Intertidal organisms 2 – animals

Considering the difficult environmental challenges of survival in the intertidal zone, there is an amazing abundance and diversity of animals living there. There are vast numbers of the common periwinkle Littorina littoria (above), which graze on the algae.

Here’s another herbivore, the Baltic isopod Idotea baltica. Not the greatest of photos, but these things are fast!

Sea urchins also feed on the algae. The gulls had already gotten to this specimen, Strongylocentrotus droebachiensis:

Sand dollars are closely related to the sea urchins, and are algal and detritus feeders. Tim found this specimen, Echinarachnius parma:

Sessile filter feeders are also abundant (they also often preserve well as fossils). We didn’t see huge numbers of live blue mussels (Mytilus edulis), but their empty shells were common. Here’s an isolated live example:

There were, however, vast numbers of barnacles of several species. There are at least two shown here. I believe the small barnacles are Balanus improvisus, while the large ones might be Semibalanus balanoides (barnacles tend to grow tall when they’re overcrowded):

Barnacles are filter-feeding crustaceans, which use their appendages into the water to capture food. They close up at low tide to avoid drying out (or being eaten), so usually you don’t see anything except the closed shell. That’s why I was pretty excited about this video that Brett was able to shoot of feeding barnacles in a tidal pool:

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2 Responses to Intertidal organisms 2 – animals

  1. Doug says:

    I remember going out to Montana de Oro in 3rd grade an looking at tide pool critters. Found this monster red crab! Did you guys see any hermit crabs? Those things are so neat!

  2. Alton Dooley says:

    No hermit crabs, and in fact very few crabs of any kind. There were lots other arthropods (barnacles, isopods, and some tiny, fast-moving critter – maybe a beach flea). Unfortunately, no starfish either. The general abundance seems to be lower than the (admittedly small number) of places I’ve been on the California coast. There were huge numbers of barnacles in places (especially the sand bar at bar harbor), but mussels seemed to be much less common than at Monterey Bay. Of course, a lack of mussels could help explain the lack of starfish. I was also suprised that I didn’t see any goose barnacles.

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