Polychaete that kills Zoas

[flying4fish]

I've had a thriving Zoa garden for over 5 years. In fact, it was getting to the point where I was thinking I need to get rid of some before they take over my entire reef tank. But over the past few months the zoas have been slowly declining, to the point where most of them are closed most of the time. I have searched and searched for zoa eating nudibranchs and crabs and I've not found anything. Last night I searched with a flashlight and I saw 3 of these light colored, orange-headed polychaetes. I managed to remove two of them with tweezers. I've done quite a bit of searching on the net for examples of worms that kill zoas and I found many posts, but in most cases people dismissed them as a potential problem. I've never seen these before, I found them on my zoas, and I've not found any other obvious culprits. I feel fairly certain these are the problem, and would love to hear if any of you recognize these worms. This picture was taken after it died, and it wasn't this brightly colored in life. It was offwhite with orange coloration on it's head, extending back just a bit from the head. It's about 1.5 inches long and much more stretched out and thin when alive. FYI, I had a 6-line wrasse for many years and it died about 6 months ago. I'm wondering if that wrasse was keeping these worms under control.

 

[World Citizen]

I can't help you, but keep in mind that most worms are atracted to dying fish/corals and rotting flesh. It could be you see them because they just eat the dead stuff.

 

[ISpeakForTheSeas]

It's possible the worms were eating the corals, but it may also just be that the bristles on the worms irritate the coral as the worm crawls over it. Fireworms, for example, are polychaetes that may eat corals (see the quote below).

Yeah, to my knowledge pretty much anything that might be called a fireworm (genera Hermodice and Eurythoe) are coral or other sedentary invertebrate eaters - that said, the way they eat is pretty abnormal:

"Fireworms are voracious predators that feed on soft and hard corals, anemones, and small crustaceans. They engulf the last few centimeters of the tip of a branching coral, such as Acropora cervicornis (staghorn coral), in its inflated pharynx and remove the coral tissue right from the skeleton. They typically spend 5-10 minutes at each branch tip, visiting several, and the “skinned” branches are apparent by their white ends."
Source:

https://www.marinebio.org/species/bearded-fireworms/hermodice-carunculata/

That said, fireworms are opportunistic scavengers that eat pretty much anything they can get, though at least some of them seem to have a strong preference for fish - importantly, they also lack teeth, so they won't be preying actively on any fish in your tank; they have to be able to fit the entire piece they're eating in their mouth.

Tough, armed and omnivorous: Hermodice carunculata (Annelida: Amphinomidae) is prepared for ecological challenges | Journal of the Marine Biological Association of the United Kingdom | Cambridge Core

Tough, armed and omnivorous: Hermodice carunculata (Annelida: Amphinomidae) is prepared for ecological challenges - Volume 97 Issue 5

www.cambridge.org

Foraging and mobility in three species of Aciculata (Annelida: Polychaeta)

Aspects of feeding, such as food capture and ingestion, as well as mobility of the polychaetes...

www.scielo.br

 

[flying4fish]

It's possible the worms were eating the corals, but it may also just be that the bristles on the worms irritate the coral as the worm crawls over it. Fireworms, for example, are polychaetes that may eat corals (see the quote below).

I'm actually an active academic in the marine biology world, with a lot of research articles published during my career. So to be honest, there's not enough data here to make a strong conclusion. But what I can say is that over the past few nights I've removed a number of these polychaetes and for the first time in months my zoas are opening. Some of them are perfectly healthy but a lot of them are ragged around the perimeter, lacking a lot of the fine tentacles on the edge of their polyps. Everything else is thriving in my tank and all parameters are stable and where they should be. But it's still circumstantial. One reason I posted this is to see if anyone has had a similar experience, and if so then some more definitive conclusions can be drawn.

 

[Renaissance corals]

I'm actually an active academic in the marine biology world, with a lot of research articles published during my career. So to be honest, there's not enough data here to make a strong conclusion. But what I can say is that over the past few nights I've removed a number of these polychaetes and for the first time in months my zoas are opening. Some of them are perfectly healthy but a lot of them are ragged around the perimeter, lacking a lot of the fine tentacles on the edge of their polyps. Everything else is thriving in my tank and all parameters are stable and where they should be. But it's still circumstantial. One reason I posted this is to see if anyone has had a similar experience, and if so then some more definitive conclusions can be drawn.

Run an experiment.
Make an isolated system or fuge.
Stock with a single zoa frag with 4 healthy polyps.
Add suspect worms
Wait to see what happens.
Finally please publish findings

 

[flying4fish]

Great idea, but not that simple. To conduct a publishable study you would need to run the experiment with multiple experimental tanks and multiple control tanks. The parameter need to be exactly the same in each tank, with the exception of the worms which are introduced to the experimental tanks (controls don't have worms). After a set amount of time you compare the condition of zoas with and without the worms, run some statistics and then you can publish.

 

[Renaissance corals]

Great idea, but not that simple. To conduct a publishable study you would need to run the experiment with multiple experimental tanks and multiple control tanks. The parameter need to be exactly the same in each tank, with the exception of the worms which are introduced to the experimental tanks (controls don't have worms). After a set amount of time you compare the condition of zoas with and without the worms, run some statistics and then you can publish.

I should have clarified. I meant published to this thread and more like a personal study.

 

[bnord]

seems like your observations are keen, and whether you are right or wrong, a new 6 line or Coris wrasse could help out the colonies..
I keep arrow crabs in the Chaeto sump for polychaete control - though never in my display for some reason