New findings on how nitrogen runoff affects marine sponges
A recent study led by researchers from Te Herenga Waka—Victoria University of Wellington sheds light on how nitrogen fertilizer runoff may influence marine sponges. The international collaboration examined seven sponge species—three from New Zealand’s Wellington coast and four from Lough Hyne, a protected marine reserve in County Cork, Ireland—to understand whether elevated nitrogen levels could threaten these early-at-sea filter feeders.
The team published their results in the Journal of Experimental Marine Biology and Ecology, with the study designed to mimic nitrogen spikes that could occur after heavy rainfall and flood events. The work is part of a broader effort to understand how agricultural practices impact coastal ecosystems and the resilience of foundational marine species in changing nutrient regimes.
How the experiment was conducted
To simulate nutrient pulses, researchers exposed the sponges to seawater containing varying concentrations of nitrogen, spanning levels that would be realistic after significant rainfall. The seven species were then monitored for several biological responses, including survival, color changes, and respiration rates—a suite of indicators that can reveal stress in stationary, filter-feeding animals like sponges.
Lead author Gabriela Wood, a Ph.D. candidate at Te Herenga Waka, described the core finding: most sponges tolerated short-term nitrogen increases with survival rates exceeding 95%. This suggests a level of resilience in the face of episodic nutrient spikes that coastal ecosystems often experience in commercial and agricultural settings.
Species-specific responses reveal a nuanced picture
Despite the overall robustness, not all sponge species displayed equal tolerance. One Irish species, Cliona celata, exhibited adverse effects at the highest nitrogen concentrations used in the experiments. Changes in color and notable shifts in respiration rates pointed to physiological stress under heavy nutrient loads. Additionally, two other sponge species from Lough Hyne showed respiration changes, indicating that even among similar environmental conditions, different species vary in their stress responses.
These findings highlight a key nuance: resilience to nitrogen is not uniform across sponge communities. While some species can withstand transient nutrient surges, others may be more susceptible to longer-term exposure or repeated events, with potential knock-on effects for the broader reef and coastal ecology.
Implications for marine ecosystems and management
Researchers warn that the lab results, though informative, may underestimate real-world vulnerability. Survival in controlled tests does not automatically translate to long-term persistence in natural habitats where nitrogen interacts with other stressors—such as temperature shifts, acidification, or changes in plankton communities. Increased nitrogen can fuel algal and plankton blooms, which in turn affect light, oxygen levels, and food webs that sponge communities rely on for nourishment and cleaning services for the reef ecosystem.
Professor James Bell, a co-author and marine biologist at Victoria University, notes that rising nitrogen levels can cascade into broader ecological shifts. “We know these blooms can result in significant reductions in sponge communities,” he says, underscoring the potential for cumulative effects that extend beyond the individual species observed in laboratory settings.
What comes next for sponge research and conservation
The study’s authors emphasize the need for long-term monitoring to track how sponges respond to chronic nutrient exposure and to identify which species possess the greatest resilience under real-world conditions. Future work could compare more broadly across sponge taxa and examine interactive factors, such as salinity changes and sedimentation, that accompany runoff events.
As agricultural practices continue to influence coastal waters in both Aotearoa New Zealand and Ireland, translating laboratory insights into effective management strategies becomes critical. The research supports the push for nutrient management plans, better land-use practices near coastlines, and ongoing ecological surveillance to protect sponge-rich habitats that contribute to water quality, biodiversity, and overall marine health.
In sum, while many sponges appear capable of absorbing brief nitrogen spikes without immediate mortality, the resilience is not universal. The outcome will likely depend on species-specific biology, exposure duration, and the broader environmental context—a reminder that protecting coastal ecosystems requires nuanced, multi-species considerations and proactive stewardship.
