What Coral Reefs tell us about Climate Change
This week, Anjani Ganase, marine biologist, shares new knowledge about Australia’s Great Barrier Reef. With a relatively newer history, Caribbean reefs and first peoples may have information important to survival on our islands; it’s time to observe and research our own environment and record the traditional stories. This feature was first published in the Tobago Newsday, on Thursday November 3, 2016.
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The Great Barrier Reef (GBR), one of the largest natural structures on planet Earth, is visible from space. This natural wonder is about 2300 km long and 344 400 km2 in area, larger than the UK, Switzerland and The Netherlands combined. It is one of the most diverse ecosystems in the world, home to as many as 6000 marine organisms, including species of corals, invertebrates, fish, marine mammals, sharks and turtles. The reef is also ancient, over 500,000 years old; over this time the edge of Australia’s continental shelf and the reef connected to it has changed with the fluctuating levels of the sea.
|View of a section of the Southern Great Barrier Reef taken by satellite. The barrier reef marks the coastline of Australia during the last glacial maximum. Image source: NASA/GSFC/LaRC/JPL, MISR Team.|
Although the modern Great Barrier Reef is roughly 20,000 years old, the first scientific observations of this reef were only a couple hundred years old, and in this time marine scientists have uncovered a wealth of knowledge about the ecosystems that lay beneath the waters. The advent of underwater diving technology has served to record marine life. With satellite imaging we are able to record the Earth’s changes even underwater. Today, we are able to observe and assess changes in the coral reef community patterns and health of the Great Barrier Reef over time; we can even predict how we affect the reef in the future. However, this story is not about the present, but the past, the beginning of the time when man first made observations of the Great Barrier Reef.
Although Captain James Cook takes the credit for discovering the Great Barrier Reef in 1770, he only stumbled upon the reef when the Endeavour ran aground near Cape Tribulation in the northern part of the GBR. He was sailing his ship along the eastern coastline of Australia, unaware of the barrier reef located to the east. Years later, the naturalist Charles Darwin, carried out scientific exploration of coral reefs from aboard the H.M.S Beagle but for some reason he did not focus his efforts on the GBR. Instead he concentrated his learning on the many other coral reef islands and atolls in the Indian and Pacific Oceans. He classified coral reefs based on their structural formations – atolls, barrier and fringing reef – and theorised on the formation of coral reefs based on growth formations and spatial distribution patterns of different reef building “polypifers.”
“ I must first observe that the reef-building polypifers, not being tidal animals, require to be constantly submerged or washed by the breakers. I was assured by Mr. Liesk, a very intelligent resident on these islands, as well as by some chiefs at Tahiti (Otaheite), that an exposure to the rays of the sun for a very short time invariably causes their destruction.” – Darwin (1842)
His observations that corals thrived in a limited depth range in the shallow clear waters surrounding these islands allowed him to come up with the theory that coral reefs form and evolve over time based on uplift and subsidence of deep sea mountains and the movement of the earth’s crust. In a stable scenario, fringing reefs can form around the island. An island that is being uplifted will carry with it the attached reefs above the water’s surface. The inability of the reef to survive above the water leaves a white limestone ring around the island. On the other hand, as the island subsides then the reefs continue to grow upwards in order to maintain the suitable water depth and thereby form a barrier reef around the island with a lagoon system. Eventually the island becomes completely submerged leaving the atoll ring of growing coral reefs and the lagoon. Eventually the coral growth can no longer keep up and soon the whole ecosystem submerges.
|Atoll of French Polynesia, showing the ring of reefs remaining after the island has subsided below the water. Image source Google Earth, LandSat|
Darwin determined that the formation of the Great Barrier Reef was similar to the barrier reefs formed around the oceanic islands based on the subsidence of these islands. However this was not true in the case for Australia’s reef. It is now thought that the formation of the GBR resulted from sea level rise about 7000 years ago following the last ice age (glacial maxima).
Today, the theory of sea level rise and formation of the Great Barrier Reef has been confirmed by science. During the last Ice Age (glacial maxima), the sea level was much lower along the coastlines around Australia. The Queensland coast occurred where the barrier reef exists today and the coral reefs fringed this coastline and outer continental islands. The sea level rose owing to the warming atmosphere and melting glaciers, the low lying lands by the sea were inundated and formed what is now the Great Barrier Reef Lagoon and the present day coastline.
Knowledge of this phenomenon was well understood by the first peoples of Australia - the Aboriginal societies who resided in Australia for over 50,000 years after arriving from New Guinea during the lower sea levels. The Aboriginal tradition of story telling allowed stories about the environment, geography and ecosystems to be passed down from one generation to the next. These stories are elemental to the aboriginal culture and crucial for their survival. Many modern scientists regarded verbal stories as unreliable, because of the level of embellishment and alteration that might be incurred as they passed from one generation to the next. However, for the Aboriginals these were not merely stories, but accurate information about the land and sea essential to their survival. And so, for 7000 years, these stories of the sea level rise were factual and accurate. A recent study showed that the comparison of 21 independent stories of aboriginal communities throughout Australia, correspond with the scientific findings surrounding the timing of the sea level rise and the rate at which the sea level rose based on the bathymetry assessment of different areas (Nunn & Reid 2016).
One example comes from the Gungganyji people who used to live in what were coastal plains in the Northeast Australia, between Cairns and the current location of the Great Barrier Reef.
“…the barrier reef was the original coast here at a time when a man called Gunya (Goonyah) was living here. Having consumed a customarily forbidden fish, the gods caused the sea to rise in order to drown him and his family. He evaded this fate by fleeing to the hills but ‘the sea ... never returned to its original limits’ (Gribble 1932, 56–57; Nunn & Reid 2015)”
It reminds us that although we observe our ecosystems today with scientific eyes and technology, what we observe about our natural world must be shared and passed on through scientific records or cultural traditions. Our stories are essential for our survival, which are intricately intertwined with the health of our environments.
Darwin, C. R. 1842. The structure and distribution of coral reefs. Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836. London: Smith Elder and Co.
Patrick D. Nunn & Nicholas J. Reid (2016) Aboriginal Memories of Inundation of the Australian Coast Dating from More than 7000 Years Ago, Australian Geographer, 47:1, 11-47.