Boletín de la RSEHN. Sección Biológica

Todavía son escasos en la Península Ibérica los estudios sobre la ecología y biodiversidad del hábitat intersticial y de las aguas subterráneas. Con este estudio se pretende contribuir al conocimiento de la biodiversidad de la fauna intersticial en ríos de la vertiente mediterránea de la P. Ibérica y relacionar los principales grupos taxonómicos con las características del medio. Para ello se han escogido 10 estaciones de muestreo en el río Turia y 5 en el río Palancia. El muestreo se ha realizado mediante el uso de una bomba de mano aplicada al método Karaman-Chappuis. Se han realizado análisis fisicoquímicos del agua y sedimento y se han identificado los principales grupos faunísticos de invertebrados. Se destaca la presencia del género endémico Haploginglymus del orden Amphipoda. El tratamiento estadístico multivariante mediante Análisis de Correspondencias Canónicas muestra una cierta segregación ecológica de los grupos más adaptados a medios intersticiales (ostrácodos, ácaros, isópodos, batineláceos, colémbolos, sínfilos y paurópodos) frente a grupos de insectos (dípteros, plecópteros y hemípteros) con menores afinidades estigobias. Así, los lugares muestreados situados a menor altitud y con mayor profundidad en su cauce parecen albergar fauna adaptada al medio intersticial con mayor abundancia, posiblemente debido al mantenimiento del nivel freático más estable que los pequeños cauces de mayor altura. De cara al futuro sería interesante obtener más muestras en aquellos puntos donde se han obtenido ejemplares peculiares de organismos estigobios y profundizar más sobre la función, estructura y biodiversidad de las aguas subterráneas.

The interstitial environment is an ecotone between surface and groundwaters. It is a particular environment whose fauna has been poorly studied, although it is known to harbour a high diversity of invertebrate groups. According to the affinity for living in groundwaters, we can classify its biota in three different groups of species: stygoxenic, stygophilic and stygobiotic. The taxonomic groups that appear most frequently in this environment are oligochaetes, gastropods, mites, crustaceans and hexapods.

Studies on the ecology and biodiversity of the interstitial habitat are still scarce in the Iberian Peninsula. Our study aims to contribute to the knowledge of the biodiversity of the interstitial fauna in Mediterranean rivers of Eastern Iberian Peninsula and relate the abundance of major taxonomic groups to habitat traits. To do so, we selected 10 sampling stations in the Turia river (Valencia province) and 5 in the Palancia river (Castelló province) (Fig. 1, Table I). Sampling was carried out by using a hand pump (TP Sealey 69) applied to the Karaman-Chappuis method according to Pryce et al. (2010). The sampling stations consisted of river banks with gravels to dig a hole and removing water by pumping. At the sampling station, we measured limnological parameters at the excavation hole and filtered the pumped water to obtain the faunal assemblages. In the laboratory, we analysed water ionic composition and sediment organic matter (Table II) and identified the major invertebrate groups (Table III) to later calculate diversity indices (Table IV).

In total, we collected 308 individuals belonging to 35 taxa distributed among 3 phyla. Regarding the habitat variability, we observed an inverse relationship between altitude and electrical conductivity in the sampled river stations (Fig. 2). The Canonical Correspondence Analysis (Fig. 3) shows an ecological segregation between some groups more adapted to the interstitial environment (ostracods, mites, isopods, bathynelaceans, springtails, symphylans and pauropods) and groups of insects (dipterans, stoneflies and hemipterans) with reduced stygobian affinities. The Bathynelacea and stygobitic Isopoda are considered to be restricted to the hypogean habitat, and were found associated to deeper rivers. Therefore, sampled sites at lower altitudes and with deeper waters seem to harbor a more abundant interstitial fauna, possibly due to the maintenance of the water table more stable than in small streams at higher altitude, which might experience drying in summer months.

The hyporheic zone is a system of high interest for ecology, evolution and zoogeography of the subterranean fauna, and it can also serve as a proxy for interstitial water quality. In addition, given the high degree of endemism presented by these organisms, and considering that some of the stygobitic crustaceans found could possibly belong to as yet undescribed species, the study of further samples at those points where they were collected should be encouraged. Finally, the finding of ecological patterns relating species to particular habitats deserves further studies on the function, structure and biodiversity of groundwaters.