliae Acta Biologica, 19, 443-453.
Tweddle G.P. & Froneman P.W. 2015. Inuence of mouth atus on
population ructure of Southern African endemic euarine-
spawning ichthyofauna in a temperate, temporarily open/closed
euary. African Journal of Aquatic Science, 40, 2, 221-225.
DOI: 10.2989/16085914.2015.1051940.
Van der Gun J. & Ahmed A. 1995. The water resources of Yemen.
a summary and dige of available at information. WRY35
Technical Report, Miniry of Oil and Mineral Resources,
Sana’a, Yemen. 106 pp. Available at: https://www.researchgate.
net/publication/282665864 [Accessed: March 10th 2014].
Ward C., Ueda S. & McPhail A. 2000. Water Resources Management
in Yemen. CDR_H2O_0112. World Bank, 39 pp. Available at:
http://siteresources.worldbank.org/INTYEMEN/Overview
/20150274/YE-Water. pdf [Accessed: March 4th 2014].
Whiteld A.K. 1992. A characterization of Southern African
euarine syems. South African Journal of Aquatic Science,
18, ½, 89-103.
Whiteld A.K., Bate G.C. & Adams J.B. et al. 2012. A review of the
ecology and management of temporarily open/closed euaries
in South Africa, with particular emphasis on river ow and
mouth ate as primary drivers of these syems. African Journal
of Marine Science, 34, 163-180.
Worldmeters, 2019. Yemen’s Population from 1955-2050. Dadax.
Available at: https://worldpopulationreview.com/countries/
yemen-population [Accessed: April 9th 2019].
Manuscrit reçu le 04/06/2020
Version révisée acceptée le 28/10/2020
Version nale reçue le 12/11/2020
Mise en ligne le 13/11/2020
... With at least 451 estuaries distributed on three different seas (Red Sea, Gulf of Aden, and Arabian Sea), Yemen is supposed to hold the highest proportion of the coastal biodiversity in the Arabian Peninsula (PERSGA 2003(PERSGA , 2004EPA 2004;Lavergne 2012;Al-Mahfadi and Dakki 2020). However, the conservation process of this biodiversity is facing serious weaknesses and barriers, mainly the lack of scientific, technical, and legislation tools (NBSAPY 2005;EPA 2009). ...
Article
A high number of wetlands were irreversibly lost in arid regions, mainly because their conservation raises the great conflict between maintaining wetland hydrology and satisfying water needs of the human population. In Yemen, as an arid developing country, the poor knowledge on wetlands is another challenge that faces their conservation. The present paper contributes to this knowledge by providing a preliminary classification of estuarine ecosystems in Yemen, using satellite data, which provide us with 15 physiographical descriptors of both estuaries, their catchment areas and sea waters. These data were extracted with GIS tools and treated with modern classification algorithms. Their treatment revealed six different types of estuaries, which are distinguished by three categories of descriptors (size and rock nature of both estuary and watershed and sea exposition). These categories confirm the significant influence of the watershed characteristics in shaping estuaries, whose influence has mainly been established during the pluvial Quaternary episodes. The sea characteristics (hydrodynamics and orography) are crucial in estuary classification; yet, despite the great effort deployed to get pertinent data, it was still difficult to find satellite descriptors of these two features. Therefore, the remote sensing has actually some limits in providing sea data for estuarine classification, which will be no longer exceeded with the increasing number of significant satellite data. Finally, we remind that the raw and compiled data gathered in this study constitute a preliminary inventory of the 451 Yemen estuaries, which is very useful for their knowledge and management.
Article
Full-text available
wetland nomenclature and classification in Morocco and North Africa
Article
Full-text available
Lake or marsh sediments in the Qa'a Jahran–Dhamār area indicate a period of higher moisture availability in the early Holocene of the highlands of Yemen. Forty-two marl–peat sediment samples from eight stratigraphic sections of that area have been collected and are examined for the first time for their ostracod associations. Eight species belonging to seven genera and four families are reported. Their ecological tolerances and preferences are used to investigate the climatic and environmental changes in the early to mid-Holocene. Our data are compared and correlated with previous archaeological results, particularly from the region of Qa'a Jahran (Dhamār) in the vicinity of the village of Beyt Nahmi. We conclude that the wettest period of the Holocene was from about 7900 to 7400 cal yr BP, when northwards incursion of the Indian Ocean Monsoon caused intensified monsoon precipitation over southern Arabia.
