When is protection not conservation? A case study of semi-natural freshwater marshes in Hong Kong

Active and abandoned paddy fields are valuable habitats for aquatic fauna in monsoonal Asia. Changes in land use and farming practices have caused substantial losses of paddy-derived marshes in recent decades. Few of those remaining have been designated as protected areas for biodiversity or are managed for conservation. Between 2014 and 2017, 35 paddy-derived marshes (13 protected and 22 unprotected) in Hong Kong were visited with the aim of sampling aquatic macroinvertebrates and assessing the vulnerability of sites to different threats. Twenty of them had been sampled in 1996, allowing the investigation of biodiversity change over time in relation to protection status. The representativeness of protected marshes was evaluated based on their alpha-, beta- and gamma-diversity. In total, 272 macroinvertebrate taxa were recorded (mean, 57 morphospecies per site). Out of the 20 resurveyed sites, five (three protected) were terrestrialized and four (all unprotected) had been filled in between 1996 and 2014-2017. The relative changes in alpha- and beta-diversity of the remaining 11 resurveyed marshes were unaffected by their protection status. The 10 remaining protected marshes had similar alpha- and beta-diversity to those of unprotected sites and, in total, hosted fewer species than the mean value obtained in 9,999 random selections of the same number of sites, indicating that macroinvertebrate diversity was not very well represented within the protected marshes. Protection alone was not successful as a conservation measure because it failed to prevent the degradation and loss of paddy-derived marshlands in Hong Kong. Furthermore, a failure to consider biodiversity when the sites were designated as protected reduced the representativeness and effectiveness of the protected area network for achieving the conservation objectives. Conservation planners need to take account of freshwater biodiversity (especially aquatic insects) during the selection of marshland sites for protection and ensure that protected sites are appropriately managed.

Automated summary

Paddy field-derived marshes in Hong Kong are facing threats, with only a few being protected, but conservation measures have not been very effective as deterioration and loss still occur. The majority of biodiversity changes between protected and unprotected marshes were independent of their protection status in the re-surveyed locations.