Study finds why once-common sponges vanished from Israel's shallow coasts

Agelas oroides once thrived in Israel's shallow waters, but 50 years later, they can only be found in habitats 100 meters below the ocean's surface.

Agelas oroides sponges are seen with other sea life in an undersea habitat. (photo credit: TAL IDAN/TEL AVIV UNIVERSITY)
Agelas oroides sponges are seen with other sea life in an undersea habitat.
Why did a once-common species of sponge completely vanish from the shallow water along Israel's Mediterranean coast?
Known as Agelas oroides, the species of sponge can now mainly be found in deep sponge grounds – habitats found 100 meters below the ocean surface. However, just 50 years ago, they were thriving in Israel's shallow waters.
But a Tel Aviv University study may have found the culprit behind this mystery: climate change.
According to the study – led by Prof. Micha Ilan and PhD student Tal Idan, in collaboration with Dr. Liron Goren and Dr. Sigal Shefer, all from TAU's School of Zoology at the George S. Wise Faculty of Life Sciences and the Steinhardt Museum of Natural History – the rise in water temperature by about three degrees Celcius in the eastern Mediterranean over the past half century has left the sponges unable to survive in the shallow depths.
The researchers gathered this data using an underwater robot belonging to the NGO "EcoOcean" to gather 20 Agelas oroides sponges from their habitats 100 meters below the ocean's surface and transplant 14 of them to shallow depths (10 meters) at a site where the sponge was once commonly found during the 1960s, while the remaining six were used as a control group in their original habitat.
From March to May, when the water temperature ranged from 18-26 degrees Celsius, the sponges thrived in the shallow depths. As the temperature continued to rise though, they began to suffer. Most stopped pumping water when the temperature hit 28 degrees. By July, when it exceeded 29 degrees, all the sponges had died. By contrast, the control group in the original habitat, which had a temperature of 17-20 degrees, continued to thrive.
“From 1960 until today, the water temperature on the Israeli Mediterranean coast has risen by three degrees, which may greatly affect marine organisms, including sponges," Ilan explained in a statement.
"Our great concern is that the changes taking place on our shores are a harbinger of what may take place in the future throughout the Mediterranean. Our findings suggest that continued climate change and the warming of seawater could fatally harm sponges and marine life in general.”
The implications of these findings could provide a way for the Nature and Parks Authority to help preserve the last remaining habitats on Israel's coasts, as well as working to change their status, so they are recognized as a vulnerable species. This is especially important, as not only can they play a role in advancements in the field of medicine – with one 2014 study from the University of Minho in Portugal even studying them for potential application in tissue engineering and regenerative medicine – but they also play a significant role in the ecosystem.
“Sponges are marine animals of great importance to the ecosystem, and also to humans," Idan explained. "They feed by filtering particles or obtain substances dissolved in the seawater and make them available to other animals, and are used as a habitat for many other organisms."
While the Nature and Parks Authority has managed to incorporate three of these research sites in its Marine Nature Reserves Program, it is still hoped that they will be recognized as official marine nature reserves.
The study was published in the academic journal Frontiers in Marine Biology.