Friday, October 26, 2007
Friday: The Missing Thursday Pics Arrive
Time and the tides wait for no man ... not even FC. I wanted these pics to be in Thursday's post because we had just enjoyed a full moon.
As you know, full and new moons give us our strongest tides of the month. These are the Spring tides. On a spring tide, we have our highest highs and our lowest lows. The name comes from a Nordic word, "springen" which means to jump up. It has nothing to do with the seasons as these are monthly events.
The opposite monthly tides are called Neap (pronounced "nip") tides, but they are weak and uninteresting.
A spring tide is an amazing thing, caused by a straight line arrangement of sun ---earth---moon.
Instead of working against each other, this arrangement allows the sun and moon to accentuate the bulge of water formed by the spinning of the earth.
That's the same arrangement that gives us beautiful full moons and mysteriously absent new moons.
If you're a feeder in the intertidal zone, the tides control when you get to eat. The fiddlers in the top pic don't feed much when the tide is up. They're either nervously wringing their chelipeds in some burrow, hoping a drum or ray doesn't suck them out, or they're hiding in the spartina grass hoping the shore birds eat their neighbor and not them.
It's tough being a small crab ... especially if that Survivor Man guy shows up on your beach.
For the egrets and other shorebirds, low tide is dinner time and a spring tide exposes even more "table" for them to use. The snowy above is chasing killifish in a tide pool left by the retreating tide. Killifish are amazingly well adapted to being left behind. I have stuck a thermometer in a tiny washtub sized tide pool on a summer day and measured the water at 100 degrees F, but the killi's in it are doing just fine. Plus, they have the ability to duck under the mud in a puddle like that and hide from wading birds. Gotta love such toughness.
Low tide concentrates food and allows access to both trapped fish and buried treats like polychaete worms, mollusks, fiddlers, and other subterranean inverts.
Of course the tide doesn't really "go out" or "come in". What's really happening is that your part of this amazing planet is spinning away from the bulge (tide is falling) or into the bulge (tide is coming in).
All tides are a important and wonderful, but spring tides are just more so. Tides flush nutrients in and out of coastal waters, disperse young and eggs to new habitats, and reshape shorelines over time. Imagine a world without them.
For the fiddlers, the changing tides mean changing predators ... fish and larger crabs beneath the high tides, shore birds during low tides.
For nerdy ocean oriented primates like me, spring tides offer challenges to navigation as bottom suddenly appears where there is normally enough water for Summer School to skim along. I have gotten out and pulled the boat behind me like Bogie more than once.
Low spring tides are fun to explore as they open up usually hidden areas to the curious.
That would be me ...
... and you.
The tides shaped that beautiful oyster bar above.
Here's a question for you.
Is the tide rising or falling in that picture?
Remember to support your answer or no credit.