Abandon aquaculture facilities: allow brackish/saline marshes or swamps to recover without active intervention
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
It may be possible that marshes or swamps will recover on their own, without any active intervention, if human activities are stopped. Such passive recovery can be cheaper than active intervention and allow development of a community well adapted to local conditions. However, plant colonization may not occur at all or, if it does, occur slowly or be dominated by invasive species (Zahawi et al. 2014). Successful recovery may be hindered by physical degradation (e.g. a water table that is too low, restricted tidal exchange), chemical degradation (e.g. acidification of wetland soils when exposed to oxygen) or an insufficient supply of propagules.
To be summarized as evidence for this action, studies must have monitored marshes or swamps after the abandonment of aquaculture facilities within them (stock removed and maintenance completely stopped, with no additional intervention). Therefore, the summarized evidence is best considered as an indication of what kind of vegetation can develop after abandonment of aquacultural facilities, and how long it takes to develop, rather than a complete survey of all relevant evidence.
Related actions: Modify aquaculture practices in watershed, including abandonment of aquaculture facilities.
Zahawi R.A., Reid J.L. & Holl K.D. (2014) Hidden costs of passive restoration. Restoration Ecology, 22, 284–287.
Supporting evidence from individual studies
A site comparison study in 1996 of an abandoned aquaculture pond in Costa Rica (Stevenson et al. 1999) reported that it had developed into mangrove forest within 14 years – containing the same four tree species as nearby natural mangroves, but a greater density of smaller trees. Statistical significance was not assessed. On average, the abandoned pond contained 15,200 trees/ha with a basal area of 18 m2/ha. The average canopy height was 4–10 m/species. In comparison, a nearby remnant of natural mangrove forest contained 7,000 trees/ha with a basal area of 29 m2/ha. The average canopy height was 8–13 m/species. Methods: In 1996, vegetation was surveyed in an abandoned shrimp pond and a nearby natural mangrove forest (two 5 x 5 m plots/site). The 4-ha pond had been used for aquaculture for 20 years, but abandoned since 1982. Its outer dike naturally breached in 1987. Only trees >2 m tall were surveyed. The study country was identified for this summary using Lewis et al. (2002).
Lewis R.R. III, Erftemeijer P.L.A., Sayaka A. & Kethkaew P. (2002) Mangrove rehabilitation after shrimp aquaculture: a case study in progress at the Don Sak National Forest Reserves, Surat Thani, Southern Thailand. Pages 108–128 in D.J. Macintosh, M.J. Phillips, R.R. Lewis III & B. Clough (eds.) Annexes to the Thematic Review on Coastal Wetland Habitats and Shrimp Aquaculture: Case Studies. World Bank, NACA, WWF and FAO Consortium Program on Shrimp Farming and the Environment.Study and other actions tested