Can Coral Move: Coral reefs, often referred to as the “rainforests of the sea,” are among the most diverse and ecologically vital ecosystems on our planet. These intricate underwater structures, primarily built by tiny organisms known as coral polyps, provide a home to countless marine species. However, their static appearance can be deceiving. One might wonder, can coral move?
The conventional image of coral live portrays them as fixed in place, rooted to the ocean floor. Yet, coral reefs possess a surprising ability to adapt and even relocate in response to environmental changes. This phenomenon challenges our preconceived notions about the mobility of seemingly immobile organisms.
Coral mobility, we delve into the mechanisms that allow coral to move, the triggers behind their movement, and the role of factors like water flow and climate change in shaping their behavior.
How fast can corals move?
Now it appears that some coral species will migrate — and fast — in response to warming waters. Some species Yamano examined migrated as fast as 8.7 miles per year. Yamano calculated that a sample of land-traveling animals migrate only 0.4 miles per year on average.
Coral movement is a fascinating but slow process, as coral polyps are not known for their agility. Corals are sessile organisms, meaning they are typically attached to a substrate and don’t move around like animals do. However, they can exhibit limited and relatively slow forms of movement:
- Growth: Coral colonies primarily expand and “move” through growth. Individual coral polyps continually deposit calcium carbonate exoskeletons, which collectively form the solid structure of the reef. This growth can vary significantly depending on coral species and environmental conditions. On average, corals grow between 0.3 to 2 centimeters per year, with some species growing even slower or faster. Therefore, over long periods, coral reefs can extend and “move” across the seafloor.
- Reproduction and Dispersal: Corals can also “move” through sexual reproduction. Coral polyps release gametes into the water, which, when fertilized, develop into larvae. These larvae can drift with ocean currents for several days to weeks before settling on a suitable substrate and establishing new colonies. This dispersal can enable coral populations to colonize new areas or migrate to more favorable conditions, albeit over extended timeframes.
While corals are not quick or highly mobile like many animals, they do exhibit various mechanisms for movement and adaptation over extended periods. Their capacity to grow, reproduce, and disperse allows them to slowly adjust to changing environmental conditions and contribute to the dynamic nature of coral reefs.
What type of corals move?
The free-living Heterocyathus and Heteropsammia corals include two species that are commonly called walking corals. These corals are able to move across the sand at lightning speed (for a coral, anyways), covering a few meters of territory in a day.
Coral movement, in the sense of relocating from one place to another, is generally not a common characteristic among coral species. Most corals are sessile, meaning they are firmly attached to a substrate and do not have the ability to move like animals. However, there are some exceptions and nuances to consider:
- Soft Corals (Octocorals): Soft corals, also known as octocorals, are a subgroup of corals that belong to the class Octocorallia. Unlike hard corals (Scleractinia), which have a calcium carbonate skeleton, soft corals have a more flexible structure and lack a solid skeleton. This flexibility allows them to sway and move with water currents. While they cannot actively swim, they are more flexible and can adapt to changes in water flow by bending and stretching their bodies.
- Zooxanthellae Migration: Some hard corals with zooxanthellae (symbiotic algae) inside their tissues can exhibit a form of movement related to the relocation of these symbionts. When exposed to high-temperature stress or other environmental factors, some coral species can expel their zooxanthellae, a process known as “bleaching.” This is a stress response, not voluntary movement, but it can lead to a temporary change in the coral’s appearance and behavior.
While most coral species are sessile and do not exhibit active movement, there are some exceptions and nuanced forms of movement related to environmental responses, larval dispersal, and the flexibility of certain coral structures. However, none of these movements involve corals actively relocating themselves over large distances in the way that mobile animals do.
Why can’t we touch coral?
By touching coral, either directly or accidentally, you damage this protective layer. Not only can this action expose the coral to pathogens, but the damage will also trigger a stress response. When corals are stressed, they will eject their zooxanthellae.
Touching coral is generally discouraged and should be avoided for several reasons:
- Fragility: Coral reefs are delicate ecosystems built by tiny coral polyps. These polyps secrete calcium carbonate skeletons that form the structure of the reef. When you touch or handle coral, you risk damaging these fragile structures. Even a seemingly gentle touch can break or kill coral polyps, which can have devastating consequences for the entire reef.
- Chemical Protection: Corals have a protective layer of mucus on their surfaces. This mucus helps deter predators and pathogens. When touched by human hands, this layer can be disrupted, leaving the coral vulnerable to diseases and other threats.
- Human Impact: Coral reefs worldwide face numerous threats, including pollution, overfishing, and climate change. Physical contact with coral can add stress to these already vulnerable ecosystems. Human touch can introduce harmful substances, such as sunscreen chemicals or oils, into the water, further compromising coral health.
- Safety Concerns: Some corals have stinging cells, nematocysts, that can release toxins when touched. While these stings are generally not life-threatening to humans, they can be painful and cause skin irritation or allergic reactions.
