Dive Dry with Dr. Bill

117: Urchin Barrens

When I first started diving southern California waters in the late 1960's, one of the major environmental issues was the decline of the kelp forests along our coast. Long-term studies by researchers like Dr. Wheeler North used information dating back before World War I to document the decline in our mainland kelp beds. The earliest studies were done by the federal government in anticipation of that war because Germany was our country's major source of potash, necessary for fertilizer... and gunpowder. It was important to identify new domestic sources of potash to make ammunition for the anticipated conflict. Giant kelp became a major source and some historians have said it helped win World War I. Certainly the harvesting of kelp for the war effort, and later for sodium alginate, had a short-term effect on regional kelp beds.

The decline Dr. North and others noted accelerated after World War II. Kelp harvesting for potash was not the issue this time. Instead it was the increasing population of our state that was responsible. Military personnel stationed in the state during that conflict liked California and returned in numbers to settle here. With an increase in the human population, pollution also increased... especially in these early days before our environmental consciousness became mainstream.

For millennia giant kelp beds had been in reasonable balance with one of their primary herbivores, the sea urchin. Before the early 1800's, sea urchin populations were kept in check through predation by sea otters. In the late 1700's ships from New England and Russia hunted sea otters for their rich fur, an important trade item with China. When these mammals were hunted to regional extinction, this control was removed and sea urchin populations undoubtedly increased. Other urchin predators like the sheephead became the dominant control.

It is believed that urchins and giant kelp remained in an erratic "balance" initially. Normally the urchins fed on detached drift kelp. However, as urchin populations increased, there wasn't enough drift material and they overwhelmed the living kelp forests. Urchins would climb the kelp forests to eaten the fronds, and cluster around the holdfast, detaching the living alga. The result was that the kelp forest died. Without their primary food source, the urchins then died and new kelp could colonize the area.

World War II changed all this. Sewage from the expanding cities in southern California was usually dumped directly into the ocean, and in increasing volume. This sewage, rich in organic "wastes," became an alternate food source for urchins. Once the kelp forests were decimated, the urchins could survive on this discharged sewage and new kelp could not gain a foothold to reestablish the forests. The areas devoid of kelp are referred to as "urchin barrens."

By the time I arrived here, divers were being asked to kill as many sea urchins as they could. Much of this was done by crushing as many as one could find on a dive. Quicklime was also spread to kill the urchins. Of course this really didn't address the root cause of the problem. In 1972 the Clean Water Act was passed and cities were required to treat wastewater before discharging it. This helped reduce or eliminate the primary cause of this ecological imbalance.

The increasing population and popularity of the State as a tourist destination led to greater fishing pressure on the remaining urchin predators like sheephead. This fishery has been closely regulated recently with many closures required. At some sites I dive in the Channel Islands, I rarely see a sheephead and urchin barrens still exist despite very low organic pollution levels. So the barrens can develop even without the organic wastes in areas where predators are minimal. The many "party" or charter fishing boats that visit Catalina and the other islands continue to reduce populations of these urchin predators.

Here in Catalina's dive park, fishing pressure is almost non-existent. Sheephead are among the most frequently encountered fish species. Because of this, we do not see urchins out in the open (at least not for long!). The urchins in the park remain hidden in their crevices and feed on the abundant drift kelp produced by the healthy forests. The protection afforded by the dive park is an example of the balance that can be achieved when protected areas like marine reserves are established.

I do encounter divers, especially instructors, who will extricate an urchin and break it open to attract fish. Some think they are doing a good thing for the environment, but this is not the case here. Others feel it has "educational" value for their classes. I fail to see that rationale since it teaches them we can kill living things simply to meet our own needs for "recreation" and "pleasure." Now eating an urchin from non-reserve areas is a different story. The fish realize the value of chomping down on this inexpensive form of caviar, and I must admit to having acquired a taste for urchin roe when I first sampled it in the Atlantic Ocean in the mid 1960's! Killing for food, rather than for "sport," is certainly acceptable since we are all part of the "mutual eating society." Yummy.

© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

An "urchin barren" in the northern Channel Islands where fishing pressure is intense;
sheephead controlling urchins in the dive park by munching on them.

This document maintained by Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia