Diadema antillarum
Encyclopedia
Diadema antillarum, also known as the lime urchin, black sea urchin or the long-spined sea urchin, is a species
of sea urchin
in the Family
Diadematidae
.
This sea urchin is characterized by its exceptionally long black spines.
It is the most abundant and important herbivore
on the coral reefs of the western Atlantic and Caribbean
basin. When the population of these sea urchins is at a healthy level, they are the main grazers which prevent algae
overgrowth of the reef.
Diadema mostly eat algae, and sometimes seagrass. Starving urchins have been known to become carnivorous.
region, where it inhabits depths down to 70 m. It is also found on the coasts of the tropical Western Atlantic Ocean
, including the Caribbean Sea
and coasts of tropical South America
. This species is ecologically important because it consumes algae that can otherwise grow to such an extent that they can smother coral reefs. They live in holes that are in the reef.
faunal zone as far south as South America and north to the Bahamas, Diadema antillarum underwent mass mortality, with more than 97% of the urchins dying. Since this time some Caribbean
reefs have been overgrown by foliose macroalgae which inhibits coral growth, and this has also has further compounded the ongoing decline the cover of scleractinian corals, as well as having an overall negative affect on coral reef resilience, which encompasses the ability of a system to resist and recover from changes stemming from perturbation events. Recent studies done in Discovery Bay, Jamaica
, and other locations appear to show a massive comeback of Diadema, and great regeneration of the reefs.
The reduced biodiversity of the coral reefs affected tourism in several small countries, which depended on the natural beauty of their reefs to help attract visitors, and because tourism was a major part of the income for these countries, the decreased flow of guests stressed their economy.
Low-density populations, predators, and waves from high-powered storms tends to impede the repopulation of Diadema antillarum. In the fertilization process, male and female urchins excrete fluid to alert other urchins to respond by releasing their eggs and sperm in mass repoduction. With more gametes available, there is a higher chance of fertilization. However, in areas of low-population, a few sea urchins may not be enough to initiate fertilization. After fertilization, there is still a high chance that predators may consume the vulnerable juveniles. Because of the movement of water in powerful storms, urchins can get swept away from their habitat and expire. It is possible to aid the increase in population growth of the urchin with more research and volunteers.
When there are still some areas of high-density urchins, it is possible to relocate urchins to other, low-density reefs. With these methods and the help of volunteer workers, it seems that the shift back to coral-dominated reefs and away from algae-dominated reefs is possible.
When re-locating Diadema it is necessary to remove most mature algae from the re-location area since there are toxins in mature algae that kills the Diadema.
Diadema re-location website.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
in the Family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Diadematidae
Diadematidae
Diadematidae is a family of sea urchins.* Astropyga **Astropyga radiata , extant**Astropyga pulvinata , extant**Astropyga magnifica , extant*Centrostephanus...
.
This sea urchin is characterized by its exceptionally long black spines.
It is the most abundant and important herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
on the coral reefs of the western Atlantic and Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
basin. When the population of these sea urchins is at a healthy level, they are the main grazers which prevent algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
overgrowth of the reef.
Anatomy
Diadema antillarum has a test, or "shell," similar to most other sea urchins. What distinguishes the Diadema is the length of its spines. Most sea urchin spines are 1-3 cm, but the spines in this species are usually 10-12 cm in length, and can grow as long as 30 cm in very large individuals.Life habits
This species usually lives at 1-10 meters in depth on coral reefs. They will often lodge themselves in a crevice, so that only their spines can be seen, but individual urchins who can't find a suitable crevice will live in more exposed situations. Individuals that have been able to find a crevice usually will roam about 1 meter from their crevice at night during feeding. Diadema is very sensitive to light, and will often pick its crevice or resting place based on how much shade there is.Diadema mostly eat algae, and sometimes seagrass. Starving urchins have been known to become carnivorous.
Ecological Importance
Diadema antillarum is still, in some areas, one of the most abundant, widespread, and ecologically-important shallow-water genera of tropical sea urchins. It is found in tropical oceans, particularly in the Indo-PacificIndo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region, where it inhabits depths down to 70 m. It is also found on the coasts of the tropical Western Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, including the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
and coasts of tropical South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. This species is ecologically important because it consumes algae that can otherwise grow to such an extent that they can smother coral reefs. They live in holes that are in the reef.
Die-off of urchins
In 1983, throughout the CaribbeanCaribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
faunal zone as far south as South America and north to the Bahamas, Diadema antillarum underwent mass mortality, with more than 97% of the urchins dying. Since this time some Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
reefs have been overgrown by foliose macroalgae which inhibits coral growth, and this has also has further compounded the ongoing decline the cover of scleractinian corals, as well as having an overall negative affect on coral reef resilience, which encompasses the ability of a system to resist and recover from changes stemming from perturbation events. Recent studies done in Discovery Bay, Jamaica
Discovery Bay, Jamaica
Discovery Bay is a town in Saint Ann Parish on the northern coast of Jamaica. The city is also known locally as Dry Harbour Bay, because it sits in the shadow of the Dry Harbour Mountains in St. Ann. There is a dispute as to whether Christopher Columbus first landed in Discovery Bay or Sevilla la...
, and other locations appear to show a massive comeback of Diadema, and great regeneration of the reefs.
Human relevance
When the sea urchins died due to an unknown disease, the biodiversity of the marine life of the coral reefs suffered a great deal. The resulting lush algae growth stunted and even reversed the development of coral, and the fish and other animals living on the reefs declined in numbers due to less food and shelter.The reduced biodiversity of the coral reefs affected tourism in several small countries, which depended on the natural beauty of their reefs to help attract visitors, and because tourism was a major part of the income for these countries, the decreased flow of guests stressed their economy.
Low-density populations, predators, and waves from high-powered storms tends to impede the repopulation of Diadema antillarum. In the fertilization process, male and female urchins excrete fluid to alert other urchins to respond by releasing their eggs and sperm in mass repoduction. With more gametes available, there is a higher chance of fertilization. However, in areas of low-population, a few sea urchins may not be enough to initiate fertilization. After fertilization, there is still a high chance that predators may consume the vulnerable juveniles. Because of the movement of water in powerful storms, urchins can get swept away from their habitat and expire. It is possible to aid the increase in population growth of the urchin with more research and volunteers.
Research on re-population of the species
Research on the species Diadema antillarum is still in its early stages. The urchins can be grown in laboratories and then relocated. Returning the mature individuals into the wild can have a positive effect on the urchin density of the reef. The increase in population can also be aided by the artificial building of reefs: material such as concrete can encourage the growth of coral, and provide more niches for the urchins to hide from predators such as larger fish.When there are still some areas of high-density urchins, it is possible to relocate urchins to other, low-density reefs. With these methods and the help of volunteer workers, it seems that the shift back to coral-dominated reefs and away from algae-dominated reefs is possible.
When re-locating Diadema it is necessary to remove most mature algae from the re-location area since there are toxins in mature algae that kills the Diadema.
External links
Diadema re-location website.