Study finds increase in seawater temperature a threat for sea anemones

A new study has found sea anemones, which provide habitat for anemone fish, may be seriously impacted by even small increases in seawater temperatures.

The study, published in Coral Reefs, has found that the sea anemone species Entacmaea quadricolor, from North Solitary Island off the NSW North Coast, is already living close to its thermal limit.

Co-authored by UTS marine scientist Dr Ross Hill from the Plant Functional Biology and Climate Change Cluster and Dr Anna Scott from Southern Cross University’s National Marine Science Centre, the study is the first of its kind to demonstrate the impact of rising temperatures on the sea anemones. The adverse impacts documented are likely to have subsequent impacts on their resident anemone fish, which are unable to survive in the wild without their anemone homes.

Sea anemones, like their coral relatives, depend on symbiotic algae for survival and are susceptible to bleaching caused by rising seawater temperatures. Until now, scientists have been unsure just how vulnerable these anemone species might be to climate change impacts.

“This region has been identified as a climate hot-spot and because this sea anemone species makes up a large part of the reef’s ecosystem it’s important to know the upper survival limits,” Dr Hill said.

Dr Scott said the East Australian Current was predicted to bring warmer water to the Solitary Islands Marine Park, which is home to the highest density of host sea anemones in the world.

“Over the years there have been studies showing that anemone bleach in the field, but we haven’t known what the temperature thresholds are. This research has given us the first information on the susceptibility of these species and a clearer picture of what might happen in the future if temperatures continue to rise,” Dr Scott said.

The scientists set up experimental tanks at the National Marine Science Centre in Coffs Harbour and exposed collected sea anemones to different temperatures and light intensities to simulate conditions predicted to occur over the next 100 years.

“At even moderate temperatures, 27°C, which is only 1°C above the summer average, algae were expelled from the host sea anemone,” Dr Hill said.

“At 29°C the bleaching process continued and in some cases the sea anemones died. This species, the anemone fish associated with it and the North Solitary Island Reef ecosystem are likely to be significantly impacted if seawater temperatures rise by between two and six degrees as predicted.”

The research also showed that, as with corals, high light intensity promotes bleaching in sea anemones; further supporting the view that sea anemones are just as sensitive as corals to climate change impacts.

The research has been funded by the Sydney Aquarium Conservation Foundation.

Photo: Anemone fish residing in partially bleached anemones.