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, pH
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