The sea cucumber is often overlooked and underestimated. However, these species are these unsung heroes of the ocean. Let’s embark on a thrilling voyage with us to unravel the interesting facts of sea cucumbers, delving into their remarkable abilities to know how they save marine ecosystems.
Class: Holothuroidea
1. Sea stars are their relatives
Although sea cucumbers may resemble plants, they are actually animals classified under the echinoderm family, sharing their lineage with sea stars, sand dollars, and sea urchins. The vast diversity of sea cucumbers encompasses approximately 1,500 different species, displaying a wide array of shapes, colors, and sizes.
These species can be very small, being less than an inch (2.5 cm), or big enough to exceed 6 feet (1.8 m). Nevertheless, on average, they have a size of between 3 and 12 inches (7 – 30 cm) in length.
These creatures exhibit a body shape resembling that of a cucumber, featuring tiny spines scattered across their skin. On their lower surface, they sport tentacle-like tube feet, which allow the sea species to move through contractions and crawling. On their body, there are 2 holes at the two ends, one is their mouth and the other is their anus.
While the majority of sea cucumbers possess a resilient, leathery outer body, certain species enhance their protection by developing hardened areas rich in calcium carbonate. They come in various colors, such as red, orange, pink, green, blue, purple, brown, and black.
Here are some types of sea cucumber:
– The curry sea cucumber (Stichopus hermanni) is a tropical species that holds commercial value in numerous countries due to its distinctive features.
– The snake sea cucumber, recognized as the largest in the world, measures an impressive 10 feet (3 m) in length. On the other hand, the orange-footed sea cucumber (Cucumaria frondosa) holds the title of being the largest in New England and the US, while the tiger’s tail claims the same honor in the western Atlantic Ocean.
– The pineapple sea cucumber, also known as the sandfish or prickly redfish, can be found from the Red Sea to East Africa and all the way to Hawaii and Polynesia. Its intriguing appearance includes pointed, star-shaped teats covering its entire body.
– The Leopard sea cucumber, also called leopardfish or tigerfish, stands out for its smooth, tough, leathery skin, and distinctive dark eye spots. Meanwhile, the conspicuous sea cucumber, notable for its flexible, wormlike body.
The other species can include the sea pigs, the Johnson, donkey dung, lion’s paw, pink warty, greenfish or black knobby, white teatfish or white teeth, sea apple, royal, thorny, hairy, or white sea cucumber.
2. They Breathe Through Their Anus
Sea cucumbers exhibit a captivating and exceptional breathing mechanism. The bodies of sea cucumbers contain a respiratory tree that links to both sides of the intestine, running from their anus and leading to the cloaca. This specialized respiratory system is crucial for their respiration process.
During respiration, sea cucumbers inhale oxygenated water through their anus. The water subsequently enters the respiratory tree, where gas exchange occurs. Within the intricate branches of their respiratory system, sea cucumbers extract oxygen from the water and transfer it into the fluids within their body cavity, ensuring their vital supply for survival.
This adaptation exemplifies the extraordinary diversity of survival strategies prevalent in the natural world.
The species do not possess a brain. Instead, they rely on a nerve ring encircling their oral cavity, from which nerves extend to their tentacles and pharynx. Interestingly, even in the absence of the nerve ring, these remarkable creatures can still function and move.
Without sensory organs, they possess dispersed nerve endings within their skin, granting them a sense of touch and a degree of sensitivity to light. However, certain species still have small eyes located near their tentacle bases or statocysts.
3. Sea cucumber Habitat
Sea cucumbers are widely distributed across marine environments worldwide, encompassing both shallow and deep-sea areas. Though their preference lies in tropical waters, they can be found in the Pacific and Indian Ocean regions. You can see them near sandy shores or on coral reefs where they actively feed.
These intriguing organisms are benthic, indicating they live on the ocean floor. However, some species, like the pelagic sea cucumber or the pink see-through fantasia (aka Spanish dancer) float and swim in the ocean.
4. They’re important to the ecosystem
Sea cucumbers are consumers, not decomposers. They primarily scavenge on small food items found on the ocean floor, in the water column, on rocks/coral reefs, or within the surrounding water. They mostly look for food at night (nocturnal). These species possess an omnivorous diet, consuming both plant and animal material such as aquatic invertebrates, algae, plankton, and waste particles. They also eat seagrass and seagrass sediment.
Their diet, however, can vary considerably depending on weather conditions, locations, and migration patterns, owing to their widespread distribution in various ocean regions. Sea cucumbers in the aquatic environment engage in filter-feeding on plankton, whereas others adopt a strategy of burrowing into the sand in search of organic matter. Some species residing at the bottom of the sea collect detritus from the seafloor with their tentacles.
These species use their tube feet around their mouth to eat.
