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

Anchialine ecosystems support distinct biological communities that sustain key biogeochemical functions. Yet, they are increasingly threatened by global change and local anthropogenic disturbances. Because routine sampling is hard, long-term biodiversity baselines are rare, limiting evidence-based management. We compiled and standardized 1980–2025 abundance records 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 and analysed data from dive transects, direct counts and photo-quadrats with generalized additive models to test for (i) interannual changes and (ii) effects of tidal forcing and light regime across cave sectors. The jameíto showed strong spatial aggregation, with densities 3–4 orders of magnitude higher in food-enriched entrances and depositional areas than in dark passages, whereas the morlocks occurred sparsely 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. Tidal dynamics explained short-term variability in both species, with densities decreasing as tidal range increased. Light effects were detectable only for the jameíto in illuminated sectors, where densities were lower during daytime. Together, these complementary bottom and water column indicators provide a practical, long-term framework for monitoring anchialine ecosystems and guiding management actions in Lanzarote and comparable coastal aquifers.