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Show Research must continue to understand the dynamics of algal populations in the lake and how brine shrimp populations relate to the changes in salinity. Brine shrimp populations diminish when salinities are low and evidence thus far suggests that forage is a cause. The current salinity levels of the north arm are too high for many species of algae. In a 1975- 78 study which found 29 species of algae living in the lake, the authors reported only two in the north arm. " The findings of ( their) study reveal that significant alterations have occurred in the algal flora of the GSL since the construction of the Southern Pacific Railroad Causeway ( northern railroad causeway). The migration of dissolved minerals from the south arm into the north arm has reduced the salinity in the southern areas of the lake to the point where viable diatom flora and species of algae previously unknown to the lake have become established. Also the abundance and frequency of occurrence of previous reported algal species has been significantly altered". ( Felix and Rushforth, 1979.) Brine Shrimp Brine shrimp ( Artemia franciscana) are found in all portions of GSL. Their occurrence is related to salinity levels and other environmental conditions. The annual life cycle of brine shrimp begins in early spring. Freshwater inflows to the lake from snowmelt and increasing water temperatures initiate egg ( cyst) hatching in late January or early February. Hatching peaks in March or early April. Decreasing lake water salinity from freshwater inflow is an important mechanism in the hatching process. The cysts survive the winter in a semi- dehydrated state. When salinities decline, the cysts rehydrate, causing the shell to swell and crack, which allows the nauplii to emerge. As they mature, brine shrimp molt through as many as 12 different stages before they become adults and begin reproducing. Brine shrimp reproduce by two methods. During the spring and summer many females give birth to live young that are hatched from eggs within their bodies. The other reproductive mechanism involves the formation of hard- walled eggs which are cast into the water by the female. These cysts must then go through a period of dormancy before they hatch. Both of these mechanisms occur throughout the summer, although the birth of live young is more prevalent. In the fall, factors such as the lack of quality food, declining water temperature, decreasing day length and increasing salinity trigger the females to start producing primarily cysts. As many as three generations of shrimp may be produced in GSL during a single growing season. When water temperatures decline below 5° C ( 42° F), live brine shrimp perish. No adult brine shrimp survive the winter. The population is restarted from the cysts which persisted over winter either floating on the lake's surface or deposited on the beaches. As the lake rises in the spring due to inflow, some of the cysts which washed up on the shore during the winter may end up back in the lake. Commercial harvesting of brine shrimp began in 1950 when adult brine shrimp were harvested for tropical fish food. Several years afterward, cysts were first harvested because they could be dried, packaged, and stored for long periods of time. The eggs could then be hatched as needed. Presently, only cysts are targeted by the harvest operations but there is a small market for the adult brine shrimp 70 |