Sea cucumbers have benefits to their ecosystems. Their feeding processes like stirring up the seabed, digestion, and excretion hold immense significance for their habitat.
By consuming sand and feeding on algae residing within it, sea cucumbers contribute to the prevention of algal blooms. They accomplish this by digesting organic matter and expelling purified sand. This behavior can be likened to the beneficial role of earthworms in enhancing soil quality. In the same manner, the species enhance the water with vital nutrients that facilitate the growth of coral and help maintain proper water acidity levels.
Sand sifting or burrowing sea cucumbers eat sediment, extracting food particles, and excreting elongated strands of sediment. This process significantly contributes to nutrient cycling in the ocean. Their excrement contributes to raising water alkalinity, which plays a vital role in countering ocean acidification. Remarkably, a solitary sea cucumber has the capacity to filter as much as 99 pounds of sediment per year.
5. They expel their organs to defend
These sea creatures are slow and vulnerable to many predators, including sea stars, sharks, seals, lobsters, seagulls, turtles, Partridge Tun snails, sea otters, some fish species, crabs, walrus, and humans. This is why they have evolved various strategies to protect themselves from harm.
Their natural defensive strategy includes revealing skeletal hooklike structures when threatened, making themselves less desirable and difficult for predators to prey upon. Nonetheless, their defense mechanism extends far beyond mere physical barriers.
When faced with threats or scared, they emit thick and adhesive white filaments, necessitating the use of a knife to remove them. Moreover, they possess the ability to spit out their internal organs through their anus, a phenomenon known as evisceration. This can shock and disorient their predators, creating a chance for them to flee from danger. The species can apply this tactic over and over again because their lost organs can be regenerated in just a few weeks. Furthermore, certain species manufacture holothurin, a deadly toxin for numerous fishes.
In addition to their dramatic defense mechanisms, sea cucumbers showcase remarkable camouflaging abilities. They possess the unique capability to “turn into liquid,” enabling them to effortlessly go through narrow passages to escape from predators. After going through, they can swiftly revert to their original state. This extraordinary ability stems from the flexibility of collagen fibers in their leathery skin, which they can loosen and tighten at will.
6. Fish Live Inside Their Anus
Sea cucumbers are hosts for various species. Notably, parasitic pearlfish have discovered an unusual residence within their anus. While the sea cucumber breathes by rhythmically pumping water in and out, the pearlfish navigate towards a suitable host using their keen sense of smell. Once found, they carefully and gradually maneuver their way inside, with some even choosing to enter tail-first.
When settled inside the cloaca, these fish peacefully coexist and thrive within their host. They get food from the remnants of the sea cucumber’s digestion, establishing an intimate and mutually beneficial symbiotic relationship. However, not all pearlfish are satisfied with this. Some species take on a more malevolent parasitic strategy, feeding on its internal tissues, including its gonads.
Apart from pearlfish, a solitary sea cucumber transforms into a miniature ecosystem, offering refuge to numerous smaller animals. Ghost gobies, crabs, polychaete worms, and cleaner shrimps are among the creatures that find shelter on its body, delighting in a feast of particulate matter, decaying tissue, and parasites.
7. Reproduction
Sea cucumbers utilize both sexual and asexual reproduction methods, in which the species generate identical clones.
In addition to sexual reproduction, sea cucumbers also reproduce sexually. Females release eggs while males release sperm into the water. They come into contact with each other, external fertilizations happen to create eggs. These eggs float in the ocean, eventually hatching into larvae that mature into adults. However, the success of this process relies on the presence of a significant population of sea cucumbers.
Both reproductive strategies come with their own set of pros and cons. On the one hand, only a small number of their caterpillars survive to reach adulthood, on the other hand, clones lack the genetic diversity necessary to ensure the species’ resilience against current and future environmental fluctuations.
Sea cucumbers’ lifespan is remarkably long, as they can live for 5 to 10 years.
8. Threats
Sea cucumbers, known for their ecological importance, are unfortunately vulnerable to various human activities. These fascinating marine creatures, highly regarded as culinary delicacies and “love drugs for man,” are particularly sought after in Asian countries. They are not cheap at all. The most expensive sea cucumber is the Japanese with $3500/kg. It is worth noting that some species are actively farmed to meet the demand for these delicacies in Asian cuisine.
Despite efforts to implement protective regulations, their populations continue to decline due to harvests. The brown sea cucumber, in particular, is at risk of extinction.
In January 2016, the seriousness of this matter came into focus as Hawaii implemented regulations to manage the harvesting of these creatures. These regulations were a response to the concerning decline in nearshore populations observed in Maui and Oahu.
Similar to sharks, which are well-known marine champions, sea cucumbers also require immediate conservation measures to ensure their survival and maintain the fragile marine equilibrium.
References:
- Thoughtco.com
- Americanoceans.org
