New study investigates nitrogen run-off and sponge health
A recent study led by researchers from Te Herenga Waka—Victoria University of Wellington explores how nitrogen fertilizer run-off could affect marine sponges. Published in the Journal of Experimental Marine Biology and Ecology, the research tested seven sponge species—three from Wellington, New Zealand, and four from Lough Hyne, a protected marine area in County Cork, Ireland—to assess their resilience to elevated nitrogen in seawater.
The experimental setup and key findings
In laboratory experiments, scientists exposed the sponges to seawater containing various nitrogen concentrations. The highest concentrations mirrored what could be expected after heavy rainfall events, a scenario where fertilizer-derived nitrogen washes into coastal waters. Lead author Gabriela Wood, a Ph.D. candidate at Te Herenga Waka, notes that elevated nitrogen levels from agricultural runoff are a growing concern in both New Zealand and Ireland.
Across most species, the sponges showed strong tolerance to short-term nitrogen surges, with survival rates exceeding 95%. This suggests a remarkable capacity to endure episodic increases in nitrogen, at least in the controlled conditions of a laboratory experiment.
Species-specific responses
Despite the overall resilience, the study identified nuanced species differences. One Irish species, Cliona celata, exhibited adverse effects at the highest nitrogen concentrations. Researchers observed color changes and altered respiration rates in Cliona celata, both indicators of stress. Two additional species from Lough Hyne also showed shifts in respiration, signaling that nitrogen stress can manifest through physiological changes even when survival rates remain high.
These results highlight that tolerance to nitrogen is not uniform across sponge communities. Some species may be better equipped to cope with nutrient inputs, while others could be more vulnerable to the secondary impacts of eutrophication and altered water chemistry.
Why this matters for coastal ecosystems
Professor James Bell, a marine biologist at Te Herenga Waka and co-author of the study, cautions that lab results capture only part of the picture. “Increasing nitrogen levels can lead to higher incidences of plankton blooms,” he explains. Such blooms can deplete oxygen, disrupt food webs, and indirectly harm sponge communities, even if individual sponges survive a short-term exposure.
The researchers emphasize that real-world outcomes depend on a range of interacting factors, including water temperature, current patterns, and the presence of other pollutants. Long-term monitoring is needed to understand how chronic exposure to elevated nitrogen affects sponge growth, reproduction, and community structure beyond laboratory timeframes.
Future directions and implications
The study authors call for continued research to track long-term effects of nitrogen run-off on sponges and to examine more species across different geographic regions. By mapping which sponge species are most vulnerable, scientists and policymakers can better anticipate ecological shifts and craft targeted management strategies to reduce nutrient inputs from agriculture and urban runoff.
As coastal nations grapple with balancing agricultural productivity and marine conservation, understanding how foundational organisms like sponges respond to nutrient loading becomes increasingly important. The new findings offer a nuanced view: sponges are not uniformly susceptible to nitrogen, yet certain species require closer scrutiny and protection as nitrogen dynamics in coastal waters evolve.
Conclusion
The Wellington-Ireland study contributes valuable insight into the complex relationship between nitrogen fertilizer run-off and marine sponge health. It confirms a general short-term tolerance among several species while simultaneously signaling potential stress for specific taxa at elevated nutrient levels. Ongoing research will be essential to determine the long-term ecological consequences and to guide effective stewardship of coastal sponge habitats.
