"Look for stromatolites in Rotto's strange lakes" Rottnest Island Things to Do Tip by CatherineReichardt
Rottnest Island Things to Do: 134 reviews and 234 photos
Just one look at the map of Rotto will indicate to you that it's not just your average desert island. The coast is a fretwork of bays, coves and headlands, and a significant proportion of the interior is occupied by a series of lakes, of which Lakes Bagdad, Herschel, Vincent, Serpentine and Government House are the most prominent.
However, in this sort of environment, be careful not to equate 'lake' with 'fresh water' - indeed, the absence of reliable fresh water supplies has imposed a considerable constraint to Rotto's development in the past (to the point where much of Rotto's water supply today comes from the reverse osmosis of salt water). The lakes are saline because Rotto has a much higher rate of evaporation than rainfall. Thus, water in the lakes becomes increasingly more saline as water vapour evaporates, leaving behind the dissolved salts, and in times past, salt has been commercially harvested on Rotto. As a result, Rotto's lakes have developed very specialised ecosystems of brine-tolerant plants and animals.
Salt concentrations in these lakes vary according to season, with the water reaching maximum salinity at the end of the summer season and rainfall during the winter period (during which coastal Western Australia receives its rainfall) diluting the salts in these lakes.
Natural science buffs will be excited to hear is that Rotto is home to some stromatolite communities. Boffins will know that these are the communities of blue/green algae (technically known as cyanobacteria) that form odd mound shaped structures that are particularly prominent in the early fossil record. Their significance is that they were the first organisms on earth to photosynthesise and release oxygen into the atmosphere way back in the Pre Cambrian, thus paving the way for an oxygen-rich atmosphere and the dawn of life as we know it.
There are a few sites around Western Australia which have stromatolite communities - notably Shark Bay - but Rotto is by far the most easily accessible. The visibility of the stromatolites varies with season, and obviously they're easier to see towards the end of summer when the water levels are lower. The best places to see them are around the fringes of Serpentine and Government House Lakes - see the website below for more detail on this.
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