GC-MS Reveals How Sea Urchins Survive Barrens

When sea urchins eat too much kelp, they can wipe it out entirely, leaving behind barren patches of ocean floor with little life and low productivity, conditions that can stick around for decades. In these barren areas, food becomes scarce, which affects the urchins' own bodies and how they function. But scientists still do not fully understand what is happening inside these urchins on a biochemical level that allows them to survive when food is so limited. To find out, a recent study used gas chromatography-mass spectrometry (GC-MS) to compare the internal makeup of purple sea urchins living in these barren zones versus urchins living just next door in healthier kelp forest areas. An article based on this study was published in the journal Scientific Reports.¹

How Do Sea Urchins Create Barren Ecosystems, and How Do They Survive Decades of Starvation There?

Sea urchins are herbivores, and when their numbers get too high, they can eat through entire underwater forests of algae. This overgrazing causes a dramatic shift in the ecosystem, turning what used to be a thriving kelp habitat into a bare, empty seafloor.^2,3 The balance between sea urchins grazing and kelp forests staying healthy can hold steady for years, but it can also shift depending on things like how much algae is present, how many predators are keeping urchin numbers in check, disease outbreaks, and storms.^4,5 When kelp forests turn into barren zones, the whole ecosystem becomes much less productive, with fewer species living there and simpler food chains. This can also hurt species that people rely on economically, like abalone, lobster, and various fish that are commercially harvested, since their numbers often drop, too.^6-10 What is surprising is that these barren zones can last for decades, and the urchins living there can survive on them for up to 50 years, somehow managing to endure long-term starvation through mechanisms scientists do not yet fully understand. Part of how they get by is by switching their diet to less nutritious food sources, like tiny algae, bacterial films, and other small organisms growing on bare rock surfaces.³

How Do Sea Urchins in Food-Scarce Barrens Metabolically Adapt Compared to Those in Kelp Forests?

The researchers report that the reproductive organs of sea urchins living in the barren, food-scarce areas showed major shifts in how they were using energy compared to urchins living in the healthier kelp forests. It appeared to the team that the bodies of the urchins were reshuffling resources to keep producing energy, maintain chemical balance, and preserve the integrity of their cells.¹

On the sugar-processing side, these urchins relied more on glucose and on making their own sugar from other sources, while using less of two building blocks (alanine and glutamine) for fuel. Another key energy pathway was also being redirected: rather than being used to support growth and building new genetic material, it was instead being funneled toward producing energy.¹

“This study,” write the authors of the article,¹ “reveals the specific metabolic adjustments purple sea urchins employ under food-limited conditions in barrens, diverting energy from reproduction to enhance long-term survival, potentially signaling challenges for kelp restoration.”

References

1. Venter, L.; Loots, D. T.; Alfaro, A. C. et al. Metabolic Adaptations of Starving Purple Sea Urchins (Strongylocentrotus purpuratus) Surviving in the Barrens. Sci Rep. 2026, 16 (1), 23643. DOI: 10.1038/s41598-026-53701-2
2. Rogers-Bennett, L.; Okamoto, D. in Sea Urchins: Biology and Ecology; John, M. L. Ed.; Elsevier, 2020, 593-608.
3. Ling, S.; Scheibling, R. E.; Rassweller, A. et al. Global Regime Shift Dynamics of Catastrophic Sea Urchin Overgrazing. Philosophical Trans. Royal Soc. B: Biol. Sci. 2015, 370, 20130269. DOI: 10.1098/rstb.2013.0269
4. Filbee-Dexter, K.; Scheibling, R. E. Sea Urchin Barrens as Alternative Stable States of Collapsed Kelp Ecosystems. Mar. Ecol. Prog. Ser. 2014, 495, 1–25. DOI: 10.3354/meps10573
5. Murie, K. A.; Bourdeau, P. E. Energetic Context Determines the Effects of Multiple Upwelling-Associated Stressors on Sea Urchin Performance. Sci Rep. 2021, 11 (1), 11313. DOI: 10.1038/s41598-021-90608-6
6. Rogers-Bennett, L.; Catton, C. A. Marine Heat Wave and Multiple Stressors Tip Bull Kelp Forest to Sea Urchin Barrens. Sci Rep. 2019, 9 (1), 15050. DOI: 10.1038/s41598-019-51114-y
7. Rogers-Bennett, L.; Catton, C. A. Cascading Impacts of a Climate-Driven Ecosystem Transition Intensifies Population Vulnerabilities and Fishery Collapse. Front. Clim. 2022, 4, 908708. DOI: 10.3389/fclim.2022.908708
8. Whippo, R.; Gravem, S.; Porter-Hughes, E. et al. The Sunflower Sea Star Reduces Grazing Rates of Purple Sea Urchins Dependent Upon Urchin Starvation State. Ecosphere 2024, 15, e4948. DOI: 10.1002/ecs2.4948
9. Johnson, C. R.; Banks, S. C.; Barrett, N. S. et al. Climate Change Cascades: Shifts in Oceanography, Species’ Ranges and Subtidal Marine Community Dynamics in Eastern Tasmania. J. Exp. Mar. Biol. Ecol. 2011, 400, 17–32. DOI: 10.1016/j.jembe.2011.02.032
10. McClanahan, T. R.; Kamukuru, A.; Muthiga, N. et al. Effect of Sea Urchin Reductions on Algae, Coral, and Fish Populations. Conserv. Biol. 1996, 10, 136–154. DOI: 10.1046/j.1523-1739.1996.10010136.xbody here.