Environmental DNA metabarcoding reveals and unpacks a biodiversity conservation paradox in Mediterranean marine reserves

Although we are currently experiencing worldwide biodiversity loss, local
species richness does not always decline under anthropogenic pressure.
This conservation paradox may also apply in protected areas but has not
yet received conclusive evidence in marine ecosystems. Here, we survey
fish assemblages in six Mediterranean no-take reserves and their adjacent
fishing grounds using environmental DNA (eDNA) while controlling for
environmental conditions. We detect less fish species in marine reserves
than in nearby fished areas. The paradoxical gradient in species richness
is accompanied by a marked change in fish species composition under
different managements. This dissimilarity is mainly driven by species that
are often overlooked by classical visual surveys but detected with eDNA:
cryptobenthic, pelagic and rare fishes. These results do not negate the
importance of reserves in protecting biodiversity but shed new light on
how under-represented species groups can positively react to fishing
pressure and how conservation efforts can shape regional biodiversity
patterns.