Density of urchins estimated from photoquadrats.
In my recent visits to the breakwater at Elliott Bay Marina in Seattle, its become apparent that the site is officially an urchin barren. Urchin barrens are a well documented phenomenon in the Pacific, but to my knowledge, have not previously been observed in Puget Sound. They occur when urchin populations go unchecked by predators and consume canopy forming kelps.
Elliott Bay Marina’s breakwater was constructed in the early 1990s, but has long been home to a vibrant seasonal forest of Nereocystis luetkeana (bull kelp). In the summer time, the site was a magical and diverse refuge for marine life in the heart of the city. Kelp stretched thirty feet or more from the sea bottom to the surface, housing a myriad of invertebrates, rockfish, the occasional wolf-eel, and obese lingcod that could not have been less than 6 feet in length.
We’ve been collecting photo quadrat data at the site since May of 2013 and had our eye on it after the density of green urchins (Strongylocentrotus droebachiensis) began to increase. It wasn’t until we returned to the site last summer, however, that it became clear the increase in urchin density had had such a large effect.
Here are some photos from my last dive there with Ed Gullekson.
We’ll keep documenting changes and will keep you posted. I’m hearing some talk of urchin densities increasing in other areas as well, but have yet to confirm. More to come…