Aims: The aim of this study was to characterise and identify vibrios isolated from the haemolymph of apparently healthy adult spider crabs (Maja brachydactyla) wild-caught in the Spanish localities of Galician coast and in the Canary Islands and also from captive animals held at IRTA's facilities in the Ebro Delta of Catalonia, north-west Spanish Mediterranean coast. Methods and Results: A total of 277 bacterial isolates were obtained, and of these, 171 were characterised with rep-PCR, resulting electrophoretic bands were analysed and clusters formed. Identification of representative strains of each cluster was made by sequencing the 16S rRNA. Samples from animals caught in Galicia and captive at IRTA (around 15-18 degrees C) rendered mostly species belonging to the Splendidus clade (72 center dot 2 and 76 center dot 6% respectively), commonly found in cold waters (below 20 degrees C). Higher species diversity was found in the haemolymph of the captive animals. In the warmer Canary Islands waters (around 21 degrees C), the diversity of vibrios is dominated by three clades, Harveyi (Vibrio core group, 39 center dot 3%), Orientalis (23 center dot 2%) and Splendidus (21 center dot 4%) with a species diversity that equals that of the colder captive animals. Conclusions: Differences in the vibrios populations were found in the haemolymph extracted from animals collected from the three localities. Potential new species were found, and their description is under way. Significance and Impact of Study: As with other invertebrates, spider crabs also contain a diverse population of vibrios. These findings should help researchers to diagnose when a crab is infected.