Sunday, January 04, 2015

Welcoming committee

For New Year's Day, I posted a photo of a brand new, freshly hatched, pinhead-sized Leafy Hornmouth snail, just starting out on his adventure. This is the backstory.

It started with the small kelp holdfast I brought back from the beach in November. It came with its own cargo of crabs and worms and starfish, but there was a small blank space on the inner side of the clamshell; here, the pair of big snails* in my tank chose to anchor their latest batch of egg cases.

The inner side of the clamshell, as it is today. Much-nibbled-on kelp "roots", and the egg cases at the bottom.

The first of the baby snails started to emerge from the cases a couple of weeks ago. I was on hand to photograph the "birth". So were some other observers, with more ominous intentions.

Three open egg cases. The siphon tip of the latest baby peeks out the exit hole of one.

Several snails hatching at once, at the beginning of the escape. Several egg cases still have their plug in the escape hatch. (Top two on the left, for example.) But look carefully at the background!


Waiting for dinner to be served. Flatworms are always hungry!

There were two flatworms, both very tiny, as flatworms go, humongous in relation to baby snails. One was green; I'd seen it before, but this purplish one has only showed up for the hatching, and has never been seen before or since.

The smallest of the black-clawed crabs, still living in the holdfast.

Against the back wall of the clamshell, too tiny to see without a lens, I found a colony of green anemones. Looking again later, I saw that one had a snail in its mouth.

Watch the holdfast for a couple of minutes, and somewhere among the roots, a worm will poke out his head. There are a dozen or so living here.

Polychaete in his tunnel made of a glued fold in sea lettuce. Tiny, but those jaws will gape as wide as the belly of the beast.

Out searching for food. The tail never leaves the burrow, but he can stretch the full width and height of the holdfast colony.

The brittle stars seem to have disappeared, which would be a relief to the snail parents, if they were of the type to fuss over their offspring. The other two stars have been deported to the shore where they came from, for crimes against snaility. (They were eating the tank cleanup crew; they would have had these babies for appetizers.)

Mortality rates are high in the intertidal zone, especially for the young. One of those egg cases would have started out with about 50 eggs; less than half would survive to hatch. And of the hatchlings, depending on where they emerge and the predator load, anywhere from 50% to 99% will die within the first few weeks.

Observations in San Juan Islands, Washington show that a newly hatched N. lamellosa (Related to my leafies - me) has a 1-2% chance to reach 3mo of age.  An individual reaching 3mo has a 35% chance to reach 1yr of age.  Older, larger, individuals have a 40-60% chance to survive through subsequent years.  Spight 1975 Oikos 26: 9. (From A Snail's Odyssey)

My baby snails, those that made it past the welcoming committee, hurried out of the holdfast to hide in the sand.

On his way.

Zooming in. Siphon to the left, leading the way. Within a few seconds, he had ballooned off the holdfast root, washed away in the current to a "safer" place.

Even out of the holdfast, there are dangers. Hermit crabs. Even the tiny hermit crabs. Shore crabs. Anemones everywhere. Any of these will relish a tender baby snail hors d'oeuvre. The ballooning snail burrowed down into the sand as quickly as he could.

But there are worms down there.

Three times, I've seen a baby on the glass, high above the sand, out of reach of all but the climbing hermits. Good choice. They may survive.

Infant snail, above the water line, surrounded by his own body bubble. Taken through the glass, against the light, which shines through the yellow button at the tip, and shows the ridges on the shell. The dark spot is the operculum, which closes the shell when the snail is resting.

*The parents were Mike and Tillie, Leafy Hornmouth snails (Ceratostoma foliatum). They have since been returned to their home beach, since my visits to the winter shores weren't providing enough juicy barnacles to keep them fed in the tank.



4 comments:

  1. What an interesting series of shots and descriptions. I knew it was tough out in nature, but that's amazing. - Margy

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  2. Judy Fournier8:00 pm

    Please don't overlook the polychaetes. I can't identify them properly from your photographs. The large polychaete in the shelly tube in the first photograph is probably an Onuphid. The smaller polychaete in the leafy tube looks like Platynereis bicanaliculata.. one of my favourites.

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  3. Thank you, Judy! I've been trying to get a good look at these very small, very active polychaetes, so that I can make a stab at identification. There are at least two different species in the holdfast and the seaweed they have glued next to it.

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  4. I knew it was a rough life for hatchlings, but not that bad... You get some amazing shots, even if your models are tiny!

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