Rising ocean acidity is affecting the development of different types of marine species, such as sea urchins and brightly-colored reef fish.

A recent study shows how sea urchin development is affected by ocean acidification. (more…)

The Great Barrier Reef is experiencing massive coral bleaching events due to ocean acidification, which negatively affects the development of brightly-colored fish in the reef. (more…)

Background Information: What is Ocean Acidification?

Full Research: Direct and latent effects of ocean acidification on the transition of a sea urchin from planktonic larva to benthic juvenile, Are fish communities on coral reefs becoming less colorful?

Study Shows How Ocean Acidification Affects Sea Urchin Early Stage Development

Ocean acidification has a significant negative impact on marine species and ecosystems. A recent study shows how ocean acidification affects the early development stages of some marine species, such as sea urchins. Here’s what you need to know about it.

The study researched the effects of pH on sea urchin’s development and transition from fertilization to juveniles. The result shows that low pH levels significantly affected the growth and mortality of the urchin’s larval stage. Even small changes in ocean pH (on the scale of .1) can have major impacts.

Larval Stage: Effects of Ocean Acidification

Sea urchin larvae were exposed to a 7.2 pH level (compared to the current ocean’s actual pH of 8.1). The sea urchins exposed to this pH exhibited the following characteristics:
- Higher mortality rates.
- Higher abnormality rates.
- Lower growth rates.

The metabolism of sea urchin larvae exposed to a 7.2 pH level increased as well. The researchers believe that because of this, the urchins may be using additional energy to boost metabolic function, which might limit their growth rates. In other words, the sea urchins adapt to ocean acidification by shifting their energy to boost metabolic function, rather than other important functionalities. Researchers believe that this shift in energy may be what’s causing mortality and abnormalities throughout their development stages.

Settlement Stage

Researchers discovered that prolonged exposure to a 7.7 pH level significantly delayed the settlement of sea urchin larvae, an important process during which larvae settle to the ocean floor where they will eventually begin their adult life stages.
However, when the sea urchin larvae were placed under a suitable algal substrate for the settlement stage, the researchers found that the larvae remained unaffected by 7.7 pH levels. This shows that algae may help reduce the effects of ocean acidification on sea urchin larvae.

Metamorphosis Stage

The study shows that in the metamorphosis stage, all the sea urchins that were grown at a 7.2 pH level failed to metamorphose. The researchers concluded that sea urchins that are exposed to low pH levels throughout their early development stages may find it hard to impossible to achieve metamorphosis.

However, the study also shows that 30% of the sea urchin larvae that were grown at a 7.6 pH level achieved the metamorphosis stage. This shows the large impact of even a pH change of .4, compared to the 7.2 pH group of urchins.

sea urchin development - ocean acidification sea urchins — The development cycle of a sea urchin.
(Source: © Natural History Museum, London)

Ocean Acidification Affects Brightly-Colored Fish Development Through Continuous Coral Bleaching

The Great Barrier Reef is experiencing massive coral bleaching events due to ocean acidification, which negatively affects the development of fish’s color in the reef. Here’s all you need to know about the study.

In the span of just three decades, the effects of ocean acidification and global warming have caused the Great Barrier Reef to lose thousands of its coral species. This phenomenon is commonly known as massive coral bleaching events. As a result of this, the number of brightly-colored fish in the Great Barrier Reef is decreasing.

According to the study, the number of different types of brightly-colored fish in the Great Barrier Reef has declined significantly since the massive coral bleaching event of 1998. Scientists believe that the composition of the seafloor (texture, colors, patterns) affects the development of the coloration of fish.

Reef fishes developed coloration to protect themselves from predators by adapting to the different coral structures and compositions. Fish would find it useless to produce vibrant colorations in the absence of coral compositions.

The study concluded that the loss of vibrant composition and structure of the seafloor due to the massive coral bleaching events has a significant relationship to the inability of many fish to develop their vibrant colors.

coral bleaching in great barrier reef — 6^th massive coral bleaching event in the Great Barrier Reef (2022).
(Source: © Earth.org)

Sources:

“Direct and latent effects of ocean acidification on the transition of a sea urchin from planktonic larva to benthic juvenile” Nature, April 01, 2022

https://www.nature.com/articles/s41598-022-09537-7

“Fish on Australia’s Great Barrier Reef are losing their colour as corals die” Independent UK, March 23, 2022

https://www.independent.co.uk/climate-change/news/great-barrier-reef-australia-fish-colour-b2041887.html

Ocean acidification occurs when the pH level of seawater decreases, which is most frequently caused by the ocean absorbing excess CO₂ from the atmosphere. Ocean acidification has negative effects on a variety of ocean ecosystems and life forms, including sea urchins.

This article will explore how sea urchins are affected by ocean acidification, as well as the importance of sea urchins to ecosystems, global cultures, and the economy.

Background information: Ocean Acidification Infographic

Table of Contents

How Are Sea Urchins Affected by Ocean Acidification?

The Importance of Sea Urchins

The Importance of Sea Urchins to the Ecosystem

The Importance of Sea Urchins to People and the Economy

How Are Sea Urchins Affected by Ocean Acidification?

Sea urchins are vulnerable to ocean acidification because rising acidity in seawater reduces the number of available carbonate ions, which are essential for building sea urchins’ shells, spines, and teeth. Here are some of the negative effects of ocean acidification on sea urchins.

Lowered Growth Rate of Sea Urchin Larvae

Because larval sea urchins are quite sensitive, ocean acidification affects the development of sea urchins at very early stages. According to a 2022 study, sea urchin larvae’s growth rate is lowered when they’re exposed to acidified water. Sea urchins, when exposed to lower pH seawater, need to use extra energy for other survival functions, including temperature self-regulation, leaving insufficient energy for them to use for their growth.

