Nutrient input of coastal aquaculture may affect growth of mangrove following intermediate disturbance hypothesis: critical thresholds and spatial relationship coupling

Limited nutrient input from coastal aquaculture ponds is on one hand beneficial to mangrove growth. However, on the other hand, surplus nutrition input would result in negative impacts on mangrove due to eutrophication. This study mainly focused on presenting an integrated framework of Intermediate Disturbance Hypothesis for identifying the nutrient threshold in sediment mostly suitable for mangrove growth and optimal area ratio between aquaculture ponds & mangroves. By using time-series of remote-sensing and field investigation, this proposed integrated framework was applied in Beibu Gulf of Guangxi Province, China. The results showed that: (1) the relationships between mangrove growth and coastal aquaculture disturbance followed an inverted 'U' trend of curve at both regional scale and local scale, verifying the intermediate disturbance hypothesis. (2) The optimal concentration of TN and TP in Beibu Gulf mostly suitable for mangrove growth is in the range of 0.743-1.783 g/kg, and 0.172-0.362 g/kg, respectively varying depending on the tide level. In light of the aforementioned analysis, the optimal ratio of aquaculture area to mangrove coverage was recommended to be controlled in the range from 1:1.65 to 1:2.85. These results are crucial for local governments with decision-making of spatial planning on coupling coastal aquaculture development and mangrove conservation. Although the aforementioned recommended control parameters should be seriously verified by adding more sampling and case studies, the proposed integrated framework was our major contribution and could be applied to other relative areas.