Urchin Crusher Robin: Part 1

— Written by Robin Grathwohl

One memory comes to mind when I think about sea urchins: my 10-year-old-self pulling spines out of my feet after a poor ending to an afternoon snorkel. Since I was 10, I have not been very fond of urchins. However, after just one week in the Caselle lab I have an entire new perspective on urchins and their role in a much larger marine system.

Off the Santa Barbara coast, these spiny little creatures help sculpt the kelp forests that fill the waters. Urchins are part of an important food chain that ultimately impacts the abundance of kelp. California sheephead and spiny lobsters prey on the urchins who rely upon algae such as kelp for sustenance.

Throughout the Channel Islands off the coast of southern California, the numerous marine reserves further the complexity of this food web. The contrast between marine protected areas and fished areas plays a direct role in the relationship between the urchins, its predators and its prey. Overtime, as more marine reserves have been introduced to the area, the structure of these kelp forests are changing, and urchins are a crucial factor in these adjustments.

In areas that are fished, fewer predators threaten the urchins, allowing the urchins to take over forming barrens. However, in the marine protected areas, where fishing is restricted or banned, more predators roam, jeopardizing the urchins, permitting more kelp growth. Different levels of restrictions in marine reserves alters the abundance and size of the urchin’s predators and prey, resulting in changes to urchin densities. There are cascading effects starting from the people who prey on the waters all the way down to the kelp, and the urchins play a principal role in this flow. Finding the perfect balance between predators, urchins and kelp is the challenge at hand in the marine reserves in the Channel Islands. These variables paired with a changing climate raise many questions for the future of the kelp forests off the coast of Santa Barbara.

This summer, I am on a journey to discover how the differing marine reserves and fished areas around Anacapa Island impact the resiliency of the urchins. In areas where fishing is prohibited or restricted, there are more fish that prey on the urchins. How will this impact the strength of these urchins to withhold predation? Will these urchins be tougher because their predators have consumed all of the weak-links and they have a larger food supply? Meanwhile, in fished areas, will the urchins be weaker because they do not have the food supply to stay strong and there is not the same abundance of predators to consume the weak-links? I plan to find these answers. Understanding the differences in urchins’ ability to resist predation is vital for grasping the relationships within these complex, ever-changing kelp forests.

How will I pursue this discovery of urchin toughness, you ask? Call me Urchin Crusher Robin because I will be spending the next seven weeks physically crushing urchins to find the toughest and weakest victims. I am finally getting revenge on the spiny little creature that punctured my 10-year old toes.

Removing spines from a purple urchin to practice preparations for urchin crushing.

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