Touching coral is discouraged to protect the fragility of coral reefs, prevent harm to coral organisms, reduce human impact, adhere to legal regulations, and promote responsible and ethical behavior in marine environments.
Why is coral so slow?
In order for a coral reef to grow, it must produce limestone (or calcium carbonate) at a rate that is faster than the reef is being eroded. Ocean acidification slows the rate at which coral reefs generate calcium carbonate, thus slowing the growth of coral skeletons.
Coral is slow-growing for several biological and environmental reasons:
- Calcium Carbonate Secretion: Corals build their exoskeletons, the hard, calcium carbonate structures that form the basis of coral reefs, through a process called calcification. This process is slow because it involves the extraction of calcium ions from seawater and the precipitation of calcium carbonate crystals. Corals rely on the availability of calcium ions, which are often limited in seawater, making the calcification process inherently slow.
- Energy Allocation: Corals allocate a significant portion of their energy and resources to growth, reproduction, and defense mechanisms, leaving relatively little energy for rapid movement or locomotion. This energy prioritization favors long-term survival and the development of stable, long-lasting structures like coral reefs over the course of decades to centuries.
- Predation and Competition: Rapid movement or mobility can expose corals to greater risks from predation and competition. Corals have evolved to be relatively sedentary to minimize these risks and establish themselves as dominant competitors in the marine environment.
- Symbiotic Relationships: Many coral species have a symbiotic relationship with zooxanthellae, photosynthetic algae that provide them with energy through photosynthesis. This mutualistic partnership allows corals to grow slowly and efficiently in nutrient-poor waters. Rapid movement could disrupt this crucial relationship.
Coral is slow-growing due to a combination of biological adaptations, energy allocation, environmental factors, and life history strategies. While their sedentary nature may seem disadvantageous in some respects, it has allowed corals to create and sustain some of the most biodiverse and ecologically ecosystems on Earth—coral reefs—over long periods of time.
Are corals easy to break?
Corals are very sensitive to being touched and can break easily, and fish are nervous around potential predators and feel more comfortable when they have space. Next time you’re on a reef, give both fish and corals more room to perform their ecosystem roles.
Corals are not inherently easy to break, but they are fragile and can be damaged relatively easily under certain conditions. Here’s a more detailed explanation of why corals can be susceptible to breakage:
- Calcium Carbonate Structure: Corals have a calcium carbonate exoskeleton that forms the framework of the coral colony. While this structure is strong, it is not as resilient as some other natural materials. Calcium carbonate can be brittle, making it prone to breaking when subjected to external forces.
- Physical Contact: Even a gentle touch or accidental contact with coral can cause damage. Human contact, such as snorkelers or divers accidentally brushing against coral, can break branches or disrupt the delicate coral polyps. This is why it’s crucial to practice “look but don’t touch” when exploring coral reefs.
- Natural Threats: Corals face threats from natural sources like storms and strong wave action. High-energy wave events can break coral branches or dislodge coral colonies from their substrate. These natural disturbances can be a part of the natural life cycle of a reef, but they can also become more frequent and severe due to climate change and human activities.
- Anchor Damage: In areas where boats anchor near coral reefs, the dropping of anchors and dragging of anchor chains across the seafloor can cause extensive damage to coral colonies. This is a significant concern in heavily trafficked or poorly managed marine areas.
While corals are not inherently easy to break, they are fragile and can be damaged by physical contact, natural forces, anchor damage, mining, and other human-related activities. Given the vital ecological importance of coral reefs and their slow growth rates, to handle them with care and take measures to protect these delicate ecosystems from harm.
Can coral move to escape environmental stressors?
Coral, as a sessile organism, cannot move in the same way animals do to escape environmental stressors. However, corals have evolved several strategies to adapt and survive in the face of changing environmental conditions:
- Symbiosis and Thermal Tolerance: Corals have a mutualistic relationship with zooxanthellae, photosynthetic algae that provide them with energy. This relationship allows corals to thrive in nutrient-poor waters but also makes them sensitive to environmental stressors like elevated sea temperatures. Some coral species have developed a degree of thermal tolerance, allowing them to withstand higher temperatures for short periods. However, prolonged high temperatures can lead to coral bleaching, where they expel their symbiotic algae and become stressed or die.
- Nutrient Availability: Corals are sensitive to changes in nutrient levels in the water. Excessive nutrients from pollution or agricultural runoff can lead to overgrowth of algae, which can outcompete corals for space and light. In such cases, corals may be outcompeted, but they cannot physically move to escape the nutrient-rich waters.
- Sedimentation: Sediment runoff from construction, deforestation, or agricultural activities can smother coral polyps and block sunlight. Corals cannot move away from sedimentation, so they rely on water flow and their mucus production to minimize the impact of sediment.
