Seagull Lake, Western Eyre Peninsula, South Australia: A Saline Lake to Benefit from Climate Change?

Abstract

As a result of climate change, salt lakes on Eyre Peninsula are predicted to have shorter hydroperiods. Already there are salinity increases due to land use changes, so major decreases in biodiversity are expected. The likely situation is different however for the few lakes receiving waters via marine springs, with Seagull Lake, 20 km south of Streaky Bay, the best example. It has been thoroughly surveyed as a base to assess future changes. This lake originated about 6000 years ago as a marine bay, since occluded by coastal dunes. Its waters are a balance between meteoric sources, groundwater and marine water via springs with seasonal fluctuations due to input variations and evaporation. A conceptual model closely matched field observations. Presently the main lake varied in salinity seasonally from 75 to 200 g/L, with the spring virtually constant at 37–40 g/L. Plants in the lake and its palustrine margins numbered 25 species arranged into 18 floristic associations. Of particular interest are the marine alga Acetabularia peniculus in the floodout lakelet from the spring, the vulnerable shrub Tecticornia flabelliformis at limited suitable habitat locations on the lake floor margins and the alga Achanthes breviceps in the soaks on beach rock. Invertebrates number 37 species, of which 17 are marine, confined to the springs, including two cnidarians, two polychaetes, four crustaceans and eight molluscs. The lake itself supports a few widespread continental saline species, and other freshwater-derived invertebrates in the peripheral lakelets. A fish, Leptatherina presbyteroides, lives permanently in the main spring and spreads to the lake in winter. Thirty-nine species of birds have been seen on the lake including regular species like the Banded Stilt, Red-capped Plover and Red-necked Stint. Sea Gulls and Fairy Terns breed on the lake islands. We postulate that with decreased rainfall and sea level rise, the marine springs will deliver more water to the lake, making it permanent and of lower salinity. But ultimately with evaporation of these new waters, the lake will eventually become a salt flat. Plant distribution will be severely disrupted, with the palustrine herblands moving landwards, Sarcocornia quinqueflora likely to overwhelm the vulnerable Tecticornia flabelliformis, and Zostera? mucronata of the spring expanding its domain initially but ultimately retreating back to the spring. Invertebrate and bird diversity will initially increase, but as the lake becomes a salt flat diversity will finally decrease towards zero.