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Sea urchins are struggling to survive because they can’t "get a grip"

Picture driving through a torrential downpour, your vehicle’s tires are all that’s keeping you grounded. Without the necessary tread, the risk of your vehicle slipping is high. As it turns out, sea urchins, the spiny little dwellers of the sea, face a similar predicament when extreme rainfall disrupts their nearshore habitats.

These downpours dilute the ocean’s salt concentration, leading to a lower salinity level. Even a small change in the salt level in water can impact the sea urchins’ capacity to secure their tube feet to their surroundings.

Imagine it as their version of gripping the road, only in their case, it’s often a matter of survival. Amidst the waves that batter the rocky nearshore environment, sea urchins are heavily reliant on their adhesive structures for movement.

A recent study, co-authored by biologists from Syracuse University, has explored the implications of changing water salinity levels on the adhesive abilities of sea urchins. The study reveals the surprisingly significant role these small creatures play in maintaining marine ecosystems.

Sea urchins are crucial to coral reefs

The data indicates that sea urchins are responsible for grazing nearly 45% of algae present on coral reefs. This means that without them, coral reefs are at risk of being overrun with macroalgae. This can hinder coral growth. Considering the crucial role of coral reefs in coastal protection and biodiversity preservation, protecting sea urchins becomes a matter of utmost priority.

This all ties into larger discussions around climate change. With extreme weather fluctuations such as heatwaves, droughts, heavy rains, and flooding becoming more prevalent, the vast amounts of freshwater entering nearshore ecosystems are drastically altering these habitats.

Austin Garner, an assistant professor in the College of Arts and Sciences’ Department of Biology at Syracuse University, led a team of biologists to study the effects of low salinity on sea urchins’ abilities to grip and move in their environment.

How sea urchins adhere to underwater surfaces

Garner, a member of Syracuse University’s BioInspired Institute, studies how animals adhere to surfaces under variable conditions, incorporating both life and physical sciences.

The team’s study was recently published in the Journal of Experimental Biology, investigating how future climatic extremes might impact sea urchin populations.

Garner explained, “While many marine animals can regulate the amount of water and salts in their bodies, sea urchins are not as effective at this. As a result, they tend to be restricted to a narrow range of salinity levels. Torrential precipitation can cause massive amounts of freshwater to be dumped into the ocean along the coastline causing rapid reductions in the concentration of salt in seawater.”

How the team studied sea urchin adhesion

Researchers conducted the study at the University of Washington’s Friday Harbor Laboratories (FHL). The researchers used live green sea urchins from the lab for the experiments. The team included Andrew Moura, a graduate student in Garner’s lab, and researchers from Villanova University.

They worked in collaboration with Carla Narvaez, a former FHL postdoctoral scholar who is now an assistant professor of biology at Rhode Island College, and Villanova University professors Alyssa Stark and Michael Russell.

In the lab, the researchers sorted the sea urchins into ten groups based on varying salinity levels within each tank. Each group underwent tests to measure their righting response (the ability to flip themselves over), locomotion (speed), and adhesion (the force at which their tube feet detach from a surface). Garner and Moura analyzed the data in their lab at Syracuse, comparing each metric.

What the team discovered

The results unveiled that low salinity levels negatively impacted the sea urchins’ righting response, movement, and adhesive ability. Interestingly, very low salinity levels were the only conditions that significantly impacted the adhesive ability of the sea urchins.

These factors indicate that sea urchins might still manage to stay attached in challenging nearshore conditions. This occurs even though all activities requiring greater coordination of tube feet might be impeded.

Moura elaborated on the implications of this, explaining, “When we see this decrease in performance under very low salinity, we might start seeing shifts in where sea urchins might be living as a consequence of their inability to remain stuck in certain areas that experience low salinity. That could change how much sea urchin grazing is happening and could have profound ecosystem effects.”

This research is a significant step forward in predicting how marine animals like sea urchins will adapt in a changing climate. Additionally, Garner and his team could use their exploration of adhesive principles to improve human-designed adhesive materials. This perfectly aligns with the mission of the Syracuse University BioInspired Institute, which aims to address global challenges through innovative research.

Garner concluded, “If we can learn the fundamental principles and molecular mechanisms that allow sea urchins to secrete a permanent adhesive and use it for temporary attachment, we could harness that power into the design challenges of our adhesives today. Imagine being able to have an adhesive that is otherwise permanent, but then you add another component, and it breaks it down and you can go stick it again somewhere else. It’s a perfect example of how biology can be used to enhance the everyday products around us.”

More about climate change and ocean salinity

Climate change has far-reaching effects on our planet, and one area that has seen considerable impact is ocean salinity. Changes in ocean salinity patterns are a direct result of alterations in the global water cycle.

These include changes in temperature, precipitation, evaporation, and ice melt. These shifts in salinity can have profound impacts on marine life, ocean circulation, and global climate patterns.

Climate change and the water cycle

The Earth’s water cycle involves the continuous movement of water on, above, and below the surface of the Earth. Climate change affects the water cycle by altering precipitation patterns, increasing evaporation rates, and accelerating ice melt.

