Mangrove Restoration Should Consider the Unique Genetic Structure of the Extant Populations

ABSTRACT

Mangroves, an essential tropical coastal ecosystem, are prioritized in conservation agendas due to their rich biodiversity, high carbon stocks, and increasing anthropogenic threats. Despite active restoration efforts worldwide, vital elements such as the genetic composition of replanted seedlings are often overlooked, sometimes leading to unsuccessful outcomes. Here, we investigated the genetic diversity and structure of 15 natural and two replanted populations of Rhizophora mucronata in the Malay Peninsula. We aimed to determine (1) if planted populations have lower levels of genetic diversity than natural populations, and (2) if there is strong genetic structure differentiation between planted and natural populations. Our results showed overall low genetic diversity (mean H _E  = 0.096) across R. mucronata populations in the Malay Peninsula, with planted populations not consistently having lower genetic diversity than natural populations. Multiple lines of evidence in our study demonstrated partial representation of the planted populations' corresponding natural populations, predominantly reflecting artificial introduction, potentially from populations in the Matang Mangrove Forest Reserve. Most notably, the natural population in Kuala Selangor Nature Park consisted of a dominant, unique inferred genetic ancestry that was observed in several individuals in the planted population. This study demonstrated that artificial genetic mixing from uninformed restoration efforts potentially altered the local genetic structures of R. mucronata populations in the two restoration sites studied. Hence, there is an urgent need for replanting initiatives to consider the genetic structure of natural mangrove populations to maintain their local adaptive capabilities and genetic evolutionary potential.