Onychogomphus costae in Andalusia, southern Spain – Mapping an overlooked species (Odonata: Gomphidae)
Discreet pair of Onychogomphus costae breeding in dry vegetation, about 500 meters away from the Guadajoz River.
RESULTS: DISTRIBUTION IN ANDALUSIA
1 – “Baetic depression”. Guadalquivir water bassin
O. costae is currently known to be present in a stretch of around 450 kilometersat the Guadalquivir and Guadiana Menor rivers from dowstream the Negratin Reservoir until Alcolea del Río’s dam. Most records of O. costae are located at the Guadalquivir in its middle section, within the province of Córdoba, which is partly a recording bias towards observers. Downstream, the species has been recorded around the town of Lora del Río and various places in the province of Sevilla. There are currently no records of O. costae asociated with the river Guadalquivir beyond Alcolea del Río and its large dam which marks the beginning of the estuary (aproximately 80 km long). It must be noted that large portions of the river Guadalquivir are hardly accesible.
The “Canal del Bajo Guadalquivir” is an irrigation channel which provides water for a large area dedicated to crop-farming, espacially rice paddles. O. costae has been repeatidly recorded at the canal where it is not difficult to observe adults. Exuviae were even found close to Sevilla (Cano-Villegas, 2009) and Lora del Río. If completing the whole life cycle proved not to be possible at the canal, then insects are most probably suctionned from the Guadalquivir waters, dispersed through the canal and emerge at various localities. Close to the city of Sevilla, all the records seem to be asociated with this artificial structure.
In the province of Córdoba, reproduction has also been confirmed at the Guadalquivir River in various locations and its main tributaries. The river Genil is a difficult one to sample in the province of Córdoba with very little access for larval survey and where concrete structures (bridges) are available for inspection at only three towns.
The Guadalimar River: there are few records, including larvae and exuviae (Salamanca et al., 2013) which indicate the presence of a population but its densities remain unknown.
Currently there are no observation of O. costae at the rivers Corbones, Guadaiza (Sevilla) and Guadalbullón (Jaén). Those three rivers have little water flow during the summer, sometimes plainely drying up or with only still water at ponds.
2 – “Baetic depression”. Others Atlantic water bassins
Recently, the species has been confirmed at various localities, including exuviae at one locality (Bernal et al., 2015). The reproduction was also confirmed upstream at Puerto Serrano.
Barbate River (Cádiz): numerous exuviae has been collected at one locality and an adult seen on its tributary, the Celemín River (Bernal et al., 2015).
3 – Mediterranean coast
A population of the species was discovered recently (Ripoll & Winter records) and exuviae were found at Guadalhorce River (Kohl records). A remarkable observation has been 20 individuals at Arroyo Piedras (Vliegenthart & van der Heijden record).
Single individuals located at the rivers Genal, Guadiaro (Chelmick records) and Hozgarganta (Vliegenthart & van der Heijden record).
A teneral and its exuvia of Onychogomphus costae on the pillars of the Guadajoz River Bridge.
DISCUSSION: WHY ONYCHOGOMPHUS COSTAE IS RARELY RECORDED?
1 – Recording effort
Given the scarcity of the available information, it is not surprising that ecological preferences of the species were not recognized and earlier field workers couldn’t plan efective campaigns.
2 – Habitat features
The banks and the stony substrates suffered from very important sedimentation from agricultural practices, especially after recent flooding events… In those conditions, it is not surprising those habitats does not usually attract the attention of odonatologists.
3 – Adult behaviour
Costae is well known for its faded yellow coloration, which is unique among Gomphidae in Europe. This colour pattern is deceiptively criptic when a specimen lands in dry grasslands. Adults O. costae tend to fly away and rest among the vegetation. Observed densities of adults at the Guadalquivir and the Guadajoz river banks are low and the species is not commonly recorded including in its best area. Rarely more than three adults were recorded.
4 – Larval behaviour
Gomphids use to emerge on rocky and stony subtrates (Corbet, 2004), but unfortunately those are actually rather scarce at the rivers located in the “Baetic depression”… Precisely during the period of emergence, the level at the Guadalquivir River changes quickly by more than 30 cm on a daily basis because of water demand in rice paddles among other crops (SAIH, 2017).
5 – General improvement of water quality
This new situation has permited the recuperation of one emblematic aquatic mammal, namely the European otter (Lutra lutra), in the province of Córdoba (Prunier et al., 2017). It is possible that the species has been favoured by the improvement of the water quality.
Acknowledgment: The author thanks all the ROLA collaborators who contributed with their data and passion for the study and conservation of Odonata in Andalusia, in particular Javier Ripoll, Paul Winter, Stefan Kohl, Albert Vliegenthart, Antoine van der Heijden, Diego Peinazo and David Chelmick for sharing unpublished records of O. costae. A special thanks to David Chelmick for his comments; Spanish odonatological groups for the support in updat-ing the Iberian map: ANSE, SOCV Parotets, ICHN Oxygastra, Zalandrana, Instituto Alavés de la Naturaleza, Biodiversidad Virtual, Observation.org; anonymous revisers for improving the manuscript; Silvia Saldaña for her constant support.