Tuesday, June 23, 2009

Underwater menu

I found a dead mussel in my dishpan aquarium yesterday morning. Dead, empty, cleaned out; not a morsel of mussel flesh left. One of the whelks is probably still digesting it.

The assorted other animals in the water get along nicely with each other. The isopods, limpets and periwinkles graze on the algae; the barnacles, anenomes and clams strain plankton out of the water; the crabs clean up the trash. But the whelks eat mussels and barnacles.

So white, so angelic, so bloodthirsty.

Whelk, showing white flesh and orange operculum.

I've been watching them; they settle on a mussel or a clump of barnacles and stay put, boring through the shell. The largest mussels are most at risk; a couple of little ones wander through the tops of the seaweed, where the snails can't reach them. The barnacles, stuck on the rocks, aren't so fortunate. A couple of days ago, three snails were working together on the largest barnacle, which now stays closed up, whether dead, anethesized, or trying to protect itself, I don't know.

A Nature Coast Marine Group (Australia) page gives a general timetable:
When feeding the whelk crawls onto the barnacle, tubeworm or shellfish and drills a hole in the calcium carbonate covering of its prey. In the case of barnacles, whelks usually attack the doors that open to allow the animal to feed. The whelk releases an acid from a gland in the front part of its foot. This softens the calcium carbonate which is then licked away by the rasp-like tongue (radula) of the whelk. When a hole has been made in the prey the whelk inserts its tube-like mouthpart into the victim and, with its radula, tears off and eats the soft tissues.

... It takes 30-40 minutes for each application of the acid then about a minute of rasping before the process is repeated. The whelk takes about 8 hours to penetrate a shell 2mm thick and can take up to 4 days to get into a larger barnacle.

My poor barnacles!

These miniature snails don't bother even the tiny barnacles: they are algae eaters.

Sitka periwinkles.

This one may have been a young Amphissa. It's just over 4mm. long. It would have been eating dead algae and other detritus.

I saw this next snail first crawling upside down on the undersurface of the water, suctioned on just as a larger snail would attach itself to a rock. It crossed the whole dishpan this way. Here it has moved to a leaf of sea lettuce.

Another algae eater.

These are a couple more residents of the mini-ecosystem: I'm not sure what they are, but I would guess some type of sponge. Alive or dead, I don't know, but they seem to provide housing for some of the smaller shrimpy things.

A yellowish, branched spongy substance, with random tunnels.

And a more rounded, purply sponge, with one hole in each "branch".

This long worm was travelling through the eelgrass and seaweed. It's a polychaete, with bristles on each foot, and a carnivore, like the whelks. It's probably eating the tiny, hair-like red worms that live in the sand.

Click on the photo to see the head structure.

And, since I don't have any starfish (nor gulls), nothing eats the clams.


1 comment:

  1. Thanks for all the observations!


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