Sea Urchin Barrens: When Balance Breaks Beneath the Waves

Along our beautiful Midwest coastline — from the Abrolhos Islands to Kalbarri — there’s a quiet shift happening beneath the ocean surface. While currently there are lush, swaying underwater forests of kelp, in the near future some areas, will be turning into rocky deserts dominated by one spiny creature: the sea urchin.

This phenomenon is called a sea urchin barren. And it’s not just a quirky marine fact — it’s a red flag for the health of our local marine ecosystems.

Sunlight filters through the vibrant strands of a kelp, showing just a small part of a mesmerizing underwater ecosystem.

What Is a Sea Urchin Barren?

A barren is a zone on the seafloor where the kelp forests have been completely grazed down by exploding populations of sea urchins. Kelp isn’t just seaweed — it’s a foundation species, like coral on a reef or trees in a forest. It provides food, oxygen, shelter, and nursery grounds for countless marine species, from fish and crabs to molluscs and even seabirds.

Without the kelp, biodiversity crashes. What remains is a bare, algae-encrusted rockscape, dominated by sea urchins, particularly species like Centrostephanus rodgersii (long-spined sea urchin), which are expanding their range due to warming waters.

Why It Matters Here in the Midwest

Our region’s kelp forests — especially around the Abrolhos Islands, Geraldton coast, and Batavia Coast — are part of the Houtman Abrolhos Marine Ecosystem, a hotspot for marine biodiversity and fishing productivity. These kelp forests:

• Support crayfish and abalone fisheries,

• Act as carbon sinks, drawing CO₂ from the water and air,

• Protect our coastlines from erosion,

• And sustain a food web from snails to seals.

But with increasing sea urchin populations — linked to climate change, overfishing of predators, and habitat fragmentation — these vital forests are under threat.

The Science Behind the Barren

Under normal conditions, predators like lobsters, sea stars, and large finfish keep urchin numbers in check. But if those predators are removed (due to overfishing or warming seas affecting their reproduction), urchins multiply rapidly.

More urchins means:

• Overgrazing on young kelp before it can regrow.

• Formation of “barrens” where only crusty algae and urchins survive.

• A feedback loop: less kelp = fewer predators = more urchins = less kelp.

In ecological terms, this is a phase shift — the ecosystem has moved to a new, less productive and less diverse state that’s difficult to reverse.

Climate Change: The Heat Beneath

Urchin barrens are expanding globally due to warming oceans. In WA, the 2011 marine heatwave was a wake-up call. It caused widespread kelp die-offs along the west coast, giving urchins an opportunity to dominate newly bare areas.

We're seeing southern species moving north and tropical species moving south, creating new predator-prey dynamics. This ecological reshuffling might explain why barrens are forming faster or in new locations.

So, What Can We Do?

There’s no easy fix, but scientists and communities are exploring options:

• Rewilding predators: Protecting or restocking rock lobsters to bring urchin numbers down naturally.

• Urchin harvesting: Some regions are trialing urchin culling or even promoting urchin roe (uni) as a commercial seafood.

  
  

  

  A plate of freshly prepared sea urchins, showcasing their vibrant orange roe, ready for a gourmet dining experience.

  
  

• Marine habitat restoration: Planting kelp and creating artificial reefs to support regrowth.

• Citizen science: Divers and fishers can report changes, helping track the spread of barrens.

Here in the Midwest, our local fisheries, Indigenous rangers, researchers, and marine parks all have a role to play in preventing a barren future.

Why This Story Matters

The ocean is not a distant wilderness — it’s part of our story in Geraldton, Northampton, Dongara, and the Abrolhos. What happens under the water affects our climate, our fisheries, and our future.

Sea urchin barrens remind us that nature thrives in balance. When one piece of the puzzle is removed — whether it’s a predator, a temperature range, or a protective policy — the whole system shifts.

And that shift is happening right now, just offshore.

Sea urchin, highlighting its detailed spines and natural beauty.

Learn More / Take Action

• Volunteer with local marine programs or reef monitoring groups.

• Ask your seafood suppliers about sustainable sourcing.

• Follow Midwest Eco Stories for updates on local ecology, restoration projects, and how you can help!