Benthic sampling was performed along all Iranian subtidal waters of the Persian Gulf during the years 2003 and 2004. A total of 56 species of crabs were caught from 174 stations using a trawler fishing net and Peterson grab. These species belong to 12 families, 15 subfamilies and 37 genera. The results of the present study revealed that families Portunidae, Leucosiidae and Pilumnidae have the highest species richness with 14, 13 and 13 species respectively.
Zoogeographical analysis shows that a high proportion (27%) of the Iranian subtidal crabs have world distribution in the Northern part of Indo-West Pacific region and only two endemic species were found.
There are few studies on marine environments of the Persian Gulf, particularly on the Iranian side. The crustacean fauna of the area is mostly unknown with incomplete references mainly devoted to the Brachyura.
Comprehensive taxonomic studies have been carried out on Brachyura of the Persian Gulf, such as: Alcock (1895, 1896, 1898, 1899a, 1899b, 1900), Stephensen (1945), Titgen (1982), Apel and Spiridonov (1998), Apel (2001). For further works see Apel (2001) and Naderloo and Sari (2005b).
Most of these studies partially covered brachyuran fauna of the area which have only been conducted on a small part of the Persian Gulf. Many of these studies have been carried out on the western part (Arabian side) of the Persian Gulf. However few studies have focused on the eastern Persian Gulf (Iranian side), they include: Stephensen (1945), Bahmani (1997), Naderloo and Sari (2005a, 2005b). Stephensen (1945), which was based on material collected during the Danish Expedition in 1937-38, was one of the most important studies. He identified 86 species and listed several more from the works of Alcock (1895, 1896, 1898, 1899a, 1899b, 1900), MacGilchrist (1905), and Nobili (1906). He listed 151 + 1? species as a total fauna of marine Brachyura of Iran in “The Brachyura of the Iranian Gulf.” Titgen (1982) has performed a systematic and ecological study on the Decapoda of Dubai and listed 196 species of brachyuran crabs for the Persian Gulf. Apel (2001) collected some specimens of crabs on the Arabian side of the Persian Gulf, revised previous collected material and subsequently presented a total of 200 species of crabs for the Persian Gulf. The important work of Apel (2001) is the last key reference for the Persian Gulf crabs.
The present survey is unique as it is merely based on the fresh material collected in the subtidal habitats. Taxonomic study on the material was performed previously by Naderloo (2005).
Materials and methods
During the years 2003 and 2004 specimens were collected from stations along the Iranian coast of the Persian Gulf (except Khuzestan province), 80 off Hormuzgan and 54 off Bushehr provinces. The specimens were collected by a fisheries vessel using Bottom trawl with mesh size in the cod end of 80 mm and head line of 72 m. In addition, specimens were collected using a Petersen grab, with 0.1 m2 coverage area, at 40 stations along the entire Iranian coast of the Persian Gulf in August 2004 (Fig. 1). These were the only available gears on board of fisheries vessel Ferdous I.
The specimens were immediately preserved in 70% alcohol and shipped to the laboratory of Zoology, University of Tehran, where they were deposited in the Zoological Museum. Identification was performed using morphological characteristics including the male gonopod. Final identification and verification was carried out in the Crustacean section of Senckenberg Nature Museum of Frankfurt. The specimens were mostly identified at species level. Fortunately, the crab material of the Danish expedition was available on loan in the Senckenberg museum, presenting an opportunity for revising and comparing specimens with the material studied by Stephensen (1945).
The present subtidal survey found 56 species belonging to 12 families (Table 1), of which 51 have been identified up to species level. The remaining five could not be identified beyond the genus level as two were juvenile (Leucosia sp. and Philyra sp.) and three taxa, which included Glabropilumnus sp., Thyphlocarcinops sp. and Pinnotheres sp., seemed to be new to science and needed to be carefully studied with adequate material. Within 51 identified species, four are newly recorded in the Persian Gulf including: Carcinoplax cf. angusta (Rathbun, 1914), Hyastenus inermis (Rathbun, 1911), Pariphiculus mariannae (Herklots, 1841), and Quadrella reticulata (Alcock, 1898).
Within these families, Portunidae, Leucosiidae and Pilumnidae are the most represented with 14, 13 and 13 species respectively. This is followed by families Majidae and Goneplacidae with four and three species respectively. Two families Parthenopidae and Xanthidae are each represented with two species. The remaining five families including Dromiidae, Dorippidae, Matutidae, Trapeziidae and Pinnotheridae show the lowest species richness (Fig. 2) with only one species per family.
Among the 134 sampling stations in which the trawler vessel was used, Portunus pelagicus (Linnaeus, 1758), P. hastatoides (Fabricius, 1798), and Charybdis (Charybdis) feriata (Linnaeus, 1758) were the most common species which were found at 130, 126 and 50 stations respectively. In contrast to these three common species, 24 species (43%) were rare and present at only one station (Table 1).
From a distribution point of view, Portunidae is the most common family in all stations. Families Leucosiidae and Pilumnidae, with high species richness, are collected from 25 and 18 stations respectively. It is noteworthy that most of these stations are located in the northern part of the sampling area (Table 1).
For an analysis of zoogeographical affinities to other regions of the Indo-Pacific Ocean, species in the present study were categorized into six distribution patterns (Table 2) including:
Northern area of Indo-West Pacific (NIWP)
Species known from Indian Ocean and Pacific Ocean up to Hawaii (IP)
Indo-West Pacific (IWP)
Indian Ocean (IO)
West Indian Ocean (WIO)
Species only known from the Persian Gulf, Pakistan, and Gulf of Oman (Endemic).
