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Marine Science: Viewpoint

The jellyfish index…

Marine Science: Viewpoint

The jellyfish index

by Professor Andrew Brierley, School of Biology, University of St Andrews

Scotland is a maritime nation with a long and complex coastline: at 18,000km it is longer than Antarctica’s, despite the fact that Scotland is 175 times smaller than the Great White Continent. Scotland’s coastline harbours a rich array of habitats and species, including tidal mudflats that are important feeding grounds for migratory birds, seagrass meadows that shelter juvenile fish, and beds of coral-like maerl. It also offers valuable opportunities for aquaculture and tourism. Beyond the coast, Scotland has a diverse seascape containing an abundance of commercially- and ecologically-important fish, and internationally-important seal and bird populations. The marine zone is also important for oil and gas supply, and for wind- and tidal-power generation. The multitude of demands placed on Scotland’s seas makes for a challenging and complex management task that must be underpinned by science, and Scotland has a vibrant marine science community that is coalesced as MASTS (the Marine Alliance for Science and Technology for Scotland,, an internationally-recognised body that includes the majority of Scotland’s marine science capacity.

The work of my research group at the University of St Andrews on jellyfish, some of which has been MASTS-funded, illustrates some of the ecological and commercial interactions at play in Scotland’s seas. I moved to St Andrews from the British Antarctic Survey, where I had worked on stock assessment of Antarctic krill. Concern about increasing abundance of ‘jelly-like’ salps in the Southern Ocean to the detriment of krill, and a need to be able to survey salps, led to my involvement in acoustic surveys for jellyfish off Namibia, where massive blooms were being reported following the crash of fish stocks. In 2003, working with Chris Lynam (one of my first PhD students at St Andrews), I found that there were more jellyfish than fish off Namibia. This international collaborative work provided the first evidence to support the prediction by Daniel Pauly, perhaps the world’s most eminent fisheries scientist, that the end-point of overfishing would be “the rise of slime.”

As scientists based in the Gatty Marine Lab, which is virtually on the beach, we wanted to explore variability in jellyfish abundance on our doorstep and to set it in an historic context for the heavily-fished North Sea. Fortuitously, colleagues at the Marine Laboratory, Aberdeen, had recorded the numbers of jellyfish caught during net surveys for fish through the 1970s and ’80s. These data showed that abundance of Moon jellyfish (Aurelia aurita) and lion’s mane jellyfish (Cyanea capillata) had varied markedly from year to year. Analysis of possible environmental drivers revealed that elevated jellyfish abundance was preceded by cold winters, and meticulous laboratory work by a more recent PhD student, Chad Widmer, has exposed the mechanistic cause: the benthic stage of the jellyfish lifecycle requires a cold snap to promote reproduction, so the mass strandings of jellyfish on Scotland’s beaches are, surprisingly, the product of cold winters rather than warm summers.

Inspired by Daniel Pauly, we also set out to investigate potential interactions in the North Sea between jellyfish and fish, and discovered a multidirectional ecological interaction between jellyfish, herring and whiting. Jellyfish are predators of herring eggs and larvae, and herring recruitment is reduced in years when jellyfish are more abundant. Juvenile whiting, by contrast, gain protection amongst the tentacles of jellyfish umbrellas, so elevated jellyfish abundance is beneficial for whiting recruitment. Since whiting are voracious predators of juvenile herring, there is a two-pronged jellyfish-mediated assault on herring. This interaction has been incorporated by government fisheries scientists into an ecosystem model of the North Sea, and has improved the ability to predict interannual variability in herring stocks. Fisheries management globally has progressed in recent years from an approach based on consideration of single species in isolation to an ‘ecosystem approach’ which considers interactions between species, and it has been rewarding to see the impact that our research has had on this.

Farmed salmon are also at risk from jellyfish. Salmon aquaculture produces one of Scotland’s major exports, and salmon health is an economically important concern. Fish older than the smolt stage are reared in pens open to the sea, and so are exposed to noxious plankton, including jellyfish. There have been high-profile mass mortalities of salmon due to skin lesions and gill damage caused by the mauve stinger Pelagea noctiluca, a species common in the Mediterranean and the Bay of Biscay which arrives periodically in large numbers in UK waters when currents carry them north. Salmon are also under threat from much smaller gelatinous plankton that are ephemeral, virtually transparent and very difficult to sample. Environmental DNA techniques offer the potential to identify these noxious agents and, hopefully, to make progress towards a jellyfish risk forecast which would help to mitigate this threat.

Jellyfish also present a threat to power stations, because en masse they can block cooling-water intakes, requiring generation to be stopped. Torness nuclear power station on the Firth of Forth has suffered millions of pounds of lost electricity production due to blooms of Moon jellyfish, and innovative approaches to bloom prediction are required for risk management. Blooms are patchy, but satellite remote sensing offers some hope. Smart prediction may trump heavy engineering because, paradoxically, building large defensive walls to keep jellyfish out may provide more habitat for benthic stages, and hence larger jellyfish blooms.

‘Problems’ related to jellyfish are being encountered around the world and we are collaborating globally, including a project jointly funded by the RSE and the National Natural Science Foundation of China. For example, we have had exchanges with scientists in Qingdao, and have visited Dalian, where we also joined
a network with South Korean jellyfish researchers, and have seen how colleagues in China are attempting to tackle ‘invasions’ of the giant Nemopilema nomurai and how they have brought salmon farming operations on to land to avoid noxious agents in the sea. Forward-looking Scottish salmon farmers are considering solutions to take their fish out of the open sea to avoid the ravages of sea lice. These solutions include floating fish pods being developed in Norway that may also bring protection from jellyfish. International collaborations have been critical to our research, since science – like jellyfish research – transcends international borders.




"Marine Science: Viewpoint". Science Scotland (Issue Twenty-one)
Printed from on 05/07/20 11:53:21 PM

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