Differences And Influencing Factors Of Fish Biodiversity Under Different Ways Of Pond-to-mangrove Reversion

Since the 1980s,mangrove wetland ecosystems have been severely degraded against the background of the rapid growth of global fish and shrimp aquaculture demand and the large-scale construction of aquaculture ponds.Mangrove restoration is one of the ecological issues globally.Large-scale aquaculture ponds are abandoned due to diseases and other factors.And the large area occupied by them is the mid-to-high tidal zone that is most suitable for mangrove growth.Therefore,it is extremely important to restore abandoned aquaculture ponds to mangrove wetland ecosystems,that is,mangroves pond-to-mangrove reversion.According to whether landfill and artificial planting of aquaculture ponds are carried out,the main methods of pond-to-mangrove reversion are divided into four types which are Artificial pond-to-mangrove reversion,Semi-Artificial pond-tomangrove reversion,Natural pond-to-mangrove reversion and Semi-Natural pond-tomangrove reversion.Artificial pond-to-mangrove reversion:Filling and planting.It is the most popular method of ponds reversion.But with high cost,low biodiversity and monospecific plantation are the main disadvantages.Semi-Artificial pond-to-mangrove reversion:Fill but no planting.Can't avoid high cost.Natural pond-to-mangrove reversion:No filling and no planting.A large amount of data support is still needed for the restoration of mangroves.Semi-Natural pond-to-mangrove reversion:No filling but planting,which can accelerate the recovery speed appropriately.Therefore,the comparison of the recovery effects of the four pond-to-mangrove reversion methods is urgent.Fish is one of the important indicators to evaluate mangrove ecosystems,but there are still few studies on fish communities combined with returning ponds to wetness.Therefore,this study combines mangrove fish communities with different pond-to-mangrove reversion,and investigates the fish biodiversity and related environmental factors to compare the restoration effects of different restoration methods and restoration times.The experiment was conducted in January 2019(dry season,winter)and August 2019(rainy season,summer).Two areas(Wenlin Village,Daoxue Village)in the Dongzhaigang Mangrove Nature Reserve in Hainan,China were selected.The plots include 2 types of recovery time(restoration for 5 and 24 years)and 4 methods of pondto-mangrove reversion.Wenlin Village:Natural pond-to-mangrove reversion for 24 years(WL-N-24y),Natural pond-to-inangrove reversion for 5 years(WL-N-5y),Artificial pond-to-mangrove reversion for 5 years(WL-A-5y),Semi-Artificial pond-tomangrove reversion for 5 years(WL-SA-5y).Control group(WL-C);Daoxue Village:Natural pond-to-mangrove reversion for 24 years(DX-N-24y),Semi-natural pond-tomangrove reversion for 24 years(DX-SN-24y),Control group(DX-C),Mudflat(DXM).The main results are as follows:1.Main mangrove species are Aegiceras corniculatum,Kandelia obovata,Sonneratia apetala,Bruguiera sexangula and Rhizophora apiculata et al.Mainly dominated species captured are Acentrogobius chlorostigmatoides,Bostrychus sinensis,Mugil cephalus et al.2.The results of comparison between different pond-to-mangrove reversion methods(same recovery time):Shannon-wiener diversity index(0.97±0.44),Margalef richness index(1.11±0.37),Catch per unit effort(1±0 ind./net)of WL-A-5y were significantly lower than WL-N-5y in summer(Shannon-wiener diversity index 1.51±0.05,Margalef richness index 2.11±0.74,Catch per unit effort 8±3 ind./net,p<0.05).The Catch per unit effort of WL-SA-5y in summer(2±0 ind./net)was significantly lower than that of WL-N-5y.The Shannon-wiener diversity index(0.26±0.34)of WL-A-5y was significantly lower than that of WL-N-5y(0.66±0.54)and WL-C(0.65±0.48);WL-A-5y's Margalef richness index(0.36±0.50)was significantly lower than WL-N-5y(0.93±0.77)and WL-C(0.90±0.66);Among the number of species,WL-A-5y(1.36±0.73)was extremely significantly lower than WL-C(2.48±1.40,p<0.01),and significantly lower than WL-N-5y(2.57±1.85).There were no significant differences in the indexes among the different recovery types in Daoxue Village.There was no significant difference in fish biodiversity index between DX-N24y and DX-SN-24y.In summary,Natural and Semi-Natural pond-to-mangrove reversion are better than the artificial and semi-artificial retreating ponds with higher fish biodiversity.3.The results of comparison between different pond-to-mangrove reversion time:The Shannon-wiener index(1.04±0.38)and Margalef index(1.35±0.57)of WL-N-24y in winter were significantly lower than WL-N-5y;The Weight per unit effort of DXSN-24y(19.55±29.06 g/net)in the total year integrated analysis is significantly lower than WL-C(38.80±36.64 g/net).In summary,the short-term recovery effect of the Natural pond-to-mangrove reversion is good,and the long-term recovery effect of Natural pond-to-mangrove reversion is unstable.4.There is a significant positive correlation between the elevation heterogeneity of various plots and fish biodiversity.Water salinity is significantly negatively correlated with Catch per unit effort,and is significantly positively correlated with Shannon-wiener diversity index,Margalefrichness index and species number in winter.Soil particle size showed a significant positive correlation with Shannon-wiener diversity index,Margalef richness index and species number.Other environmental parameters including water turbidity,plant density,total organic carbon in the soil and other environmental indicators have no significant correlation with fish biodiversity.To sum up,the restoration effect of Natural and Semi-Natural pond-to-mangrove reversion is better than that of Artificial and Semi-Artificial pond-to-mangrove reversion,and the long-term recovery effect of Semi-Natural pond-to-mangrove reversion is similar to that of Natural pond-to-mangrove reversion.