Dahlak Archipelago Research Articles

Genetic variation in morphologically divergent mainland and island populations of Soemmerring’s gazelles (Nanger soemmerringii)

This study focuses on the taxonomic, evolutionary and conservation implications of a striking reduction in body size previously observed in an island population of gazelles by comparing the genetic structure of island and mainland populations. Mitochondrial sequence diversity of the mainland population was found to be comparable to that of other true gazelles of East Africa. We discuss this in the context of the prolonged armed conflict in our study region. In contrast, the gazelles on Dahlak Kebir, one of the over 200 islands and islets of the Dahlak archipelago on the Red Sea, were found to be genetically depauperate. Nucleotide and haplotype diversity estimates were a sixth and a third of that of the mainland population respectively. Using estimates of Tajima’s D statistic, we inferred that the Dahlak population has undergone expansion after a recent bottleneck. A minimum spanning genealogical network of mitochondrial control region sequences produced testable hypotheses on the route and timing of the colonization of Dahlak Kebir by gazelles from the mainland. Our mitochondrial DNA dataset has resolved the taxonomic ambiguity of the island gazelles. Their genetic distinctiveness and, their striking conformity to the Island Rule that was highlighted in a previous study, are discussed from evolutionary and conservation perspectives.

Do genes lie? Mitochondrial capture masks the Red Sea collector urchin’s true identity (Echinodermata: Echinoidea: Tripneustes)

Novel COI and bindin sequences of the Red Sea collector echinoid Tripneustes gratilla elatensis are used to show that (1) discordance between mitochondrial and nuclear loci exists in this echinoid genus, (2) Tripneustes gratilla as currently defined possibly comprises a complex of cryptic species, and (3) Red Sea Tripneustes form a genetically distinct clade in the bindin tree, which diverged from other Tripneustes clades at least 2–4million years ago. Morphological reassessment of T. gratilla elatensis shows perfect congruence between identification based on skeletal features and genetic data based on a nuclear marker sequence. Hence the Red Sea Tripneustes subspecies established by Dafni in 1983 is a distinct biological unit.All T. g. elatensis samples analyzed are highly similar to or share mtDNA haplotypes with Philippine T. g. gratilla, as do representatives from other edge-of-range occurrences. This lack of genetic structure in Indo-Pacific Tripneustes is interpreted as a result of wide-spread mitochondrial introgression. New fossil specimens from the Red Sea area confirm the sympatric occurrence of T. g. elatensis and T. g. gratilla in the northern Red Sea during Late Pleistocene, identifying a possible timing for the introgression. In addition, present-day distribution shows a contact zone in the Southern Red Sea (in the Dahlak Archipelago).T. g. elatensis, is yet another example of a Red Sea taxon historically identified as conspecific with its Indo-Pacific relatives, but which turned out to be a morphologically and genetically distinct endemic taxon, suggesting that the level of endemism in the Red Sea may still be underestimated.

Forbidden islands. The absence of endemics among the insular non-volant terrestrial mammalian fauna of the Red Sea

The Red Sea is a land-locked sea that is globally significant in terms of the unique biodiversity and endemism of its marine species. In contrast, the terrestrial biodiversity on its islands is poor and mainly composed of species present also on the mainland. To profile the non-volant terrestrial mammalian fauna, we reviewed all available records in the literature and report some recent captures; in particular, we point out two additional species from the Dahlak archipelago: the Northeast African spiny mouse (<em>Acomys cahirinus</em>) and a still undetermined shrew (<em>Crocidura</em> sp.). As far as we know, the only endemic vertebrates are three species of snake (Squamata, Serpentes) and perhaps one gazelle (<em>Gazella arabica</em>). The composition of the insular mammalian fauna of the Red Sea is olygotypic, consisting of only a few taxa, mostly anthropochorous, that are shared with the mainland of eastern Africa and/or western Arabia, and which are repeated monotonously on the few islands inhabited by mammals. A lack of endemic mammals can be explained as the result of the only recent connection of almost all the islands with the mainland during the Last Glacial Maximum and by the harsh climatic conditions that allow the survival of only a few xeric specialists.

