Sea Urchin Struggles: Impact Of Pollution On Their Lives

Sea urchins are important herbivores on coral reefs, and their grazing activity can cause canopy-forming macroalgal communities to collapse, transforming large extensions of rocky bottoms into sea urchin barrens. Sea urchin population explosions have been linked to several factors, including the loss of natural predators due to disease, warming sea waters, and pollution. For example, the recent proliferation of purple sea urchins in California and Oregon has been attributed to a combination of factors, including warmer-than-usual waters, a disease that wiped out their main predator, and increased breeding. This has resulted in the destruction of kelp forests, which are crucial carbon sinks that help in the battle against climate change. In addition to climate change and pollution, other human activities such as coastal urbanization and ocean noise pollution have also been found to impact sea urchin populations.

Noise pollution

Marine habitats are under threat from noise pollution, which is caused by manmade noises in the ocean. These sounds include those from vessel traffic, oil drilling, wind farms, and oil prospecting. This noise pollution has disrupted the lives of many marine organisms, including sea urchins.

Sea urchins are sensitive to ocean noise, and it can be challenging to determine how they are affected as their physical behaviour does not always indicate their reaction to the noise. However, studies have shown that even sea urchins experience stress due to the acoustic environment.

One study, in particular, examined the impact of noise on the black sea urchin species Arbacia lixula, which is mainly found in the Mediterranean Sea. Researchers collected urchins from the Gulf of Palermo in Italy, where they feed on red algae covering the rocky seafloor. Over the years, ocean noise in this area has increased, potentially impacting the lives of these sea urchins.

The researchers exposed the sea urchins to high-frequency noise and found that it did, in fact, elicit a stress response. They observed changes in protein expression and enzyme activity, specifically noting an increase in the expression of the HSP70 gene, which is associated with stress. This study provided evidence that noise pollution can affect the physiology of sea urchins, causing them to experience stress.

Overall, noise pollution in the ocean is a significant issue that can affect sea urchins and other marine life. It can cause stress, impact behaviour, and disrupt vital biological activities such as foraging, predation, and mating. More research is needed to fully understand the extent of the problem and find ways to mitigate the effects of noise pollution on marine ecosystems.

Ocean acidification

Studies have shown that continuous exposure to low pH negatively affects larval mortality and growth rates in sea urchins. The formation of the rudiment, which is the primordial juvenile, can be delayed, and the increased energy cost to maintain vital functions can lead to reduced energy available for growth. This can have implications for population survival, as growth delays and abnormalities have been observed in sea urchin larvae under acidified conditions.

However, some sea urchin species exhibit potential to adapt to ocean acidification. For example, purple sea urchins (Strongylocentrotus purpuratus) have genetic variations that allow them to be resilient in the face of changing ocean pH. Additionally, sea urchin populations in naturally acidified habitats, such as upwelling regions and intertidal pools, indicate a certain level of resilience and species-specific adaptive strategies to low pH conditions.

The effects of ocean acidification on sea urchins can be influenced by other factors such as temperature and food availability. Moderate warming and sufficient food supply can reduce the negative impacts of acidification on sea urchin growth. Understanding the interactive effects of multiple stressors is crucial for assessing the potential outcomes for sea urchin populations in a changing ocean.

Nutrient pollution

Nutrient enrichment, or nutrient pollution, occurs when excessive nutrients are introduced into an ecosystem, disrupting its natural balance. In the case of sea urchins, increased nutrient levels can promote the growth of algae, which serves as a food source for the urchins. This, in turn, can lead to an increase in the sea urchin population, as they have more food available to sustain themselves and reproduce.

However, while nutrient pollution can contribute to sea urchin outbreaks, it is important to note that other factors also play a role. For example, the loss of natural predators due to overfishing or disease can also lead to an increase in sea urchin populations. Additionally, factors such as climate change, ocean acidification, and ocean noise pollution can also impact sea urchin populations and the ecosystems they inhabit.

The impact of nutrient pollution on sea urchins is a complex issue that involves interactions between multiple environmental factors. It is crucial to understand these relationships to effectively manage and conserve marine ecosystems and maintain their health and stability.

