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Gelatinous zooplankton

Bergen Museum hosts meeting of gelatinous zooplankton experts

October 16-20 a small group of gelatinous zooplankton specialists gathered at Bergen Museum, University of Bergen, to analyse the gelatinous zooplankton collection from the G.O.Sars cruise of 2004.

The workshop was led by gelatinous zooplankton specialist, Francesc Pagès from the Department of Marine Biology and Oceanography at the Mediterranean Marine and Environmental Centre in Barcelona Spain.

Pagès explains that the collection of gelatinous zooplankton is generally given a low priority on research cruises: the organisms are so fragile that it is difficult to get a whole sample using net gear. In addition, some are large and need large storage containers that could, instead, be used for other organisms.

Most cruises, he explains, just count and identify specimens as best they can and then throw them overboard!

Aino Hosia, a Research Fellow at the Department of Biology at the University of Bergen participated in the second leg of the G.O.Sars cruise. Together with Marsh Youngbluth and Tom Sørnes, she was responsible for analysing the video data from the ROV excursions.

After returning to Bergen, however, Hosia took over responsibility for identifying much of the gelatinous zooplankton material collected and preserved during the first leg of the G.O.Sars cruise.


Researchers on MAR-ECO’s G.O. Sars cruise in summer 2004, however, did collect some gelatinous zooplankton specimens.

This effort was led by Tone Falkenhaug, a researcher from the Norwegian Institute of Marine Research, who estimates that she sorted and fixed around 200 samples from the cruise’s pelagic trawling during the first leg of the cruise. These are stored at Bergen Museum, University of Bergen.

Importance of scientific collections

Professor Endre Willassen and Department Engineer Jon Kongsrud at Bergen Museum, University of Bergen are responsible for curating the extensive invertebrate collection at the museum. In addition to the extensive amount of material that was collected during the G.O. Sars cruise in summer 2004, there is material dating from pioneering marine efforts of the late 19th and early 20th Centuries.

Much of this early material includes type specimens for the many new species that were discovered at that time. In addition, explains Kongsrud, there were extensive collecting efforts in the North and Norwegian Seas during the 80s and 90s. A large portion of this collected material is relatively unstudied and represents an undiscovered treasure trove for invertebrate scholars.

Museum scientific collections are a global resource. However, making a major collection accessible demands considerable and continual administration efforts.

Material needs to be curated, documented and stored so that it is available for study either here in Bergen when various groups of international experts who come to Bergen Museum to work with it, or shipped to other research institutions around the world.

This autumn alone Bergen Museum has hosted two workshops of international invertebrate experts; one in cephalopods and this current one in gelatinous zooplankton.

"It is great to welcome visiting researchers here," says Kongsrud, "there are so many fascinating things to learn from this material."

Bergen Museum

What are gelatinous zooplankton organisms?

The presence of the gelatinous zooplankton community in the oceans has been recognised for several hundred years, but little is known about it because the creatures are so fragile and difficult to sample. Before the advent of ROV and AOV viewing opportunities, very few intact animals had been seen.


Now people from around the world have been thrilled and stunned by underwater digital images showing these amazing organisms gliding gracefully with the water currents through the twilight waters of the deep ocean. Some are tiny while others attain sizes of several meters.

MAR-ECO videos of gelatinous zooplankton

There is an amazing array of gelatinous zooplankton organisms in the ocean. Most well-known are the "jellyfish" (hydromedusae and scyphomedusae), which are actually relatives of coral and sea anemones. A number of other animal phyla have also evolved gelatinous lifestyles.

These include: siphonophores, ctenophores (comb jellies), gelatinous molluscs (heteropods, thecosome pteropods, gymnosome pteropods), pelagic tunicates (salps, doliolids,pyrosomes) and appendicularians.

Some of these organisms are individual animals; others are colonies of polymorphic individuals. In addition, many invertebrates have a gelatinous plankton larval phase.

All gelatinous zooplankton have relatively fragile, gelatinous bodies that are at least 95% water and which lack rigid skeletal parts. They thus have relatively neutral buoyancy; and need to expend little energy on movement (although some medusa undertake large vertical migrations).

Their fragile bodies also make them difficult to collect intact and undamaged using traditional net methods. In addition, they are digested quickly so they are undoubtedly under-reported in studies of gut contents.

What role do they play in marine ecosystems?

Gelatinous plankton organisms are relatively ancient organisms. Pagès explains that they were around before crustaceans, for example. They are very plastic, adaptable, and opportunistic. By simply reducing their body size, they can survive for long periods of time without food. In many areas of the world where the natural species diversity has been affected by pollution, over-fishing and, now, climate change, gelatinous plankton organisms may be becoming the dominant predator species.

What did the MAR-ECO cruise find?

Falkenhaug was concerned that despite her efforts to secure specimens, the G.O. Sars collection of gelatinous zooplankton would be too poorly damaged to be useful. But working over a microscope in the cellar of Bergen Museum, Pagès quickly became excited as they sorted through the material; there were a number of interesting specimens.

The overall findings of the G.O. Sars cruise suggest a higher than expected abundance of gelatinous zooplankton in the waters around the mid-Atlantic Ridge. The footage from the submersibles showed more gelatinous zooplankton than fish, especially in the 300-1000m zone. Little is known about many of the species present. Pagès says that it may be that some gelatinous zooplankton have life-cycles that last for many years in the deep ocean.

cruise record

Pagès is particularly interested in siphonophores. Unlike medusae or jellyfish, siphonophores are composed of colonies of polymorphic individuals; each polymorphic type is specialised to perform different functions. This complexity is intriguing, says Pagès.

One of the questions that MAR-ECO set out to address was the effect of a huge geological feature such as the mid-Atlantic Ridge on marine populations. It was a unique opportunity for gelatinous zooplankton scientists explains Pagès, because it is the first ever sampling of these types of organisms in this area.

One of the unusual findings during the G.O. Sars cruise was collecting four more or less complete specimens of a very large Halistemma sp. siphonophore.

These organisms had first been described 200 years ago in 1806, but only bits and pieces have been collected since. They are relatively large, colonial organisms that tend to live in the calmer waters of the deeper ocean.

They are carnivorous and eat crustaceans. Bits of these large Halistemma sp siphonophores have previously been found in the southern ocean. Pagès says that it is interesting to have found a few in the north.

 Historical records

On the work bench amid the ampoules containing the gelatinous zooplankton organisms were a number of open textbooks. Much of the literature relating to gelatinous zooplankton organisms dates to the 1950’s or before. Unfortunately, these resources pre-date internet’s efficient accessibility. Gelatinous zooplankton taxonomists have a challenging task. Pagès underlines the importance of accessing as many early description sources as possible to avoid re-describing and "re-discovering" species.

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