Miles Tangaroa under the sea 2

A DTIS image of the deep seafloor (433 m) off the Northern Victoria Land coast, home to a range of large sponge colonies. Photo: Miles Lamare (Otago University), Sadie Mills (NIWA) and Steve George (NIWA).

Case study: Filter-feeding sponges as eDNA traps to monitor marine biodiversity baselines and change

21 July 2023

Antarctic Science Platform researchers have contributed to the development of a new environmental monitoring technique using filter-feeding sponges as natural environmental DNA (eDNA) samplers. This technique has been successfully demonstrated to monitor the marine biodiversity and biogeography in the Antarctic and Southern Ocean and to identify changes. This new approach will support the monitoring ambitions of the Ross Sea region Marine Protected Area.

Ongoing data collection and monitoring is a key component of sound environmental management, but Antarctica is vast, and its ecosystems are complex. Biological sampling in coastal and marine environments requires boats, helicopters, planes, equipment to drill holes in the ice, specially-trained divers…and a lot of good luck ­— cooperative weather and sea-ice conditions are critical to enable safe site access.

Traditional population and biodiversity surveys rely on visual observations (e.g., photographs, video) and physical sample collection, which are time and cost intensive, as well as destructive to the environment (e.g., bottom trawling). Recently, eDNA techniques have been revolutionising how researchers monitor the marine biome. This molecular method takes advance of the fragments of genetic material (e.g. skin cells, waste products) organisms shed as they move through an environment. These minute traces of DNA can be collected from water, air and soil samples to reveal a snapshot of who is present in an ecosystem.

In this way, scientists can use eDNA to assess temporal and spatial biological diversity patterns, track endangered or rare species, and detect invasive species. Over time, eDNA can also be used to determine how environmental change affects population biodiversity and their geographic range.

Four sponges Ian Hawes

Examples of Antarctic sponges, clockwise from top left: Mycale acerate (Tera Nova Bay), Sphaerotylus antarcticus, Glass sponge – Anoxycalis joubini, Homaxinella balfourensis (Cape Armitage). Photos: Ian Hawes

In the Antarctic, the use of eDNA to monitor the vast marine ecosystem is a relatively new offering. Researchers are currently optimizing the methodology for successful implementation into the Southern Ocean’s harsh environment, including looking for ways to minimise the time required to be in the field for sample collection. Currently, scientists filter seawater to concentrate the eDNA to levels suitable for detection, usually by using a vacuum pump or manual filtration using a syringe. While these processes are effective, they take a long time, potentially leading to eDNA degradation, and require specialist equipment.

Our researchers are exploring the use of filter-feeding Antarctic sponges as eDNA traps to inform biodiversity surveys. To feed, sponges can filter up to 900 times their volume of seawater daily. This strategy means sponges also naturally accumulate eDNA from the surrounding ecosystem.

During COVID, when researchers couldn’t access Antarctic field sites, the focus was on analysis of eDNA in archived sponge samples (collected during past field seasons) and new deep-water sponges collected by fishing boats in the Southern Ocean. On the 2023 Tangaroa voyage, we gathered new information on shallow ecosystems and collected complimentary eDNA water and sponge samples from along the Northern Victoria Land coastline.

Miles Tangaroa under the sea 1

The seafloor off Cape Hallett Peninsula, with diverse marine life at a depth of 100m. The photo, showing about 1m2 in area, was taken using NIWA’s towed imaging system (DTIS) and shows the sponges, soft coral, ascidians seastars and crinoids that cover the sea floor. Photo: Miles Lamare (Otago University), Sadie Mills (NIWA), Steve George (NIWA)

ASP researchers, together with collaborators, have shown that:

  • The technique is accurate: eDNA signals obtained from water samples and marine sponges are capable to provide new information on spatial biodiversity patterns in Antarctica.
  • Sponge bycatch specimens could aid fish monitoring: eDNA analysis of marine sponge specimens caught as bycatch capture a more complete picture of the fish diversity in the Ross Sea compared to catch records and are able to estimate regional fish catch abundances.
  • Sponge eDNA traps capture population change over time: Analysis of historic and recent samples show changes in ecosystem biodiversity and the geographic range of individual species.
  • This method for sampling marine ecosystems could support large-scale eDNA surveys of coastal Antarctica. eDNA monitoring is a useful tool, to be used together with a toolbox of complementary techniques, for building a picture of Antarctic’s biodiversity and biogeography – past, present and future.

This Case Study was prepared as part of the Platform’s annual reporting to MBIE for the 2022-2023 year. It illustrates how filter-feeding sponges are natural eDNA samplers, and thus can be used to monitor marine biodiversity in the Antarctic.

Contributors: Miles Lamare, Gert-Jan Jeunen