Sponges are in danger – not the ordinary synthetic kind you use to wash dishes in the kitchen sink, but living marine sponges (called Porifera by experts) in the Mediterranean Sea, Red Sea, West Indies, Indian Ocean and elsewhere around the globe. Due to climate change, Tel Aviv University (TAU) researchers believe that the significant warming the oceans and seas could lead to the death and disappearance of some sponge species from the shallow water of Israeli shores. 

In their study, the researchers transplanted sponges of the Agelas oroides species from a depth of 100 meters to a shallow rocky habitat at a depth of 10 meters, where it had been commonly found in the past. Once the water temperature exceeded 29 degrees Celsius, all of the transplanted sponges in the experiment died.

Prof. Micha Ilan and doctoral student Tal Idan, in collaboration with Dr. Liron Goren and Dr. Sigal Shefer, all from TAU’s School of Zoology at Wise Faculty of Life Sciences and the Steinhardt Museum of Natural History, have just published their findings in the journal Frontiers in Marine Biology under the title: “Sponges in a changing climate: Survival of Agelas oroides in a warming Mediterranean Sea.”  

They noted that during the past six decades, the water temperature in the eastern Mediterranean has risen by three degrees Celsius. “Our findings suggest that continued climate change and the warming of seawater could fatally harm sponges and marine life in general.” Sponges are very important for reefs, as they filter huge quantities of water and keep it clear and clean, provide important homes for loads of other animals and protect reefs from erosion by binding the reef together.

The Tel Aviv scientists embarked on an underwater journey to solve a mystery: Why did sponges of the Agelas oroides species, which used to be common in the shallow waters along the Mediterranean coast of Israel, disappear? Today, this species can be found in Israel mainly in deep sponge grounds – rich habitats that exist at a depth of 100 meters. The researchers suggest that the main reason for the disappearance of the sponges was the rise in seawater temperatures during the summer months.

“Sponges are marine animals of great importance to the ecosystem, and also to humans. They feed by filtering particles or obtain substances dissolved in the seawater and making them available to other animals, and are used as a habitat for many other organisms. Also, the sponges contain a wide variety of natural materials – chemicals that are used as a basis for the development of medicines,” said Idan. 

The team used a research vessel and an underwater robot belonging to the voluntary group “EcoOcean,” and with their help, they located very-rich rocky habitats on the seabed at a depth of about 100 meters, about 16 kilometers west of Israeli shores. The most dominant animals in these habitats are sponges, which is why the habitats are called “sponge gardens.” The researchers collected 20 specimens of the Agelas oroides sponge, 14 of which were transferred to shallow waters at a depth of 10 meters, at a site where the sponge used to be commonly found in the 1960s. The remaining six specimens were returned to the sponge gardens from which they were taken, and used as a control group.

The findings of the study showed that when the water temperature ranged from 18 to 26 degrees. the sponges grew and flourished: they pumped and filtered water, the action by which they feed, and their volume increased. But as the water temperature continued to rise, the sponges’ condition deteriorated. At a temperature of 28 degrees Celsius, most of them stopped pumping water; in July, when the water temperature rose above 29 degrees, within a short period of time all of the sponges that had been transferred to the shallow water died. At the same time, the sponges in the control group continued to enjoy a relatively stable and low temperature (between 17 and 20 degrees), which allowed them to continue to grow and thrive.

The researchers suggest that the decisive factor that led to the sponges’ disappearance from the shallow area was prolonged exposure to high seawater temperature. “In the past, the temperature would also reach 28.5 degrees in the summer, but only for a short period of about two weeks – so the sponges, even if damaged, managed to recover. Today, seawater temperatures rise above 29 degrees for three months, which likely causes multi-system damage in sponges, which leaves them no chance of recovering and surviving.”

“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,” said Ilan. “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.”