Does size really matter?

The intertidal zone is one of the most unforgiving marine ecosystems. Waves constantly crash on you, and when the tides are low you are likely to get eaten by voracious predators, stomped on by curious scientists, or fried sunny-side up.

Rocky intertidal shores are also rich in their abundance of invertebrates and seaweeds. If you aren’t out-competed, then you are likely to die from the harsh elements, unless of course you evolved to not only survive but thrive.

Survival and success are dominated by factors including nourishment acquisition, mobility, reproduction, flexibility, and, of course, SIZE!

As I said before, the intertidal is a rough place to live, but many are adapted and thrive in this ecosystem. An organism’s response to wave strength with respect to its size will almost always result in smaller organisms outliving the larger. Not the result you expected, right?

The size of an organism is important in many other ways. Smaller organisms respond to viscous forces more readily than inertial forces, they can create their own feeding currents (barnacles and copepods), and they are less likely to get ripped off a rock by waves. (Don’t forget that the smallest organisms are basal food sources for marine consumers and therefore are very important to the biological success of the ocean).

Big WIN for the little guy!

Barnacles are one of the smallest invertebrate organisms on rocky shores and are still the most efficient at staying on the rocks.

(They can also attach themselves to ships, wharves, and other marine animals)

This graph shows, on a logarithmic scale, how easy it is to remove an object from a rock with respect to the height of a breaking wave.

So, the next time you step on a barnacle, squishing its little crustacean head into the rock, think about how if it could laugh at you when you get swept off the rock by a wave, it probably would.