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Global change in the trophic functioning of marine food webs
The development of fisheries in the oceans, and other human drivers such as climate warming, have led to changes in species abundance, assemblages, trophic interactions, and ultimately in the functioning of marine food webs. Here, using a trophodynamic approach and global databases of catches and life history traits of marine species, we tested the hypothesis that anthropogenic ecological impacts may have led to changes in the global parameters defining the transfers of biomass within the food web. First, we developed two indicators to assess such changes: the Time Cumulated Indicator (TCI) measuring the residence time of biomass within the food web, and the Efficiency Cumulated Indicator (ECI) quantifying the fraction of secondary production reaching the top of the trophic chain. Then, we assessed, at the large marine ecosystem scale, the worldwide change of these two indicators over the 1950-2010 time-periods. Global trends were identified and cluster analyses were used to characterize the variability of trends between ecosystems. Results showed that the most common pattern over the study period is a global decrease in TCI, while the ECI indicator tends to increase. Thus, changes in species assemblages would induce faster and apparently more efficient biomass transfers in marine food webs. Results also suggested that the main driver of change over that period had been the large increase in fishing pressure. The largest changes occurred in ecosystems where 'fishing down the marine food web' are most intensive.
Full Text
File | Pages | Size | Access | |
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Publisher's official version | 21 | 5 Mo | ||
S1 Table. Quantitative and qualitative supplementary variables tested in the clustering. | - | 21 Ko | ||
S2 Table. Indicators TCI and ECI time-series per large marine ecosystem. | - | 94 Ko | ||
S1 Appendix. Large marine ecosystems (LMEs) map and characteristics. | - | 781 Ko | ||
S2 Appendix. Sensitivity analysis based on an Ecopath model for the North Sea. | - | 109 Ko | ||
S3 Appendix. Sensitivity of the results to non-fish species’ influence on the clusters trends for the functioning indicators TCI and ECI. | - | 733 Ko | ||
S4 Appendix. Case studies of species assemblages. | - | 353 Ko | ||
S5 Appendix. Complementary statistical analysis on worldwide indicator trends. | - | 1 Mo | ||
S6 Appendix. Complementary results of the clustering performed on TCI. | - | 23 Ko | ||
S7 Appendix. Complementary results of the clustering performed on ECI. | - | 20 Ko |