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New research investigating whether nitrogen fertilizer run-off affects marine sponges suggests these animals have a high tolerance to nitrogen, but some species may be better able to cope than others.

The , led by researchers at Te Herenga Waka—Victoria University of Wellington, looked at the potential effects of nitrogen run-off on three sponge species found along Wellington's coast and four species from Lough Hyne in Ireland, a marine reserve in County Cork.

The findings are published in the Journal of Experimental Marine Biology and Ecology.

"Elevated levels of nitrogen flowing from rivers into coastal waters can adversely affect marine species. In both Aotearoa New Zealand and Ireland, sources of this nitrogen include agricultural run-off from animal urine and fertilizer applied to farmland," said Gabriela Wood, the study's lead author and a Ph.D. candidate at Te Herenga Waka.

To test how the sponges might respond to this run-off, the seven species were exposed to seawater with different concentrations of nitrogen. The highest concentrations used in lab tests were set at levels that could be expected after large rainfall events.

Results suggest most of the sponges were able to tolerate short-term increases in nitrogen, with survival rates above 95%. However, one species from Ireland, the Cliona celata, showed evidence of adverse effects at the highest nitrogen concentrations used.

"The Cliona celata showed visible changes in color and significant changes in respiration rates, both indicators of stress. Two other species from Lough Hyne also showed changes in respiration rates," said Gabriela.

Although survival rates remained high during the lab tests, outside the lab the sponges' survival could be hampered by secondary effects on the marine environment from increases in nitrogen concentrations.

"Increasing nitrogen levels can lead to higher incidences of plankton blooms. We know these blooms can result in significant reductions in sponge communities," said Professor James Bell, a marine biologist at Te Herenga Waka and co-author of the study.

More research was needed to track the long-term effects of nitrogen run-off on marine sponges and to investigate how other sponge species may be coping, he said.

"There are more than 9,000 marine sponges worldwide but, despite their ecological importance, there's a lack of research to show how they are responding to nitrogen run-off."