UBC Theses and Dissertations

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UBC Theses and Dissertations

Changing jellyfish populations : trends in large marine ecosystems Brotz, Lucas


Although there are various indications and claims that jellyfish have been increasing at a global scale in recent decades, a rigorous demonstration to this effect has never been presented. As this is mainly due to scarcity of quantitative time series of jellyfish abundance from scientific surveys, an attempt is presented here to complement such data with non-conventional information from other sources. This was accomplished using the analytical framework of fuzzy logic, which allows the combination of information with variable degrees of cardinality, reliability, and temporal and spatial coverage. Data were aggregated and analysed at the scale of Large Marine Ecosystem (LME). Of the 66 LMEs defined thus far, which cover the world’s coastal waters and seas, trends of jellyfish abundance (increasing, decreasing, or stable/variable) were identified (occurring after 1950) for 45, with variable degrees of confidence. Of these 45 LMEs, the overwhelming majority (31 or 69%) showed increasing trends. Recent evidence also suggests that the observed increases in jellyfish populations may be due to the effects of human activities, such as overfishing, global warming, pollution, and coastal development. Changing jellyfish populations were tested for links with anthropogenic impacts at the LME scale, using a variety of indicators and a generalized additive model. Significant correlations were found with several indicators of ecosystem health, as well as marine aquaculture production, suggesting that the observed increases in jellyfish populations are indeed due to human activities and the continued degradation of the marine environment.

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