By Olivia Wix: Pacific Media Centre
An undersea volcanic eruption off the coast of Tonga this month worries marine biologists over a risk to Pacific feeding grounds for sea turtles.
The volcano spewed ash into the sea and into the air near the low-lying volcanic islands of Hunga Tonga and Hunga Ha’apai.
The area is a common turtle feeding ground for some turtle species.
Massey University vulcanologist Dr Jerome Lecointre says an event like this can have severe consequences for species within the sea.
He says the eruption may have killed many nearby creatures.
“The eruption was sudden. There was no warning and people couldn’t do anything to lessen the impact,” he says.
Dr Lecointre says the heat of the water would be the most devastating to the marine life.
“At the surface it was boiling, it would have been much hotter in the sea,” he says.
The water continues to boil until the volcano stops erupting.
“It makes sense that the marine life would be killed. The eruption would have had much more devastating effects if it was land-based.”
Sea turtle populations have been on the decline for years, although fears surrounding the impacts of climate change on them are only now being realised.
World Wildlife Fund (WWF) and the Secretariat of the Pacific Regional Environment Programme (SPREP) believe an increase in extreme weather events, rising sea levels and increased temperatures are the main contributing factors towards the decline of the turtle populations.
The “red list” classifies all six sea turtle species in the Pacific as endangered. The leatherback and hawksbill species are considered critical.
SPREP and WWF predict that increased air and water temperatures would be the main climate related reason sea turtles become extinct.
SPREP’s marine species officer Lui Bell says warmer air temperatures increase the heat of sand. This can impact on the species as the temperature of the nests determines the sex of a turtle.
WWF South Pacific’s regional marine officer Penina Solomona says: “Research has indicated that climate change can influence the sex ratio of hatchlings.
"This means a hotter beach can result in the inundation of nests, further decreasing the number of hatchlings recruited into the population.”
Bell says the ideal temperature for incubation is 30 deg C. This means that if the eggs are buried in sand less than 30 deg C it will produce a male – higher will create a female.
Kelly Tarlton’s fish department team leader and turtle expert Nik Hannam says that as temperature rises more female turtles will be born.
“This is making them becoming the predominant gender.”
Bell says: “As more females will be born they will not be able to maintain their population for long.”
Research has shown that currently only one in 1000 turtle eggs will stay alive until sexual maturity at the age of 25 to 35. Bell says this will also play a major role in the declining population.
“Female turtles usually lay between two to five different clutches of eggs per nesting season, each having been fertilised by a different male,” adds Bell. This means that the amount of clutches a female turtle can lay will decrease.
Sea turtle conservation groups have discussed a strategy for when populations start to become predominantly female. In these situations, eggs would be incubated below 30 deg C to produce more males.
The warming of the sea has also had major implications for the turtles. Warming sea levels have caused extreme coral bleaching in South Pacific nations.
WWF says this will negatively impact on the sea turtle populations as many rely on coral as their main food source. Hatchlings will be most severely impacted, as coral is their main food source until they are old enough to migrate to bigger feeding areas.
The death of many young turtles has also been attributed to the warming sea. This means turtles venture further out of their normal migratory zones.
Hannam says New Zealand tends to end up with turtles from Australia and the Pacific.
The turtles that usually come to New Zealand are sexually immature (under 10 years old) and get caught in the trans-tasman current.
“The turtles get too cold, so end up with hypothermia and are too sick to return to their nesting and feeding areas,” adds Hannam.
He says this is where his team at Kelly Tarlton’s steps in. They care for the turtles and get them back to full health. They then release them when the waters are warmer and they are strong enough to swim back.
Sea warming also alters nesting times. The usual nesting times are from October to February.
Bell says turtles “sense when to nest by the temperature. When the seas become warmer the nesting season will be delayed, it will give them less time to lay their eggs.”
Rising sea levels and extreme weather events also play a major role in the future of the species.
During the 20th century, sea levels rose 15cm. The United Nations Framework Convention on Climate Change indicates that this is expected to increase, with the Pacific islands being most severely effected.
Countries such as Tuvalu and Tokelau are among the worst affected – and both are common nesting areas for many sea turtle species.
Solomona says the rise in sea level can result in the overcrowding of nests which further decreases the number of hatchlings in the population.
She says that cyclones and king tides are among the most destructive extreme weather events that affect the turtle populations.
“Storm surges and strong tidal action only make the problem of habitat loss worse,” she adds.
Floods and tsunamis that hit the islands wash up turtle eggs buried in the sand and wash them to sea, potentially killing thousands of turtles.
Picture: Dizzy, a rescued green turtle found on a Northland beach and being cared for by Kelly Tarlton's marine centre. Photo: Olivia Wix.
Olivia Wix is a student journalist on the Asia-Pacific Journalism course at AUT University.
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