The Great Barrier Reef is suffering one of the worst coral bleaching events ever – its seventh in five years - and scientists fear it might not be able to recover. Australian Museum's Lizard Island Research Station Director Anne Hoggett has lived on the reef for over 30 years, studying its changes amid increased heat stress on the reef. Lizard Island, a small tropical slice of paradise 270 kilometres north of Cairns, is among the worst bleached areas. The island hosts a research centre where scientists from around the world study Australia’s unique marine ecosystem.
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00:00 These extra vivid corals are signs of a reef fighting for its life.
00:07 After another sweltering summer off Australia's northeast coast, scientists are piecing together
00:11 the scale of damage to the world's largest reef system, the Great Barrier Reef.
00:16 Up until about eight weeks ago it was just beautiful.
00:19 Then in early February the corals started to bleach.
00:23 The only time we've seen bleaching this bad was in 2016 when just about everything died.
00:28 As global sea temperatures rise and damaging storms become more common driven by climate
00:33 change, reefs around the world are increasingly threatened.
00:37 Biologist Anne Hoggart has been closely monitoring the reef around the Australian Museum's Lizard
00:41 Island Research Station on the northern end of the Great Barrier Reef for over 30 years.
00:47 About 50% of the corals that we saw out there just now are dead and covered with algae.
00:52 Aerial surveys by the government authorities who work to conserve the marine park say increased
00:56 sea temperatures have impacted three quarters of the Great Barrier Reef.
01:01 About half of the 1,000 reefs studied showed high or very high bleaching.
01:06 But the full impact is still being measured, says Great Barrier Reef Marine Park Authority
01:11 Chief Scientist Roger Beedon.
01:14 What we saw over the summer months was very prolonged elevated temperatures across most
01:19 of the Great Barrier Reef.
01:21 And so we don't know what the full consequences of this event currently are.
01:25 Coral bleaching occurs when underwater temperatures are more than one degree warmer than their
01:29 long-term average.
01:31 As corals come under heat stress, they expel algae living within their tissues, draining
01:36 them of their vibrant colours and eventually turning bone white.
01:41 Without the algae, which is also their food source, they will die if temperatures don't
01:45 drop in time.
01:46 And so these beautiful colours, you know, the pinks and the blues, they're corals screaming
01:52 out because that's their sunscreen.
01:55 They make this sunscreen.
01:56 And they look actually prettier than when they're healthy, because when they're healthy
02:00 they've got a lot of brown on them.
02:02 All these brown ones, they've turned up their toes and died.
02:06 And that's, you know, this is an area that was only just starting to recover.
02:11 These are small corals that are bleaching, you know, who knows if they'll survive.
02:17 For the seventh time in five years, parts of the reef, which stretches across the size
02:22 of Italy, are struggling through another mass bleaching, with effects in the shallows clear
02:27 even above the waves.
02:33 In the coral sea, James Cook University marine ecologist Andrew Hoey and his team are investigating
02:39 the deeper reaches of the reef.
02:41 So what we're seeing in the shallows is a lot of bleaching and a lot of coral mortality.
02:45 But what we're seeing down deeper is that there is areas there that were close to 100
02:49 per cent, 80, 90, 100 per cent coral cover, down at 80 to 100 metres depth.
02:55 The cooler depths and water flow afford a safe haven for the rich and diverse coral
03:00 communities as their shallower neighbours experience mass die-off.
03:04 But Hoey says that might not last.
03:06 Obviously as the surface waters are heating that much, it's got to attenuate down, right.
03:12 It's got to be extending further and further down.
03:14 And so we're going to see more and more bleaching at depth.
03:17 Coral reefs are often referred to as the rainforest of the seas, as they are home to a huge amount
03:22 of biodiversity.
03:24 As temperatures rise, this is rapidly changing.
03:26 A bit like if you have a bushfire, there's some things that grow back quickly and other
03:31 things take a lot longer to grow back.
03:32 We have some species of corals that can live a thousand years or more and if one of those
03:39 dies, then it takes that long for them to come back.
03:42 Other ones can bounce back in a matter of five, ten years and that's what we've seen.
03:46 Professor Terry Hughes, one of Australia's foremost reef scientists, says that even though
03:51 some corals quickly regrow, the overall make-up is changing as reef health and diversity reduce.
03:58 So the resilience of the reef is actually compromised by the rapid recovery of these
04:03 heat-sensitive species, which is a very good species at growing quickly and recovering
04:09 after a major die-off.
04:12 But unfortunately it's also the most susceptible group of corals to the inevitable heat waves
04:18 that are continuing.
04:19 We lose a lot of those structure-forming corals, so a lot of the plating ones, a lot of the
04:24 branching corals, and these are a lot of the corals that fish rely on.
04:29 So we lose them, we lose the fish, we lose the whole ecosystem.
04:33 Back on Lizard Island, Hoggett and her husband Lyle are eyeing retirement from a very different
04:39 reef.
04:40 It makes me so sad and angry.
04:42 Coral reefs are so beautiful and I love them so much, and they do so much good for the
04:45 world.
04:46 It just makes me angry that it's within our power to stop this from happening and we are
04:50 not doing anywhere near enough, quickly enough.
04:53 We need massive cuts to big things like our industrial carbon pollution.
04:58 And that's up to governments and it's not just up to a single country.
05:01 Every country has to play their part.
05:11 (water bubbling)