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FIRST RECORD OF EIGHT BRACHYURAN CRABS’ SPECIES (CRUSTACEA-DECAPODA) IN SOCOTRA ARCHIPELAGO IN THE INDIAN OCEAN-YEMEN

Yemen has a number of islands on the Red Sea, including Kamaran, Uqban, Hanish Archipelago Islands, Mayun (older name: Perim), and many islands at the Gulf of Aden, in the Indian Ocean, this also includes the Socotra Archipelago located 240 km from the east of the Horn of Africa and 380 km from Yemen. Socotra Island has a variety of habitats including sandy shores, rocky shores, mud flats, sponge areas, coral reefs, and freshwaters. This study aims to record the brachyuran crab’s species in different habitats in Socotra Archipelago. The specimens of the brachyuran crabs collected by hand, hand nets, and snorkeling up to 3-meter depth. The specimens were collected from 6 sites in Socotra Islands during separate periods time from 1984 to 2000, these specimens were kept in Rostock University and Zoologische Staatssammlung München (ZSM)-Germany. In this present study 32 brachyuran crabs’ species were recorded belonging to 11 superfamilies, 14 families, and 29 genera. Eight of these species represent the first records in Socotra Islands. The dominant brachyuran crab families in this region were Xanthidae, 35% with 11 species recorded, followed by Grapsidae, 19% with 6 species.


Introduction
The Republic of Yemen situated on the southern tip of the Arabian Peninsula covers 531000 square kilometers, it shares 1458 km of borderlines with Saudi Arabia and 288 km with Oman [1,2].
The Yemeni coastline covers 2350 kilometers which has high tourist and economical potentials. The living marine resources are diverse, rich and have high economic value [3]. The coast along the Gulf of Aden with 1690 km includes both 1200 km of mainland coast and 490 km in the Socotra Archipelago [4].
Yemen has a number of islands on the Red Sea, including Kamaran, Uqban, Hanish Archipelago Islands, Mayun (older name: Perim), and many islands at the Gulf of Aden (17 islands in Aden city and four islands in Bir Ali and others). In the Indian Ocean, this also includes the Socotra Archipelago located 240 km from the east of the Horn of Africa and 380 km from Yemen. Socotra Archipelago has four islands. The largest island, called Socotra (130 km long and 40 km wide), and three smaller islands of Abd al-Kuri, Samhah and Darsa [5,6,7,8]. Socotra Islands have high diversity and endemism of significance at the international level. The island has more than 850 species of plants of which 30% are endemic and 8 species have been listed as endangered species by the International Union for Conservation of Nature (IUCN). 120 bird species have been recorded in the island of which 30 species breed on the island and 7 bird species are endemic [3]. On this basis Socotra Islands were designated a UNESCO World Heritage Site in 2008 [7]. Among species with high marine biodiversity in Socotra Islands are crustaceans, especially brachyuran crabs. Scientists have conducted many studies in this field for a long time. The early study first mentioning a freshwater crab from Socotra was by Hilgendorf (in: Taschenberg, 1883), who described Telphusa socotrensis from material collected in 1881 by E. Riebeck and G. Schweinfurth. According to Pocock (1903), however, B. Balfour and A. Scott, carrying out zoological and botanical studies on the island in 1880, were actually the first collectors to bring Socotran freshwater crabs to Europe [9].
The last study of coastal and marine habitats in Socotra Island was the most extensive one by [10] covering 185 sites and recording 77 brachyuran crab's species. There are some scattered studies that recorded some brachyuran crab species in Socotra Islands. Among these [11] recorded 29 brachyuran crab species, [12] and [13] recorded 3 species from the genus Ocypode. [14] recorded 23 brachyuran crab species. [15] recorded 2 species from Trapezioidea.
[9] recorded a new species, Socotrapotamon nojidensis, in addition [16] recorded a new genus and new species which is, Socotra pseudocardiosoma (Cumberlidge & Wranik, 2002) furthermore, Potamidae and [17] recorded 78 brachyuran crabs' species in Socotra Archipelago. From the above, it is obvious that Socotra Archipelago needs further research. Therefore, the main objectives of this study as follows.
 Extension of knowledge on brachyuran crab species that exist in Socotra Islands and creation of a first data base in this field and provision of an overview on brachyuran crabs from recorded during previous studies.  Provide knowledge on the environments appropriate for the presence of these brachyuran crabs in the different marine habitats.

Samples
In the present study, 105 brachyuran crab specimens were examined. The specimens were collected from 6 sites ( Fig. 1 shows the locations on a map of Socotra Islands. See also table 1 which provides the names of the sites, the coordinates and habitat descriptions of these) in Socotra Islands at the Indian Ocean (101 specimens collected by Wolfgang Wranik from Rostock University-Germany (RUWW), and 4 specimens collected by Michael Apel (SMF) during separate periods time from 1984 to 2000. These samples were collected from different habitats such as sandy shores, rocky shores, mud flats, sponge areas, coral reefs and fresh waters.

