First record of Vanderhorstia mertensi Klausewitz, 1974 (Pisces, Gobiidae) in the Mediterranean Sea

A dense population of the slender shrimpgoby, Vanderhorstia mertensi Klausewitz, 1974, was observed in Fethiye Bay (Turkey), in association with burrows constructed by the alpheid shrimps, Alpheus glaber and A.rapacida. This is the first record of the species in the Mediterranean Sea, and the fifth alien goby in the region.

Gobiidae is the most species rich family among marine fishes, represented by possibly more than 2000 species. Nearly 130 goby species of about 13 Indo-Pacific genera are known by their mutualistic relationships with the Alpheid shrimps, living together in the same burrow (Wirtz 2005). Current knowledge on gobyalpheid association is mostly based on in situ observations carried out at the Pacific, Indian oceans, Red Sea, West Indies and the tropical western Atlantic, but behavioral studies in aquaria are also available (Karplus et al. 1972;Syms and Jones 2004;Thompson 2004;Wirtz 2005). In the Mediterranean, few gobies are known to be associated with other invertebrates: Chromogobius zebratus (Kolombatovic, 1891), Millerigobius macrocephalus (Kolombatovic, 1891) and Zebrus zebrus (Risso, 1827) with sea urchins, and Gobius bucchichi Steindachner, 1870 with the Anemonia viridis (Forsskål, 1775), however, these interactions are not regarded as true symbiosis (Patzner 1999).
On 18 September 2008, a single specimen of V. mertensi (21 mm SL, 26 mm TL) was collected ( Figure 1) from Kizilada (36º39'59"N, 29º02'06"E), during a scuba dive made at a depth of 23 m. The site is characterized by muddy sand, with moderately dense Halophila stipulacea (Forsskål) beds in the vicinity. The specimen were preserved in 4% formalin, and and Pauly 2008), Japan (Shibukawa and Suzuki 2004) and Australia (Yearsley et al. 2006). We report the presence of this species for the first time in the Mediterranean Sea, and also the first documented case of an alpheid -goby association in the sea.
On 18 September 2008, a single specimen of V. mertensi (21 mm SL, 26 mm TL) was collected ( Figure 1) from Kizilada (36º39'59"N, 29º02'06"E), during a scuba dive made at a depth of 23 m. The site is characterized by muddy sand, with moderately dense Halophila stipulacea (Forsskål) beds in the vicinity. The specimen were preserved in 4% formalin, and kept in the Zoology Museum of Adnan Menderes University (ZMADU). All measurements and counts were made according to the methodology proposed by Randall (2007). Morphometric and meristic characters of the Fethiye bay specimen are as follows: Dorsal finrays VI-I, 15 (last ray branched to base); anal finrays I+16 (last ray branched to base); pectoral finrays 16; ventral finrays I+5; caudal fin segmented rays 15; scales in longitudinal series on body 52. Body elongated and laterally compressed; body depth at pelvic fin origin 14.3% of SL, body depth at anal fin origin 10.5% of SL; head length 26.7% of SL; head width 13.8% of SL and 51.8% of head length; mouth large and oblique, maxilla reaching beyond a vertical through the middle of the eye; upper jaw length 35.7% of head length; preorbital distance small, 17.9% of head length and 55.6% of eye diameter; postorbital distance 50.0% of head length; eyes dorsally located with very narrow interorbital distance, horizontal eye diameter 32.1% of head length; long caudal fin exceeding head length, caudal fin length 27.6% of SL; caudal peduncle length 32.1% of head length and 8.6% of SL; caudal peduncle depth 23.2% of head length and 6.2% of SL; longest dorsal finray 14.8% of SL; pectoral finrays extend as far as to second ray of D2, longest pectoral finray 26.2% of SL; pelvic fins reaching to anus, longest pelvic finray 17.6% of SL; longest caudal finray 28.6% of SL. Color (in life): Dark stripe on the maxilla, numerous yellow/orange spots on head and the dorsal part of the body, a dark spot on the opercle, a vertical dark stripe (not extending down the belly) below the 4th ray of first dorsal fin, three large dark spots below the second dorsal fin and one dark spot on the caudal peduncle, all fins with distinct yellow spots (except for the pelvic fins). Color (preserved): Body pale, with four lateral spots. A fainted dark stripe on the maxilla. All fins are colorless.
Of a total of 243 (daytime) scuba dives made along the coast of Fethiye Bay, the slender shrimpgoby was observed on 78 dives at 26 different localities (Figure 2). The shallowest burrows occupied by the shrimpgoby were at 2 m, the deepest was at 52 m. This finding differs from the depth distribution (2-10 m) indicated by Froese and Pauly (2008). The population of V. mertensi was most dense over sandy/muddy bottoms (up to 7 individuals/m 2 ), and decreased to ca. 0.1 individual/m 2 in the vicinity of Zostera spp., Posidonia oceanica (Delile) and Cymodocea nodosa (Ucria) meadows (Figure 3). The alpheids collected from the burrows inhabited by V. mertensi were identified as Alpheus glaber (Olivi, 1792) andA. rapacida De Man, 1908. A single Lessepsian penaeid prawn, Metapenaeopsis aegyptia Galil and Golani, 1990, was also captured from a burrow at 20 m, but does not signify an association with the shrimpgoby.  All V. mertensi individuals were observed hovering near the entrance of burrows, keeping their position if unthreatened. When the divers tried to approach nearer the burrow, the goby darted inside performing a swift "U-turn".
The Indo-Pacific fish genus Vanderhorstia Smith, 1949, includes 21 species worldwide, several species being described recently. Among all Indo-Pacific shrimpgobies, Vanderhorstia is most similar to Cryptocentrus Valenciennes, 1837 and Amblyeleotris Bleeker, 1874, and can be distinguished by the head papillae pattern (longitudinal in Vanderhorstia vs. transverse in the latter two). Comparison with Vanderhorstia species known from the Red Sea, V. delagoae (Barnard, 1937) and V. opercularis Randall, 2007, with V. mertensi shows the latter differs in having more dorsal and anal fin soft rays (15 dorsal / 16 anal vs. 13-14 / 13-14 and 12 / 12, respectively), and a unique color pattern.
We assume that the well established population of V. mertensi in Fethiye Bay originates from the Red Sea and entered the Mediterranean via the Suez Canal, but the possibility of a shipmediated introduction should also be considered.