From: BShrimp@aol.com
To: brine-l@uga.cc.uga.edu
DIATOM BLOOMING AT GREAT SALT LAKE
All evidence points to the Artemia nauplii as being a "nondiscriminate particulate feeder". This exact discussion is underway now here at the Great Salt Lake wherein the primary productivity is dominated by a pennate diatom that, except in its juvenile stages is too large for Artemia nauplii to ingest. The usual dominate algal species, Dunaliella, has been overwhelmed by these diatoms.
If Artemia ingest an algal species such as a Coccochloris sp they will excrete the cells live without digesting them. The fecel matter is a pellet. At the GSL there are tremendous quantities of oolitic sands which primarily consist of a brine shrimp fecal pellet surrounded by calcium carbonate, making a very "egg" shaped grain of sand.
Howard W. Newman
Excerpts from article by J. Wolf in the "Salt Lake Tribune":
Scientists speaking Saturday at a public forum on the lake, sponsored by Friends of the Great Salt Lake, sad the well-documented drop in brine shrimp numbers is linked to declining salinity of the lake as a result of recent wet weather. This has triggered dramatic changes in the shrimp's food supply.
Doyle Stephens, a research hydrologist for the U.S. Geological Survey, said the salinity level of the lake in 1995 was 14 percent. Today it is about 10.5 percent. While that may not sound like a lot, he noted it is the difference between fresh water and the ocean.
Back when the salinity level was 14 percent, Stephens said, the lake was filled with tiny green algae. They are just the right size to be eaten by young brine shrimp and have soft cell walls easily punctured by the toothless jaws of tiny crustaceans. He compared green algae to marshmallows and said brine shrimp were thriving on them.
But as salinity level dropped over the past three years, green algae were replaced by several types of diatoms - another type of algae. They are much larger than green algae and are protected by a tough cell wall.
Young brine shrimp seen unable to feed on the diatoms, leading to a dramatic drop in their numbers.
Gary Belovsky, a professor at Utah State University, said experiments show green algae algae are most prolific at salinity levels around 14 percent. Their numbers decline rapidly at salinity levels above and below that point.
The downward trend in brine shrimp numbers first was noted last fall when so few cysts were counted that Utah Division of Wildlife Resources biologists canceled the annual brine shrimp harvest after 4.5 million pounds of cysts were skimmed off the lake's surface. That was far below the record harvest of 14.7 million pounds the previous two years.
Belovsky said researchers don't know if those years of heavy brine shrimp harvests contributed to the decline, but stressed the main cause of the drop appears to be related to salinity.
The Great Salt lake produces 90% of the world's brine shrimp cysts. The largest customers are prawn farmers in Thailand, China, Indonesia and Ecuador who use brine shrimp as a food supplement.
Changes in brine shrimp numbers could have significant impacts on dozens of species of birds that stop at the Great Salt Lake during their annual migration, said Joel Flory, a biologist for the Utah Division of Wildlife Resources.