Construction and Interpretation of Particle Size Distribution Spectra From 19 Ecopath Models of Chinese Coastal Ecosystems

Lu Zhai,Daniel Pauly

doi:10.3389/fmars.2020.00298

Abstract

To assess the changes that fisheries have imposed on the functioning of coastal marine ecosystems in China, nineteen published Ecopath models were used to construct particle size distribution (PSD) spectra. The results show that high biomass of jellyfish from ranching operation impacted almost all of the ecosystems studied here. As well, an increasing impact of fisheries was demonstrated, via steeper PSD slopes, for ecosystems with models covering two or more periods. Models of nearshore areas, i.e., bays and estuaries, exhibited steeper PSD slopes that models of offshore areas. The PSD slopes were also correlated with total catch (TC), with the mean trophic level of catch and with the Shannon-Wiener diversity index (H’) that can be computed from Ecopath models. A multiple regression predicting the PSD slopes from year and mean trophic level of the catch explained 38.5 % of the variance in the slopes. Overall, this study confirmed the status of depletion in China’s marine fisheries resources. Also, it established that including a PSD while constructing an Ecopath model, which is straightforward, will improve it, and allow more insights to be obtained from it regarding the impact of fishing on marine ecosystems.

Highlights

Marine ecosystems provide habitats to marine organisms and supply them with their nutrients (Odum and Barrett, 1971); the diversity of species and the multitude of interactions between them are difficult to identify and represent in models (Limburg et al, 2002; Fulton et al, 2003)
The key insights emanating from this study are, in our opinion, that: (1) Constructing particle size distribution (PSD) plots from balanced Ecopath models is straightforward; (2) but jellyfish and mariculture require special treatment; (3) PSD do reflect fishing pressure on ecosystems, and (4) PSD should become part of the completion and verification of Ecopath models
The routine of Ecopath with Ecosim (EwE) 6.6 that can be downloaded from www

Summary

Introduction

Marine ecosystems provide habitats to marine organisms and supply them with their nutrients (Odum and Barrett, 1971); the diversity of species and the multitude of interactions between them are difficult to identify and represent in models (Limburg et al, 2002; Fulton et al, 2003). The Ecopath with Ecosim (EwE) modeling approach has become widely used, notably because of the relative ease with which its parameters can be estimated (Christensen and Pauly, 1992; Pauly et al, 2000; Coll et al, 2015; Colléter et al, 2015) and its ability to realistically represent the structure of food web within a given period (with Ecopath), to simulate over time the changes of trophic interactions between species or group thereof (with Ecosim). The depletion of fisheries resources in China’s coastal seas was partly mitigated by the development of mariculture. The high density of mariculture enterprises and the escape of farmed animals exacerbate coastal pollution (Cao et al, 2007)

Methods

Results

Conclusion