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Biological forensics

CSI in MAR-ECO

Senior MAR-ECO researcher, Tracey Sutton, explains that the current MAR-ECO workshop at Bergen Museum can be considered a kind of crime scene investigation.

A group of MAR-ECO researchers gathered again for a two-week workshop in Bergen, Norway. The group included Tracey Sutton, from Harbor Branch Oceanographic Institution, Vanda Carmo from the Department of Oceanography and Fisheries (DOP) at the University of the Azores and Amy Heger from OceanLab, University of Aberdeen, Scotland.

 

The group came to take advantage of the fish collection at Bergen Museum. The material which was collected during the MAR-ECO research cruise aboard the RV G.O.Sars, summer 2004, is one of the largest deep-pelagic, depth-specific nekton sample collections ever obtained. Not only is the collection extensive in terms of numbers of specimens, but, as Tracey Sutton explains, it is one of the best administered collections around.

Spoiling researchers!

Beginning aboard the G.O.Sars, taxonomic specialists were part of the research team and efforts were made to identify and document the catch material to the lowest taxonomic level possible. Each item was given a unique label that recorded its identification (as complete as possible), the location of its find, date etc.

Information specialist from the Norwegian Institute of Marine Research, Thomas de Lange Wennick, was responsible for developing the database system which has made it possible for researchers from around the world, and particularly from within the international MAR-ECO project, to come to Bergen and to find the material they need quickly and efficiently.

“Between Thomas and the excellent curating work of Ingvar Byrkjedal and Gunnar Langhelle at Bergen Museum, we researchers are really spoiled!” explains Tracey Sutton.

Often researchers do not have the time, resources or competency to identify the raw material at sea. That is the best time to do it, according to Sutton.

Once back on land, it is much more difficult to find an equivalent amount of time in which undivided attention can be allocated for this task, particularly as it relates to the identification of those specimens that require detailed further examination. As a result, a fair percentage of cruise collections may sit around, unidentified in cruise jars for several years or even decades, before it is identified and accessible for further research activities.

The G.O.Sars cruise in 2004 involved a number of taxonomic specialists able to identify a broad range of organisms. The cruise leaders put a great deal of emphasis on identification and documentation of the historic cruise findings.

The MAR-ECO collection is a fantastic resource, and it means that young researchers such as PhD student Vanda Carmo from the Azores, do not need to spend two years, as Tracey Sutton did, just sorting through a cruise collection before he could begin his work.

The big picture

The overall aim of MAR-ECO is to determine the ecology of the communities living along the mid-Atlantic Ridge. Tracey Sutton explains that there is something special about the waters around the Ridge.

This was evident from the first results in 2003 from the Russian Mir manned submersibles that dove deep in the Charlie-Gibbs Fracture Zone, where researchers were astonished to observe high quantities of marine snow; much more that was anticipated, and indeed more than was usually seen during Mir dives. In addition, incidental fishery data gathered the past few decades, as technological developments have enabled ships to fish the Ridge waters, have suggested that these waters are much richer than the waters over the Atlantic abyssal plains.

In many ways the Ridge community of organisms can be considered as something of an oasis – a somewhat unique but areally immense environment. What lives there? How do the organisms living there interact? How can researchers use the latest tools and techniques to learn more about the trophic relationships present?

In order to find out what organisms are eating what, researchers need to do forensic work on trace evidence gleaned from the stomach contents of the organisms collected and work backwards to find out what was eaten. “In other words,” says Sutton, “the ‘crime’ has already happened – we need to determine the identity of the victim, and when and where the ‘crime’ occurred.”

The stomach contents of fishes that are “grazers”, that is, those that eat planktonic organisms, often contain amorphous masses of material that needs an alternative approach, such as molecular analysis, to break it down into organism type. Fishes that are predators may have more readily identifiable stomach contents, but Tracey Sutton explains that the scarcity of food in the deep sea means that maybe as few as one fish in ten collected will have something in their stomach.

Using CSI to do biology

Vanda Carmo has begun her PhD work studying the feeding ecology and food-web relationships in some species of midwater fishes from the northern mid-Atlantic. Once she has dissected out the stomach contents from a fish, she will identify and quantify what is present as well as trying to quantify how much food or what kinds of food have been eaten over the fish’s lifetime.

Vanda is focusing her research on several groups of mid-water fishes: Stenoptychidae, Gonostomatidae, Phosichthyidae, Stomiidae and some species of Myctophidae. Her results will be integrated with other similar on-going research projects on other groups of organisms as well as projects using different tools. Together the various results will help form a more complete picture of the trophic relationships existing in this ecosystem.

Some of the other CSI tools that other projects are using include stable isotope analysis, bone fragment analysis derived from an Anatomical Reference Collection that is currently being built, and genetic analyses, such as barcoding. There are complementary molecular projects underway at the Department of Biology at the University of Bergen, involving Professor Christoffer Schander and Researcher Jens Christian Nejstgaard and others, developing tools for identifying the food of zooplankton that can also be used in gut contents studies. A zooplankton DNA barcoding project is also underway in Ann Buckland’s lab at the University of Connecticut. The two genetic approaches will complement one another very well, says Sutton.

At Bergen Museum an extensive project is also underway to photograph and make digitally available the enormous collection of complete skeletons prepared from the dominant fish species sampled during the G.O. Sars 2004 cruise. Undigested bone fragments that can be identified include jaw bones, teeth, opercular bones and otoliths (actually “ear stones”). These ‘hard parts’ are often the only ‘clues’ left after prey are digested by the fish that consumed them.  Amy Heger is also visiting Bergen Museum during this two-week workshop period and is working hard to photograph the osteological collection. In total, 1674 ‘best of’ pictures from 40 species (51 specimens, average of 7 bones per fish) were acquired. These images will be published in an atlas for future research. Researchers will then be able to determine the identity, size and weight of fish prey from a single bone, using size/weight regressions determined from this collection.

What about the jellies?

Video footage from remotely operated vehicles is showing that there are many more gelatinous plankton organisms present in the waters of the deep sea than trawl hauls would indicate. These fragile organisms are easily destroyed in trawls and are digested extremely rapidly, leaving little conventional evidence of their presence.

In addition, explains Sutton, “jellies” are complex members of food-webs. Classified as zooplankton because they tend to drift freely in the water column, they are actually carnivorous and thus belong to a higher trophic level than most zooplankton.

Fish are much easier to deal with, states Sutton. They tend to be niche feeders – consuming specific species or types of food. Jellies, on the other hand, consume a wide variety of prey that become entangled in their tentacles. The combined DNA projects at the University of Connecticut and the University of Bergen may help work to identify the trophic role of gelatinous plankton in the deep sea.

Dr. Tracey Sutton’s work is being supported by a grant from the US National Science Foundation Ocean Sciences Division – Biological Oceanography Program (OCE 0623551) as well as a Norwegian Marshall Fund grant from the Norge-Amerika Foreningen.

Cephalopods are another major group of organisms that is also a major player in oceanic food webs, but which is also difficult to study using conventional methods. 

Determining the full picture of the trophic relationships among the organisms living along the mid-Atlantic Ridge is a tremendous challenge for MAR-ECO researchers, but each project, each new tool developed, like a huge CSI investigation, brings scientists closer to more complete understanding.

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