Article
Full-text available
The wetlands of Saudi Arabia are located in a water-stressed region that is highly vulnerable to climate and other global changes. Sebkhas, mudflats, mangroves, and wadis are the dominant wetlands in the arid regions of North Africa and the Arabian Peninsula. These unique wetlands are recognized as a sanctuary for biodiversity and for their economic services generated from mineral extraction, agriculture, and grazing. Despite their ecological values and societal services, the long-term permanence of Saudi Arabia's wetlands faces strong challenges resulting from human activities associated with sustained population growth, habitat degradation, and coastal development. This paper consolidates a literature review of Saudi Arabia's wetlands from local to global importance, highlights their biodiversity, and identifies threats and evolution of these vulnerable ecosystems in the arid Arabian Peninsula by focusing on the status of key freshwater taxa (Odonata, freshwater fishes, amphibians, and waterbirds) and documenting changes affecting important wetlands.
Article
Full-text available
A survey of the fish assemblages of Hadramaut and Shabwa provinces of the Republic of Yemen, in the north-eastern Gulf of Aden, reveals regionally high levels of diversity in some families of coral reef fishes, and striking local and regional species distribution patterns. The following species of fish are recorded for the first time from the coast of Arabia: Chaetodon trifasciatus, Chaetodon zanzibarensis, Halichoeres cosmetus, Thalassoma quinquevittatum, Ecsenius lineatus, Acanthurus leucocheilus and Acanthurus triostegus. A preliminary checklist of shallow coastal fishes of the north-eastern Gulf of Aden is provided, and a discussion of zoogeographic affinities of the species assemblage presented. A 'zoogeographically displaced' component of the northern Gulf of Aden fish community is almost entirely limited to a single small island, and may occur here because of complex oceanographic conditions arising from the seasonal monsoons of the Arabian Sea. This unusual assemblage raises the possibility that settlement strategies of larval reef fishes may in some cases affect species distributions at zoogeographic scales.
Article
Full-text available
Apart from representing the vast majority (71%) of South Africa's 258 functional estuaries, temporarily open/closed estuaries (TOCEs) are common in Australia, on the southeastern coasts of Brazil and Uruguay, the southwestern coasts of India and Sri Lanka, but are poorly represented in North America, Europe and much of Asia. The regular change between open and closed mouth phases makes their physico-chemical dynamics more variable and complicated than that of permanently open estuaries. Mouth states are driven mainly by interplay between wave or tide driven sediment transport and river inflow. Mouth closure cuts off tidal exchanges with the ocean, resulting in prolonged periods of lagoonal conditions during which salinity and temperature stratification may develop, along with oxygen and nutrient depletion. Mouth breaching occurs when water levels overtop the frontal berm, usually during high river flow, and may be accompanied by scouring of estuarine sediment and an increased silt load and turbidity during the outflow phase. Microalgae are key primary producers in TOCEs, and while phytoplankton biomass in these systems is usually lower than in permanently open estuaries, microphytobenthic biomass is often much higher in TOCEs than in permanently open systems. During the closed phase, the absence of tidal currents, clearer water and greater light penetration can result in the proliferation of submerged macrophytes. Loss of tidal action and high water levels, however, also result in the absence or disappearance of mangroves and have adverse effects on salt marsh vegetation. Zooplankton are primary consumers both in the water-column and within the upper sediment, due to diel migrations. A prolonged period of TOCE mouth closure leads to poor levels of zooplankton diversity, but also to the biomass build-up of a few dominant species. Benthic meiofaunal abundance is usually greater during closed phases and is generally dominated by nematodes. Macrobenthic densities, and occasionally even biomass, in TOCEs are higher than in permanently open systems. The dominance of estuarine and estuarine-dependent marine fish species in TOCEs is an indication of the important nursery function of these systems. Marine juvenile fish recruit into TOCEs not only when the mouth opens, but also during marine overwash events when waves from the sea wash over the sand bar at the mouth. The birds that occur in TOCEs are mostly piscivorous, able to catch a variety of fish species either from the surface or by diving underwater. Waders are absent or uncommon because of the infrequent availability of intertidal feeding areas when the mouth is closed. Addressing the challenges facing the sustainable management of TOCEs is critical, as in some cases their ecological integrity, biodiversity and nursery function have already been compromised.
