Scientists uncover the mystery of Cork lake's disappearing marine sponges

Change in water chemistry could have affected the delicate ecosystem — but happily, there are signs of recovery at Lough Hyne

There was a strong decline in the numbers of sponges between about 2010 and 2015, with several possible causes, including outbreaks of disease, increases in nutrients or heatwaves. Picture: Professor Rob McAllen

The mystery of disappearing marine sponges from one of Ireland’s most incredible nature reserves may have a happy ending.

Scientists who’ve been studying and monitoring the loss of possibly thousands of sponges from the underwater cliffs inside Lough Hyne in West Cork have discovered a potential natural recovery of the affected species.

“While we were obviously very concerned to see the sponge populations in the lough decline so much, we were very surprised to see new sponges reappearing after just a short time,” said Professor of Marine Biology, James Bell, from Te Herenga Waka Victoria University of Wellington in New Zealand.

He, along with Prof Rob McAllen from UCC, and their team, secured funding from the National Parks and Wildlife Service to study this unusual event in the semi-enclosed saltwater lough on the south coast near Skibbereen.

Decline in sponge population

There was a strong decline in the numbers of sponges between about 2010 and 2015, with several possible causes, including outbreaks of disease, increases in nutrients or heatwaves.

Research is ongoing into the cause but changes in water chemistry could be the most likely cause.

However, the team says there have been signs of a potential natural recovery of the affected species.

In a paper published in Science of the Total Environment this week, Prof Bell and his co-authors discuss their research and the implications for life in other temperate mesophotic ecosystems (TMEs) — a layer of the seafloor typically extending from about 20m to 30m below the surface to 150m, and home for numerous invertebrates such as sponges, sea fans, and sea anemones.

Findings could help conservation efforts

Their findings could result in more regular monitoring of TMEs and help improve conservation of these delicate ecosystems around the world.

The Lough Hyne Marine Nature Reserve is the only one of its kind in Ireland. 

It is a magnet for marine biologists because it hosts many rare species and contains a high number of habitats within a small area of just half a square kilometre.