Gulf Coast Fisherman Magazine Vol 39 No 2 - Spring 2015 - Page 28

by John H. Hook The Bay Naturalist SHARING the WEALTH... A 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. 28 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