Scientists working to study the destruction of kelp forests on the Pacific Coast have discovered that the critically endangered sunflower starfish plays a vital role in maintaining the region’s ecological balance and that starfish restoration efforts could potentially help restore kelp forests as well.
A multidisciplinary team that includes Florida State University assistant professor of biological sciences Daniel Okamoto has published a new study showing that a healthy starfish population can keep purple sea urchins, which have contributed to the destruction of kelp forests, under control.
Their work is published in Proceedings of the Royal Society B.
“Our work is focused on understanding what factors support healthy kelp forests as well as healthy sea urchin populations,” Okamoto said. “That is, what scenarios lead to the collapse, rather than the coexistence of these important species.”
In recent years, a debilitating starfish disease caused by rising water temperatures has caused the species to largely disappear from its natural ranges from Alaska to Baja in Mexico. This extinction is thought to be responsible for the dramatic increase in purple sea urchin populations in many parts of the West Coast. Overgrazing by sea urchins – along with rising sea temperatures – has led to the loss of kelp forests, which are among the most productive ecosystems on the planet and provide suitable habitats that support biodiversity and ecological well-being in coastal waters.
By combining data collection, laboratory experiments and modeling to scale up laboratory research, the research team found that pre-illness sunflower starfish populations were likely able to control sea urchin populations through predatory behavior. Sunflower starfish can consume 0.7 sea urchins a day, or five per week, and they will eat any urchin in their path, whether a well-fed urchin or a nutrient-poor zombie hedgehog.
“Even when we assumed that starfish eat fewer urchins than we measured in the lab and studied various predation scenarios, we found that sunflower starfish can control sea urchin populations and maintain healthy algae forests,” Okamoto said. “Our task now is to test whether these results are true in the wild. There the behavior of starfish and urchins can be very different from the behavior in the laboratory. No model is perfect, but even when we were careful, the results still indicated that sunflower starfish play a critical role in sea urchin population control.”
The relationship between sunflower starfish, which are listed as endangered by the International Union for Conservation of Nature, and sea urchins has never been quantified before.
“So far, no studies have been published testing the level of sunflower starfish predation on purple sea urchins, and therefore there is no way to reasonably assess the impact of sunflower starfish predation on purple sea urchin populations,” said Aaron Galloway, Associate Professor. Institute of Marine Biology at the University of Oregon and principal investigator of the study. “This study bridges that gap and the results are significant and somewhat surprising.”
Restoring starfish by breeding and relocating species in captivity as part of an active management plan can be an important tool to control sea urchin population growth and stimulate the recovery of kelp forests.
“Restoring species is critical,” said Vena Saccomanno, co-author of the study and an ocean scientist with the Nature Conservancy. “The time has come to take swift and decisive action to restore this iconic species to conserve biodiversity and further restore kelp.
This study, funded by the Nature Conservancy and the National Science Foundation, was led by Galloway and Sarah Graveme of Oregon State University, with additional contributions from scientists at the University of Washington.
Visit the Nature Conservancy website to learn more about this work.