Abstract
The critically endangered estuarine pipefish, Syngnathus watermeyeri, is one of Africa’s rarest fish species and currently faces a significant risk of extinction. A combination of anthropogenic and natural factors threaten submerged macrophyte beds in the two South African estuaries (Bushmans and Kariega) in which the species’ only two known remaining populations reside. Here, we genotyped 34 pipefish from both populations using genome-wide data to determine whether the two estuaries harbour distinct genetic diversity, such that translocating individuals between them might improve the genetic health of both. Our results show that both populations are highly inbred, and no statistically significant genetic structure was found between them. Moreover, individuals both within and between estuaries were very closely related to each other. These results indicate that the remaining populations of the estuarine pipefish suffer from the adverse genetic effects of small population sizes. Even though recent surveys have estimated population sizes in the order of thousands of individuals, these may fluctuate considerably. Although the translocation of genetically similar individuals between habitats will not increase local genetic diversity, the creation of additional populations across the species’ historical range may be a suitable conservation strategy to prevent further loss of genetic diversity, and to minimise the overall extinction risk posed by environmental stochasticity.
Highlights
Intertidal submerged macrophyte beds dominated by seagrass are ecologically important habitats that provide foraging sites, shelter, and nursery grounds for many aquatic species, thereby supporting a greater density of animals per unit area than any other habitat type within estuaries and lagoons (Alfaro, 2006; Rasheed and Unsworth, 2011)
The final dataset used to assess genetic structure contained 4,883 SNPs, and the selectively neutral dataset contained 3,769 SNPs (Supplementary Table 2)
No genetic structure was found between estuaries, with FST = 0.01 (P = 0.36) and Discriminant Analysis of Principal Components (DAPC) (Supplementary Figure 1A) identifying a single population cluster
Summary
Intertidal submerged macrophyte beds dominated by seagrass are ecologically important habitats that provide foraging sites, shelter, and nursery grounds for many aquatic species, thereby supporting a greater density of animals per unit area than any other habitat type within estuaries and lagoons (Alfaro, 2006; Rasheed and Unsworth, 2011). Despite the ecological significance of seagrass, only two of these estuaries (Langebaan and Knysna) have some formal protection status (Adams, 2016). Their macrophyte beds harbour animal species with high conservation status, including the Endangered Knysna seahorse, Hippocampus capensis Boulenger, 1900, which is found in Knysna and two nearby estuaries (Mkare et al, 2017), and the Critically Endangered pulmonate limpet Siphonaria compressa Allanson, 1958, which occurs in both Langebaan and Knysna (Allanson and Herbert, 2005). A third species of conservation concern, the Critically Endangered estuarine pipefish, Syngnathus watermeyeri Smith, 1963, is strongly associated with macrophytes in two estuaries (Kariega and Bushmans; Figure 1) that have not been afforded any formal level of protection (Whitfield et al, 2017)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call