It seemed like a scene from an alien planet on the sands of Dee Why Beach, in Australia.  Hundreds of green sphere-like objects were scattered all over the sand, looking like a horde of aliens left their eggs on the shore.

Some beach-goers reported that the balls were spongy and felt like live algae of some kind, which is probably not far from the truth.

According to Alan Millar, of The Royal Botanic Gardens and Domain Trust, the spheres of algae were most likely 'aegagropilious,' a kind of habitat where living algae forms into balls, rather than attaching themselves to rocks or other hard surfaces.

It is a rare occurrence and it is not known exactly why the algae form into balls.  

Locals who walked the beach everyday said that they had never seen such a sight before in their lives.

The conditions of the sunshine and warm weather brought on by Spring along with rough waves crashing on the beach created the perfect conditions to bring the balls ashore. 

"Obviously these biophysical conditions do not align every spring to produce these balls," Professor Millar said. 

One hypothesis is that, the spherical shape of the habitat, allows the algae to easily roll back into the water before they dry up on the sand.  Other scientists believe that the round shape helps protect the algae from predators.

The unusual presence of the balls on algae on the beach made for impromptu games of soccer and catch with the spheres between beach-goers who found the balls interesting and amusing.  

During another alien-like phenomena just a month previously in Manly Beach, also in Sydney, blue bioluminescent waves made the beach look like it was a scene from a science fiction movie for three nights.

This seemingly magical occurrence was caused by another kind of algae called 'agitated' phytoplankton and it signaled the beginning of spring.