Abstract
Robust time-series of direct observations of jellyfish abundance are not available for many ecosystems, leaving it difficult to determine changes in jellyfish abundance, the possible causes (e.g. climate change) or the consequences (e.g. trophic cascades). We sought an indirect ecological route to reconstruct jellyfish abundance in the Irish Sea: since zooplankton are jellyfish prey, historic variability in zooplankton communities may provide proxies for jellyfish abundance. We determined the Bayesian ecological network of jellyfish–zooplankton dependencies using jellyfish- and zooplankton-abundance data obtained using nets during a 2-week cruise to the Irish Sea in 2008. This network revealed that Aurelia aurita abundance was dependent on zooplankton groups Warm Temperate and Temperate Oceanic as defined by previous zooplankton ecology work. We then determined historic zooplankton networks across the Irish Sea from abundance data from Continuous Plankton Recorder surveys conducted between 1970 and 2000. Transposing the 2008 spatial dependencies onto the historic networks revealed that Aurelia abundance was more strongly dependent over time on sea surface temperature than on the zooplankton community. The generalist predatory abilities of Aurelia may have insulated this jellyfish over the 1985 regime shift when zooplankton composition in the Irish Sea changed abruptly, and also help explain its globally widespread distribution.
Highlights
Robust time-series of direct observations of jellyfish abundance are not available for many ecosystems, leaving it difficult to determine changes in jellyfish abundance, the possible causes or the consequences
2) By taking weekly averages and having zero counts as a separate bin we reduced the number of zeros to 39%: the Bayesian Network Inference Algorithms (BNIAs) we used requires that the data are evenly distributed across all the bins, so 39% is adequate for a 3 bin system
Note that because these two zooplankton groups are connected to other zooplankton groups, the implication is that Aurelia will be effected indirectly by all these other zooplankton groups too[38]
Summary
Robust time-series of direct observations of jellyfish abundance are not available for many ecosystems, leaving it difficult to determine changes in jellyfish abundance, the possible causes (e.g. climate change) or the consequences (e.g. trophic cascades). Whilst jellyfish used to be considered merely a trophic dead-end with few predators, through the use of new approaches such as stable isotope analysis, metabarcoding and ‘critter cams’ we know that jellyfish are embedded in complex networks of trophic interactions[5] Understanding how these jellyfish interactions change through time is hampered because jellyfish abundance data are sparse compared to fish stock assessments, fisheries landing and mesozooplankton records. Regime shifts in the phyto- or zooplankton communities such as in the northern Benguela upwelling system have been shown to potentially impact jellyfish abundance and fish stocks[9,16] It is key for fisheries management and marine ecosystem-based management more broadly, and for quantification of fundamental biogeochemical processes such as carbon cycling, to understand the timing, causes and consequences of changing jellyfish abundance[11,17]. Whether this shift is reversible remains to be seen but, for fundamental ecological understanding and for management of a sometimes commercially important marine living resources, it is important to understand how jellyfish populations change through time, and to understand if these are in concert with or independent from changing temperatures or changing zooplankton communities[1,18,19,20,21,22]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