While corals cannot physically move to escape environmental stressors, they rely on a combination of physiological, ecological, and evolutionary strategies to survive and adapt to changing conditions. Unfortunately, the pace of current environmental changes, driven largely by human activities, often outstrips the ability of corals to adapt, putting these critical ecosystems at risk. Conservation efforts and reducing stressors are to help coral reefs persist in the face of ongoing challenges.
How do coral species differ in their ability to move?
Coral species vary in their ability to move, with some exhibiting limited forms of mobility while others remain mostly sessile. These differences are primarily influenced by biological and ecological factors. Here’s a detailed explanation of how coral species differ in their ability to move:
- Sessile vs. Semi-Sessile: The majority of coral species are considered sessile, meaning they are firmly attached to a substrate and do not have the ability to actively move. Sessile corals include the stony corals (Scleractinia), which are the primary reef-building corals, and many soft corals (Octocorallia). These corals typically rely on other mechanisms for survival and reproduction, such as growth and polyp extension.
- Soft Corals (Octocorals): Soft corals are a subgroup of corals belonging to the Octocorallia class. They are often referred to as “soft” because they lack the rigid calcium carbonate skeleton found in stony corals. While soft corals are still primarily sessile, they have more flexibility in their structures and can sway and bend with water currents. This allows them to adjust to changing flow conditions.
- Coral Polyp Behavior: Even within sessile coral species, individual coral polyps can exhibit limited mobility. Polyps can extend their tentacles to capture planktonic prey or retract them for protection. While this movement is relatively small-scale, it helps corals feed and defend themselves.
- Larval Dispersal: Corals, regardless of species, have a dispersal phase during their life cycle. When coral colonies reproduce, they release gametes into the water, which combine to form larvae. These larvae are transported by ocean currents and can travel for several days to weeks before settling on a suitable substrate to establish new colonies. While this movement is part of their reproductive strategy, it does not involve adult corals actively relocating themselves.
While most coral species are sessile, there are variations in their ability to move or adapt to changing conditions. Soft corals have some flexibility and can sway with water currents, and all corals rely on the dispersal of larvae for reproductive purposes. However, the primary mode of existence for coral colonies is attachment to a substrate, where they employ various strategies for survival, growth, and reproduction.
What are the mechanisms through which coral polyps can relocate?
Coral polyps, which are the individual organisms that make up a coral colony, are generally sessile, meaning they are firmly attached to a substrate and do not have the capacity for active movement. However, there are some mechanisms through which coral polyps can relocate or adjust their positions, albeit on a relatively small scale. These mechanisms include:
- Polyp Extension and Contraction: Coral polyps can extend their tentacles and body parts to capture food, maximize light exposure for photosynthesis (in the case of symbiotic algae), or defend against threats. They can also contract their bodies to protect themselves from physical disturbances or environmental stressors. While this movement is limited in scope, it allows polyps to adjust to local conditions and optimize their immediate surroundings.
- Epithelial Crawling: Some coral species, such as the blue coral (Heliopora coerulea), are capable of a slow and limited form of crawling through a process known as “epithelial crawling.” In this mechanism, the coral polyps secrete a mucus layer and then contract their bodies rhythmically. The mucus acts as a lubricant, allowing the polyps to move short distances (typically millimeters to centimeters) over the substrate. While this movement is relatively slow, it can help corals find optimal conditions for growth or adapt to changes in their microenvironment.
- Tentacle Movement: Coral polyps can actively move their tentacles to capture planktonic prey. They use specialized stinging cells called nematocysts to immobilize and capture small organisms. This movement helps polyps obtain nutrients and adjust their feeding behavior based on the availability of prey in the water column.
These mechanisms of movement and adjustment are primarily adaptations to optimize local conditions and immediate survival, rather than long-distance relocation. Corals are fundamentally sessile organisms, and their ability to move is limited in comparison to mobile animals.
Coral can move reveals the intriguing complexities of these vital marine organisms. While coral is primarily characterized as sessile, firmly anchored to the ocean floor, this apparent stillness belies a fascinating array of adaptations and mechanisms that allow corals to navigate their environment in their own unique way.
Coral’s ability to adjust its position is limited compared to mobile animals, with mechanisms like polyp extension, epithelial crawling in some species, and tentacle movement serving to optimize immediate surroundings rather than enable long-distance relocation. Coral’s life cycle also involves a dispersal phase, where coral larvae drift with ocean currents before settling in new locations, contributing to population dynamics and reef expansion.
Ultimately, coral’s resilience and survival depend on a suite of strategies, including symbiotic relationships, growth, and reproductive dispersal. While they may not be agile in the conventional sense, coral’s capacity to adapt and endure in the face of environmental challenges underscores their importance as foundation species in marine ecosystems. Protecting and conserving these precious and fragile habitats is crucial to safeguarding the future of coral and the myriad species that depend on them.