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)
Comments