Methods
One hundred and five specimens of brachyuran crabs were examined which had been collected by hand and hand nets and snorkelling up to 3 meter depth. All the specimens were kept in Rostock University and Zoologische Staatssammlung München, Germany. All the specimens were preserved in 70% Ethanol and labeled in plastic containers with parameters such as location, date of collection and scientific name. Geographical coordinates were recorded with a hand-held Global Positioning System (GPS).

Specimen identification
Two methods were used in the present study to identify brachyuran crab species:

The Results
In the present study, 105 specimens of brachyuran crabs were examined. Of these, 68 were females, 33 males, 4 juveniles. Their analyses revealed 32 species belonging to 29 genera, 14 families related to 11 superfamilies recorded in Socotra Island sites 1-6 (see table 2). Eight of these species considered the first records in Socotra Islands. Fig. 2 shows number of species, genera and families in all the superfamilies in Socotra islands.   Also, the dominant brachyuran crab superfamily in this region was Xanthoidea, 35% with 11 species recorded, followed by Grapsoidea, 19% with 6 species. Carpilioidea, Eriphioidea, Majoidea, Pseudozioidea, Pilumnoidea and Potamoidea were less species-rich and contribute 3% of all species with 1 species only from each superfamily (Fig. 3).
Most brachyuran crab species in Socotra Islands were recorded in four habitats only, subtidal rock with corals, rocky habitat, sand and freshwater. In subtidal rock with corals 25% percent of the total numbers of species were recorded. This corresponds to a total of eight species three of these being dominant in this habitat, i.e. Trapezia cymodoce and Trapezia tigrina from Trapeziidae, and Cymo andreossyi from Xanthidae.
In the rocky habitat, 15.5% percent of the total number of species was recorded, in total five. Two of them were dominant in this habitat, Grapsus albolineatus from Grapsidae and Eriphia smithii from Eriphiidae.
In the habitats of sand and fresh water fewer brachyuran crab species were recorded than in the other habitats, i.e. 3% of all species with one species only per family: Ocypode saratan from Ocypodidae in the sand habitat and Socotrapotamon socotrensis from Potamidae in the fresh water habitat.
In addition, Socotra Island has mangrove trees in five locations in the northern part but, unfortunately, no samples were collected from this habitat in the present study.  In the following, 8 brachyuran crabs which record first time in Socotra Islands in this present study are presented including species name, synonyms, type localities and regional distribution, sex of the specimens, collection sites, collectors, local distribution, and some remarks.

Discussion
The Socotra Island sites (1-6) have a variety of habitats including sandy shores, rocky shores, mud flats, sponge areas, coral reefs and fresh waters. In these sites, 32 species were recorded belonging to 11 superfamilies, 14 families and 29 genera.
The dominant species in corals habitat were the two species Cymo andreossyi and Trapezia cymodoce. The sandy shore habitats in Yemeni coastal waters harbour four species of Ocypode (ghost crabs), three of them recorded in this present study (Ocypode saratan, Ocypode cordimana and Ocypode jousseaumei), while the fourth species Ocypode ryderi Kingsley, 1881 was recorded in Socotra Island by [10] and [13].
A special case in this study is the freshwater habitat. Here we recorded only one endemic species on Socotra Island: Socotrapotamon socotrensis. Two more species from this family were recorded in freshwater in Socotra Island by [9] and [16].
The overall most common species in this study are Leptodius exaratus from the habitat sand with rock in the intertidal, Grapsus albolineatus from rocky intertidal zone, Ocypode saratan from sand medio-and supralittoral and Austruca albimana from muddy intertidal flats. According to previous studies these species, along with 23 other ones, are considered widespread around the Arabian Peninsula [25,32].
Some earlier studies of brachyuran crabs exist in Socotra Islands. [11] [41] recorded another species of Parthenopidae, [12] recorded one species and [13] two more species of Ocypodidae (see table 4 where details of all the previous studies are summarized). Table 3: The brachyuran crabs which were recorded in Socotra Island sites in the present study.

Superfamily Family Taxon
The total brachyuran species number from these previous studies is 151 species belonging to 81 genera and 26 families, of which 127 species were not found in the present study.
The most recent and intensive study in Socotra Islands was done by [10], in which they recorded 77 species, while in the present study recorded 32 species. Eight of these species are first records in the present study. [10] did not report the families Carpiliidae, Potamidae, Tetraliidae and Trapeziidae) found in the present study on Socotra Islands.
The land crabs Cardisoma carnifex of Grapsoidea was recorded in Socotra Island by [39] and [10]. This species was not recorded again in the present study, neither on Socotra nor the Red Sea or the Gulf of Aden. Cranuca inversa (Hoffmann, 1874) -+ -+ + 5