What Makes Catalina’s Underwater Forests Grow and Shrink Year After Year?
By: Deidre Sullivan, Co-Principal Investigator of the CIMI Kelp Restoration Project
Kelp forests are dynamic, ever-changing ecosystems that can dramatically change in size from one year to the next. But what exactly causes these underwater forests to thrive one year and wither the next? Changes in water temperature, nutrient availability, light levels, storm activity and oceanographic conditions can all influence the health and size of a kelp forest!
Seasons of Change
Similar to forests on land, kelp forests also undergo seasonal changes. In the spring and early summer when the sunlight and nutrient availability are ideal, Giant Kelp can grow at an astonishing rate — more than two feet per day under perfect conditions! However, as summer progresses and water temperatures exceed 70°F, kelp fronds undergo senescence — a natural process of kelp deterioration — leading kelp forests to shrink in size. During winter kelp continues to grow, but it faces additional challenges from powerful swells and storms.
A vibrant, healthy kelp forest thriving underwater.
A ragged kelp frond, undergoing senescence.
Catastrophic Destruction from Storms
Storm activity can have an enormous impact on the kelp forests the CIMI Kelp Restoration project is working to restore! On Catalina, both the Fox Landing and Toyon Bay sites are somewhat protected from the most severe winter storms from the west or northwest. However, these sites remain highly vulnerable to other types of storm activity.
Illustration of the wind and swell direction around Catalina Island, highlighting how different storm types impact local conditions.
Santa Ana winds are warm, dry winds that occur during the cooler months from October to March. These powerful winds can create choppy conditions and powerful waves that may damage and even uproot kelp.
In the summer and early fall, large swells generated by tropical storms from the south can also devastate these kelp forests. The occasional winter storms from the north can also be very destructive to the CIMI kelp forests.
In September 2014, waves generated by a hurricane 900 miles to the south pummeled the Fox Pier. This storm significantly damaged the pier’s structure and destroyed kelp forests at CIMI's Fox Landing and Toyon Bay sites.
The Impacts of El Niño and La Niña
Climate phenomena — such as El Niño and La Niña — can also impact kelp forests for extended periods, ranging from months to years. El Niño typically brings warmer, nutrient-poor waters, which reduce kelp abundance. Meanwhile, La Niña conditions introduce cooler waters that enhance upwelling and nutrient availability, fostering growth.
These maps showcase the transformation of kelp coverage between 2013 (during La Niña) and 2016 (after El Niño).
One of the greatest challenges kelp forests face is the growing impact of climate change. We’ve seen firsthand how rising ocean temperatures and changing ocean conditions can impact kelp distribution and productivity. However, there is still time for us to make a difference.
Adopting a plant-based diet, using public transportation or carpooling and minimizing energy use at home are simple, powerful ways to reduce one's carbon footprint. Small changes, like reducing food waste and supporting renewable energy, can collectively make a big impact.
Another way to make a difference is by supporting CIMI Kelp Restoration. Every donation directly supports the monitoring of the site, educational components, ongoing communications about the project and more.
