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Show some positive consequences for wildlife productivity. The multiplicity of GSL ecosystems, lake dynamic interactions and lake level fluctuation makes it difficult for resource managers to detect undesirable changes and determine their causes. Gaps in the information base limit knowledge and understanding of the GSL ecosystem and its many sub- ecosystems. A well- designed monitoring and research program can help improve lake management, evaluate lake impacts and help protect sustainability while still allowing for a wide variety of multiple uses. ( SRC, 1999b and c) Planning Team Ecosystem Health and Salinity Conclusions The planning team has considered concerns regarding declining numbers of brine shrimp in the south arm ( Gilbert Bay). Changes in salinity can change the abundance of brine shrimp ( Stephens, 1998b). Brine shrimp eggs are important consumers of algae and are also an important food source for GSL birds. Brine shrimp are also commercially harvested which complicates an ecosystem analysis. Brine shrimp population studies indicate that lower salinity levels in the south arm are impacting algal community compositions, specifically Dunaliella virdis. These green algae are a major food source for brine shrimp and are being replaced by larger pennate diatoms, which are difficult to digest ( Stephens, 1998b). Reduced salinity appears to contribute to a higher winter loss of brine shrimp cysts, making it difficult for the population to restart when conditions are favorable in the spring. Research studies in 1998- 99 identified this problem. However, other environmental variables may also impact brine shrimp population numbers, and according to the SRC, brine shrimp are not the best indicator of ecosystem health or of the overall condition of the lake ( SRC, 1999c). DNR resource managers are concerned that the south arm of the lake may be trending beyond its natural range of variability due to human- induced impacts to the lake. This concern raises a sustainability issue regarding ecosystem function. The northern railroad causeway has restricted flow between the north and south arms of the lake ( see " Chemistry" and " Hydrology" sections). As resource managers, how should we then evaluate " ecosystem health?" The planning team has considered using brine shrimp as an indicator of ecosystem functioning. The SRC suggest that algae would be a good indicator since they are widespread and trackable in GSL sediments over time, plus are responsive to human- induced and environmental change. Some historical measurements of lake level and salinity are available and, along with future paleolimnological studies ( SRC, 1999c), can be useful to assess the health of GSL ecosystems. An additional method would be to investigate a community or group of species response to ecosystem change, but historical data of this type are very limited. No single species is a reliable indicator of GSL ecosystem condition. The SRC suggests that we should also 107 |