Nature has an uncanny way of healing itself from its own natural disasters, like forest fires, hurricanes and wind storm damage, and even volcanoes. The damage can be devastating but, given sufficient time, nature recovers. Time is the key factor. Time to rejuvenate and time for it to prepare for the next calamity, many of which being cyclical.
But when events happen one right after another or are working in concert to weaken the ecosystem's ability to withstand a particularly powerful disaster, or if we add man-made factors into the mix, then nature can find itself in dire peril.
Such is the case following the heavy rains and flooding that have recently taken place in and around Queensland, Australia. The flood waters don't simply evaporate but, instead, continue to move towards open sea. Swollen rivers feed into the ocean and they bring along three elements that are dangerous to the coral reef systems, offshore and to the north, that make up Australia's famed Great Barrier Reef: fresh water, sediment, and fertilizers/herbicides.
When great quantities of fresh water are introduced into a coral reef, the corals suffer tremendously as they are strictly salt water creatures. As the fresh water moves further offshore, it blends with the salt water and so the negative effects of too much fresh water are primarily limited to reefs and islands relatively close to shore.
Sediment that fans out at the mouth of rivers can also block sunlight and cover the corals. These fine particles essentially choke the corals, preventing them from feeding effectively and, with the loss of sunlight, starving the symbiotic algae that grows within the coral's tissues. Through photosynthesis, the algae converts sunlight into organic energy for the coral's benefit. But, with floating sediment, that life-giving process is disrupted.
Perhaps the corals could withstand those abuses, but then we must add man's contribution: fertilizers and herbicides. Washed down from farmlands, these chemicals stimulate plant growth, in particular seaweed and algae. Both compete for space with the coral and typically the coral loses. Nature has a way of balancing the relationship between plants and corals so that both can coexist, but with the introduction of fertilizers and other plant stimulants, that balance is thrown off kilter. Corals are rather slow growing, whereas sea plants, particularly when chemically stimulated, are very fast growing. It becomes an aquatic land grab and the seaweeds and algae soon take over.
However, even with the added impact of man-made fertilizers, coral reef ecosystems could deal with these three factors were it not for the fact that they are continually being bombarded and weakened by other hazards. Climate and temperature change, acidification, pollution and disease - one hit after another can have a cumulative effect that can leave the coral reefs exposed and overwhelmed by the negative effects of a natural disaster like the one that occurred in Australia.
The Queensland flooding has been a recent event and researchers are only now beginning to see and monitor the residual effects of the floods working their way out to sea. Coral damage from flooding has happened before and the reefs were able to heal themselves within a decade. But life in the Great Barrier Reef is different now, more precarious and fragile.
"The problem is that all forms of disturbances, loads of sediments/nutrients/pesticides, as well as bleaching events from warming seawaters, more intense cyclones and more frequent outbreaks of coral predators such as the crown-of-thorns starfish, all increase in frequency and intensity," says Dr. Katharine Fabricius of the Australian Institute for Marine Science. "This gives the reefs often not enough time to recover before they get hit again."
Read about the effects of Australia's floods on BBC News.