Sea cucumbers play a vital role in maintaining the overall health of the Great Barrier Reef through a process of bioturbation.
" These environmental and ecosystem benefits only happen when sea cucumbers occur in good numbers" ....CSIRO.
Sea cucumbers are a class of echinoderms, the Holothuroidea and play a vital role in recycling nutrients, removing detritus and cleaning the marine environment, they are often an overlooked but fascinating creature on the coral reefs here.
Holothurians may be found to be unevenly distributed living in a range of habitats from shallow coastlines to reef areas and deep ocean environments where they have a number of beneficial impacts on their marine environment and to the ecosystem, these include:
Bioturbation of reef sediments by sea cucumbers aerates the upper sediment layers and also cleans it whilst releasing organic material to benthic communities. These benefits occur through the behaviour of sea cucumbers which include burrowing, ingestion, and defecation of sediment grains.
Sea cucumbers ingest sand that has organic matter mixed with it, thereby removing the organic matter in the digestion process, leaving the excreted sand cleaner.
Organic matter in the sediment is also mixed through burrowing.
An individual sea cucumber can clean a vast amount of sand in a year, which is vital to ecosystem health.
Too much organic matter in coastal benthic systems can lead to low oxygen levels, as well as increasing harmful algae species that out grow and dominate other species.
Nutrient recycling - Is when sea cucumbers excrete phosphates and nitrates, which are absorbed by microalgae and bacteria, enriching them with nutrients, that sea cucumbers then in-turn consume, creating a cycle.
Food chain value - Sea cucumbers are thought to have a positive effect for coral production, as they alkalize the water from sediment cleaning. This creates a ‘buffer’ for corals, particularly in areas of low water flow.
Host species - Sea cucumbers are host to numerous species, both parasites and commensals (organisms that live on, or in another without causing harm). Many parasite species that live within and on sea cucumbers are believed to only survive due to this relationship. There are nine species of fish that are known to find refuge inside a sea cucumber (including Lollyfish), mainly in the digestive tract. Some even use this space as part of their life-cycle.
Sea cucumbers are a class of echinoderms, the Holothuroidea and play a vital role in recycling nutrients, removing detritus and cleaning the marine environment, they are often an overlooked but fascinating creature on the coral reefs here.
Holothurians may be found to be unevenly distributed living in a range of habitats from shallow coastlines to reef areas and deep ocean environments where they have a number of beneficial impacts on their marine environment and to the ecosystem, these include:
Bioturbation of reef sediments by sea cucumbers aerates the upper sediment layers and also cleans it whilst releasing organic material to benthic communities. These benefits occur through the behaviour of sea cucumbers which include burrowing, ingestion, and defecation of sediment grains.
Sea cucumbers ingest sand that has organic matter mixed with it, thereby removing the organic matter in the digestion process, leaving the excreted sand cleaner.
Organic matter in the sediment is also mixed through burrowing.
An individual sea cucumber can clean a vast amount of sand in a year, which is vital to ecosystem health.
Too much organic matter in coastal benthic systems can lead to low oxygen levels, as well as increasing harmful algae species that out grow and dominate other species.
Nutrient recycling - Is when sea cucumbers excrete phosphates and nitrates, which are absorbed by microalgae and bacteria, enriching them with nutrients, that sea cucumbers then in-turn consume, creating a cycle.
Food chain value - Sea cucumbers are thought to have a positive effect for coral production, as they alkalize the water from sediment cleaning. This creates a ‘buffer’ for corals, particularly in areas of low water flow.
Host species - Sea cucumbers are host to numerous species, both parasites and commensals (organisms that live on, or in another without causing harm). Many parasite species that live within and on sea cucumbers are believed to only survive due to this relationship. There are nine species of fish that are known to find refuge inside a sea cucumber (including Lollyfish), mainly in the digestive tract. Some even use this space as part of their life-cycle.
"A large portion of sand in the ocean has been cleaned through the gut of a sea cucumber".
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Not to be underestimated is the benefit to coral species as sea cucumbers move away from sandy area's to fossick around corals on solid structures removing organic matter to maintain a healthy standard that corals have evolved in over thousands of years.
By removing detritus from sand and reef substrate this reduces the percentage of organic matter overall and also that which can become suspended in the water column thereby improving visibility but more importantly reducing the spread of algae and disease by removing such algae fibers and disease carrying particles which are transported along the water column via currents and tidal movement. |
An exceptionally low metabolic rate allows sea cucumbers to feed on a substance low in energy value such as sand.
The rarely sighted Stichopus vastus.
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Sea cucumbers have no faces and the soft long body is basically to house a digestive tract with an inlet and outlet at either end.
The outside is covered in a leathery skin, quite often patterned. Underneath, tube feet called 'podia' are used to move, these can have suckers on them to help stay attached easily and their intelligent skin allows flexibility in the skin and body allowing them to squeeze into small or unusual shaped areas. While they vary in shapes typically cucumber in shape, others are more squat or long and elongated like a snake. |
Skin of sea cucumbers is made of catch connective tissue (CCT) or mutable collagenous tissue that shows large stiffness changes in response to stimulation under nervous control and is found in the body walls and ligaments connecting skeletal elements. The dermis of sea cucumbers is a typical example of CCT which is the tissue specific to echinoderms
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Around the mouth numerous feeding tentacles can be extended when required and as food is collected the tentacle is retracted into the mouth opening. Different species have varying shaped/sized and number of feeding tentacles. This species has black tentacles with the light colored 'roundish' shaped 'feet' which mop up particles placing them in the mouth for digestion.
There are 2 types of feeding practice, some species use suspension feeding whereby sea cucumbers place tentacles in the water column to capture phytoplankton and other species are deposit feeders as discussed above. |
There are two ways by which evisceration occurs in sea cucmber species: from the mouth (anterior) or the anus (posterior).
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Sea cucumbers breathe as water is pumped in through the anus into two respiratory trees located on each side of their digestive tract.
Under a stress response sea cucumbers can eviscerate and eject part of their own digestive system out through the anus and even other associated organs, along with defensive chemicals which vary in identity and toxicity between species. A new set of organs can grow within a few weeks under ideal conditions however without ideal conditions the sea cucumber will die. |
Sea cucumbers exhibit a high capacity for regeneration, such that, following ejection of inner organs in a process called evisceration,
a means of defense, the lost organs regenerate.
a means of defense, the lost organs regenerate.
Some of the species sighted on the Great Barrier Reef here.
