Handy Joe's Crab Den

Handy Joe's Crab Den is a tide pool of about 21 square meters, or approximately 200 square feet. Located in the midintertidal zone, just southeast of the High Intertide Pool, at low tide the den averages about 18 cm or 7 inches in depth.
Much of the pool is covered with surf grass, and many of the large rocks have rockweed (Fucus) growing along their sides. With abundant plant cover and numerous rocks throughout the pool, Handy Joe's is an ideal setting for crabs. If you move some surf grass or lift a rock, you're almost certain to see a hermit crab, huddled in a snail shell or other cover, scurrying about the bottom of the pool. Larger crustaceans, such as red crabs and helmet crabs, may also be found beneath rocks or in crevices that edge the pool.
All organisms that live in tide pools must withstand great changes in their environment. As the ocean rises and falls twice a day, tide pools vary in temperature and salinity, and local residents have to learn to adapt to these changes. In the course of a day, the salinity may rise from 29.5 parts per thousand (ppt) to 36 ppt. Temperatures also fluctuate, from 11 degrees C to 16 degrees in early July. Using a temperature data logger, we collected 48 hours of temperature fluctuations in the pond:

The arrival of the tide is punctuated by a drop in temperature, and during the summer a gradual warming follows after the tide subsides. These fluctuations are substantial, but they are not as severe as the changes that affect the rocks surrounding the pool. The animals on exposed rock are subject to changes in temperature and must resist desiccation when exposed to the sun and air.  Tide pools in the midintertidal typically harbor abundant and diverse animal life, in part because they are isolated from strong surges and predators that reside in the subtidal zones.
To get an idea of just how much diversity can be found in a small area of this pond, we used a quadrant (a measured square, in our case 0.25 square meters or just over 3 square feet) to count the number of animals in the center of the pond. We found:
500 spiral tube worms (Spirorbis spp.)
15 limpets (Patellacea)
7 hermit crabs (Pagurus spp.)
4 bryozoan colonies (Membranipora membranacea)
2 acorn barnacles (Semibalanus cariosus)
2 top-shell snails (Calliostoma spp.)
1 isopod (Isopoda)
1 clam worm (Nereis virens)
1 dogwinkle (Nucella sp.)
1 bread-crumb sponge (Halichondria panacea)
1 decorator crab (Oregonia gracilis)
1 hairy chiton (Mopalia sp.)

With so many species at Handy Joe's, it's clear why tide pools have been so important in the ecology of shoreline areas. Ecologists have studied basic principles of competition and predation in these areas for decades. As in any community, there are antagonisms and alliances. Many species have developed strong defenses against invaders or would-be predators.

Looking at a kelp blade, one might see a roughened patch.  This is actually a colonial organism, a bryozoan, with hundreds of genetically identical units, or zooids.  If one zooid dies, the colony can replace it.  And if the lophophores, which resemble little palm trees, are under threat, all the zooids will retract simultaneously, to avoid further attack.

There are more conventional forms of protection here: spiral tube worms, helmet crabs, and barnacles use calcareous plates to fend off attack. This armor is strong enough to repel many hungry predators. But sometimes, the best defense is a strong offense, and though crabs will almost never attack if unprovoked, a curious finger placed too close to waiting claws will prompt a viscous nut-cracker squeeze from the large front claws, or chelipeds.

Though the barnacle can protect itself from wave action and many predators with its hard calcium carbonate shell, it still falls prey to the small whelk, Nucella. This marine snail that can drill a hole through hard barnacle shell plates using its radulla, a toothlike structure made of chitin. Once the hole is complete Nucella secretes a toxin which stuns the barnacle. The snail then inserts its proboscis between the plates and sucks the guts right out of the shell.

Species you might find while visiting Handy Joe's Crab Den include:



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