The Bay Behind the House

As a student of local stuff like geography, I decided to write about a stinky old muddy bay. One of the more interesting geologic formations in the US is the Lower Laguna Madre Bay near South Padre Island, Texas. It is the only hyper-saline bay system in the US, at least from what I’ve learned so far. In theory, the environment would be so harsh that nothing could live. However, from Port Mansfield down to the town of South Padre Island, there are more fish per acre than about anywhere. It is trout and redfish heaven, with reports of catching over 100 per day not uncommon. What’s the deal?

Cyanobacteria.



OK, that’s a mouthful but think back in school when they said that the simplest cell that could make photosynthesis was “blue-green algae.” Gosh, this turns out to be a complete misnomer, because cyanobacteria are simple bacteria, not algae. It is present in most waters but down here in the Laguna Madre it is the ruler of the ecosystem. The nice thing about cyanobacteria is that is can convert nasty things such as ammonia and nitrate into nitrogen and oxygen. The nitrogen is “fixed” so aquatic plants can use it and the oxygen is dissolved so fish can breathe it. When oxygen gets low the fish start dying, as has been recently seen to the north of our area. But we have our cyanobacteria. We don’t have that fish-kill problem except during heavy freezes or during red tide.

The only bummer is that the boogers form dense mats of their stuff, some of which dies and some of which is eaten. The result: black nasty mud. The more I learn about this the more gross and complex it seems. The black sediment forms a layer under which other chemical reactions occur to release stinky sulfur compounds, which is why low tide usually smells so bad.

But back to the story, the cyanobacteria are even more important because the average depth of the Laguna Madre is only about two feet. The entire bay system is over 30 miles long and varies between several hundred yards and three miles wide. Except for a few shipping channels and dredge spoil islands, it is almost flat as a table. A truly remarkable landscape, I intend to keep studying it. Some fish for dinner would be good, too!