Flagship species as subterranean monitoring tools: a case study in anchialine ecosystems from Lanzarote (Canary Islands)

Anchialine ecosystems host distinctive biological communities that sustain key biogeochemical functions, yet they are increasingly threatened by global change and local anthropogenic pressures. Because routine sampling is logistically challenging, long-term biodiversity baselines are rare, limiting evidence-based management. We compiled and standardized abundance records (1980–2025) from Lanzarote (Canary Islands) for protected crustaceans that act as conservation flagships: the jameíto Munidopsis polymorpha (Decapoda, Munidopsidae) and the Canarian morlocks Morlockia ondinae and M. atlantida (Remipedia, Morlockiidae). We integrated data from dive transects, direct counts and photo-quadrats and analysed them with generalized additive models to test for (i) interannual changes and (ii) the influence of tidal forcing and light regime across cave sectors. The jameíto exhibited strong spatial aggregation, with densities 3–4 orders of magnitude higher in food-enriched entrances and depositional areas than in dark passages, whereas the morlock remipedes occurred at low densities in water-column habitats. Apparent interannual changes were highly specific to cave localities and sections for both taxa, consistent with their redistribution within the anchialine network rather than a system-wide population trend. Short-term variability in both taxa was strongly associated with tidal dynamics, with lower observed densities under stronger tidal forcing. Light effects were detectable only for the jameíto in illuminated sectors, where densities were lower during daytime. Together, these benthic and water column taxa provide complementary, operational indicators of ecological variability in anchialine systems, offering a practical basis for long-term monitoring of the coastal aquifers of Lanzarote and comparable systems.