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Global warming sending reefs deeper and fish further

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Reef Life Survey diver

Reef Life Survey diver

Graham Edgar

Graham Edgar

Reef Life Survey diver

Andrew Fewster, Reporter

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Due to global warming, rising water temperatures are having dramatic effects on the ecology of coral reefs, recent studies have shown.

One study shows that as waters warm, fish are able to extend their hunting range, which will impact on invertebrates such as crabs, lobsters, and sea urchins.

“As fish extend their range further from the equator with warming water, their advantage as predators will affect the abundance and diversity of large mobile invertebrates,” said lead author of the study, Professor Graham Edgar of the Institute for Marine and Antarctic Studies (IMAS).

“The effects of climate change on marine life vary greatly between geographic regions.

“In South Eastern Australia and Tasmania the ‘tropicalisation’ of marine life is already underway, but similar effects have not yet been detected in New Zealand.”

The study utilised data collected from the Reef Life Survey, a citizen science project founded by Professor Edgar.

“Species monitoring of shallow reef communities at national scales is only possible with the support of citizen scientists, such as the RLS divers who contributed data to our study,” Professor Edgar said.

“The RLS data set now includes information on 4000 species in 50 countries, allowing a better understanding of how and why species are distributed, while also providing an early-warning mechanism for climate-induced changes.”

Another study examining the effect that warming waters are having on reef life found that as waters warm, corals at deeper depths suffer less from bleaching.

The study suggests the deeper corals may be a vital part of the effort to save shallow reefs.

Museum of Tropical Queensland’s Coral Collection Manager Dr Paul Muir said it was quite clear that global warming was to blame for the “record sea surface temperatures”.

“When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.

“To date, limited understanding of the effects of coral bleaching in deeper waters and within individual coral species has impeded global management of its devastating impacts.”

Dr Muir was part of a team of experts from Australia, New Zealand and Maldives who studied the 2016 bleaching event in the Maldives, where they measured bleaching among nearly 200 coral species ranging from depths of three to 30 metres.

“We found great variation in the effects of bleaching between species, and overwhelming evidence that coral bleaching reduces as water depth increases,” Dr Muir said.

“We believe deep corals, which are less susceptible to bleaching, may be essential in minimising species extinctions and providing coral larvae to reseed damaged shallow reefs.”

Describing coral bleaching as “a bit like ripping up a thousand Mona Lisa paintings every year”, Dr Muir stressed how important reefs are, not just as some of the most diverse ecosystems on the planet, but for their economic value as well.

“In economic terms millions of people rely on reef systems for their food, income and culture. The Maldives for example is totally dependent on these reefs,” Dr Muir said.

The research team hopes to study more of the reefs at the Maldives sites, as well as others to get more information.

Queensland Museum’s Acting CEO Dr Jim Thompson said: “The researchers want to conduct a similar study of Great Barrier Reef corals, and further investigate how deep corals may help reseed damaged reefs and assist them to become more resilient to bleaching.”

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Quality journalism by ECU students
Global warming sending reefs deeper and fish further