Climate change

Sea urchins are small spiny creatures that play a vital role in maintaining balance within marine ecosystems. They are also an important commercial fishery species, particularly along the California coast. However, their populations and survival are threatened by climate change.

The Impact of Climate Change on Sea Urchins

Sea urchins rely on their adhesive tube feet to attach to their surroundings and move effectively. Even slight changes in salinity can affect their adhesive abilities, impacting their survival. This is because they are not as effective as other marine animals at regulating the amount of water and salts in their bodies, and they are adapted to a narrow range of salinity levels.

Research by biologists at Syracuse University, published in the Journal of Experimental Biology, found that sea urchins' righting response, movement, and adhesive ability were all negatively impacted by low salinity conditions. While sea urchin adhesive ability was not severely affected until very low salinity levels, the ability to perform tasks requiring greater coordination of tube feet, such as righting and movement, was impaired.

These findings suggest that sea urchins may struggle to survive in certain areas that experience low salinity due to climate change. This could have a significant impact on marine ecosystems, as sea urchins are responsible for grazing around 45% of algae on coral reefs. Without sea urchins, coral reefs can become overgrown with macroalgae, limiting the growth of corals and disrupting the balance of the ecosystem.

In addition to the effects of hyposalinity, sea urchins are also vulnerable to other aspects of climate change. A study by UC Santa Cruz researchers, published in Science Advances, investigated the vulnerability of red sea urchin populations in Northern and Southern California to climate change factors. They found that while both regions' sea urchin populations are adapted to their local conditions, they differ in their vulnerability to future environmental changes. Red sea urchins in Southern California, already adapted to warmer conditions, may be more vulnerable to further warming than their northern counterparts.

The study examined the effects of water temperature, dissolved oxygen, and pH (a measure of ocean acidification) on sea urchin populations. Climate change, driven by increased carbon dioxide in the atmosphere, is causing warming oceans, reducing oxygen levels, and leading to ocean acidification. The researchers predicted that breaking down the environmental covariance structure that sea urchins are adapted to could make them more vulnerable to climate change.

Additionally, sea urchins are also affected by the destruction of kelp forests, which are crucial carbon sinks that help mitigate climate change. Sea urchins thrive in these forests, but when their populations get out of control due to factors such as the decline of their main predator, sea stars, they can destroy these underwater habitats. This, in turn, can have negative consequences for the climate.

Overfishing

The depletion of coastal predatory fish stocks through overfishing has been linked to an increase in sea urchin grazing activity. Without sufficient predators to keep their numbers in check, sea urchin populations can explode, leading to overgrazing of kelp forests and other marine vegetation. This, in turn, can result in the creation of "urchin barrens" or "marine deserts", where large areas of the seafloor are stripped of vegetation and left barren.

For example, in the 1970s, overfishing of predatory fish such as Atlantic wolffish, haddock, and Atlantic cod off the coasts of Norway and Russia led to a massive bloom of sea urchins. This resulted in the denuding of over 2000 square kilometres of kelp forest, turning it into a marine desert. Similarly, in the Caribbean, the overfishing of groupers and snappers has led to an increase in the population of their competitor, the Threespot Damselfish, which is an aggressive reef predator of the long-spined sea urchin.

The impact of overfishing on sea urchin populations can also have indirect effects on the spread of diseases among sea urchins. In southern California, for instance, areas where sea urchin predators like the California spiny lobster were heavily fished had four times as many sea urchin epidemics as in unfished areas. This suggests that removing top predators can favour disease transmission in prey populations.

Additionally, overfishing of sea urchins themselves can also have negative consequences for marine ecosystems. Sea urchins play a crucial role in controlling algal populations and maintaining the health of coral reefs. When sea urchin populations decline due to overfishing, it can lead to excessive algae growth, which can smother and kill corals. This has been observed in the Caribbean, where the loss of long-spined sea urchins due to a combination of disease and overfishing has resulted in many coral reefs becoming overgrown with algae.

To address these issues, sustainable fishing practices, such as regulated quotas, size limits, and protected areas, are essential. By managing fishing activities and preserving key predators of sea urchins, we can help maintain the delicate balance of marine ecosystems and ensure the long-term viability of sea urchin populations.

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