Rising global temperatures largely drive these changes. This consequence of climate change increases the rate of evaporation from the ocean’s surface and the amount of moisture in the atmosphere, leading to changes in rainfall patterns.

Higher global temperatures cause polar ice caps to melt at an accelerated rate, leading to an influx of fresh water into the ocean. This disrupts the normal balance of salinity, particularly in the polar regions.

At the same time, altered precipitation patterns can result in increased rainfall in some regions. This further dilutes sea water and reducing salinity.

Impact on ocean salinity

Climate change is leading to significant shifts in ocean salinity. Areas experiencing higher evaporation rates, typically in the subtropics, are seeing an increase in salinity as water evaporates and leaves the salt behind. Conversely, areas with higher rainfall or significant ice melt, such as the polar regions and parts of the equator, are seeing reduced salinity as fresh water influx dilutes the sea water.

Changes in salinity are not uniform across the world’s oceans, leading to a patchwork of regions with varying salinity levels. This can disrupt the normal patterns of ocean currents and stratification, affecting the mixing of surface and deep ocean waters, altering nutrient distribution and impacting marine ecosystems.

Implications for ocean circulation

Differences in temperature and salinity largely drive ocean circulation. We know this phenomenon as thermohaline circulation. Warmer, less saline water is less dense and tends to float on the surface.

Conversely, colder, saltier water is denser and sinks. This creates a global “conveyor belt” of ocean currents that circulates heat, nutrients, and gases around the planet.

Changes in salinity due to climate change can disrupt this circulation. Reduced salinity in the polar regions can make surface waters less dense.

This impedes their ability to sink and slowing down the conveyor belt. This could have significant implications for global climate patterns, as ocean currents play a crucial role in distributing heat around the planet.

Impact on marine life

Changes in ocean salinity can have a significant impact on marine life. Many marine species, adapted to a specific range of salinity, may struggle to survive if salinity levels change.

These changes can impact the growth, reproduction, and survival of marine species. This can potentially lead to shifts in species distributions and impacting biodiversity.

Furthermore, changes in ocean circulation and stratification due to altered salinity can impact the distribution of nutrients in the ocean. This harms species’ primary productivity and the marine food web. In particular, changes in salinity can have significant impacts on sensitive ecosystems like coral reefs and polar habitats.

The impact of climate change on ocean salinity is a complex issue with far-reaching implications. Changes in salinity can disrupt ocean circulation, alter marine ecosystems, and impact global climate patterns.

As such, understanding the link between climate change and ocean salinity is crucial for predicting future changes in our oceans and developing strategies to mitigate and adapt to these changes.

More about sea urchins

Sea urchins, members of the Echinoidea class, are a group of marine invertebrates known for their distinctive round shape and spiny exterior. They play a crucial role in marine ecosystems, contributing to the maintenance of biodiversity and the health of habitats like coral reefs and kelp forests.

Description and distribution

Sea urchins possess a hard, round shell covered with sharp spines that they use for protection and locomotion. Their size can range from a few centimeters to over 30 centimeters in diameter. They are equipped with a unique jaw-like structure, the Aristotle’s lantern, which they use for feeding primarily on algae.

Sea urchins are globally distributed across all oceans and depth zones, from the intertidal to the deep sea. They inhabit various habitats including rocky shores, coral reefs, seagrass meadows, and kelp forests.

Ecological Role

Grazing and bioturbation

Sea urchins are primarily herbivores and feed on a variety of algae and seagrasses. They are considered keystone species in many ecosystems due to their substantial influence on community structure. Their grazing activity helps control the growth of macroalgae, promoting biodiversity by preventing a single species from dominating the environment.

Sea urchins also participate in bioturbation – the process of significantly altering the distribution and availability of sedimentary materials and associated nutrients. This activity helps mix and aerate the seafloor, promoting nutrient cycling and contributing to the overall productivity of their habitats.

Impact on coral reefs

In coral reef ecosystems, sea urchins play a critical role in maintaining the balance between corals and macroalgae. By grazing on algae, they prevent the overgrowth that could overshadow corals and limit their growth. This is especially crucial considering that coral reefs, often referred to as “rainforests of the sea”, are some of the most biodiverse and productive habitats on Earth.

Impact on kelp forests

In kelp forest ecosystems, sea urchins serve a similar role by controlling the growth of kelp. However, in the absence of their predators, sea urchins can overgraze and create urchin barrens.

Urchin barrens are areas devoid of kelp and other macroalgae. This demonstrates the importance of keeping urchin populations in check to maintain the balance of these ecosystems.

Conservation and threats

Climate change, overfishing, and habitat destruction pose significant threats to sea urchin populations. Changes in ocean temperature and salinity can impact their survival, growth, and reproduction.

Overfishing of their predators can lead to overpopulation of urchins and subsequent destruction of kelp forests and coral reefs. Therefore, managing these threats and conserving sea urchin populations is crucial for the health of marine ecosystems.

Sea urchins, while often overlooked, play a fundamental role in maintaining the health and balance of marine ecosystems. Their contribution to grazing, bioturbation, and the maintenance of biodiversity makes them indispensable in their habitats.

Understanding the role and importance of sea urchins can guide conservation efforts and inform strategies to protect and enhance the resilience of marine ecosystems.

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