Two decades of methodological progress have made marine forest restoration technically feasible. Yet large-scale recovery remains elusive, suggesting that the principal bottlenecks are no longer technical but biological.

A first and more fundamental constraint precedes these limitations: unresolved taxonomic boundaries within the Cystoseira sensu lato complex complicate species delimitation, potentially encouraging species-agnostic restoration approaches that treat ecologically distinct taxa as functionally equivalent.

Building on this, current restoration programmes are often dominated by fast-growing, restoration-responsive species, whereas the most threatened taxa are typically characterized by slow growth, delayed sexual maturity, low propagule output and high early-stage mortality. These traits constrain scalability and generate species-specific recovery trajectories that decouple persistence from function: restored populations may survive for years while contributing little to habitat structure, propagule supply or natural recolonization. Climate-driven phenological shifts further amplify these limitations by reducing the predictability of fertility windows and constraining propagule availability for restoration.

Restoration success may therefore depend less on technical optimization than on constraints intrinsic to the biology of individual species, raising the possibility of a recovery paradox in which the most threatened marine forest species are also the most difficult to restore at ecologically meaningful scales. This paradox exposes a structural misalignment between conservation priorities and current success metrics: high transplant survival can coexist with failure to reach target areal extent, because slow growth and limited natural recolonization prevent functional expansion. As a consequence, restoration success may increasingly reflect species tractability rather than conservation priority.