KKzzldenizzin Stratejik Dehlek Adalarr ve Osmanll daresindeki Konumu (Strategically Dahlak Archipelago of the Red Sea and its Status Under the Ottoman Rule)

Turkish Abstract: Kizildeniz’in en stratejik noktalarindan biri Habesistan aciklarindaki Dehlek adalar toplulugudur. Islâmiyet, adalara 702 yilinda ulasir. Emeviler doneminde mucrimler, siyasi ve ahlaki suclular ile burokrasiden el cektirilenlerin surgun yeri olan Dehlek-i Kebir, Abbasiler doneminde de ayni amacla kullanildi. Burasi, Kizildeniz’in en islek limani Sevâkin’e yakin olmasi sebebiyle Hindistan ve Misir arasindaki deniz ticareti ve Yemen icin onemli bir noktaydi. Dehlek, ayrica Becce (Becâ/Beja) kabilelerine mensup bazi Habeslilerin korsanlik faaliyetleri icin onemli bir siginakti. Ada, IX. Yuzyilda Abbasi idaresinden cikarak, Yemen’deki mahalli hanedanlarin eline gecti. Daha sonra bazen Habesistan’da guclenen Hiristiyan krallara, bazen de Misir’daki Musluman sultanlara tâbi oldu. 1093-1250 yillari arasinda Dehlek Sultanligi adiyla kendi mahalli meliklerince yonetildi. Osmanlilarin yardimlariyla 1526’da butun Habesistan’i hâkimiyeti altina alan Harar Emiri Ahmed Gran (o.1543) yerel sultanliklari korudu ve bu durum 1557’de Turklerin gelip Portekizlileri bu topraklardan cikartmasina kadar surdu. Suleyman I doneminde(1520-1566), Cerkes Ozdemir Pasa(o.1561) eliyle hâkimiyet altina alinan adalarin idaresi, Habes Eyaleti’nin kurulmasiyla buranin tahsisatina eklendi. Kizildeniz’in en islek limani Musavva’nin bir kazasi konumundaki Dehlek, XVII. yuzyilda da ticaret yolunun en islek noktalarindan biri olmayi surdurdu. 1865 yilinda padisahin fermaniyla Musavva ve Sevâkin ile birlikte Misir emlâkine dâhil edilinceye kadar Habes Eyaleti’ne bagli kalan Dehlek’i, 1885 yilinda Italya isgal etti. Gunumuzde Dehlek’i sinirlari icinde bulunduran Eritre, Nisan 1993’te referandumla bagimsizligini elde etse de Israil’in peyki olma ihtimali hala sicakligini korumaktadir. English Abstract: Of the most strategic islands in Red Sea is Dahlak archipelago off the coast of Ethiopia. The introduction of Islam to Dahlak islands in a considerably early period. The Grand Dahlak Island was used as a place of exile for culprits, political and moral criminals during the reign of both Umayyads and Abbasids. This place was an important point in maritime trade between India and Egypt and a bridgehead for Yemen especially because it was closest to Sawakin-one of the busiest ports in Red Sea. Also Dahlak Islands were an important haven for piracy activities of some Ethiopians from Becce (Becâ/Beja) tribes in Red Sea and neighboring islands. After Abbasids lost control in IXth century, Dahlak was captured by local dynasties in Yemen. Afterwards it sometimes subjected to Christian kings getting stronger in Ethiopia and at other times to Muslim sultans in Egypt. From 1093 to 1250 more than 150 years “Dahlak Sultanate” was governed by their own local meliks (kings). With the help of Ottomans the Harar Ruler Ahmed Gran (d. 1543) took control of the whole Ethiopia and became the protector of local sultanates and this situation lasted until Turks came and banished Portuguese from these lands in 1557. The rule of Dahlak Islands which was taken control by Circassian Ozdemir (d.1561) Pasha during the conquest of Yemen in the reign of Suleiman I (Suleiman the Magnificent/1520-1566) was given to Ethiopian State (1555) as a subvention after it was founded. Dahlak as a town of Massawa, one of the busiest ports in Red Sea, continued to be one of hectic points in maritime trade in Red Sea during XVIIth century. During the reign of Khedive Ismail Pasha until it was added to the realm of Egypt together with Massawa and Sawakin in 1865 through the sultan's decree, it was owned by Ethiopian State and invaded by Italy in 1885. Today Eritrea, which encompasses Dahlak, gained independence in April 1993 through referendum though it is still likely to be a satellite of Israel.

Platyceps largeni (Schätti , 2001) — sixth specimen and a distribution extension

We describe the finding, in a museum jar, of the sixth known specimen of the Eritrean snake Platyceps largeni (Scätti, 2001) (synonym, Coluber largeni). The specimen is from Museri Island, Dahlak Archipelago in the Red Sea. This record is the first one for this island and it represents a ca. 50 km range extension of this species, hitherto known from five specimens in a tight cluster of three other islands. This find verifies Schätti’s (2001) prediction that the species might be found in the nearby archipelago islands.

