Sea Urchin Struggles: Pollution's Impact Explored

Sea urchins are an important part of marine ecosystems, playing a critical role in maintaining the balance between coral and algae. However, their populations have been affected by various factors, including pollution. Nutrient pollution on coral reefs has been found to contribute to sea urchin outbreaks by increasing algal growth, which sea urchins feed on. Additionally, chemical pollution from plastics has been shown to cause deformities in sea urchin larvae, with chemicals added to plastics or accumulated from ocean pollutants being the likely culprits. Noise pollution has also been found to stress sea urchins, with high-frequency noise causing increased enzyme activity and stress-related genes in black sea urchins. These various forms of pollution can have detrimental effects on sea urchin populations and the ecosystems they inhabit.

Noise pollution

Sea urchins have been found to be sensitive to ocean noise. A study on the black sea urchin species Arbacia lixula, which is mainly found in the Mediterranean Sea, showed that these organisms do respond to high-frequency noise. The study, conducted by Vazzana et al., found that the activity of certain enzymes increased in urchins exposed to noise, and that the expression of the HSP70 gene, associated with stress, was higher in these urchins. This indicates that black sea urchins experience stress due to ocean noise.

Another study by Dr. Steve Simpson of the University of Bristol also found that human noise pollution in the ocean can negatively impact sea urchins. Baby reef fish were found to use sounds made by sea urchins, among other organisms, to locate coral reefs. With increasing noise pollution from ships, wind farms, and oil prospecting, this crucial behaviour is under threat.

Overall, noise pollution is a significant stressor for sea urchins and can have detrimental effects on their behaviour, physiology, and population dynamics. More research is needed to fully understand the impacts of noise pollution on sea urchin life cycles and to develop effective mitigation strategies.

Plastic chemicals

Sea urchins are among the many marine organisms affected by plastic pollution. Research has shown that plastic chemicals released into the ocean cause deformities in sea urchin embryos, leading to developmental abnormalities and, in some cases, death.

In a study conducted by the University of Exeter, scientists soaked various plastic samples in seawater, removed the plastic, and then raised sea urchin embryos in the water. The study found that the urchins developed abnormalities, including deformed skeletons and nervous systems. These deformities were caused by chemicals embedded in the plastics that leached into the water rather than the plastics themselves.

The plastic-to-water ratio in the study is typically only seen in severely polluted places. However, it raises concerns about the potential impact of plastic contaminants on marine life. The study also highlighted the role of industrial additives and environmentally absorbed contaminants in causing these abnormalities.

Another study, led by Dr. Eva Jimenez-Guri from the University of Exeter and the Anton Dohrn Zoological Station, investigated the effects of plastic pollution on sea urchin larvae. They found that exposure to plastic pollution caused developmental abnormalities, including malformation of the skeleton, neural and immune cells, and radialization, which resulted in the larvae being largely formless and unable to survive.

The research revealed that new PVC nurdles released high concentrations of zinc into the water, causing damage to the larvae. In contrast, beach-collected plastic samples gathered in Cornwall, UK, did not release high levels of zinc as most additives had already been released in the sea. However, these particles can still collect organic pollutants, which were responsible for the abnormalities observed in the study.

The studies underscore the detrimental effects of plastic pollution on sea urchin development and the urgent need to reduce plastic contamination in the marine environment.

Climate change

Sea urchins are a vital part of marine ecosystems, playing a critical role in maintaining the balance between coral and algae. However, they are also susceptible to the effects of climate change, which can have both positive and negative impacts on their populations.

One of the main ways climate change affects sea urchins is through ocean acidification. As the oceans absorb more carbon dioxide, the increasing acidity of seawater can cause "acid indigestion" in sea urchins, making it harder for them to digest their food. This can lead to reduced growth, fertility, and even death. Additionally, ocean acidification can interfere with the process of calcification, which is how marine animals build their shells and skeletons. This is particularly concerning for sea urchins as they have hard shells that may become more difficult to grow and maintain in an acidifying ocean.

The warming of the oceans due to climate change is another factor that influences sea urchin populations. Warmer waters can boost the growth rate of baby sea urchins, leading to larger individuals. However, this benefit may be counteracted by the negative impacts of ocean acidification on their reproductive abilities. Warmer waters can also contribute to the destruction of kelp forests, which are a crucial habitat and food source for sea urchins. The loss of kelp forests can have cascading effects on the entire marine ecosystem, including the sea urchin population.

The complex interactions between climate change factors, such as ocean acidification and warming, can have varied effects on different species of sea urchins. Some studies have found that certain species may be more resilient to the changing conditions, while others struggle to adapt. The long-term impacts of climate change on sea urchin populations are still uncertain, but it is clear that their future persistence will depend on their ability to adjust and adapt to these changing ocean conditions.

Nutrient pollution

In some cases, sea urchin populations can reach outbreak densities, and their grazing can remove coral recruits and important coralline algae, leading to unsustainable bio-erosion. While there may be more serious, systemic issues causing urchins to become a problem, nutrient pollution can be a contributing factor.

For example, in the Azores, Webbnesia, and Cabo Verde archipelagos, sea urchin population explosions have been linked to the loss of canopy-forming macroalgae. These macroalgae are important habitat-forming species, and their loss can have negative effects on the associated benthic assemblages.

Ocean acidification

Sea urchins have been used as a model group to study the impacts of climate change on marine species, and research has shown that ocean acidification has a detrimental effect on sea urchin growth, resulting in smaller larval and adult skeletons. This effect is largely caused by energetic constraints and reduced Ω. However, these negative consequences can be mitigated by moderate warming and sufficient food supply.

The impact of ocean acidification on sea urchins is species-specific, indicating that some sea urchin species exhibit greater resilience to low pH environments. For example, populations of purple sea urchins have been found to possess genetic variations that allow them to adapt to changes in ocean pH. Additionally, sea urchins living in naturally acidified habitats, such as upwelling regions and CO2 vents, demonstrate their potential to adapt to ocean acidification.

The effects of ocean acidification on sea urchins are not limited to their growth and development. A study on the green sea urchin, Strongylocentrotus droebachiensis, found that continuous exposure to low pH during the larval stage led to higher mortality and abnormality rates, as well as lower growth rates. Moreover, the formation of the rudiment, an essential structure for metamorphosis, was delayed by two days at a pH of 7.2.

The impact of ocean acidification on sea urchin populations can have ecosystem-level consequences. Sea urchins play a critical role in maintaining the balance between coral and algae in some ecosystems, and their grazing contributes to reef resilience. Therefore, the negative effects of ocean acidification on sea urchins can indirectly affect coral reef health and resilience.

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