While the bleaching of the Great Barrier Reef regularly makes global headlines, a far more complete ecological collapse has unfolded quietly beneath the waves of Tasmania. Ninety-five percent of its giant kelp forests have vanished, and most Australians never knew they existed (Johnson et al., 2011; Butler et al., 2020).
Nearly a century of observations from Tasmania’s Maria Island tell the story of how it happened, and why it is still not over.
It starts with temperature.
The trend is unmistakable. Maria Island’s waters are warming.
For giant kelp, that is a problem. Growth declines as temperatures move beyond its optimal range (Le et al., 2022; Drakard et al., 2023)
The warming has not occurred in isolation.
Across the same period, the same waters are becoming increasingly salty, a sign of the strengthening influence of the East Australian Current. The EAC waters are also nutrient-poor, reducing the resources giant kelp needs to grow and recover (Kelly et al., 2015).
At the same time, dissolved oxygen shows corresponding variability across the record, co-occurring with warmer conditions
Taken together, these records indicate a coherent shift in the environmental conditions in Maria Island’s coastal water. However, these changes are not confined to a single island.
Across Tasmania, kelp distribution data show widespread contraction of giant kelp forests, with remnant populations persisting only in limited areas.
In response to this widespread decline, restoration efforts have been initiated, including projects led by CSIRO and Google (CSIRO, 2026) aimed at re-establishing giant kelp forests. However, the persistence of these ecosystems ultimately depends on whether current and projected ocean conditions remain within the species’ growth limits.
Juvenile kelp growth varies with season, with stronger performance in cooler periods and weaker growth during warmer conditions. These results suggest that kelp recovery is more likely to succeed under cooler conditions, and less likely to persist as temperatures remain elevated.
Restoration is no longer just a logistical challenge; it is a race against a warming ocean that the data shows is already being lost. The question is no longer whether Tasmania’s kelp forests can recover, it is whether the window for recovery will remain open long enough to try.
Butler, C., Lucieer, V., Wotherspoon, S., & Johnson, C. (2020). Multi-decadal decline in cover of giant kelp Macrocystis pyrifera at the southern limit of its Australian range. Marine Ecology Progress Series, 653, 1–18. https://doi.org/10.3354/meps13510 CSIRO. (n.d.-a). Caring for algae, big and small.
CSIRO. (2026). National collaboration to save Australia’s invisible, endangered forest of giant kelp using AI. https://www.csiro.au/en/news/All/News/2024/February/National-collaboration-to-save-Australias-invisible-endangered-forest-of-giant-kelp-using-AI
Drakard, V. F., Hollarsmith, J. A., & Stekoll, M. S. (2023). High‐latitude kelps and future oceans: A review of multiple stressor impacts in a changing world. Ecology and Evolution, 13(7), e10277. https://doi.org/10.1002/ece3.10277
Johnson, C. R., Banks, S. C., Barrett, N. S., Cazassus, F., Dunstan, P. K., Edgar, G. J., Frusher, S. D., Gardner, C., Haddon, M., Helidoniotis, F., Hill, K. L., Holbrook, N. J., Hosie, G. W., Last, P. R., Ling, S. D., Melbourne-Thomas, J., Miller, K., Pecl, G. T., Richardson, A. J., . . . Taw, N. (2011). Climate change cascades: Shifts in oceanography, species’ ranges and subtidal marine community dynamics in eastern Tasmania. Journal of Experimental Marine Biology and Ecology, 400(1–2), 17–32. https://doi.org/10.1016/j.jembe.2011.02.032
Kelly, P., Clementson, L., & Lyne, V. (2015). Decadal and seasonal changes in temperature, salinity, nitrate, and chlorophyll in inshore and offshore waters along southeast Australia. Journal of Geophysical Research Oceans, 120(6), 4226–4244. https://doi.org/10.1002/2014jc010646
Le, D. M., Desmond, M. J., Pritchard, D. W., & Hepburn, C. D. (2022). Effect of temperature on sporulation and spore development of giant kelp (Macrocystis pyrifera). PLoS ONE, 17(12), e0278268. https://doi.org/10.1371/journal.pone.0278268
Layton, C., Shelamoff, V., Cameron, M. J., Tatsumi, M., Wright, J. T., & Johnson, C. R. (2019). Resilience and stability of kelp forests: The importance of patch dynamics and environment-engineer feedbacks. PLoS ONE, 14(1), e0210220. https://doi.org/10.1371/journal.pone.0210220