Coral in the lagoon at the most southerly tropical reef in the world is showing signs of bleaching.

Key points: Researchers found bleaching at five of the six sites they visited

Researchers found bleaching at five of the six sites they visited Some of the reef was thriving and the more severe bleaching was on coral closer to the shore

Some of the reef was thriving and the more severe bleaching was on coral closer to the shore As coral suffers, so can the animals who can't move on to other areas

A monitoring program to survey the extent of the bleaching is underway at Lord Howe Island Marine Park, off Port Macquarie on the NSW mid-north coast, with researchers performing underwater assessments and aerial mapping.

PhD candidate at the University of Newcastle Tess Moriarty spent most of March surveying the corals in the lagoon as part of a project which began last November.

"We were informed that there was a bit of bleaching during March — we went to six sites and five of them had been impacted by coral bleaching to some extent," Ms Moriarty said.

"At the most highly impacted site there is about 5 per cent that are dead at the moment.

"These corals are usually used to a more highly variable temperature threshold than say corals that are closer to the equator which are just used to a couple of degrees difference.

She said the coral on Lord Howe Island could handle temperatures from 18 degrees Celsius to about 26 degrees.

"But now that we're seeing that it's getting higher above that, we're seeing these bleaching events occurring more often — that could impact those sites and it could be a more algae-dominated reef and really change the ecosystem there," Ms Moriarty said.

The corals closer to the shore were the most affected. ( Supplied: Tess Moriarty, University of Newcastle )

Bleaching not everywhere

The corals closer to the shore were most highly impacted and the ones further out were the healthiest, Ms Moriarty said.

"The ones closer to shore were at least 40 per cent impacted by bleaching whereas the ones further away it could be as small as 5 per cent," she said.

"What we learn from this is what species are going to be okay for the future and what are succeeding, what are the winners and losers in that regard.

Ms Moriarty said some coral species were doing well and were not bleaching at all, but some other species had 100 per cent bleaching in particular spots.

"So we're going back to the need to reduce our carbon emissions and carbon footprint and then look at maybe small-scale projects for small-scale reefs," she said.

"Maybe shading the corals or something like that.

"The big picture is climate change but this one in particular is due to higher than normal temperature regimes so there was a thermal heatwave."

Drought had contributed to the problem too, Ms Moriarty said.

"So you're not having fresh water come in, you're not having cloud cover and so forth," she said.

"The sun was really exposing the corals and this heat for months on end as they didn't have any cloud cover to help shade and protect the corals."

Five of the six sites surveyed had been impacted in some way. ( Supplied: Tess Moriarty, University of Newcastle )

Associate professor at the University of NSW School of Biological, Earth and Environmental Sciences, Dr Tracy Ainsworth, said it wasn't the first time there had been signs of bleaching.

"There was bleaching in 2010 and 2011 and also back in 1998 when there was a large bleaching on the Great Barrier Reef and also in 1992 and these are really characteristic of when waters get too warm," Dr Ainsworth said.

"This looks to be quite severe.

"Where the bleaching has occurred it's affected most of the corals that are on the reef and we're actually starting to see a little bit of mortality starts," she said.

But she said there was some good news with areas where the corals had not been affected doing well.

"I think we can really learn a lot about bleaching and about the reefs where corals might start to do a little bit better or can withstand warming oceans a little bit better," Dr Ainsworth said.

"But we're trying to understand things like water flow, currents — how these local conditions can be just enough to give corals a little bit of relief and help them through these hot periods in summer."

Tess Moriarty says coral provides protection and food to the inhabitants of the reef. ( Supplied: Tess Moriarty, University of Newcastle )

Many animals that lived on the reef needed corals, she said.

"There's little crabs and shrimp that live in amongst the coral — there's fish that rely on corals," Dr Ainsworth said.

"There's such a diverse eco-system because of that relationship between the coral and the algae that makes this beautiful 3-dimensional home for all these other animals.

"So as the corals start to suffer the other animals start to suffer as well and some of them can't just move on to another area.

"They live amongst those corals and moving away is really not possible," Dr Ainsworth said.

Bleaching events are are occurring more often, Tess Moriarty says, as the water temperature gets warmer. ( Supplied: Tess Moriarty, University of Newcastle )

Ms Moriarty said tour operators were explaining the event to a lot of their tourists.

"So I think at the moment it's okay but obviously this is something we're concerned about and we hope that tourists keep coming for the locals who are living there and rely on the reef for so many different resources," Ms Moriarty said.

Recovery monitoring

Ms Moriarty said researchers would be returning at the end of April to look at the recovery phase.

"It just depends on the mortality levels," she said.

"The next step is looking at the recovery and seeing how many have recovered.

"So we will know from the recovery monitoring about the likelihood of those particular sites to grow back, more corals to be there in the future, so forth.

The project began in November last year. ( Supplied: Tess Moriarty, University of Newcastle )

"I have heard that they have had some cooler temperatures which is good for the corals, so hopefully we see that the corals regain some colour back, regain their symbiotic algae back but we're expecting to see some mortality as well.

"I have read in some papers that it can take just hours for them to regain their symbiotic algae."