Marrawah, at the northern end of Tasmania’s west coast, the furthest town from Hobart (491 km) on the island, is best known for huge swells and waves breaking from an ocean uninterrupted between Argentina and Tasmania, and for the remarkable Preminghana (Mount Cameron West) Aboriginal petroglyphs.
For a botanist, these landscapes translate to habitat for bull kelp (Durvillaea potatorum), along the high-energy rocky coastlines, and refuge for the last population of endangered cliffdwelling daisy Craspedia preminghana in the Preminghana Indigenous Protected Area. Driving south from Marrawah, the spectacle of bull kelp hanging out to dry presents a strange image for a species that grows tethered to rocky platforms and floats in an ocean buffeted by waves and currents. The life of Earth-bound trees, only tethered by their roots, but essentially floating in air buffeted by winds and storms might be better interpreted by simile with the bull kelp’s reality.
The first scientific description of bull kelp was by French botanist Jacques Labillardière during Admiral Antoine Bruni d’Entrecasteaux’s search for Lapérouse’s ill-fated expedition that disappeared after leaving Botany Bay in 1788.
Labillardière perhaps collected the type specimen at Recherche Bay in the south-east of Tasmania in 1793. Bull kelp’s broad, shiny, golden-brown, gelatinous and leathery fronds and constant motion amongst heavy surf breaking on rocky coasts make it one of the most conspicuous and spectacular of plants (although many contemporary botanists would argue that brown algae aren’t, technically, plants). Bull kelp grows to 12 metres long and to 75 kg wet weight, although even larger specimens of up to 200 kg have been reported. Labillardière observed the use of the broad fronds by Tasmanian Aboriginal people to make substantial containers for carrying water – the specific name potatorum comes from the Latin ‘of the drinkers’ – these kelp water containers are still made today by contemporary Tasmanian Aboriginal artists such as Verna Nichols.
While the drying racks at Marrawah Kelp Pty Ltd might qualify as a contemporary art installation, their purpose is commercial – here the cast kelp, washed up on local beaches, is collected, dried and prepared for NatraSol products utilised for stock and plant feed supplements.
The major Australian producer on King Island exports granulated bull kelp to Norway and Scotland for alginate extraction – sodium alginate extracted from brown seaweeds are the gels referenced as E401 in the food industry and widely utilised as a gelling agent in jelly, ice cream, soup and even the pimento or red pepper filling in stuffed olives. Alginates also have broad application in textile printing, pharmaceuticals (such as the common antacid Reckitt Benckiser’s Gaviscon), for chelating and removing certain radioactive isotopes from the body, and even for dental impressions.
While less widely consumed unprocessed, the NatraSol website provides recipes for pickling kelp, and for ‘kelp chicken delight’ – perhaps on the menu for my next holiday in the south-east of Tasmania. Local cattle are inclined to avoid to the middle-man and are happy to feed on fresh kelp on beaches or when brought to them.
In South Australia, the Chinese company Gather Great Ocean Group (GGOG) signed a contract in late 2013 to purchase Australian Kelp Products at Beachport, which held the only commercial licence for kelp harvest in South Australia. GGOG is currently working in partnership with Flinders University’s Centre for Marine Bioproducts Development to explore the potential for higher value compounds in seaweeds. The diversity of South Australia’s seaweeds, the rich collection in the State Herbarium and the remarkable history of phycological research in Adelaide is another story.
Bull kelp is endemic to the exposed rocky coasts of south-eastern Australia from Robe to southern NSW, Victoria and Tasmania including Bass Strait islands. Alan Millar, the phycologist (seaweed specialist) from the Royal Botanic Gardens Sydney, observes that the distribution of bull kelp has already retreated 50 km south since 1940 from New South Wales towards Victoria. He attributes the move primarily to rising sea temperatures.
Bull kelp is distinct from the famed giant kelp. While bull kelp is the most impressive seaweed from the shore, the giant kelp, Macrocystis pyrifera, is the foundation species for the celebrated giant kelp marine forests – forests essentially defined by this species anchored at depths beyond eight metres. These giant kelp forests occur primarily along the east and south coastlines of Tasmania extending to coastal waters of northern and western Tasmania, as well as to south-eastern mainland Australia as far west as Margaret Bock Reef near Robe (and at depths of up to 35 m), and as far east as Gabo Island in Victoria.
The size and number of giant kelp marine forests have dramatically declined over the past 30 years largely as a result of rising sea temperatures.
The impacts of other changes in marine ecology require further research. For example, the long-spined sea-urchin decimating giant kelp creates extensive sea-urchin ‘barrens’ on Tasmanian coasts. The sea urchins may have extended their range from mainland Australia to Tasmania due to rising sea temperatures, or they may previously have been controlled by higher populations of southern rock lobsters.
Wonders such as the bull kelp and the giant kelp forests deserve our attention – Douglas Adams and Mark Carwardine’s admirable pilgrimage in search of charismatic endangered animals was retraced by Stephen Fry and Mark Carwardine 20 years later in 2008/09. These Last Chance to See BBC radio, film and books are compelling narratives.
The plants that provide the foundations of all ecosystems deserve a similar pilgrimage to draw attention to their plight – the bull kelp and the giant kelp should be high on the itinerary. Last chance to see?
Stephen Forbes is the Director at the Botanic Gardens of South Australia.
Originally published in The Adelaide Review, 29 January 2015.