Below the surface, two divers are taking the first photographs of sea slugs as part of what is to become one of Australia's most successful marine citizen science programs - the Sea Slug Census (SSC).

Commencing in Nelson Bay in December 2013 as a collaboration between scientists from the National Marine Science Centre, NSW Department of Primary Industries (Fisheries) and the group of local divers and naturalists in the Combined Hunter Underwater Group, the SSC has now expanded to cover 12 locations in Australia, two overseas locations (Vanuatu, Indonesia), with additional expressions of interest from across the Indo-Pacific region.

So far, the 2252 participants have photographed a staggering 758 species, with many being undescribed.

The marine habitats within Port Stephens are ideal for sea slugs, a fact that is well known to the thousands of divers who visit the region each year in the hopes of finding and photographing the Bay's marine life.

It was therefore the perfect choice as 'ground zero' for the SSC.

The strong currents and continuous supply of suspended organic materials provide the ideal conditions for growth of habitat-forming species on which sea slugs, and other charismatic species, depend for food and habitat.

To date, we have conducted 26 census events in the Bay and recorded 264 species, many of these at their southern limit of distribution on the Australian east coast.

The ongoing passion for the SSC is such that, even though COVID restrictions led to the cancellation of the formal event in early September, local divers managed to get into the water and continue data collection.

Those who did so were rewarded with some rare sightings including the small, but highly distinctive southern species Polycera janjukia.

This highlights one of the main reasons that the SSC has been so successful - you never know what you might find, which builds excitement and anticipation before every dive, even amongst seasoned local divers.

The SSC program is not only helping to fill gaps in our knowledge of the biology, ecology and distribution of sea slugs but also providing an important opportunity for participants to learn as they participate.

The SSC team generates reports after every event, featuring images of all the species found, allowing participants to familiarise themselves with the local species.

However, the data are also incorporated into scientific publications and, to date, observations by SSC participants have contributed to 12 scientific papers in international journals.

Stephen Smith is a Southern Cross University professor and marine benthic ecologist with a focus on the biodiversity that can be found in marine and estuarine environments.

The September 2021 Sea Slug Census was cancelled due to the COVID-19 lockdown. However, seven local divers still took to the water on September 11-12 and observed 72 sea slugs.

To showcase the Port's incredible underwater world the Examiner is collaborating with regular Bay divers and photographers on a new series that explores life Beneath the Surface.