Essays

Moseying: Exploring the Natural World

The pluvial ecosystem of a salina
October 31, 2020

"Everything is connected." Ecology is about relationships. All along the shores of every salina (salt lake) pocket gopher mounds can be found. Pocket gophers eat vegetation (usually starting with the roots, and then the stems which they pull down into their burrow tunnels. Vegetation around a salina is usually succulent, because plants that grow in high pH soils have physiological characteristics that illustrate  adaptions to the salty soil.  Pocket gophers  seem to be able to adjust to a salt laden diet (but until a university student does a master's or doctorate project on salt and pocket gopher diet, we will not know how they do so, or if there is a long term cost to the pocket gopher.)

(You can learn more about succulent plant physiology on this web page.)

During a recent Llano Estacado Master Naturalist field trip to a salina, a tiger salamander was found mostly hidden in the soft powdery soil of a pocket gopher mound. Pocket gophers create extensive tunnel systems. Researchers at the Texas Tech University have discovered over forty species of animals that take advantage of the underground complex provided by pocket gophers. Most merely use the tunnels to hide away from dryness, light, or heat. Besides salamanders, snakes, lizards, spiders, beetles, crickets and other invertebrates  were found by the Tech researchers. The pocket gopher does not bother them, and only the larger snakes (like bullsnakes and kingsnakes) would bother the pocket gophers.

The salamander population might have a higher density in the tunnel systems near the salina, for the group of naturalists discovered that millions of damselfly and dragonfly larvae had left the water of the lake and come on shore to climb up on every available plant stem. Some sticks had larval husks stacked several deep.  After finding the right spot, each larvae then molted, becoming an adult odonate (dragonfly or damselfly.) With such incredible mass emergences of easily caught food, the salamanders could gorge themselves on the slow moving larvae before they climbed out of reach.

Since a salina does not fill at the same time every year (they fill only after a major rain event, and it may be a year or more between fillings) the mass emergence of the odonates is not temperature or day length dependent. This leads to the next question -- What would else cause a mass emergence? Could it be when the fresh rainwater that filled the salina finally reaches a certain salinity level, as the lake dries up? When we asked experts, neither Dr. John Abbott of the University of Texas or Dr. Nancy McIntyre of Texas Tech thought so, and reported there had been studies done.

The freshwater in the salina is at first turbid with soil washed in from the surrounding landscape, and over time, the silt settles, and the water becomes clear. Various species of algae begin to grow in the underwater silt, including several species that are plant like in form, with long stems and "leaves."  This dense algal mat provides a great habitat for the larval odonates, and they feed on the billions of brine shrimp that hatched from eggs laying on the salina floor, as well as other micro invertebrates that  appear in algal mats.  These algal mats are eventually left high and dry, forming black crusts. 

Other invertebrates are present, too. Brine flies (sometimes by the billions) breed in the wet soil and drying algal mats. Tiger beetles are also found along the shore of a salina, sometimes in impressive numbers. Their larvae live in short tunnels and have large pincers that grab anything that walks over the hole, including odonate larvae. The adults will also kill the smaller odonate larvae.

When a salina fills, waterbirds also appear. Egrets and ibis work the shores -- the egrets eating the odonates and the salamanders, while the ibis eat the brine shrimp, odonate larvae, and can dig the tiger beetle larvae out of the wet sand with their long curved beaks.  Walking along the shore long enough, an observer can usually end up finding feather piles of both the egrets and ibis. Coyotes, foxes, mountain lions, and bobcats visit a filled salina, knowing that a filled salina means several months of incredible biomass production and the chance for food becomes much easier. If it is winter, the coyotes have a chance at catching the thousands of sandhill cranes that come to a filled salina during the coldest months, too.

A pluvial ecosystem (an ecosystem that only occurs after a major rain event) is a rare and wonderful thing to witness!