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. 2021 Feb 16;4(1):212.
doi: 10.1038/s42003-021-01732-y.

Recovery of tropical marine benthos after a trawl ban demonstrates linkage between abiotic and biotic changes

Zhi Wang  1   2   3 , Kenneth M Y Leung  4   5   6 , Yik-Hei Sung  7 , David Dudgeon  8 , Jian-Wen Qiu  9   10
Affiliations

Recovery of tropical marine benthos after a trawl ban demonstrates linkage between abiotic and biotic changes

Zhi Wang et al. Commun Biol. .

Abstract

Bottom trawling, which is highly detrimental to seabed habitats, has been banned in some jurisdictions to mitigate the problems of habitat destruction and overfishing. However, most reports of ecosystem responses to trawling impacts originate from temperate latitudes, focusing on commercial species, and recovery of invertebrate macrobenthos from trawl ban has hardly ever been studied in the tropics. In Hong Kong (lat. 22.4°N), a history of intensive trawling with various types of gears has long degraded coastal ecosystems. To facilitate the recovery of fisheries resources and associated benthic ecosystems, the Government of the Hong Kong Special Administrative Region implemented a territory-wide trawl ban on December 31, 2012. Comparison of surveys conducted in June 2012 (before the trawl ban) and June 2015 (2.5 years after the ban) revealed higher organic contents in sediment and lower suspended-solid loads in water column, as well as a significant increase in site-based abundance, species richness, functional diversity and among-site similarity of macrobenthos after the trawl ban. Our results suggest that the imposition of a trawl ban can be an effective measure for biodiversity conservation in tropical coastal waters.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. An infographic showing the abiotic and biotic responses to the territory-wide trawl ban in Hong Kong waters.
Abiotic responses to the trawl ban include: (1) lower bottom water suspended-solid loads, (2) higher sedimentary organic contents; and Biotic responses include: (3) higher site-based abundance, species richness, functional diversity, niche occupancy and among-site similarity of macrobenthos.
Fig. 2
Fig. 2. Survey sites in Hong Kong waters and comparison of abiotic parameters before (2012) and after (2015) the trawl ban.
a The 28 survey sites located in three hydrological regions (i.e. Estuarine, Transitional and Oceanic) and seven Water Control Zones (i.e. (A) Deep Bay, covering sites 1, 2, 3, 4; (B) Western Waters, covering sites 5, 6, 7; (C) Victoria Harbour, covering sites 9 and 10 outside the harbour, and sites 11, 12, 13, 14 inside the harbour; (D) Southern Waters, covering site 8; (E) Eastern Waters, covering sites 15, 16, 17, 18, 19; (F) Mirs Bay, covering sites 20, 25, 26, 27, 28; (G) Tolo Harbour, covering sites 21, 22, 23, 24) in Hong Kong. The red pentagram represents the location of Stonecutters Island. b Principal components analysis (PCA) biplot showing changes in abiotic variables towards increased total organic matter and decreased suspended-solid loads in the survey sites after the trawl ban. Blue and orange circles represent data from the 2012 and 2015 surveys, respectively. Positive or negative correlations between abiotic variables and the two principal components are represented by the direction of the arrows. Abbreviations of abiotic variables refer to Supplementary Table 1. c Abiotic variables with significant changes (paired samples t-tests) between the 2012 and 2015 datasets. For SUS in c, error bars represent the means + standard deviation (SD) of 11 or 12 independent experiments. Between 2012 and 2015, there was a significant decline in bottom water SUS (mg/L), but significant increases in sedimentary TOM (w/w%), COD (1000 mg/kg) and TKN (100 mg/kg).
Fig. 3
Fig. 3. The biotic responses and spatial distribution of macrobenthos among-site groups before (2012) and after (2015) the trawl ban.
a Total abundance (number of individuals). b Total biomass (g). c Species richness. d Functional groups. The biotic variables at each site were calculated based on the pooled data from five grab samples covering a total area of 0.5 m2. e Site groups in the 2012 survey before the trawl ban. f Site groups in the 2015 survey after the trawl ban. The distribution pattern of site groups was made based on the results of CLUSTER analysis (Supplementary Fig. 3) showing nine significantly distinct site groups before and six after the trawl ban (SIMPROF procedure, P < 0.05).
Fig. 4
Fig. 4. Results of Canonical Analysis of Principal Coordinates (CAP) comparing the abundances of macrobenthos in the 28 sites among the three surveys conducted in 2001, 2012 and 2015.
The analysis was based on fourth-root transformed family abundance data (resemblance: Bray–Curtis similarity; number of permutations = 999). Data from the three surveys diverge significantly from each other (pairwise tests, P < 0.01).
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