Chapter
Full-text available
Coastal wetlands are among the most productive, valuable, and yet most threatened ecosystems in the world. They provide a variety of functions that reduce the impact of land-based management on the coastal zone such as slowing the fl ow of water from the mountains to the sea, trapping of sediments, and retaining or transforming nutrients. Numerous studies have reported that increased soil erosion and nutrient export from land-based management are threatening estuaries and coastal zones. Coastal wetlands are located at a critical interface between the terrestrial and marine environments and are ideally positioned to reduce impacts from land-based sources. There are various types of coastal wetlands including riparian wetlands, tidal freshwater marshes, tidal salt marshes, and mangroves. Some classifi cation systems also consider seagrass beds and coral reefs to be wetlands. Coastal wetland ecosystems vary in their ability to reduce impacts from land-based management in both space and time. These wetlands can retain, and transform, or sometimes even act as sources of nutrients and sediments. Some wetland types are more effective at sediment retention and others at nutrient retention. Watershed size, climate, and position of wetlands in a watershed are other important factors that determine the effectiveness of coastal wetlands in reducing the effects of land-based activities. Wetlands do not appear to be infi nite sinks for sediment or nutrients. Once critical sediment and nutrient loading thresholds have been crossed, coastal wetlands are subject to degradation and even loss. While many coastal nations have developed coastal-zone management policies and legislation, degradation and losses of coastal wetlands continue to occur due to altered hydrology, increased sediment and nutrient loading, urban development, agriculture, and aquaculture. While we have made signifi cant progress in our ability to restore and create tidal marshes and mangroves, other coastal systems such as seagrass beds and coral reefs appear to
Article
Full-text available
The effect of mouth status on the population structure of three endemic estuarine-spawning fish species was assessed using seine nets from November 2005 to October 2007 in the temporarily open/closed Mpekweni Estuary, Eastern Cape, South Africa. Collectively, these three species accounted for more than 60% of the total fish abundance within the estuary. Monthly length frequency data were analysed. Two species, Gilchristella aestuaria and Glossogobius callidus, displayed normally distributed populations throughout, with recruitment/abundance peaks between spring and autumn, and were unaffected by open mouth and extended marine connection conditions. Atherina breviceps, however, displayed multiple modal peaks in its combined population distribution, suggesting a greater influence of mouth condition on its population structure. Retrospective analyses of the various cohorts for A. breviceps identified peaks in recruitment/abundance during summer, coinciding with open-mouth conditions and, to a lesser extent, with overwash events. This study highlights the importance of mouth phase, not only on the recruitment and population distribution of marine-spawning species, but also on estuarine-spawning fish in temporarily open/closed estuaries along the South African coastline.
Article
Prolonged mouth closure in estuaries is often associated with hypersalinity, mainly as a result of reduced freshwater inflow. However, on the KwaZulu-Natal coast, South Africa, temporarily open/closed estuaries have a tendency towards hyposalinity during closed mouth conditions, primarily because of their perched nature reducing saltwater intrusion, but also due to persistent freshwater inputs, together with seepage of saline water through the sand berm into the sea. We investigated a system, the uMdloti Estuary, experiencing extended periods of mouth closure over two years with the aim of documenting the response of invertebrates to such conditions. Specifically, estuarine invertebrate biodiversity was severely diminished, which was attributed to persistently low salinity, rather than poor water quality due to the absence of flushing. Secondly, a distinct brackish/freshwater community established itself within the mesozooplankton and benthic invertebrate assemblages, including invasive species. Marine overwash of the berm and a short mouth breaching aided the return of estuarine species for only very brief periods (weeks). We conclude that although estuarine species are quick to re-colonise the estuary after a breach, prolonged mouth closure along extended stretches of coast might severely reduce estuarine invertebrate biodiversity. Management options are preferably the provision of an adequate freshwater inflow to allow natural breaching, or else artificial breaching, to facilitate several openings per year as well as for a long enough tidal phase to permit the establishment of an estuarine salinity gradient.
Article
The main purposes are to collate information of the region, to review marine systems and processes in the intertidal and shallow sublittoral parts of the Arabian seas, and to highlight human utilisation and environmental consequences. The first section presents the geological, geographical, climatic and oceanographic background to the area. The second section examines what is known of the region's marine communities, interpreting the relationships between the marine systems and physical conditions for: reefs and coral communities; coral reef fish assemblages; other reef components and processes; seaweeds and seasonality; seagrasses and other dynamic substrates; intertidal areas - mangal associated ecosystems, marshes, sabkha and beaches; and the pelagic system. The next section synthesizes and concludes the biogeographical material and interprets the effects of natural stress on the biota. The final section describes and discusses the human use and management of the region, including fisheries. -after Authors