We began diving in the Mooloolah River estuary (Sunshine Coast, Queensland, Australia) in January 2019 and mainly focused on Nudibranchs, but there are so many amazing creatures in the river that we just had to share them all with you.

This is muck diving at its best - sometimes the visibility is crystal clear with critters everywhere, other days we have 1 meter visibility and a ton of silt. Below are some divers searching for nudibranchs and an aerial shot of the Mooloolah River estuary with the red line marking the roughly 400 meter area where we dive. Worldwide there are about 3000 known species of Nudibranchs of which roughly 33% have been seen on the Sunshine Coast of Australia. New species are discovered here all the time.

Nudibranchs are a group of soft-bodied, marine gastropod mollusks which shed their shells after their larval stage. Nudibranchs are often casually called sea slugs. A pair of rhinophores on the Nudibranch's head have scent receptors that allow the Nudibranch to smell its food or other Nudibranchs. Most Nudibranchs have the ability to withdraw the rhinophores and gills and hide them if the Nudibranch senses danger. They are carnivorous, so their prey includes sponges, coral, anemones, hydroids, barnacles, fish eggs, sea slugs, and other Nudibranchs.

Nudibranchs are hermaphroditic, thus have a set of reproductive organs for both sexes, but they cannot fertilize themselves. Nudibranchs typically deposit their eggs within a gelatinous spiral, which is often described as looking like a ribbon. The number of eggs can vary from as few as just 1 or 2 eggs or as many as an estimated 25 million. The eggs contain toxins from sea sponges as a means of deterring predators.