Changes in the stygobiont polychaete community of the Jameos del Agua, Lanzarote, as a result of bioturbation by the echiurid Bonellia viridis

The Jameos del Agua is a natural anchialine cave lagoon that has been developed as a tourist attraction. It is semi-illuminated due to a partial collapse of the ceiling (known as "jameo"). A fine carpet of benthic diatoms covers the bottom, in 0.5-2 m depth of water, of the tidally influenced and fully marine lagoon. Interstitial polychaetes inhabit this diatomean carpet and the lava rubble mixed with sand and gravel. During the last decades, the echiurid Bonellia viridis became very abundant and its bioturbation activities have changed the natural bottom conditions. The whitish fecal material from B. viridis formed sediment mounds that sharply contrast with the black volcanic rock. This new habitat have been colonized by several endemic species (e.g., Fauveliopsis jameoaquensis), but also by abundant stygoxene macro- and meiofaunal opportunistic species that compete with the endemic stygobities. The most recent colonizers are mainly deposit-feeding polychaetes that take advantage of the high amount of trophic resources available (e.g., Notomastus spp., Trichobranchus glacialis, Aphelochaeta marioni, Cirrophorus lyra). As a result of the recent colonizations, it is necessary to establish monitoring of the communities and to evaluate the viability of controlling the population of B. viridis in the lagoon, since these alterations can also affect the endemic populations living in the water column.