Increased irrigation in Mar Menor linked to reduction of tenebrionid beetles

Researchers from the University of Murcia and the Miguel Hernández University have studied tenebrionid beetles and how their numbers have declined as a result of increased ground moisture and salinity.

Researchers from Murcia and Alicante studied coleopterae (specifically carabid and tenebrionid beetles) in areas close to the Mar Menor from 1984 to 2003. Their research analysed changes in the species’ functional activity and structure, as well as in their response to changes in moisture and salinity levels in the coastal wetland area of Marina del Carmolí.

“The ecology and biodiversity of the hypersaline lagoon of the Mar Menor and its coastal wetlands are under threat from hydrological alterations caused by changes in land use within the basin, in particular increased irrigation,” SINC was told by Julia Martínez Fernández, a researcher from the University of Murcia’s Observatory on Sustainability in the Murcia Region.

In order to test the effects of irrigation, precipitation and the discontinuance of agriculture on these insects, the researchers took samples in 1984, 1992 and 2003. The results, published in the most recent issue of the Journal of Arid Environments, show that rises in the water table, increases in the length of periods during which the land is below water and of ground moisture levels have led to a decline in the abundance of tenebrionid beetles.

These beetles were used by the researchers as bio-indicators for arid systems. Tenebrionid beetles are a key link in the trophic chain of these ecosystems since they form the main foodstuff of numerous reptiles and birds. They were affected by the increase in ground moisture levels since they are better suited to semi-arid environments where they fulfil an important function as recyclers and “mobilisers of matter and energy in systems where microbial action is restricted”.

Changes in the make-up of species

Changes in hydrology and agricultural practices have led to an increase in carabid beetles, however, through the appearance of halophile (salinity tolerant) plants and halobiont plants, which grow in salty soils and only rarely in other locations, within the wetland area. Such plants were virtually absent between 1984 and 1992.

“The combination of the results obtained suggests that changing long-term trends in the water table and moisture conditions within the wetland are reflected by changes in the make-up of species,” said Martínez. The researcher added that the biggest impact on the wealth and diversity of species is due to “increases in moisture levels resulting from exceptionally rainy years, as well as successive changes derived from the discontinuance of farming”.

The changes being experienced within animal populations cannot be explained by variations in moisture or salinity alone, however. According to the researcher, the multi-faceted analysis revealed changes such as the existence of three groups of species. “The first of these are associated with more arid conditions (tenebrionids), the second are linked to greater homogeneity of moisture and salinity (carabids), and the third group is characterised by halobiont and halophile species, which are associated with permanently saline soils resulting from long-term changes in the water table.”

The appearance of this last group of salinity-tolerant plants has led to the introduction of species that are characteristic of unstable environments. The populations of animals that were to be found in 1984 were “species more typical of more stable environments”, said Martínez. She added that the increase in water from irrigation “is leading to a decline in the value of the habitats and in the uniqueness of the coastal wetlands of the Mar Menor, which make up protected areas that are even included in the Red Natura 2000 (network of natural areas of special environmental interest)”.

This study is part of a wider research programme looking into changes in the Mar Menor wetlands caused by changes in use of the basin, and their environmental implications.