KRAEMERIA NUDUM (REGAN)—FIRST RECORD OF THE FAMILY KRAEMERIIDAE IN THE RED SEA

ABSTRACT Kraemeria nudum (Regan, 1908) is reported for the first time from the Red Sea. The fish were collected in the Dahlak Archipelago, Ethiopia. The Red Sea population is described. The validity of the species is discussed.

Geologic setting of the Abdur Archaeological Site on the Red Sea coast of Eritrea, Africa

The Abdur Archaeological Site was defined initially by the discovery and dating (125 +/− ka by Ur/Th) of in situ stone tools within uplifted marine terrace deposits located along the southern Red Sea coast of Eritrea, near the small village of Abdur. These tools represent some of the earliest well-dated evidence for human occupation of coastal marine environments. The site is located on the Buri Peninsula along the eastern shoreline of the Gulf of Zula and covers an area of approximately 7 km by 1 km. Three main stratigraphic units are defined and discussed from oldest to youngest: (1) The Buri Formation is defined herein as a sequence of brackish–freshwater (estuarine) and fluvial–deltaic sediments consisting of mudstones, siltstones, sandstones, conglomerates and limestones with ash and pumice beds. Ar–Ar dating of pumice and tephras puts the time of deposition of this unit from about 0.91 to 0.72 Ma (Early–Middle Pleistocene). Several stone tools were discovered in the Buri Formation, indicating early human occupation of a coastal environment during the Early to Middle Pleistocene. (2) The Abdur Volcanic Complex (AVC) is a small basaltic shield complex that forms the highlands along the eastern part of the Abdur Site and extends to the north and south of the area. Basalts from this center were dated from 2.12 to 0.17 Ma, indicating that the volcanic complex has been tectonically and magmatically active prior to, during and after deposition of the Buri Formation. (3) The Abdur Reef Limestone (ARL) is the remnant of a shallow marine reef system deposited approximately 125 ka (last glacial highstand, isotope stage 5e) along the margins of the Abdur volcanic highlands. The ARL consists of a basal transgressive lag deposit overlain by extensive buildups of mollusks, echinoderms, bioclastic sands and corals up to 11 m thick. Numerous stone tools in the ARL fall into two tool kits, bifacial hand axes of the Acheulian industry and Middle Stone Age-type (MSA) obsidian flakes and blades. Their distribution suggests that foraging activities of early humans varied with environmental setting. The Buri Formation has been folded and faulted prior to deposition of the ARL, with dips as high as 36° and vertical locally along fault zones. The ARL has been uplifted up to 8–15 m and tilted 1°–5° in a seaward direction. The area is cut by numerous faults, part of a regional NNW-trending fault system. Occurrences of Buri Formation equivalents to the north along the Buri Peninsula as well as in the area southwest of the Alid volcano suggest the area west of the escarpment was a broad lowland characterized by rivers, coastal lakes, and estuaries along the Red Sea coast during the Early to Middle Pleistocene. Reefs equivalent to the ARL covered large parts of the adjacent Buri Peninsula, the north end of Mt. Ghedem across the Gulf of Zula, and the Dahlak Archipelago to the north.

The Byzantine-Aksumite period shipwreck at Black Assarca Island, Eritrea

Lying astride the Massawa Channel, between the mainland of Eritrea and the Dahlak archipelago, the two islands known as the Assarcas became the focus of archaeological investigation beginning in 1995 (Fig. 1). Both are ancient coral outcrops, with just enough accumulated topsoil to support euphorbia cacti, scrub grass, and the associated insects and arachnids. The southern island is known as White Assarca for its surrounding of white sand beaches. The northern island is called Black Assarca as it is encompassed on all sides but one by coral cliffs stained dark by the sea. In places, the cliffs reach approximately two metres above the sea. As the uppermost parts of the reefs surrounding Black Assarca are exposed only at low tide, and are hidden during high water, they present a danger to watercraft as they lie very close below the surface. The reefs extend outward from the island for ten to twenty metres, if not more in places, before gradually dropping off to a sandy bottom. Here, at the edge of the reefs on the northern side of Black Assarca Island a ship wrecked some 15 centuries ago and lay undiscovered until 1995.

Endangered Coral Islands: a Case Study of Dahlak in Red Sea

The geo-chemical nature of coral island in relation to the Dahlak archipelago has been revisited. The mechanism behind the symptom of cracks, pot-holes and caves has been discussed in the back-drop of chemical weathering of coral deposits and calcite rock. This study highlights the vulnerability of Dahlak reef ecosystems and calls for protecting the biodiversity hotspot on priority basis.

