Comparing seabed communities – The Chatham-Challenger Project

Located to the east of New Zealand, the Chatham Rise supports large and diverse deepwater fisheries such as hoki, hake, ling, orange roughy and oreos.

These fisheries are supported by high levels of plankton in the surface waters of the region.

Here, warm, salty subtropical waters meet cooler Antarctic waters producing a nutrient rich environment. The plankton support an abundance of small mesopelagic fish (small midwater fish known as ‘feed’), which in turn support the stocks of larger fish species. The Chatham Rise is an important commercial fishing ground that has been fished extensively to 1,200 metre depths.

To the west of New Zealand, the Challenger Plateau is much less productive and has far fewer commercial size fish living there. It has not, therefore, faced the same level of fishing as the Chatham Rise and has extensive areas of relatively undisturbed seabed.

Over the past two years seabed habitats and the benthic communities that live on or near the seabed in these two areas have been mapped. Although the two areas are in similar depths, scientists are asking if the differences in productivity flow down to the benthic communities.

Three voyages were carried out on R.V. Tangaroa to answer this question. During the first voyage, high resolution echo sounding equipment was used to physically map parts of both areas. From that information, scientists selected over 430 sites to be sampled in two further voyages. These later voyages used cameras, sleds, beam trawls and sediment corers to plumb depths between 30 and 1,800 metres to learn about the animal communities on the seabed.

The specimens and data collected will be analysed over the next three years to provide definitive results in 2010. Preliminary results indicate that the types of animals found in both areas vary substantially with depth, but overlap in terms of the range of organisms recorded (diversity). However, the abundance of organisms (biomass) is much higher on the Chatham Rise than the Challenger Plateau.

Other interesting findings include iceberg scours that date from the last ice age; evidence of currents 1,000 metres down so strong that they cause large sand ripples to form on the seabed; and indentations that are several metres deep and wide on the seabed around Veryan Bank on the Chatham Rise, and also to the west off Cook Strait in shallow water. The latter are believed to be some kind of hydrocarbon seep. Several new species have already been identified, and more are expected as analyses proceed.