Living on the Edge Chapters 11 Between

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Living on the Edge Chapters 11

Between the Tides

Life on the Edge • We’ve all lived on the edge once in a while, or at least wanted too. • As we will see in the next two chapters, living on the edge isn’t always bad, but isn’t always good either. • Animals near the edge (ANNEs) must endure a hard life. • We’ll focus on edge effect in marine communities.

It’s likely you wouldn’t want to even visit here, let alone live in this place, right? This is technically part of the intertidal zone, an area of shoreline between the high and low tide marks.

This is more like it…Animals basking in the sun, right? Not really, these Periwinkles (Littorina cicta) are battling for survival at low tide. They hold fast to cracks and crevices to retain moisture until tide waters return. Emersion time or time spent out of the water, becomes more and more of an issue the higher in the intertidal zone you get.

Even when you’ve think you’ve got it made, you still risk dessication, or drying out as these chitons (Sypharochiton pelliserpentis) have discovered. Other hazzards, include extreme salinity changes, p. H imbalances, temperature spikes, and predation.

If you have a Spring Tide, one with a large range, then you might find yourself waiting a long time before water returns to your resting spot. Alage often dries out. In contrast, Neap Tides, short range, are much friendlier on some organims…. like these mussels (Mytilus californianus)!

ANNEs survive in other ways too. Coloration is certainly beneficial when you don’t want to be scorched! The ridges in this snail, (Nerita plicata) look nice, but also serve to cool the animal.

Nice waves, eh? Intertidal zones are constantly churning and bubbling. As a result many sessile organism rely on filter feeding and not deposit feeding.

It looks pristine, but wave action is one of the chief concerns of ANNE. As waves approach shore, wave action moves animals in all directions. As a result they hold on any way they can.

Figure 11. 09

Some are underachievers… on surpose! Height exposes you to more wave action and can “littorally” rip you from house and home. oooh…that was bad.

Others, like this sea anemone, Anthopleura xanthogrammica, grow tall in light tidal action, yet grown short and wider when in the rough seas. This limits the forces they must endure. Keeping your feet is a matter of using hold fast (seaweeds) and byssal threads (mussels).

Being flexible is an option as well.

Lets not forget that even in the midst of chaos is…more chaos!! Food webs, prey and predation still apply when your fighting for your life.

Figure 11. 21

Real estate is a hot commodity near the edge. mussels, barnacles, sea limpets, and anemones all compete for space. Often growing right over top other their neighbor in an attempt to crush the competition. Competetive exclusion yet again rears its ugly head!

In an intertidal zone, keystone species are very important to community structure.

Figure 11. 23

Figure 11. 24

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