Welcome to Wonderful Waterful Thursday! WWT as I like to call it is the extra special blog post that follows what would otherwise have been Wonderful Waterful Wednesday, if I hadn’t spent an extra five hours waiting in Baltimore-Washington Airport for a flight to California…

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What is a “Sometimes Ocean”?

If you’ve ever visited the shore and poked among the rocks, you’ve seen them: shallow puddles on the edge of the sea, cut off from the great Mother Ocean for hours, even days at a time. They’re tidepools of course, and a whole host of organisms have become adapted to living in them.

Some of the marine creatures common to tidepools in North America are sea stars and urchins, snails, barnacles, and crabs. And of course various kinds of seaweed or algae thrive in tidepools, providing all important cover and shade for the creatures who live there.

Living on the Edge

Life in a tidepool is a study in extremes. Temperatures rise and fall over the course of the day. Salinity too. A water evaporates the pool itself can shrink and at times disappear. Considering that conditions are relatively constant in the open ocean, these kinds of conditions are pretty unusual for marine creatures.

And while they may seem idyllic, dangers lurk in those placid little ponds. In the sea, there’s lots of space to flee and find food. Not so in a tidepool, where you’re trapped until the next high tide, which can be hours or days away. Some parts of the intertidal zone (the area between the high and low tide levels) are only submerged at the highest of high tides, while other areas are only uncovered during the lowest of the low.

The Whys of Tides

The rise and fall of the tides is caused by the gravitational pull of the sun and the moon on the oceans. When all three celestial bodies are arranged in a line (called syzygy), we get spring tides, which are higher and lower than usual. Quadrature is when the sun, Earth and moon form a right angle. This occurs during the quarter phases/half moons. The tidal range is smallest at this time – the highs are lower than

Every shoreline has its typical tidal range determined by the shape of the basin and where on Earth it’s located. In some areas the range can be as little as a few inches a day; in others many feet. The Bay of Fundy in Nova Scotia holds the record for the largest range: more than 53 feet during a spring tide!

Most coasts have semi-diurnal (twice daily) tides, but a few shores experience only a single cycle.

Tidepooling at its Best

Rocky shores like those found in New England and the Pacific Northwest are my favorite places to explore. I have a very clear memory of holding a sea cucumber given to me by a park ranger in Acadia National Park in Maine. My dream of becoming a marine biologist was cemented that day.

I also saved a couple of sea urchins from a grim fate as souvenirs, but that’s another story.

Marine Mammals Poster Giveaway

This month’s giveaway is an out-of-print NOAA poster of Marine Mammals of the Western Hemisphere. Every comment left in the month of May equals one entry. Every link or reference to this blog on your site equals two entries. The drawing will be held on the 1st of May, so start your entries now!

Have you ever held a prickly sea star, caught sight of a crab scuttling through a tidepool forest, discovered a sea star clinging to the underside of a wet rock? Share your tidepool discoveries – and any other fond seaside memories – in the comments section below!

Danielle Meitiv is an oceanographer by training, an advocate for all things marine and a writer of science fiction and non-fiction. Danielle is also a huge fan and sales affiliate for Holly Lisle’s online courses: How to Think Sideways: Career Survival School for Writers, and How to Revise Your Novel. Follow @Danielle_Meitiv on Twitter, and on Facebook: Brave Blue Words, and Danielle Meitiv.