Sunday, May 29, 2011

Worth the work

A marine invertebrates aquarium needs babying; the ocean the residents come from is a complex environment, always changing, always refreshing itself, always in motion. They won't tolerate stale or quiet water or boring food.

I have a routine; I check and adjust the water pump daily, check the temperature and lighting, and add an appropriate amount of foodstuffs, taking care to vary the diet as much as possible. Every second day, I clean the filter, replace about an eighth of the water with fresh sea water, and remove large chunks of leftovers. As needed, I re-arrange or replace the plantings and playground equipment (large curvy shells, clumps of barnacles and/or mussels, stones); the crabs are constantly uprooting, tunneling, rock-flipping, sometimes to their own disadvantage.

Tiny hermit up a eel-grass and sea lettuce "tree".  All the ambulatory critters love these.

At least once a month, I call it low-tide day*; drain out most of the water, remove the animals and seaweeds, scrub the algae off the inner walls, and rinse the sand beneath. The first rinse water comes out thick with decaying plant matter. I always have to check it carefully and run it through a filter (coffee) to see if any of my critters got washed out with it. There are usually a few amphipods and plenty of copepods. Barnacle and anemone food, on the hoof. I put them in clean water and return them to the tank when I'm done.

Some of the animals, yesterday, refused to leave the filter. They ran around the bottom, holding on, not swimming like amphipods do. They were almost transparent, and too small to see clearly; what I was seeing was the way the light glinted off their wet bodies. I had to swish them around in the water to dislodge them, then shake the filter to get them out. Interesting.

But I was busy, so I set them aside until the aquarium was full again, and then poured them all in.

Later, my work finished, I was checking the leftover rinse water before I dumped it, and another of these beasties turned up in the filter. This time, I went for the magnifying glass. And it was a hermit crab! I've never seen one so tiny.

Newborn greenmark hermit, not wearing a shell  yet. About 2 mm. long.

I had noticed some mating behaviour in the tank, earlier. Male hermit crabs choose a female, and hold onto her, sometimes for days, until she consents to mate.** I'd seen a couple of adult greenmarks dragging occupied shells around; it's springtime, after all. But I never expected anything to come out of it, not in my small tank. But here they were; a whole family of baby hermits!

Green shore crab with rider.

Here's a tiny one, walking on the pincer of a green shore crab. I saw this guy for the first time last week, and wondered how he got here. Now I think I know. He's much bigger than yesterday's babies already.

"Got my eye on you." Greenmark hermit with the crab's eye in the background. The crab is about 1/2 inch across the shell.

*I know; the ocean does it twice daily. I'm not an ocean.
**See two previous posts on mating hermits: "A friend for Boy Blue" and "Little Bo-Peep is fast asleep".


  1. Awwww! I hope they can all find enough tiny shells to slip into.

  2. Good reminder: I have a collection of miniature shells. I'll put some in the tank for them, just in case.

  3. Well done! Sounds like you've earned it, that tank is hard work!

  4. Wow. Well this is somewhat magical, eh? So interesting and surprising and enchanting. SO glad you're so careful and observant. Thanks for sharing!! =)

  5. Congratulations! It's a a a hermit crab!
    Really. It seems like you're flying without a parachute - resource material - and making a lot of wonderful discoveries along the way.

  6. JSK, Yes, you're right. It does feel like flying without the chute.


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