Among the 56 brachyuran taxa collected in this study, five were only recognized up to the genus level and as such were excluded from this analysis. Fifteen species (27%) have a distribution pattern of NIWP, one-third of which (34%) belong to the family Leucosiidae (Arcania erinacea, Iphiculus spongiosus, Ixoides cornutus, Nursia plicata, Pariphiculus mariannae).
Eleven species (20%) are widespread in the Indo-Pacific region (IP pattern), these are distributed from the east coast of Africa to Hawaii and New Caledonia. More than half of these species (56%) belong to the family Portunidae (represented by Charybdis (Charybdis) helleri, Gonioinfradens paucidentata, Podophthalmus vigil, Portunus pelagicus, P. sanguinolentus, P. hastatoides). As mentioned earlier, this family is widely distributed in all the sampling areas throughout the Persian Gulf. Eight species (13%) have an IWP distribution pattern which include species of families Portunidae (Charybdis (Charybdis) feriata), Leucosiidae (Myra pernix, Philyra platycheir), Pilumnidae (Pilumnus longicornis, P. minutus), Majidae (Hyastenus hilgendorfi), Parthenopidae (Parthenope longimanus) and Goneplacidae (Eucrate haswelli). Seven species (11%) are represented only in the Indian Ocean including: Liagora erythematica, Libystes nitidus, Philyra globulosa, Parthenope carenatus, Thyphlocarsinus rubidus, Thyphlocarcinops stephenseni and Urnalana hilaris.
Similarly for the IWP pattern, eight (13%) out of 56 species show the WIO distribution pattern from the east coast of Africa to the Red Sea, Persian Gulf, Pakistan and Arabian Sea.
Two endemic species (4%) were found in this survey including Phalangipus persicus and Thyphlocarcinus dentatus.
The brachyuran fauna of the Persian Gulf, in terms of species number is comparable with the adjacent waters in the Indian Ocean. According to Apel (2001), there are about 180 and 200 recorded species for Pakistan and Socotra Archipelago respectively. Therefore, these figures are about the same as 200 species that are recorded by him from the Persian Gulf. This result is surprisingly in contrast with Jones (1985) which emphasizes that the Persian Gulf's harsh environment conditions influenced the intertidal fauna of the area.
In the present study, only subtidal crabs have been considered and 56 taxa were collected using a wide mesh trawl and relatively few grab samples, hence the number of species is not comparable with previous works (Stephensen, 1945; Titgen, 1982; Apel, 2001). There is no doubt that more will be found with further studies but in terms of species composition and diversity, the result of the present study completely agrees with their finding. In all earlier studies and also the present survey, two families Portunidae and Leucosiidae have the highest species richness amongst crab families of the Persian Gulf. This observation is very much related to the habitats in the Persian Gulf. Compared to the Red Sea, the Persian Gulf has fewer coral reefs and more soft bottom habitats (i.e., mud). This results in a specific taxonomic composition of the brachyuran fauna.
Zoogeographical analysis revealed that about one-third of the subtidal crabs have wide distribution in the Northern part of the Indo-West Pacific region. Therefore it can be concluded that subtidal brachyuran fauna of the Persian Gulf are more influenced by the East Indian Ocean and West Pacific elements rather than the Western Indian Ocean including the Red Sea and East Africa. This result supports previous findings based on leucosiid species affinity in the Persian Gulf (Naderloo and Sari, 2005a). However, this is not supported by the existence of a large percentage of portunid species of the Persian Gulf around the Arabian Peninsula which is documented by Apel and Spiridonov (1998).
Regarding the four newly recorded species, Carcinoplax angusta was only previously found in the Philippines (Guinot, 1989), hence a new record for the Indian Ocean. According to Griffin and Tranter (1986), Hyastenus inermis occurs in the Western Indian Ocean (East of Mombassa, Seychelles, Amirante and Red Sea), and the present record has extended its distribution further north of the Indian Ocean. Occurrence of Pariphiculus mariannae in the Persian Gulf is not surprising with regard to previous records from Pakistani waters by Tirmizi and Kazmi (1986). Quadrella reticulata has an Indo-West Pacific distribution pattern and its discovery in the Persian Gulf is the first record of Q. reticulata from north-western Indian Ocean (Naderloo and Sari, 2005b).
The rate of endemism is low, only two species (4%) out of the listed 56 taxa (Table 1) are found to be endemic. However, the frequency of endemic species of intertidal brachyura (Ocypodidae and Grapsidae) is 12%, which includes four out of the 27 intertidal crabs recorded by Apel and Türkay (1999).
Based on the results of present study, species composition of subtidal crab fauna of the region is more influenced by its soft bottom habitat type. In total, 56 species including two endemic species found so far in the current survey. These are categorized in six distribution patterns. Zoogeographically, it seems that most species show affinity to East Indian and West Pacific Ocean crabs.
We are very grateful to Professor M. Türkay, Nature Museum Senckenberg, Germany and Dr. M. Apel, Nature Museum Wiesbaden, for their valuable help and command in identification of the material. Our special thanks are extended to Professor P. Ng, Dr. B. Galil, and Dr. P. Castro for providing literature and useful guidance and assistance during this study. We are indebted to Dr. T. Valinasab from Fisheries Research Organization of Iran for providing sampling opportunities. Financial support was provided by a grant from the Office of Research Affairs, University of Tehran.