Marine biodiversity - more than meets the eye

A common seastar, Diplasterias brucei, amongst a complex mix of epifaunal species including sponges and polychaete fan worms near Davis station
A common seastar, Diplasterias brucei, amongst a complex mix of epifaunal species including sponges and polychaete fan worms near Davis station. (Photo: TNE Dive team)
Mix of soft sediment and hard substrate in O’Brien Bay near Casey station, with starfish and sponges visible in the sedimentAn ostracod, Philomedes charcoti - a small, sediment dwelling crustacean

New research combining traditional taxonomy with DNA technology has found that Antarctic marine communities are more biologically diverse than previously thought.

Few organisms brave the rare, exposed rocky sections of Antarctica’s coastline, but just a few metres below the ocean’s surface, diverse and colourful marine communities thrive throughout the year.

Epifaunal habitats – hard, rocky substrates – support a profusion of colourful marine life, including groups that are common inhabitants of rocky reefs the world over; sea urchins, starfish, sponges, seaweeds, sea cucumbers and a multitude of other critters. Infaunal habitats – soft sediments such as mud and sand – support an abundance of small species. These are less well known and mostly just a few millimetres long, but present in large numbers – thousands to more than 100 000 individuals per square metre.

Infaunal communities are widely used as biological indicators of the health of marine environments. These dynamic communities thrive in surprisingly stable environmental conditions, which vary relatively little throughout the year; a constant −1.8oC water temperature and low current, wave and wind action due to sea ice cover that can last for 10 months or more each year.

The Terrestrial and Nearshore Ecosystems group at the Australian Antarctic Division has been sampling these communities for various purposes since the mid-1990s. Using traditional taxonomic methods combined with genetic techniques we have identified over 530 species of infaunal and epifaunal invertebrates from nearshore habitats (to 30 m depth) around Casey and Davis stations. This effort represents perhaps the most intensive and long-term sampling to date of shallow coastal marine habitats in East Antarctica; an area that is relatively poorly sampled compared to other coastal Antarctic regions.

Ongoing work to curate this valuable collection of reference specimens has involved identifications by taxonomists in Australia and overseas, as well as the sequencing of DNA identity markers. This work has uncovered new species and, potentially, a new genus, each separated from one another in remarkably subtle ways.

A prime example is the unanticipated diversity uncovered for a critter that is relatively featureless to the untrained eye. Ostracods are small (mostly 1–2 mm across), somewhat unremarkable crustaceans, whose hinged shells superficially resemble bivalve molluscs. Very fine details separate species; details not always obvious even to ecologists that work with them regularly. Taxonomic work on what we thought was a single species, Philomedes charcoti, has revealed four other Philomedes species, differentiated from each other by fine shell details and the number of bristles on their legs and antennae. Even more surprising was the presence of five potentially new and undescribed species, as well as a new Ostracod genus, in the same samples. Such diversity, hidden until now, suggests far greater diversity may be uncovered as taxonomic and genetic work continues and future sampling explores a wider variety of habitat types.

The proximity of these marine communities to coastal Antarctic stations makes them vulnerable to local and global impacts and useful systems in which to monitor natural and human induced ecological change. Continuing work to describe, identify and catalogue the nearshore marine invertebrates of East Antarctica is fundamental to this monitoring work and to efforts to remediate past impacts from human activities. Both traditional taxonomy and current and evolving genetic techniques will be key to understanding, protecting and conserving Antarctic marine biodiversity and to fully realising their potential as indicators of global issues, such as climate change and ocean acidification.

Glenn Johnstone, Jonny Stark and Felicity McEnnulty
Australian Antarctic Division