NS Branch meeting 19th MAY 2021
Our theme for May was Rottnest Island. The mini-symposium, Rottnest in an Hour, attracted about 40 people, the largest audience so far this year, no doubt lured by the four experienced presenters – all Rottnest Volunteer Guides and with one exception, Nats members.
Peter Alcock took us through the last 150,000 years of geological history. During this period there have been two very substantial drops in sea level and retreats of the seashore. The first about 140,000 years ago and more recently about 18,000 years ago. In both cases, the sea level was approximately 125-130 metres lower than at the present time. We also learnt that Rottnest only became separated from the mainland around 6,000 years ago when the sea level was about 2.5 metres higher that it is today.
Judith Harvey who has visited Rottnest on numerous occasions each year since she first sailed there as child on her father’s yacht, not only covered the flora of the island, but advised us of the distribution of many of the species on other islands she has visited along our coastline. Pam Ghirardi was in the original batch of trainee guides and 35 years later is still guiding. Pam’s photographic skills were displayed in the many action and sometimes humorous shots of birds she showed us. Graham Ezzy, the organiser of our night and the field trip, finished off the symposium with a short verbal presentation on the marine environment and its inhabitants which includes over 120 species of sub-tropical and tropical fish due to the Leeuwin Current, a colony of Long-nosed Fur Seals and several species of migratory whales. All the speakers provided the 20 or so members and non-members who signed up for the excursion to Rottnest the following week, with valuable information and a considerable list of what to look for when they got there.
NS Branch Field trip 27th MAY 2021
The participants at Rottnest Visitors Centre
Photo credit: Peter Alcock
On Thursday 27th May, 24 of us were met by Graham and Pam at the Rottnest Visitors Centre between 8am and 8.30am, depending on whether we came from Fremantle or Hillarys, and were given until 9:00am to visit the bakery, “a must”, grab a warm drink (there was still a cold wind blowing) and fill our water bottles.
Graham then led us on a walk to Vlamingh’s Lookout. On the way, we paused at the cemetery to hear Pam tell us about the oldest inscription – a duel fought on the island between two friends from Baudin’s ship, Geographe, in 1801, resulted in one being killed. Thirty years later the survivor returned as the master of another ship and asked for a plaque to be erected in memory of his dear friend.
The lookout provided spectacular views of the lakes and vegetation. This enabled Peter to recap the effects of the two large sea level changes as well as the many smaller changes, all of which resulted in the build-up and then erosion of the dunes until the numerous coves and beaches were eventually closed off to form the lakes we see today.
Pam told us to look out for the three characteristic trees or bushes that make up the upper layer of vegetation, the Rottnest Cypress or Pine (Callitris preissii), the Rottnest Tea-tree (Melaleuca lanceolata) and Cheesewood (Pittosporum phylliraeoides). Among our participants was Elizabeth Rippey who more than 30 years ago provided the illustrations for Plants of the Perth Coast and Islands. Elizabeth told us that the stands of tea-tree near the lookout were probably about 100 years old as that is when the island stopped being used as an Aboriginal prison. The prisoners had hunted the quokka to almost extinction which consequently allowed tea-tree seedlings to survive. On our return to the settlement, Leigh, our bus driver, was waiting with the bus we had hired for a tour of the island. Our first stop was Parker Point where Peter pointed out that the high angle of the sloping beds in the Tamala Limestone indicated they are ancient sand dunes.
Our walk from Parker Point to Little Salmon Bay allowed us to examine the numerous plants that make up the lower storey of vegetation. Along the path we found, Prickle Lily, Sharks-tooth Wattle, Rottnest Guichenotia, two Beard-heaths, Coastal Daisy Bush, Grey Saltbush, Berry Saltbush, Fan Flower and masses of Coastal Westringia. At Jeannie’s Lookout, named after Jeannie Lyall a volunteer who helped survey the road, we were able to see three Osprey and one of their nests.
The rocks at Fairbridge Bluff are of world significance and a major geoheritage site. A bed of brain and staghorn coral which grew about 132,000 years Before Present (BP) overlies a fossilised dune system which has been dated as 140,000 years old. The corals indicate a warmer climate and higher sea level. The bed of coral is overlain by a much younger quartz rich dune system deposited only 47,000 BP.
West End has changed for the worse and the better. It now has toilets and a coffee van which takes away the feeling of isolation enjoyed on so many former visits. On the other hand, the raised walking path ensures people are no longer traipsing through the hundreds of Wedge-tailed Shearwater burrows.
Due to the choppy seas, the 20 or so Long-nosed Fur Seals chose to haul out on the rocks in the distance instead of cavorting in the waters below the lookout and the Crested Terns sought shelter on the leeside of the rocks.
Our last stop was at Pink Lake. Its pink colour is caused by the algae, Dunaliella salina, which contains naturally occurring beta-carotene. The pink algae not only make the lake look pink; being the main food source of the brine shrimp, impart their colour to the tiny crustaceans.
Our walk back along the causeway allowed us to examine two samphire species, Tecticornia halocnemoides and Tecticornia indica, some Woody Layered Bracket Fungi, and to catch our first view of the Red-capped Plovers and Ruddy Turnstones.
Graham did a wonderful job in organising the speakers, the itinerary, and keeping us on time. Thanks also to Pam, Peter and Judith for passing on their knowledge. I heard nothing but, GOLLY, that was a good day!
See page 2 for species lists