From: Andy Soos, ENN
Published October 14, 2010 05:02 PM

Turtles and Dugongs

The "turtle and dugong capital of the world", the northern Great Barrier Reef and Torres Strait region, faces increased pressure under climate change from human actions such as fishing, hunting, onshore development and pollution. The Great Barrier Reef is the world's largest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 1,600 miles over an area of approximately 133,000 square miles. The reef is located in the Coral Sea, off the coast of Queensland in north-east Australia. The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms.

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The Great Barrier Reef supports a great diversity of life, including many vulnerable or endangered species, some of which may be endemic to the reef system.

Thirty species of whales, dolphins, and porpoises have been recorded in the Great Barrier Reef, including the dwarf minke whale, Indo-Pacific humpback dolphin, and the humpback whale. Large populations of dugongs (sea cow) live there.

Six species of sea turtles come to the reef to breed — the green sea turtle, leatherback sea turtle, hawksbill turtle, loggerhead sea turtle, flatback turtle, and the olive ridley. The green sea turtles on the Great Barrier Reef have two genetically distinct populations, one in the northern part of the reef and the other in the southern part. Fifteen species of seagrass in beds attract the dugongs and turtles.

The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is also the only sirenian in its range, which spans the waters of at least 37 countries throughout the Indian and Pacific Oceans, though the majority of dugongs live in the northern waters of Australia between Shark Bay and Moreton Bay. The dugong is the only strictly-marine herbivorous mammal, as all species of manatee that utilize fresh water to some degree.

"Depletion of turtle and dugong numbers increases their vulnerability to other threats and lowers their ability to cope with climate change," states Dr Mariana Fuentes of the ARC Center of Excellence for Coral Reef Studies and James Cook University.

Dr Fuentes says that turtles in particular are vulnerable to the effects of climate change, which include decreases in hatching success, loss of nesting areas and overheated beaches, which will decrease the turtles' reproductive output and may significantly alter the sex ratio of their offspring.

Dr. Fuentes' research into the green, hawksbill and flatback turtles and well as dugongs in the northern GBR and Torres Strait is seeking to establish priorities for the management of marine megafauna to increase their resilience to climate change.

Of particular concern is the effect of climate change on the gender balance of turtle population, Dr Fuentes says: "The temperature of the beach sand determines the gender of the hatchlings — warmer sand produces more females while cooler sand produces more males."

"Under current conditions the nesting grounds are already producing more females. With an increasing temperature, these turtles are at risk of stretching out the ratio, though we can't yet predict exactly when it will cause an unbalanced population."

"While sea turtles have survived large climatic fluctuations during their evolutionary history, modern rates of climate change are much faster, and are coupled with additional human pressures," says Dr Fuentes. "We still do not know whether turtles can adapt to modern rates of climate change."

Dugongs may experience indirect effects of climate change and human activity through impacts on their main food source, seagrass. Seagrass diebacks are linked to lower reproduction, increased mortality and emigration of dugongs.

She says it will be important to institute a range of short-term and long-term measures to protect turtles and dugongs from climate change, including:

1. Actively trying to change the habitat they use (e.g. by shading nests, re-vegetating beaches, and replacing lost sand).

2. Protecting areas that seem to offer the best conditions as refuges in the future.

"However, as the impacts of climate change become more extreme, more active adaptation strategies may be necessary. The success of each adaptation option will depend on climatic impact and local social, economic and cultural conditions, and therefore needs to be considered on a case by case basis, and at a local scale," Dr Fuentes explains.

For further information: http://www.eurekalert.org/pub_releases/2010-10/acoe-td100610.php

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