Beneath the waves of Nelson Bay this weekend a band of divers will search the seabed on a now-familiar neon Easter egg hunt for the 15th Sea Slug Census.

The seasonal slug survey began as a way for divers and Southern Cross University researchers to track the bay's marine life, and confirmed Port Stephens as a hub for 250 species of the nudibranch variety of sea slug.

Nembrotha rosannulata.

The slugs' fever dream patterns have filled volunteers' underwater lenses with a saturation of colour and silent, strange behaviours.

Slugs can be hot pink or burnt orange, polka dot with lilac frills, armed with cruel blue spikes or plump and frosted like desserts.