Urchin barren

However, determining which factors contribute to shifting a kelp bed to an urchin barren is a complex problem and remains a matter of debate among scientists.

Loss of "top" predators, particularly the historic hunting of sea otters (Enhydra lutris), has often been cited as a cause of these barrens.

Today, many scientists acknowledge that there is a mix of top-down and bottom-up factors that affect when, how, and where these ecosystems shift between a kelp bed and an urchin barren.

In other words, a kelp bed can re-establish itself when urchin grazing intensity decreases to the threshold density triggering the initial shift.

Alternatively, another theory posits that both sea urchin barrens and kelp-beds represent alternative stable states, meaning that an ecosystem can exist under multiple states, each with a set of unique biotic and abiotic conditions (i.e. barren except for urchins or flourishing with kelp).