A review of deep-sea benthic biodiversity associated with trench, canyon and abyssal habitats below 1500 m depth in New Zealand waters

We review the state of knowledge of benthic biodiversity and ecosystem functioning in deep-sea abyssal, canyon and trench habitats in the New Zealand Exclusive Economic Zone and the Ross Dependency, and make recommendations for future deep-sea research in depths exceeding 1500 m.

All biological information in scientific papers and reports from New Zealand below 1500 m was reviewed and an exhaustive search of multiple data sources was conducted.

The area of the deep seafloor below 1500 m covers more than 65% of New Zealand’s Exclusive Economic Zone. A total of 1489 benthic gear deployments have been conducted by New Zealand based sampling initiatives since 1955, most of which were focused on obtaining geological samples. Less than 0.002% of New Zealand’s deep-sea environment (i.e. in terms of seabed area) below 1500 m has been sampled.

All taxonomy-based studies of all taxa reported in New Zealand waters below 1500 m have been reviewed. To date, 8 species of Bacteria, 293 species of Protozoa, 785 species of invertebrates, and 56 fish species have been recorded from water depths greater than 1500 m. Most of these species are known only from single or relatively few stations collected mainly during historical, non-New Zealand sampling initiatives, notably the British Challenger, Danish Galathea or Russian Vityaz expeditions. Many of these specimens are held at the associated institutions in London, Copenhagen and Moscow, and are therefore not immediately available for scientific study in New Zealand.

Few ecological studies in New Zealand waters have focused on assemblage patterns or processes at depths exceeding 1500 m. Of these, most have been on the Chatham Rise and surrounding areas, with sampling conducted across a wide depth range (from shallow to deep-sea sediments), sometimes as part of interdisciplinary research of particular ecosystem processes. Ecological information on benthic fauna and demersal fish from depths below 1500 m is restricted to the Kermadec Trench. Process-orientated studies are limited to pelagic-benthic coupling (and ocean productivity) research on the Chatham Rise slopes, and trophic interactions research in hadal environments (below 6000 m) of the Kermadec Trench. The scarcity of information from New Zealand is particularly evident when compared with other regions worldwide, for which detailed descriptions of invertebrate and fish assemblages exist, and where the availability of long-term and experimental data has enabled the elucidation of deep-sea ecosystem processes.

More than 8000 images are known to have been taken of the seafloor below 1500 m in the New Zealand region, covering an area of approximately 0.016 km². Over 4000 of the images held at NIWA exist either as paper prints or negatives and ideally should be digitised for future storage and access for analyses. Analysis of these photographic images should yield considerable information about deep-sea biodiversity and ecosystem function in the New Zealand region and could be used to answer a number of research questions (especially around deep-sea benthic biodiversity).

Recommendations on how to potentially further analyse existing data from images, databases and actual specimens are provided. The technical challenges, including gear requirements to sample deep-sea New Zealand benthos and potential future investments, are summarised.

Recent research in the Southern Ocean highlights the ecological and evolutionary importance of the southeastern Pacific Ocean. There are clearly many research questions about benthic ecosystems in New Zealand waters below 1500 m depth that if addressed could increase knowledge to levels similar to those in other regions of the globe. This would require expanding New Zealand’s deep-sea sampling capabilities and developing a long-term, integrated research programme, potentially in collaboration with overseas research institutions.