Camera catches reef-building worms in the act
Researchers in Australia have discovered that a common marine worm works in the dark, gathering together lumps of coral to build its home, which may explain how reefs can initially establish amid shifting sands.
John Chisholm, previously of the Australian Institute of Marine Science, and now of Observatoire Océanologique Européen, Monaco, and Russell Kelley of Watermark films in Townsville, Queensland, used infrared illumination to capture the curious nightly excursions of the worm in an ornamental aquarium. Their work is reported in this week's Nature.
"It was a completely serendipitous observation," Kelley told ABC Science Online. "We'd all gone away on holiday and when we came back we found the corals in John's aquarium had started dying."
Kelley says that all that remained were fragments of the coral (Lobophyllia hemprichii) scattered across the floor of the aquarium.
And it's then that they noticed the strangest thing. Overnight, the fragments of coral appeared to move themselves, becoming attached to a piece of reef rock in the aquarium.
Removing and replanting corals in the aquarium bottom simply resulted in a repeat performance the following night. This happened 21 times over a one-month period, even when the researchers changed the reef rock's position.
"We hypothesised that the corals were moving themselves and we set up recording equipment to try and catch what we thought was new coral behaviour," says Kelley.
|A time-series of five images captured using infrared illumination which shows the worm constructing a coral reef in the aquarium (Pic copyright: J. Chisolm/R. Kelley)|
"Less than one hour after darkness, the head and upper body of a bootlace-thick eunicid worm appeared from a hole in the rock. The worm sought out a coral and dragged it to the reef rock in less than two seconds."
After hauling coral fragments over distances of up to 16 centimetres, the eunicid worm would firmly glue them onto its reef rock home.
"We know worms are present in marine environments everywhere and we should be looking more at what happens after dark," Kelley says. "Because biology doesn't stop out of office hours."
The researchers argue that in the general marine environment, larger worms -- reaching up to 2 metres in length -- could be responsible for building stable patches on unstable soft sediments.
"By creating these patches, the worm provides a raised three-dimensional structure, a colonising surface for the larvae of other animals to settle upon, and this in turn provides shelter and food for the worm," says Kelley. "In shallow tropical environments these patches could serve to initiate the development of reefs."
"This observation is an example of how a biological community can be self-organising and helps explain why seafloor communities are patchy or clumpy -- a universal feature of the marine environment."
He says similar worms are found in the fossil record extending back to the middle Cambrian period, approximately 500 million years ago, so they may have had a role in reef development since that time.