The IN2017_V03 expedition of Australia’s premier research vessel ‘Investigator’ was the first to systematically sample lower bathyal to abyssal habitats (2000-5000 m) in Australia’s Exclusive Economic Zone. It traversed seven newly declared marine parks in Commonwealth waters off the eastern margin of Australia from 15^th May to 16^th June 2017, including Freycinet, Flinders, East Gippsland, Jervis, Hunter, Central Eastern and Coral Sea Marine Parks. The voyage mapped much of the deeper water habitats of these parks using high resolution multi-beam data and systematically sampled the habitats, principally using video transects, small beam trawls and epibenthic sleds.

The scientific objectives of the voyage included:

1. Describe latitudinal and bathymetric patterns of biodiversity of Australia’s eastern bathyal (1000-2500 m) and abyssal (4000 m) fauna from 42 to 24°S. Test whether patterns of latitudinal turnover described for the shelf and upper bathyal are replicated at deeper depths.
2. Survey and photograph the lower-bathyal and abyssal ecosystem of Commonwealth marine parks for the first time.
3. Describe the faunal communities and correlate biodiversity patterns against measured and modelled oceanographic and geological environmental factors.
4. Sequence DNA of selected species to examine the evolutionary history of the fauna.
5. Convey the excitement of deep-sea marine science and the conservation importance of Australian Marine Parks to the general public by having specialised science communicators on the voyage.
6. A further objective of the NESP Marine Biodiversity hub was to compare the community composition and richness of beam trawl samples between the IN2017_V03 survey and the various surveys (IN2015_C01, IN2015_C02, IN2017_C01) recently conducted in the Great Australian Bight.

We report here on a diverse set of products and outcomes ranging from real-time information products, delivered through daily blogs and YouTube videos, to a new fundamental understanding of the origins of deep sea biodiversity over the last 100 million years based on new and existing data. This diversity of products was only possible because of the resources and effort given to collaborations, both with communication experts and management agencies (especially Parks Australia) for the extensive communication products, and ecologists and taxonomists over many years for the biogeographic products. Consistent approaches, best practice and verified taxonomies are just some of the tools needed to support these long-term collaborations that enable the results from this “voyage to the abyss” to have a far greater and more enduring impact than might be expected from a single marine survey.

This report contains the analyses and results from these objectives and is structured as follows.

Chapter 1: contains descriptions, maps, seafloor imagery and representative animals that were found to occur in the seven Marine Parks surveyed. These samples provide a baseline for understanding how AMPs are distributed with regard to deep sea biogeography.

Chapter 2: describes the novel biodiversity highlights of the voyage across the dominant faunal groups from sponges to fish. Taxonomic investigations are ongoing, but to date the total number of taxa identified is 1061 from 25,661 specimens, predominantly from the 35 beam trawl samples but also including some taxonomic groups from the 28 Brenke sled samples. Of these taxa, only 405 could be assigned scientific names, indicating that up to 60% of the fauna is new to science. This chapter has been submitted for publication in the scientific journal “Marine Biodiversity Records”.

Chapter 3: uses model-based statistics to explore patterns of latitudinal diversity along the east continental margin of Australia at bathyal and abyssal depths. The results indicate that separate faunas occur at each bathymetric layer analysed (~1000, 2500 and 4000 m) and that each of these bathymetric assemblages is separated into a temperate and tropical subgroups. The results are of international significance as this is the first time a temperate-tropical transition has been reported from the deep-sea. This transition occurs despite almost uniform temperature, salinity and dissolved oxygen concentrations occurring across latitudes at these depths. Conversely, the flux of organic matter to the seafloor does vary with latitude, from being relative high in the productive temperate off Tasmania and Bass Strait to low in more-oligotrophic tropical waters, and may drive large scale faunal distribution patterns. This chapter has been submitted for publication in the scientific journal “Deep Sea Research I”.

Chapter 4: uses model-based statistics to analyse the difference in abundance, richness and evenness for lower bathyal and abyssal beam trawl samples from the Great Australian Bight and from off the east Australian margin. The results indicate that samples from off SE Australia have the highest abundance and species richness. These indices are correlated with levels of particulate organic carbon flux to the seafloor, which is higher under the seasonal plankton bloom around Tasmania and Bass Strait. The greater abundance leads to increased species richness. Evenness was most closely associated with the seasonality of net primary production. The samples from the Great Australian Bight were collected north of the enhanced temperate plankton belt and thus do not show elevated abundance or richness. However, they are compositionally distinct from samples from the east coast. Some taxonomic groups, such as sponges, are represented by an almost totally distinct set of species. The lower bathyal and abyssal fauna of the Great Australian Bight is thus compositionally different from other sampled regions. Additional sampling, particularly from off the south-western Australian coast and western Bass Strait, is required to determine the spatial extent of this fauna. This chapter has been submitted for publication in the scientific journal “Diversity and Distributions”.

Appendix A: is a pre-print of a paper published in the scientific journal Nature in January 2019 ¹. This paper combined DNA sequences from animals collected on the IN2017_V03 voyage with a large dataset accumulated for a previous Marine Biodiversity Hub project (on marine phylogenetic endemism) to examine the origin and regional evolutionary trajectory of the marine fauna from Australia to Antarctica. This project focused on brittle stars, a group of echinoderms that are abundant across the seafloors and make an ideal group to research large scale patterns of marine biodiversity. The results show that patterns of diversity in the deep sea (seafloors deeper than 200 m) were profoundly different from those in shallow water. Although the number of species and genetic diversity were much higher in the tropics at all depths, evolution appears to have proceeded differently in shallow and deep seas. Shallow water patterns were like those that occur on land, tropical regions were generating more species than colder areas. This conforms to the well-known theory that higher temperatures increases evolutionary processes. However, the reverse was true for the deep sea. Speciation rates were highest in the coldest region (Antarctica) and lowest in the tropical deep sea.