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Sea turtles to hatch fewer males
by Sara Coelho
Global warming is likely to make marine turtles to hatch more females than males and may reduce nesting success, according to a review of the effects of increasing temperature on the turtles' biology.
Sea-level rises awill also affect sea turtles by reducing the beach area available for nesting.
Sea-level rises awill also affect sea turtles by reducing the beach area available for nesting.
Marine turtles spend most of their lives at sea, hunting for prey. Females come ashore only every few years to lay their eggs on beaches.
'The problem is that marine turtles can be very faithful to their hatching site,' says lead author Dr Matthew Witt from the University of Exeter. 'They can come back to lay their eggs on the beach where they hatched,' he says. This makes the turtles vulnerable to local environmental changes caused by global warming.
Rising temperatures are likely to become a problem. 'The sex of marine turtles is determined by temperature during the middle third of the incubation period,' explains Witt. Warmer conditions lead to clutches with a higher proportion of females. Males are favoured by colder incubation temperatures, for example in white beaches where sand reflects lots of sunlight.
Witt and colleagues looked at 30 years of data collected at key turtle rookeries around the Atlantic Ocean and Mediterranean Sea and tried to see how global warming is likely to change local breeding conditions. The findings, published in the Journal of Experimental Biology, show that raising temperatures at nesting sites are likely to affect sea turtles.
'It's reasonable to say that sex ratio will be skewed towards females,' says Witt. Also, 'hatching success is also likely to decline with global warming.'
'But we don't know how female turtles will react to the changes,' says Witt. 'Maybe they'll compensate for the increasing temperatures by laying their eggs earlier in the year, or by burying them deeper in the sand where it's cooler.'
Marine turtles are cold-blooded reptiles and their distribution depends mostly on seawater temperature. 'Global warming may open new areas for marine turtles, but we also need to find out if there is an upper limit to the temperature they can tolerate,' he says.
The sea-level rises predicted by climate change models are also going to bring consequences for marine turtles. As seawater rises, 'the area available for nesting will decrease and some rookeries may be lost,' says Witt. This 'coastal squeeze' is most likely to happen in popular tourist areas where buildings and roads constrain beach area and prevent sand to retreating as the sea levels rise.
Coral-like creatures survived the last ice age
by Sara Coelho
Bryozoan colonies may look like frail miniature corals but they were sturdy enough to survive being bulldozed by advancing glaciers during the last ice age. When the ice retreated, they evolved into the unique bryozoan fauna of the Antarctic continental shelf.
Bryozoans are tiny bottom-dwelling organisms that build coral-like colonies that can reach up to one metre tall and wide. They may not be a household name, but they are very common: 'you would have to try hard to find an aquatic environment without them, apart from the deepest trenches,' says Dr David Barnes, a biologist based at the British Antarctic Survey.
They are exceptionally common in Antarctica's Weddell Sea, where scientists have identified around 300 species, many of them not found anywhere else. The extraordinary biodiversity of bryozoans in Antarctica is puzzling, since the continental shelf was covered with glaciers at the height of the last ice age.
'So how do you account for this diversity, especially of endemics, in an area that is supposed to be wiped out whenever there is a glacial maximum? Where do they come from?,' asks Barnes.
Barnes joined forces with Dr Piotr Kuklinski, from the Natural History Museum in London, and set out to catalogue the many hundreds of bryozoan samples dredged out during research cruises in Antarctica. The team analysed bryozoans from many island locations around Antarctica, including the shallow Antarctic continental shelf, the continental slope and the deep abyssal plain of the Southern Ocean.
The idea was to create a combined distribution map for most bryozoan species, to see which assemblages live where and at what depth.
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Bryozoan colony (Melicerita obliqua) from the Southern Ocean. Bryozoans live inside individual units called zooids. Scale bar is 200 micrometers in A and 100 micrometres in B.
They found that the bryozoans living in the deep sea were very different from the ones thriving on the continental shelf – 'it's a completely different fauna,' stresses Barnes. This means that the bryozoans that live on the shelf now did not come from the deep sea.
It is also unlikely that they migrated from distant areas that remained free from the advancing glaciers. 'Bryozoans are attached to the ground as adults, their larvae are short-lived and do not travel far,' explains Barnes, adding that here too, as in the deep sea, the fauna show few species in common.
'The simplest explanation to the patterns we have found is that many bryozoans are indeed endemic to the Weddell Sea continental shelf,' says Barnes. The bryozoans did not recolonise most of the wide and deep shelf until after the glaciers retreated – they managed to survive there in refuges and secluded areas, even at the height of the last ice age.
'This is the first convincing evidence that life survived on the Antarctic shelf during the last glacial maximum,' he concludes. The hunt is now on for the smoking gun of exactly where those refuges are.
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