Why Are Starfish Dying? Threats and How You Can Help Save Them

One of British Columbia's largest starfish photographed while diving around the southern Gulf Islands.

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Unlike their name suggests, starfish aren't actually fish, but marine invertebrates. That's why you might also see them being referred to as sea stars. As they belong to the class Asteroidea, scientists often refer to them as asteroids.

These charismatic marine organisms face huge population losses that in turn affect their broader habitat. In this article, we'll tell you more about the main threats to starfish, as well as what's being done to protect them.

Threats to Starfish

The main worldwide threat to starfish is thought to be sea star wasting (SSW) disease, also called sea star wasting syndrome (SSWS).

While this is a problem in its own right, it can also be linked to other threats including rising sea temperatures due to climate change. Independently, these threats have the potential to decrease starfish populations in affected areas. The combination of SSW disease and rising sea temperatures may have even more devastating effects.

How Long Do Starfish Live?

Around the world, there are almost 2,000 different species of starfish. In the wild, the average lifespan across all species of starfish is 35 years. Due to threats like climate change and sea star wasting disease, many starfish won't reach those upper limits of their age range.

Sea Star Wasting Disease

First properly documented in 2013, seastar wasting disease can cause the mass mortality of starfish. It can manifest as a wide range of different signs and symptoms including discoloration, twisting of arms, deflation of starfish, and lesions of the body wall.

The lesions caused by SSW disease are often white and develop on the body or arms of a starfish. As the lesions spread, the starfish's affected arm falls off. Usually, most starfish can recover from this stress response, but in the case of sea star wasting syndrome, the remaining body tissue starts to decompose and the starfish dies soon afterward. This is usually through rapid degradation, where the starfish literally melts away.

This disease progresses extremely quickly and can decimate local populations of starfish within days.

The exact cause of SSW disease is still unclear. While early research suggested the cause was a desnovirus (Parvoviridae), it's thought this may only affect one species of starfish, the Pycnopodia helianthoides, or sunflower star. More recent research suggests the cause is more likely to be microorganisms located at the animal-water interface.

So far, 20 different species of starfish have been identified as suffering from SSWS. This disease is most common along the West Coast of America and has been recorded from Mexico to Alaska.

Climate Change

The rising temperatures of our oceans are thought to play a role in SSW disease. While the exact link between higher temperatures and SSW disease isn't clear yet, some scientists think this may be due to the fact that warmer waters contain less oxygen yet higher levels of nutrients.

Lower levels of oxygen in seawater make it harder for starfish to diffuse oxygen across their body surface. If the oxygen levels in the surrounding ocean are too low, starfish cannot obtain enough and will effectively suffocate.

This effect is exacerbated by the fact that warmer waters contain higher levels of bacteria, which are also linked to algal blooms and ocean dead zones.

The problem with higher levels of bacteria is that they reduce the oxygen levels in the waters they inhabit. As starfish start to die, this organic matter becomes available to any bacteria in the surrounding area. Bacteria levels then increase, creating even worse environmental effects for the starfish.

Studies have also found that fewer starfish are found in areas of the ocean with higher temperatures. In areas where starfish cannot retreat to deeper, cooler waters, there's a higher chance of them becoming infected with SSW disease, leaving whole areas devoid of these marine organisms.

The Impact of Decreasing Starfish Populations

Sea star underwater

Ayman Shalaby / Getty Images

As the population of starfish within a particular habitat decreases, this affects the other species within the same area. For example, certain species of starfish help control the local population of sea urchins. As the starfish die, the sea urchin population explodes out of control. The sea urchins then overgraze kelp forests. Kelp is an important marine habitat and has the potential to sequester carbon and reduce pollution levels.

Some starfish species are also what's known as keystone species within their habitats. Their existence is critical for the health of the overall ecosystem because they either provide essential resources for other species within the habitat or control the population of species that could potentially dominate it. 

Pisaster ochraceus, one of the starfish species affected by SSW, is considered a keystone species within specific areas along the northwest coast of the U.S. When the starfish in these regions are removed, the mussel population that they would usually feed on explodes. As a result, other species cannot establish themselves. These kinds of population changes have serious consequences for the overall health of an ecosystem.

Evolution Helps Starfish

In some areas, certain starfish species seem to be evolving rapid adaptations to cope with the threats.

Scientists compared DNA taken from starfish before and after the largest outbreak of SSW disease in 2013. They found evidence of "microevolution," indicating the species ochre/purple star (Pisaster ochraceus) responded to this extreme event by undergoing a rapid genetic shift.

After a mortality rate of 81% between 2012 and 2015, significant genetic differences were found in the surviving population. There was also an increase in the density of juvenile starfish.

This may be an isolated occurrence, and while promising for this particular species, the results don't necessarily indicate that all species of starfish will be able to rapidly respond to and recover from environmental threats. Action still needs to be taken to protect starfish species and their habitats.

What Is Being Done to Protect Starfish

As well as researching the causes of starfish death, in particular the causes of SSW disease, marine scientists are finding ways to try and rebalance the population. One of the main species affected by SSW disease, the sunflower star, is now on the IUCN critically endangered list.

Scientists at the University of Washington are breeding sunflower stars in captivity. The goal is to learn more about the species and work towards reintroducing captive-bred starfish into the wild, if appropriate.

Many research institutions are taking collective action calling for increased efforts to protect marine species impacted by mass mortality events like those caused by SSW disease. Long-term monitoring of existing populations is still ongoing, in an attempt to understand more about these marine species and their wider ecological impact.

federal petition has also been submitted by The Center for Biological Diversity, calling for the sunflower sea star, one of the main species affected by SSW disease, to be listed as a threatened or endangered species, under the U.S. Endangered Species Act. Granting the species endangered status could help inform coastal development projects that risk impacting the population of this already rare species.

How You Can Help Save Starfish

Even if you don't live near the beach, there are actions you can take to protect populations of starfish. We all have personal power when it comes to taking action against climate change, which appears to be a significant driver of SSW disease.

Don't be tempted to bring starfish home from the beach as a memento. Preserving starfish for decoration decreases their population in the wild.

If you observe any starfish you think may be affected by SSW disease, send the details and location to MARINe (Multi-Agency Rocky Intertidal Network). You can also use this form to submit details of healthy starfish.

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