Bizarre marine crop circles and an unknown culprit

Over 25 years ago, Japanese divers made a miraculous discovery: crop circles on the sandy ocean floor. They were large, ringed circles with a dappled centre of fine sand particles and coral artfully arranged around the edges. In 2011, these creations were finally attributed to a white-spotted pufferfish. However recently, similar sand patterns were found off the coast of Western Australia. 

No one has been able to identify the white-spotted puffer. The plot thickens.

Last month, researchers from the University of Western Australia were surveying an offshore oil field with a robotic underwater car. They found 22 of these crop circles in water over 100 metres deeper than those found in Japan. Whilst it is suspected that these can also be attributed to pufferfish, being unable to find white-spotted puffers is making scientists buzz at the possibility of a new species.

Whilst they look pretty cool, I can’t help but ask myself why? Why are these little fish compelled to make such intricate 2 metre wide sandy patterns? Like most animal behaviours, the answer lies in evolutionary behaviour and reproduction. It’s a nest!

https://www.youtube.com/watch?v=hpdlQae5wP8

Observations have determined that male pufferfish take 9 days to build them, using their body and fins to shovel sand. Whilst the shovelling is hard work, the longest part of the process is the decoration phase. Males collect shells and coral fragments from nearby. This is strikingly similar to how bowerbird males collect blue items for their nest, or a male peacock boast their feathers. The more impressive the nest, the greater the chance of a female mating with them. Once eggs have spawned, the male cares for them and allows the nest to slowly disassemble with water flow. After the eggs hatch, the process is repeated, starting from scratch.

This is only one example of the remarkably complex and dynamic behaviours of fish, and some scientists are now advocating for further research into fish nesting and the similarity to birds. Just like birds, the ability to build a nest and care for offspring successfully makes a fish evolutionarily fit and a popular choice under natural selection. With the quality of design and construction under scrutiny by females, the process becomes remarkably competitive.

Of course, there are also significant differences between fish and birds in how and why they make their nests. Whilst we don’t know who these crop circle nest builders in Western Australia are, future research looks exciting as ecology biologists dive deep into the fundamentals of nesting and how animals engineer their environment. 

References

Barber, I. (2013). The Evolutionary Ecology of Nest Construction: Insight from Recent Fish Studies. Avian Biology Research, 6(2), 83–98. https://doi.org/10.3184/175815513X13609538379947

Bond, T, Mueller, RJ, Birt, MJ, et al. (2020) Mystery pufferfish create elaborate circular nests at mesophotic depths in Australia. J Fish Biol. 1– 7. https://doi.org.ezproxy1.library.usyd.edu.au/10.1111/jfb.14506

Kawase, H., Okata, Y. & Ito, K. (2013) Role of Huge Geometric Circular Structures in the Reproduction of a Marine Pufferfish. Sci Rep 3, 2106. https://doi.org/10.1038/srep02106

Smith, N. (2020). Mysterious pufferfish circles discovered in Australia’s north-west. The University of Western Australia. Retrieved from https://www.uwa.edu.au/news/Article/2020/September/Mystery-pufferfish-circles-discovered-in-Australia-north-west