Finding the vultures of the sea

Image: Niel Bruce

Niel Bruce from the Museum of Tropical Queensland in Townsville – a campus of the Queensland Museum – has been on Lizard Island to study the "diverse" crustacean group, the isopods.

This is Niel's fourth trip to Lizard Island, this time as part of the CReefs project.

He specialises in isopod taxonomy and crustacean systematics and has been on the island to collect samples, record data and do the taxonomic work involved in finding new species of the crustacean.

"We currently have really big gaps in the knowledge about isopods; very little is known about the biology of some species. Around 1,000 marine species from Australia are known so far (about 5,000 world wide); 300 of those are from Queensland," Niel said.

"In two days of collecting I've got around 45 species. Of those, there are about 10 are species that not yet been described. I'm trying for maximum diversity for the expedition," he said.

Most isopods are small, growing between only two and 10 millimetres, but some giant isopods, or Bathynomus, have been found to have grown to half a metre.  

There is, though, one particular group that is most famous, or more appropriately "infamous": those species named cymothoids.

These little isopods live parasitically on fish and eat off their tongues, essentially replacing the tongue by attaching to the host's mouth, hence their common name, the "tongue biter".
"The parasites on crustacea are permanently fixed to the hosts," Niel said.
Some isopods are predators, some strong scavengers feeding on dead fish and some are parasitic, burrowing into the flesh of live fish.

"The scavenger latches on and starts to eat its way in, they can actually switch to anaerobic respiration for a short time," Niel said.
Niel has been collecting dead coral and rubble around the island to survey the free-living isopods.
"I love to get out and see the animals myself. At the moment I'm collecting a 20 litre bucket of rubble per dive or snorkel. From one of the buckets alone, I got 22 species of isopod," he said.
Although little is known about their predators, fish seem to be one of the main animals to eat isopods.

Isopods could be seen as the "vultures of the sea"; Niel said. They are a very important part of the food chain, as the fish that die are eaten by isopods.
Niel said that one of the greatest things about studying a little known crustacean is that there is a "great element of discovery and new knowledge".
Niel enjoys the "problem-solving" aspect of the taxonomy and that fact that little is so far known about them.
"When you study isopods you discover new families, new genera – your scale of discovery is very high and you can set the standard for the whole world," he said.
Niel said isopods are also interesting because they can be a monitor of the environment. The abundance of isopods can be indicative of the health of the area.
"It's a simple premise that by the time the bigger animals start to disappear, like the fish and the birds, the damage is done. It's the little things that are really sensitive to habitat disturbance," he said.