longspined sea urchin

What is a longspined sea urchin?

The longspined sea urchin (Centrostephanus Rodgersii) or just “Centro” is an echinoderm, meaning this animal belongs to a group of marine invertebrates including sea stars and sea cucumbers which all have “spiky skin”.

As its name implies, the longspined sea urchin is armed with exceptionally long, black, moveable black spines. Well protected from predators, the spines contain an irritant toxin, which is dispersed when pricked.

A Native Species on the Move

Centro naturally occurs along the New South Wales coast, but over recent decades its range has expanded south into Victoria and Tasmania as ocean temperatures have warmed. Scientists link this expansion to changes in the East Australian Current, which is transporting larvae further south than in the past.

Today, longspined sea urchins are one of the biggest ecological challenges facing some temperate reef ecosystems in south-eastern Australia.

The spatial distribution of Centro,  The colour and size of points denotes the abundance of Centro 2006–2024 (Tebbett et al. 2005)

When Too Many Urchins Graze

Longspined sea urchins feed on seaweed, including kelp.

At natural densities they are part of a healthy reef ecosystem. However, when urchin numbers become very high they can overgraze reefs, removing kelp and creating large areas of bare rock known as urchin barrens.

When kelp forests disappear:

Fish habitat is lost
Biodiversity declines
Productivity of reefs falls
Important fisheries can be affected

Kelp forests support hundreds of species and underpin valuable fisheries including abalone and southern rock lobster.

What is an urchin barren?

An urchin barren is a reef where sea urchins have removed most of the large seaweeds.

Instead of a dense underwater forest, the reef becomes dominated by bare rock and grazing urchins.

Research shows that once extensive barrens form, they can persist for decades because urchins can survive with very little food. This makes recovery difficult unless urchin numbers are reduced significantly.

Why are longspined sea urchins spreading south?

Longspined sea urchins were first recorded in Tasmania in 1978. Since then, populations have increased dramatically along the east coast. Scientific surveys estimated around 6.7 million individuals in 2001, rising to almost 20 million by 2016-17.

The main driver is climate change.

As Australia's oceans warm, the East Australian Current is extending further south and carrying urchin larvae into areas where they previously could not survive. Warmer winter temperatures have also improved survival rates in Tasmania.

Don't predators control them?

However, once extensive barrens are established, predator recovery alone is unlikely to reduce urchin numbers enough for kelp forests to recover quickly. At that stage, active management such as targeted urchin removal, commercial harvesting and reef restoration is often needed.

Predator roles also differ between regions. In New South Wales, longspined sea urchins are native and have long been part of reef ecosystems. In Tasmania, they are a climate-driven range extension, so the balance between urchins, predators and kelp forests may work differently.

Predators play an important role in keeping reef ecosystems in balance, but their effect varies between places.

In Tasmania, large southern rock lobsters are one of the main known predators of adult longspined sea urchins. Research shows that healthy lobster populations can help prevent new urchin barrens from forming, especially where barrens are still small or just beginning.

what can be done?

There is no single solution.

Scientists, fishers, Traditional Owners and governments are working on a range of approaches:

Commercial harvesting

Longspined sea urchins are harvested for their roe, known as uni, a premium seafood product.

Tasmania's fishery has grown rapidly over the past decade and now removes hundreds of tonnes of urchins each year. Harvesting can help reduce urchin numbers while creating jobs and supporting coastal communities.

Targeted culling

In some locations, divers remove or destroy urchins directly.

This can be effective on priority reefs where rapid action is needed, although it requires ongoing investment.

Restoring kelp forests

Where urchin numbers are reduced enough, kelp can recover naturally. In some cases, active kelp restoration may also help accelerate recovery.

Long-term monitoring

Tracking changes in urchin populations, kelp forests and reef health helps managers identify priority areas and measure the success of interventions.

Can reefs recover?

Yes.

Research from Tasmania, Victoria and elsewhere has shown that when urchin densities are reduced below critical thresholds, kelp forests can return. In some cases, substantial recovery has occurred within a few years of urchin removal.

However, recovery is not guaranteed and becomes more difficult as barrens expand.

A National Challenge Needs a National Response

The longspined sea urchin challenge extends across multiple states and is driven by climate change, making it far bigger than any single fishery, community or government agency can tackle alone.

The Centro Task Force brings together scientists, fishers, Traditional Owners, industry and conservation groups to develop a coordinated national response. Their proposed plan includes investment in reef monitoring, urchin removal, fishery development, research and habitat restoration to help protect Australia's kelp forests and the communities that depend on them.

Learn more about the centro task force

Did You Know?

A longspined sea urchin can live for more than 25 years.
Their larvae can drift in ocean currents for around three months.
Tasmania's east coast population increased from about 6.7 million to almost 20 million individuals between major surveys.
Once barrens form, longspined sea urchins can survive for years with very little food, making recovery difficult without reducing their numbers.
Kelp forests can recover when enough urchins are removed.
The edible reproductive organs, known as "roe" or "uni", are considered a delicacy in many countries and support a growing Australian fishery.

Eat an Urchin, Help a Reef

Longspined sea urchins are harvested for their roe, known as uni, a prized seafood enjoyed around the world. By creating demand for sustainably harvested urchins, consumers can help support commercial fisheries that remove urchins from reefs affected by barrens.

Harvesting alone won't solve the problem everywhere, but it is one of the few management tools that can reduce urchin numbers while creating jobs, supporting coastal communities and helping kelp forests recover.

Australia's longspined sea urchin fishery has grown rapidly in recent years and is increasingly recognised as a model for tackling a marine environmental challenge through sustainable seafood.

Want to give it a try? Learn more about why eating urchins matters, where to find them, and how to prepare them on our Eat an Urchin page.

eat an urchin