Endangered coral islands: A case study of Dahlak in Red Sea

The geo-chemical nature of coral island in relation to the Dahlak archipelago has been revisited. The mechanism behind the symptom of cracks, pot-holes and caves has been discussed in the back-drop of chemical weathering of coral deposits and calcite rock. This study highlights the vulnerability of Dahlak reef ecosystems and calls for protecting the biodiversity hotspot on priority basis.

Temporal dynamics and nestedness of an oceanic island bird fauna

ABSTRACTAim To examine temporal variation in nestedness and whether nestedness patterns predict colonization, extinction and turnover across islands and species.Location Dahlak Archipelago, Red Sea.Method The distributions of land birds on 17 islands were recorded in two periods 30 years apart. Species and islands were reordered in the Nestedness Temperature Calculator, software for assessing degrees of nestedness in communities. The occupancy probability of each cell, i.e. species–island combinations, was calculated in the nested matrix and an extinction curve (boundary line) was specified. We tested whether historical and current nested ranks of species and islands were correlated, whether there was a relationship between occupancy probability (based on the historical data) and number of extinctions or colonizations (regression analyses) and whether the boundary line could predict extinctions and colonizations (chi‐square analyses).Results Historical and current nested ranks of islands and species were correlated but changes in occupancy patterns were common, particularly among bird species with intermediate incidence. Extinction and turnover of species were higher for small than large islands, and colonization was negatively related to isolation. As expected, colonizations were more frequent above than below the boundary line. Probability of extinction was highest at intermediate occupancy probability, giving a quadratic relationship between extinction and occupancy probability. Species turnover was related to the historical nested ranks of islands. Colonization was related negatively while extinction and occupancy turnover were related quadratically to historical nested ranks of species.Main conclusions Some patterns of the temporal dynamics agreed with expectations from nested patterns. However, the accuracy of the predictions may be confounded by regional dynamics and distributions of idiosyncratic, resource‐limited species. It is therefore necessary to combine nestedness analysis with adequate knowledge of the causal factors and ecology of targeted species to gain insight into the temporal dynamics of assemblages and for nestedness analyses to be helpful in conservation planning.

A Taxonomic Survey of Seaweeds from Eritrea

A survey of seaweeds was made in Eritrea in December 1995 and January 1996 on some islands of the Dahlak Archipelago and the surroundings of the port town of Massawa. During our study 101 specific and infraspecific taxa were identified, including 26 Chlorophyta, 20 Phaeophyta and 55 Rhodophyta. The survey resulted in 36 new records for Eritrea (11 Chlorophyta, 7 Phaeophyta and 18 Rhodophyta). Of these Eritrean records, 26 are new for the Red Sea (5 Chlorophyta, 4 Phaeophyta and 17 Rhodophyta). Comparison of records of seaweeds from localities in Eritrea to those from other localities in Eritrea as well as from other coasts of the western Indian Ocean have revealed that the regional distribution of seaweeds in the Red Sea is very patchy and that generally the area seems to be undersampled. The comparisons have also underscored the stressful seasonal environmental conditions for macroalgae in the southern Red Sea.

Terrestrial bird community patterns on the coralline islands of the Dahlak Archipelago, Red Sea, Eritrea

ABSTRACTAim This study aims to explain the patterns of species richness and nestedness of a terrestrial bird community in a poorly studied region.Location Twenty‐six islands in the Dahlak Archipelago, Southern Red Sea, Eritrea.Methods The islands and five mainland areas were censused in summer 1999 and winter 2001. To study the importance of island size, isolation from the mainland and inter‐island distance, I used constrained null models for the nestedness temperature calculator and a cluster analysis.Results Species richness depended on island area and isolation from the mainland. Nestedness was detected, even when passive sampling was accounted for. The nested rank of islands was correlated with area and species richness, but not with isolation. Idiosyncrasies appeared among species‐poor and species‐rich islands, and among common and rare species. Cluster analysis showed differences among species‐rich islands, close similarity among species‐poor and idiosyncratic islands, and that the compositional similarity among islands decreased with increasing inter‐island distance. Thus, faunas of species‐poor, smaller islands were more likely to be subsets of faunas of species‐rich, larger islands if the distance between the islands was short.Main conclusions Species richness and nestedness were related to island area, and nestedness also to inter‐island distances but not to isolation from the mainland. Thus, nestedness and species richness are not affected in the same way by area and distance. Moreover, idiosyncrasies may have been the outcome of species distributions among islands being influenced also by non‐nested distributions of habitats, inter–specific interactions, and differences in species distributions across the mainland. Idiosyncrasies in nested patterns may be as important as the nested pattern itself for conservation – and conservation strategies based on nestedness and strong area effects (e.g. protection of only larger islands) may fail to preserve idiosyncratic species/habitats.

