While the possibility of invasion by friendly green aliens certainly grabs the headlines, what the public had actually witnessed was an unusual natural event: the sudden appearance of balls of living green seaweed.
Seaweeds rarely make sensational headlines unless they wreak havoc, like when the world’s biggest algal bloom choked the sailing course at the Beijing Olympics. Much more appealing, and totally harmless, are these cute green balls that washed up en masse.
While seaweeds are usually fixed to the seafloor, they can grow happily when unattached or drifting in the currents, most famously in the Sargasso Sea where floating brown seaweeds cover a vast area (described by Jules Verne as an “inextricable mass of plants and seaweed” in Twenty Thousand Leagues Under The Sea).
Occasionally, these free-living seaweeds are rolled around by the currents and grow into balls. Seaweed biologists call this growth form aegogropilous – admittedly not quite as catchy as alien eggs.
Using DNA sequencing and reference to herbarium collections, scientists at Macquarie University and the Royal Botanic Gardens, Sydney have identified the algal balls as Chaetomorpha linum, a green seaweed found all around the world, usually growing as dense mat.
Dead seagrass can also roll around to form Neptune’s balls, a common sight in the Mediterranean and used for insulation. Marine scientists in the late 1970s ran some experiments to show that you could make these with some seagrass fibres and a domestic washing machine: three cycles of 10 minutes each will create a nice ball if you want to make one at home!
Living balls of seaweed are rarely seen in the ocean, but balls of green algae from freshwater lakes are popular in the aquarium industry, sold as “moss balls” or marimo. In Japan, a lake where they are found is a site of national significance visited by half a million people annually. The Ainu people hold a three-day festival in their honour and the balls have even inspired a popular cartoon character, Marimokkori. The character’s name is a weird combination of marimo and mokkori – roughly translated as the sound of something rising quickly under cloth. This is why the festival mascot and the well-endowed soft toys are always rather pleased to see you.
In the ocean, drifting seaweeds are not just a novelty item but an important part of the functioning of natural ecosystems, transporting animals and moving food resources between habitats. When they wash onto our sandy beaches, they provide food and habitat for many small invertebrates which are essential food for visiting shore birds. Keeping beaches clean of rotting seaweed is obviously great for swimmers, but it does impact the biodiversity of our coastlines.
Far from being aliens, these algal balls are part of the wonderful natural world around us and show us that the ocean still has the capacity to surprise.