Comparison of the coexistence pattern of mangrove macrobenthos between natural and artificial reforestation

Abstract

The abandoned pond-to-mangrove restoration project provides greater advantages than tidal flats afforestation in restoring mangrove ecosystem services and will be the primary method for mangrove restoration in the future. The existing methods for abandoned pond-to-mangrove restoration include artificial restoration through 'dike-breaking, filling with imported soil and tree planting' and natural restoration through 'dike-breaking and natural succession'. However, little is known about which restoration strategy (natural or artificial restoration) provides more benefits to the biodiversity of mangrove macrobethos. Given a prevailing view suggested that artificial restoration should be the preferred approach for accelerating recovery of biodiversity and vegetation structure in tropical regions, we hypothesised higher macrobenthic biodiversity and more complex community structure in artificial restoration than in natural restoration. To test this hypothesis, macrobenthic biodiversity and ecological processes were monitored in a typical abandoned pond-to-mangrove area of Dongzhaigang Bay, China, where artificial and natural restoration methods were used concurrently. Differences in macrobenthic biodiversity, community structure and ecological processes were compared using diversity indices, complex network analysis and null models. Similar species composition and ecological niche overlap and width among macrobenthos were observed at artificial and natural restoration sites. The biotic heterogeneity and interaction among macrobenthos were higher at the natural restoration sites than at the artificial restoration sites. Macrobenthos community assembly at natural and artificial restoration sites was both determined by deterministic processes, with environmental filtering dominating, which explained 52% and 54% of the variations in macrobenthic community structures respectively. Although our findings did not validate the research hypothesis, higher biotic heterogeneity and species interaction among macrobenthos could support natural restoration as the primary method for abandoned pond-to-mangrove projects, because it is a nature-based solution for mangrove restoration.

Keywords: biodiversity; community assembly; macrobenthos; mangrove; mangrove restoration.

FIGURE 1

Overview of the study. (a) Location of Dongzhaigang Bay on Hainan Island, China, and the study area within the bay (coloured dots), where abandoned pond‐to‐mangrove restoration programmes were conducted from 1995 to 2018. (b) Schematic of restored hydrological conditions. (c, d) Diagram showing the two abandoned pond‐to‐mangrove restoration methods compared in this study. The artificial restoration method included hydrological restoration and planting (c), and the natural restoration method included hydrological restoration only (d).

FIGURE 2

Comparison of macrobenthos species richness between artificial and natural restoration (a), observed Shannon–Wiener index, Simpson index and Pielou index of macrobenthos between artificial and natural restoration (b), and non‐metric multidimensional scaling (NMDS) ordination of macrobenthos between artificial and natural restoration (c). *, p < .05; ns, p > .05.

FIGURE 3

The co‐occurrence pattern of macrobenthic communities (a) and positive correlation of core species (b) at natural restoration sites. The co‐occurrence pattern of macrobenthic communities (c) and positive correlation of core species (d) at artificial restoration sites.

FIGURE 4

Observed niche overlap and niche width among species pairs within the macrobenthos at artificial and natural restoration sites. The median and quantile values from 25% to 75% were used in the boxplot. ns, p > .05.

FIGURE 5

RCbray values (a) and relative importance of limiting similarity, dissimilarity and stochastic processes (b) in shaping the mangrove macrobenthos at artificial and natural restoration sites. The median and quantile values from 25% to 75% were used in the boxplot. Relationships between community dissimilarities and environment at natural restoration sites (c) and artificial restoration sites (d) based on the Mantel test and Spearman's rank correlation. Pairwise comparisons of the environment are shown in the upper right panel, with a colour gradient representing Spearman's correlation coefficients. Macrobenthos composition was correlated with each environment using Mantel tests. The line width represents Mantel's r statistic for the corresponding correlation, and the line colour indicates that the significance was tested based on 999 permutations. DBH, diameter at breast height; DO, seawater dissolved oxygen; Ele, elevation; MaxT, MenT; MinT, monthly maximum temperature, monthly average temperature, monthly minimum temperature; NTU, seawater turbidity; S_OM, soil total organic matter; S_pH, soil pH; S_SAL, soil salinity; S_TN, soil total nitrogen; T, seawater temperature; TH, tree height; W_pH, interstitial pH; W_SAL, interstitial salinity.