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Cruising around with jellyfish

Professor Ulf Båmstedt began his Easter vacation by heading out to sea to learn more about medusae (jellyfish). 

Ulf Baamstedt, MAR-ECOBåmstedt is a professor at the Institute of Fisheries and Marine Biology at the University of Bergen (UiB). He is also a steering group member in the MAR-ECO project (see web link below). During the cruise, Båmstedt planned to study the ecology of the coronate deepwater medusa, Periphylla periphylla as well as investigating the biodiversity of gelatinous macro-zooplankton. Journalists from Germany accompanied him on the cruise.

What role do medusea play in the sea?

The following is Professor Båmstedt's brief and very general description of the role of medusae in the sea.

Medusae are generally pelagic predators. They sense their prey either by direct contact or through chemical stimuli over very short distances. Compared to visual predators such as fish, their detection distance is very short and they are not able to pursue their prey. Thus, in well-illuminated habitats visual predators have an advantage over medusae in competing for prey. However, since medusae are not dependent on light, they have a competitive advantage over fish in darker environments.

Medusae are not very edible for larger predators. As a result, they tend to be neglected by many predatory fish, in preference for small fish.

Medusae have the ability to be able to eat enormously when prey is abundant. They can capitalise on good food conditions to grow and reproduce.

The over-harvesting of fish by man seems to have caused an imbalance between fish and jellyfish. A number of scientists feel that we are seeing an increasing abundance of jellyfish in the marine environment. However, methods for quantifying this hypothesis have not yet been developed.

One of Båmstedt's research goals is to develop accurate and reproducible methods to quantify studies of these creatures.

Out at sea

During the cruise the researchers undertook field work in Lurefjorden, Sognefjorden, and on fjord-open Atlantic transects. They made extensive use of UiB's remotely operated vehicle (ROV), the Aglantha in their work.

The Aglantha makes it possible to take videos deep under the surface. From these video records, the researchers hope to be able to identify siphonophores and ctenophores. These organisms belong to low diversity taxa and usually have visible morphological characters that are species specific, such as bell shape, colour, size, tentacle shape etc. Båmstedt regrets that they do not, as yet, have a still-camera system on the Aglantha, as such a system is essential for high-quality pictures, which could be used for more advanced identification.

On the cruise, the researchers also plan to study the dynamics of the vertical distribution of Periphylla in relation to environmental variables. They will compare the populations of Periphylla in the two fjords, morphologically and at the population level. They will look, in particular, at the size distribution and vertical distribution. They also hope to collaborate with German scientists in a study using molecular techniques to try to quantify the exchange rate between the two populations. (see the cruise plan)

Using the Aglantha

ROV Aglantha, UIBBåmstedt explained how the Aglantha has greatly facilitated the research of these fragile organisms, which live in a rather inaccessible environment. Data collected by the Aglantha can be used as a quantitative tool because the video profiles provides size distribution and vertical distribution. Other traditional techniques have failed to do that.

Behavioural studies on deepwater medusae are also possible with the Aglantha. It is even possible to sample individual medusa at depth and to bring them up for further studies, completely undamaged. The Aglantha also gives researchers the possibility of using red light for studying the natural behaviour of the medusa, since white light disturbs them severely.

The sense of vision is extremely important to the way humans function as organisms and for how we describe phenomenon of different kinds. Båmstedt explains that in many ways, we have been studying the sea "blindly" before submersibles began to be used in research.

He feels that their use has been a major revolution to deep water research and that a new era in marine science began since the use of submersibles gave researchers visual access to remote habitats. It is impossible to see these habitats from dredge or net samples. He also points out that the submersible's additional possibility of integrating video and instrumental data from precisely defined locations in the habitat is a tremendous advantage. Previously, our understanding of the depth below around 30m is based upon the data provided by "blind" sampling.

Read more about the ROV Aglantha.

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