Gulf Coast Fisherman Magazine Vol 39 No 2 - Spring 2015 | Page 28
by John H. Hook
The Bay Naturalist
ll living things depend on
energy to survive and thrive.
Trout, reds and flounder get
their energy from baitfish and shellfish.
Those baitfish get it from smaller
crustaceans and baitfish who got it from
yet even smaller critters. Go down the
chain far enough and you find something
capturing solar energy by photo-synthesis.
The secret to how many fish of how
many kinds that we have in any bay
system, or any ecosystem for that matter,
is tied to how much energy enters via
photosynthesis. A smaller amount might
be imported, but bays are solar energy
driven machines. Up to a point, or unless
something strange is going on, the more
photosynthesis that’s happening in the
bay, the more fish we have to chase.
Which fish are there is determined
by other factors, but the poundage of fish,
(biomass to marine scientists),
completely depends on photosynthesis
by plants and algae. They need access
to sunlight, water, nutrients and carbon
dioxide in order to maximize the energy
in the bay. There is plenty of most of
that stuff, so the thing that limits how
many fish we have is having a steady
supply of nutrient filled freshwater
coming from land.
Some systems depend more on plant
and algae species attached to the bottom
of shallow bays to maximize energy and
that usually happens when there isn’t
much freshwater entering, like what
happens in the Laguna Madre. In those
cases, nutrients are gathered from muddy
bottoms by seagrasses and water is
usually clear. Bays in the northern Gulf
get lots of freshwater from rivers
delivering nutrients gathered inland.
Tiny algae, phytoplankton, are the
beneficiaries here and do astounding
amounts of photosynthesis. Galveston
Bay may not boast crystal clear flats, but
those turbid waters are teeming with life
thanks to all the river delivered nutrients.
GULF COAST FISHERMAN
Regardless of how much energy enters
a bay, it has to be distributed. Biologists
look at spreading that energy in a number
of ways, but it starts with its vertical
movement from those photosynthesizers up
through the biggest bay predators.
Transferring energy is a sloppy process. As
a very general rule, ninety percent of
available energy never makes it to the next
higher level. It gets dissipated as waste or
moves into decomposers, but from our
perspective it’s just lost.
A pyramid is usually used to illustrate
this but it is an inaccurate picture. A
wedding cake with each layer being a tenth
the size of the one below would be better.
Redfish that ate crabs that ate shrimp that
ate seaweed would only get one thousandth
of the energy that was originally converted
by seaweed! If it seems that we have
hundreds of times more veggie-eating
mullet than redfish, that’s why.
The other perspective on energy flow
is how it is shared within one of those
levels. Here you have all sorts of species
competing for a very limited resource and
it’s very definitely a fish-eat-fish world.
Competition drives specializatio