Increased Metabolism

Sea urchins feed on various types of marine organisms, including algae, planktons, and even kelp. Feeding is crucial to the growth, development, and survival of sea urchins. However, 2013 research discovered that increasing ocean acidity affects the metabolism of sea urchin larvae, forcing them to eat more than normal. A lower pH level reduces the capability of sea urchin larvae’s digestive enzymes, known as “gastric juice.” In order to attempt to make up for less effective digestion, sea urchin larvae exposed to acidification increased their feeding by as much as 33%. If this increased eating was not possible due to a lack of food, the sea urchin would suffer. Additionally, this increased energy devoted to eating reduces energy reserves for other vital functions such as growth and temperature self-regulation.

Increased Developmental Abnormalities and Mortality Rates

Ocean acidification forces sea urchins to reallocate their energy sources in order to adapt. This might sound positive, but experts have found that it is one of the causes of mortalities and abnormalities in sea urchins. In a 2022 experiment, sea urchin larvae were exposed to acidified water with a 7.2 pH level (much lower than the ocean’s current pH of 8.1). This showed a significant effect, causing abnormalities to the sea urchin’s structural development.

In the same experiment, when larval sea urchins were exposed to acidified water with a pH of 7.2, they were unable to grow into juvenile sea urchins. These abnormalities may threaten their survival rate.

sea urchin study - sea urchin ocean acidification — *Comparison of two sea urchins, where the sea urchin on the right is exposed to ocean current conditions, and the sea urchin on the left is exposed to ocean acidification.*
*Source:* *Phys.org*

The Importance of Sea Urchins

Sea urchins contribute to the ecological balance in the ocean ecosystem and provide products that are used in traditional cuisines. However, ocean acidification threatens sea urchin populations, and thus, the benefits they offer to ecosystems and people. Here are some of the ways sea urchins are important to ecosystems and people.

The Importance of Sea Urchins to the Ecosystem

Reef Gardeners

Sea urchins are herbivores and they feed on algae and other marine plants in the reef. Their feeding activities are essential to the balance of the reef because as they remove overgrown weeds and algae, they create room for corals to flourish. This provides more habitat for fish while also preventing the negative effects of overgrowing algae on the reef.

This service that sea urchins provide plays an essential role in maintaining a healthy and habitable marine ecosystem. They are great alternatives to the decreasing population of other algae controllers that are commonly overexploited by people, such as parrotfish and rabbitfish. If ocean acidification continues, the service of sea urchins to reef maintenance could be affected. Without sea urchins and other algae controllers, the reefs as we know them might become uninhabitable for many organisms in the future.

Source of Food for Other Species

sea otter eating urchins - sea urchin ocean acidification — *Sea otter eating sea urchins*
*Source:* *Katherine johns / listal*

Sea urchins are a food source for several other species. Sea urchins’ high protein provides essential nutrients to animals that rely on this diet. Animal species that feed on sea urchins include:

Other shellfish, such as crabs and lobsters
Multiple fish species, such as sheephead wrasse and wolf eel
Sea otters
Seagulls

Some of these animals use sea urchins as their primary source of food, which is why the negative impact of ocean acidification doesn’t only affect sea urchins directly; it can also cause an indirect effect on species that rely on their services.

The Importance of Sea Urchins to People and the Economy

How Sea Urchins Benefit the Cultural Food Industry and Economy

Like any other commercialized shellfish on the market, sea urchins are also in demand in some countries’ food industry. Here is an overview of some of the countries that use sea urchins as part of their food industry.

Chile

Chile has a long tradition of eating sea urchins, as sea urchins have been part of Chilean food since the 1500s. Today, sea urchin is still a part of the Chilean diet. In 2002, Chile consumed around 3,000 tons of sea urchins, and in 2013, Chile ranked as the world’s largest supplier of fresh and frozen sea urchins and urchin roe. Sea urchins are not only a part of Chilean tradition and culture, but they also make a significant contribution to Chile’s economy today.

Japan

sea urchin sushi - sea urchin ocean acidification — *Sea urchin sushi*
*Source:* *Sushi Making Kit*

Eating sea urchins in Japan is traditional, with consumption accounting for around 90% of the global supply. Japan is the largest consumer of sea urchins in the world, where it is commonly eaten as sushi and sashimi, two of Japan’s most iconic dishes. The sea urchin also contributes significantly to Japan’s economy since the country is considered a major exporter of sea urchins globally.

The population of sea urchins may decline as a result of the effects of ocean acidification. This could have a damaging effect not only on the economic contribution of sea urchins, but also on culinary cultures that have been passed down for centuries.

Health Benefits from Sea Urchin in the Diet

Despite their threatening appearance, sea urchins can provide various health benefits and nutrients to people. Here are some examples:

Sea urchins are high in protein, which can help maintain and grow our muscles.
Sea urchins are also rich in dietary fibers that are good for digestion.
Sea urchins contain vitamin C and Zinc, which are great for the immune system.
They also contain vitamin A, which is good for our organs, such as the heart, kidneys, and lungs.
Just like other fish, sea urchins are rich in omega 3 fatty acids, which are useful for maintaining a healthy heart.

Sea urchins provide a variety of valuable benefits to the environment, wildlife, and humans. Several studies have already proven how the acidifying ocean affects their development, preventing them from thriving. This could alter the important services they provide that help in maintaining ecological balance. This is why it is essential to assure that sea urchins, like all other species, are protected from the damaging consequences of ocean acidification.