Clonal and genetic diversity of the threatened seagrass Halophila beccarii in a tropical lagoon: Resilience through short distance dispersal

Halophila beccarii is a threatened tropical seagrass which has a narrow, restricted distribution in the shallow coastal areas of the Indo-Pacific. The monoecious H. beccarii reproduces both sexually or asexually and such mixed reproduction mode is important to stay resilient in a dynamic coastal environment. This study examined genetic diversity and structure of H. beccarii to determine its survival strategy within a tropical coastal lagoon of Southeast Asia (Central Viet Nam). Seven microsatellite loci gave an overall low level of allelic richness (Ar = 1.9), gene diversity (HE = 0.233) and clonal diversity (R = 0.27). A small neighborhood size and short dispersal distance together with a significant fine-scale genetic structure within each site indicated that its survival strategy is through local seed recruitment over very short distances and a limited local clonal extension (< 5 m). These estimations together with a low selfing rate, no inbreeding and significant recent bottlenecks, all indicated that the main resilience strategy of H. beccarii meadows is through sexual reproduction and within site dispersal. Implications for conservation are that environmental conditions of the lagoon should allow to maintain a local recruitment, establishment and development of H. beccarii beds at site level.