Deeper understanding of ecosystems critical to recovery of West Coast abalone populations

Summer 2015

Abalone play an important ecological role in marine ecosystems by helping to stabilize kelp forests and rocky reefs. Unfortunately, the decline in abalone populations has drastically altered these marine habitats—a phenomenon scientists have witnessed across the West Coast.

Among the California coast’s intertidal zones, black abalone were once a prominent feature. Peter Raimondi, a well-known ecologist and professor at the University of California Santa Cruz, has studied intertidal zones for over three decades. In 1982, black abalone were so abundant that individuals were found stacked on top of each other.

“Black abalone clearly dominated the intertidal zones, and then just a few years later El Niño and disease wiped out entire populations on the mainland coast,” recalls Raimondi.

Photographed in 1986

Photographed in 1988

Photographed in 1999

Above: Three views of the same intertidal zone show the effects of El Niño and disease on black Abalone populations and their habitat. The top photo is from 1986, the middle was photographed in 1988, and the bottom was photographed in 1999. Photos by Brian Tissot, Humboldt State University

Years later, Raimondi published a peer-reviewed article that documents how the community structure, or species that dominated these zones, changed dramatically when black abalone disappeared. His work demonstrated that these intertidal zones shifted to a community dominated by “fouling” organisms, such as fleshy algae, tube worms, and sponges.

The main problem with this shift in community structure is that black abalone, as well as other abalone species, actually requires the presence of specific type of algae for metamorphosis from larvae into juveniles.[1] The abalone receive a chemical cue from the algae indicating these habitats are a good place for them to settle. The absence of vital algae, and subsequent lack of suitable habitat, presents problems when trying to restore black abalone populations in the wild.  

Raimondi is now testing a new approach to restoring black abalone: first, restore the intertidal habitat to make it once again suitable to abalone.

“We basically cleared some cracks and crevices using brushes and scrapers in intertidal areas on San Clemente Island where black abalone were historically abundant—similar to how one would clean off a BBQ in the summertime,” explains Raimondi. “We plan to go back this fall, one year later, to see if we have any newly settled juveniles. It is a pretty simple approach, but a critical one for restoring black abalone.”

Kelp forests in southern California have also suffered from the loss of abalone in the last twenty years. Scientists first discovered the presence of urchin barrens in the 1970s when they started sampling the ocean floor extensively. Urchin barrens are areas of subtidal habitats where sea urchins multiply at an alarming rate, causing destruction of kelp forests because their growth goes unchecked. Since their discovery, urchin barrens have grown steadily across the coast due, in part, to the lack of several types of abalone species to keep urchin populations constrained. In an urchin barren, poor water quality from coastal degradation, lack of predators, and the absence of key species, like abalone, all contribute to uncontrolled population growth. The urchins then begin moving away from cracks and crevices where they normally live and search for any kelp or algae in their path, eventually destroying kelp forest areas.

The decline in abalone populations has altered marine habitats. Photos  by David Witting, NOAA

As part of an ecosystem-wide approach to restoring kelp forests in southern California, NOAA Fisheries recently worked with partners to outplant green abalone in newly restored kelp forests. With the help of divers and novel techniques applied by The Bay Foundation, the kelp forests were first restored by removing urchins and limiting their densities. Following these efforts, kelp forests immediately began to grow back, and the reintroduction of green abalone into this environment will support healthy, functioning kelp forests.  

Understanding the role abalone play in different ecosystems is important for their recovery and the health and resiliency of the marine habitats they support. We now understand that restoring abalone to self-sustaining levels coast-wide requires both boosting abalone numbers and maintaining healthy rocky intertidal and subtidal ecosystems. This approach will ensure the resilience of abalone and their habitats in the face of future challenges.  

Home page photo by David Witting, NOAA

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[1] Crustose coralline algae is required for abalone to transform from larvae into juveniles.