Halichondramine, a New Tetracyclic Bipiperidine Alkaloid from the Marine Sponge Halichondria sp.

Halichondramine (1), a new tetracyclic alkylbipiperidine alkaloid, has been isolated from the marine sponge Halichondria sp., collected in the Dahlak archipelago (the Red Sea), Eritrea. The structure of halichondramine was elucidated by interpretation of MS, COSY, HMQC, HMBC, TOCSY, and HSQC-TOCSY data.

Marine algae and seagrasses of the Dahlak Archipelago, southern Red Sea

Marine algae and seagrasses of the Dahlak Archipelago, southern Red Sea

SOFT CORALS (OCTOCORALLIA, ALCYONACEA) OF THE SOUTHERN RED SEA

The species composition of soft corals of the families Tubiporidae, Alcyoniidae, Nephtheidae, and Xeniidae is presented for the Dahlak Archipelago (15-16oS) in the southern Red Sea in Eritrean waters. A comprehensive collection was made during several field trips (1993-2002) to various sites in this archipelago. Some unexamined specimens obtained during the Israeli South Red Sea expeditions (1962 and 1965) to the region were also included in the study. A systematic list of soft corals is presented, comprising 28 species based on the material and previous literature. The list includes five genera (Rhytisma, Sinularia, Paralemnalia, Scleronephthya, and Heteroxenia) and sixteen species recorded for the first time in the southern Red Sea. Seven of these species belong to the genus Sinularia and three to Ovabunda. All the species found belong to the Indo-Pacific faunistic province and have been previously recorded elsewhere in the Red Sea. A distinct north to south latitudinal diversity attenuation of soft cor...

New Triterpenoids from the Red Sea Sponge Siphonochalina siphonella

Clear differences were found when comparing the chemical content of the northern, Gulf of Eilat, to the southern-central, Dahlak archipelago, Red Sea sponge Siphonochalina siphonella. The Dahlak sponge was found to be richer in the more polar triterpenes. Nine new compounds (1-4, 7, 8, 15-17) were isolated and identified, among them two sipholane glycosides, sipholenoside A and B (7 and 8), and one compound, dahabinone A (17), possessing a new skeleton.

A New Species of Coluber ( sensu lato ) from the Dahlak Islands, Eritrea, with a Review of the Herpetofauna of the Archipelago

A new racer species, Coluber ( sensu lato ), is described from the small islands of Andeber, Nocra, and Sarad in the Dahlak archipelago. This polymorphous species is most closely related to C. ( s.l. ) florulentus (Geoffroy) and C. ( s.l. ) taylori Parker. Phylogenetic relationships and generic allocation of East African and Palaearctic racer genera are briefly discussed. Three species of amphibians are known from Dahlak al-Kabir, and a total of fifteen terrestrial reptile species including two endemic snakes, viz. the new species of Coluber ( s.l. ) and Echis megalocephalus , have been recorded from nine islands in the Dahlak archipelago.

Asmarines A-F, novel cytotoxic compounds from the marine sponge Raspailia species.

Three pairs of nitrogen-containing metabolites, asmarines A-F (1-6), were isolated from the Red Sea sponge Raspailia sp., collected in the Dahlak Archipelago, Eritrea. Although the first pair could fully be separated to give compounds 1 and 2, the other two pairs could only be enriched up to about 80% of one isomer. The structures of the new compounds were established by spectroscopic means. Besides the asmarines, methyl 3-oxo-cholan-24-oate (12) was also isolated. The absolute configuration of asmarine A (1) was determined on the basis of CD measurements of its unstable 18-oxo derivative (7) and mainly the Cotton effect of the dicarbonyl derivative (9) of chelodane (8). A O,N(7')-dimethyl derivative (10) and a second, unexpected, methylated product (11) were obtained from 2.

Bilosespens A and B: two novel cytotoxic sesterpenes from the marine sponge Dysidea cinerea.

[formula: see text] Two novel sesterpenes, bilosespens A and B (1 and 2) were isolated from the Red Sea sponge Dysidea cinerea collected in the Dahlak archipelago, Eritrea. The structure of the mixture of the two inseparable compounds was established by spectroscopic analysis, mainly by 1D and 2D NMR measurements. The mixture of bilosespens A and B is cytotoxic to a few human cancer cells.