Friday, January 15, 2021

Roaming anemones: an experiment

A month ago, I posted a photo of a hermit crab wearing an anemone on his shell. In the comments, Tim wondered how long a hermit had to sit still for an anemone to climb on board. I decided to do some experimentation.

Pink-tipped green anemones on broken moon snail shell. Dec., 2019

I scraped 8 small anemones off the wall of the aquarium, or off smooth shells (smooth, so as not to damage the anemones more than necessary), and placed them in a tray with shells nearby, then watched what they did.

Third batch: two pink-tipped, and one tiny (these are all tiny) orange-striped green anemone.

I put one pink-tipped down almost touching a shell. The other, I set beside a stone. Now watch:

Larger anemone expanding its base.

And moving away from the stone.

The anemones move by slowly expanding and shrinking. And they had definite preferences.

Medium anemone has chosen a different shell. Large one has cemented itself to the tray. So has the tiny orange-striped.

On one trial, an anemone managed to select a shell and glue itself down in 10 minutes. Another took 15 minutes. The slowest (one of the tiny orange-striped ones) took the better part of an hour. Average time, in 10 trials, about 40 minutes.

The largest of the anemones attached itself to the tray twice. Each time, I scraped it off and let it try again. It took longer on the second try; probably had a sore foot. The third time, instead of leaving it free, I dropped it inside a shell. It glued itself down quickly this time.

Loose in the shell, all hunkered down. Tired of this harassment.

An hour and a bit later, recovered, happy, feeding.

I noticed that the smaller pink-tipped anemones relocated and glued themselves down faster, possibly because I did less damage to them scraping them off their perches in the tank.

The orange-tipped green anemone, still upside-down after almost an hour, not bothered, it seems. In the tank they float around and attach themselves to everything; walls, shells, crabs, seaweeds, sand. Both of the ones I tried out took their time at settling.

Hermit crabs often sit still for long periods of time. Sleeping? Or just contemplating the universe? I don't know, but it's definitely enough time for a roaming anemone to move in.

Thanks for the idea, Tim!


Hace un mes, subí una foto de un cangrejo ermitaño que llevaba en su concha una anémona. En los comentarios, Tim se preguntaba cuánto tiempo tomaría una anémona en adherirse a un ermitaño. Decidí hacer unos experimentos.

Desprendí 8 anémonas de las paredes y conchas más o menos lisas en el acuario, y los sumergí en agua limpia en una charola. A su lado, añadí unas conchas. Luego, con el reloj a la mano, observé los resultados.

Segunda foto: dos anémonas Anthopleura elegantissima, y unapequeña (como lo son todas estas) Diadumene lineata. Una de las dos la coloqué junto a una concha; la otra está cerca de una piedra. Ahora, mira lo que hacen:

Fotos 3, 4, 5: La más grande estira su base, y se aleja de la piedra, inflando y contrayéndose alternativamente.

Y tienen sus propias ideas de donde quieren ir. La mediana, escogió la concha que yo había dejado al lado. La grande se pegó al fondo de la charola. La desprendí, y se volvió a adherir otra vez al fondo.

En una de las pruebas una de las anémonas logró adherirse dentro de 10 minutos. Otra tomó 15. La más lenta (una de las miniaturas) tardó casi una hora. El tiempo promedio, en 10 pruebas fue de aproximadamente 40 minutos.

La que se pegó al fondo dos veces tomó más tiempo en la segunda prueba. Probablemente tendría un poco de malestar en la base, por haber sido desprendido dos veces. La tercera vez la puse dentro de una concha para asegurar que no tendría que despegarla otra vez. Allí, se estableció muy pronto. (Fotos 6 y 7.) Dentro de una hora, ya estaba abierta, feliz.

Noté que entre más pequeñas las anémonas Anthopleura, las que tienen los tentáculos color de rosa, más rapidamente se establecen, tal vez porque les hice menos daño al desprenderlas.

Foto #8: La pequeña Diadumene l., después de casi una hora, todavía volteada, pata arriba, sin preocuparse, parece. En el acuario, flotan y se adhieren a todo; las paredes, conchas, cangrejos, algas marinas, hasta la arena. Las dos que incluí en este experimento tomaron su  tiempo en asentarse.

Los cangrejos ermitaños muchas veces se quedan quietos por un buen tiempo. ¿Dormidos? ¿O contemplando el universo? Quien sabe, pero esto da más que suficiente tiempo para que una anémona peripatética se les adjunte.

¡Gracias por la idea, Tim!


  1. Haha, cute experiment, and so considerate of you about not hurting their feet. Maybe the hermit had temporarily deserted its shell while trying on a new one, and the anemone took that as an opportunity to hitch a ride? Very fascinating. It would be fun to see a time-lapse of how the anemones move about the tank.

    1. Interesting idea! I'll have to think about how to do it.

    2. Does your camera have an intervalometer? That might be the easiest way, especially if your camera battery/memory card won't last long enough to do a long multi-hour video. I have old equipment, so I bought an external intervalometer that plugs into the remote trigger of my SLR.

    3. I don't have one of those. I think my camera has some sort of timer, though. I'll have to re-read the manual. Or if not, I'll look into the intervalometers. Thanks!
      The main difficulty, though, is setting up a situation inside the tank, where the anemones will stay within the camera's range, unless I'm working with one of the larger anemones, so can back off a bit. Some planning to do!


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