In 2006, NIWA’s research vessel Tangaroa took part in an international expedition (RENEWZ) to explore for cold-seep sites on New Zealand’s Hikurangi Margin – an area that extends from East Cape to Cook Strait.
The principal aim of the voyage was to find and describe communities of organisms associated with cold-seep sites. Cold seeps are areas of the seafloor where hydrocarbon-rich fluids seep out of the seabed. Often associated with cold seeps are communities of organisms whose survival is totally dependent on chemosynthetic bacteria that can use the hydrocarbon content of the water as an energy source. This study was part of a Census of Marine Life project known as ChEss, which aimed to establish a global biogeography of chemosynthetic fauna.
While there was some evidence for the existence of cold seeps in the target area, no live examples of New Zealand’s seep fauna had been collected or imaged at that time, so it was important to plan an expedition that would:
- locate known or suspected seeps using multibeam and single-beam sonar
- conduct a visual survey of the site using a deep towed imaging system (DTIS)
- sample seep-site fauna using a sled, grab and multicorer
- preserve collected specimens for later identification.
The depth of these sites ranged between 500–1500 metres, and in order to locate, sample and image such sites, sophisticated sonar techniques and high-tech camera systems were needed. The huge expense of such an expedition (3 weeks at sea) requires international involvement as well as scientific collaboration.
This voyage involved three organisations from New Zealand (NIWA, University of Otago and GNS) and three from the United States of America (Woods Hole Oceanographic Institution, University of Hawaii and the Scripps Oceanographic Institution). The principal funder of the voyage was the USA’s National Oceanographic & Atmospheric Administration.
Locating the cold-seep site
On arrival at the site, two different echo-sounders were used. A multibeam sounder produced maps of the seafloor that showed the topography as well as an indication of the soft/hardness of the seabed. Hard bumps and lumps among soft flat seabed could be an indication of carbonate structures associated with seepage on the seafloor. A single-beam sounder gave images of the water above the seafloor. Water containing gas bubbles, indicative of a cold-seep site, give distinctive images known as flares.
Once a site had been identified, a camera survey using the DTIS was conducted. This involved towing a camera in a frame 2 metres above the seafloor in a series of transects, often centred on the location of the flare. The images obtained would then confirm if a site had been located.
Once the size of the seep had been established, samples of living organisms from both the rocky areas and soft sediment were taken. This was achieved using sleds, grabs and corers. Once back on board, the samples were carefully washed, photographed, preserved and catalogued.
Identifying cold-seep fauna
All the samples collected from the eight cold-seep sites surveyed were brought back to NIWA for storage. Since most of the collected samples are not only unique to New Zealand waters but had also never seen before, the task of positively identifying each species (taxonomy) has proved to be a long and arduous one. Taxonomists from around the world are slowly working their way through the backlog.
Why this research is important
By investigating extreme environments like cold seeps and carefully analysing the community of animals that live there, scientists gain a deeper understanding of how living forms have evolved. Chemosynthetic communities are thought to be among the first types of communities to exist on Earth.
New Zealand has an obligation to understand, protect and conserve its biodiversity, and in order to do this, we need to find out about life at special habitats like cold seeps. This same obligation towards biodiversity extends internationally, and as a means to manage human impact on marine biodiversity, it is useful to know how different or similar chemosynthetic communities are from one place to the next.
Nature of science
Twenty or more years ago, to have predicted the existence of chemosynthetic communities that live in the extremely hostile conditions around cold seeps and hydrothermal vents would have met with disbelief from most biologists. However, science is not a closed body of knowledge. It demands and relies upon evidence. Sometimes, this evidence requires new ways of thinking and, in the case of cold-seep communities, about how some living systems work.
Find out more about Cold-seep carbonates and Cold-seep communities.
In the activity, Multibeam seafloor survey students create a model seafloor and create a map of it through taking depth readings.