This time of year Antelope Island State Park is crawling with spiders.
Specifically, the western spotted orb weaver. There are thousands, if not millions, covering the island between late July and the beginning of August, estimates Weber State University zoology professor Rebecka Brasso.
While this might not be the place for those with arachnophobia, these critters are an indicator of how much mercury is getting into the food web, like to birds, and also the health of the Great Salt Lake ecosystem.
Every year since 2019, Brasso has collected spiders and tested them to see how much mercury they contain. The mercury, she said, can come from eating the brine flies that are at the lake. Scientists have previously documented that the spiders contain high concentrations of mercury. They’ve also documented the high levels of mercury in the lake. Brasso’s focus with repeating this research is to understand how the concentration in spiders changes from year-to-year. So far she’s found “it really does [change] significantly.”
In the years the lake has been lower, she found lower mercury levels in spiders. In higher water years, the concentrations have been higher. She was expecting the opposite.
Brasso said there’s also a difference between mercury just sitting in the lake and it being converted into an organic form that’s being consumed by brine flies and then other creatures up the food chain. Depending on how much mercury is consumed by birds, Brasso said it can possibly cause brain damage or reproductive problems, like birds laying fewer eggs or fewer of them hatching.
“We also know that a lot of our bird populations are suffering as those lake levels are changing. And so this is an additional stressor that could be causing more harm.”
Bill Johnson, a professor of geology and geophysics at the University of Utah, has worked on research involving mercury and the Great Salt Lake, but is not involved in Brasso’s work.
Year-to-year research on the mercury levels can be helpful, he said, because “you may pick up a variation that happens to match a change in the lake.” He was intrigued by Brasso’s observation of mercury concentration levels being lower in low-lake level years and said it would be interesting to figure out why the connection exists.
While there has been lots of research on the Great Salt Lake ecosystem, Johnson said there are still lots of questions out there, especially as the lake changes.
“Anyone’s study sheds light on a piece of the picture.”