Kelp in the Depths

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Science  19 Oct 2007:
Vol. 318, Issue 5849, pp. 363
DOI: 10.1126/science.318.5849.363b

Kelp forests are exceptionally productive marine ecosystems, iconic of high-latitude, shallow, cold waters. There are a few rare records of tropical deep-water species, but these are thought to be relicts of glacial-era populations. Graham et al. suggest that kelp may not be as restricted in distribution as once thought. By modeling the coincidence of the water temperature, bottom depth, and light penetration with nutrient circulation, they derive a map of potential tropical kelp beds, a rough contour of 25 to 236 m. A quick look offshore of the Galapagos Islands indeed revealed kelp at around 60 m depth. The authors also predict extensive kelp forests off Brazil, West Africa, and the Malay Archipelago. Essentially, wherever clear tropical water allows light to penetrate into cooler depths and bathymetries allow nutrient upwelling, kelp should survive in the tropics. Hence, even in strong El Niño years, tropical kelp can escape surface warming. — CA

Proc. Natl. Acad. Sci. U.S.A. 104, 10.1073/pnas.0704778104 (2007).

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