''Tripneustes gratilla'', the collector urchin or halloween urchin, is a species of

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

. Collector urchins are found at depths of in the waters of the

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

, the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

, and The Bahamas. They can reach in size.

Description

Collector urchins are dark in color, usually bluish-purple with white spines. The pedicles are also white, with a dark or black base. Individuals found at Green Island had orange-tipped spines. The spines of some specimens are wholly orange, while those of others are only orange-tipped or completely white. This color disappears when the individual dies or is taken out of the

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

, and is difficult to preserve. Collector urchins reach in size. Debris tends to "collect" on these urchins, hence their name. Unlike some other sea urchins, collector urchins graze continually, day and night. They graze near the substrate, and their diet includes

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

periphyton Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs ( German "surface growth" or "overgrowth", ) refers to the ...

, and

seagrass Seagrasses are the only flowering plants which grow in marine (ocean), marine environments. There are about 60 species of fully marine seagrasses which belong to four Family (biology), families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and ...

. Most collector urchins feed on seagrass fronds; this has an ecological impact varying with the season and abundance of the urchins. They feed voraciously between November and January; one study found they consumed up to or in excess of half of seagrass production. On an annual basis, however, the same study concluded that about 24% of seagrass production is consumed by the collector urchin. The seagrass species grazed are mainly ''

Thalassodendron ciliatum ''Thalassodendron ciliatum'', the sickle-leaved cymodocea, is a species of plant in the ''Thalassodendron'' genus of seagrasses in the family Cymodoceaceae Cymodoceaceae is a family of flowering plants, sometimes known as the "manatee-grass fa ...

'' and '' Syringodim isoetifolium'', but other algae may also be consumed. Collector urchins are prey for puffer fish,

octopus An octopus (: octopuses or octopodes) is a soft-bodied, eight-limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. Like oth ...

es, and humans. T. gratilla collector.jpg, ''Tripneustes gratilla'' covering itself with rocks (

Réunion Réunion (; ; ; known as before 1848) is an island in the Indian Ocean that is an overseas departments and regions of France, overseas department and region of France. Part of the Mascarene Islands, it is located approximately east of the isl ...

island). Tripneustes gratilla.jpg, ''idem''. T. gratilla podia.jpg, This urchin has long and obvious podia. T. gratilla face orale.jpg, Aboral side. File:Tripneustes gratilla Asia.jpg, More colored specimen in Asia. File:Tripneustes gratilla 10070605.jpg, Even more colored specimen from Polynesia.

Distribution and habitat

Collector urchins are found in the waters of the

, the

, and

The Bahamas The Bahamas, officially the Commonwealth of The Bahamas, is an Archipelagic state, archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of ...

. They are distributed from

Mozambique Mozambique, officially the Republic of Mozambique, is a country located in Southeast Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west, and Eswatini and South Afr ...

to the Red Sea, westward to Hawaii and

Clarion Island Clarion Island (), formerly Santa Rosa, is the second largest, westernmost and most remote of Mexico, Mexico's Revillagigedo Islands. The island is located west of Socorro Island and just under from the Mexican mainland. It has an area of an ...

, eastward to

Paumotu Tuamotuan, Paumotu or Paumotu (Tuamotuan: ' or ') is a Polynesian language spoken by 4,000 people in the Tuamotus, Tuamotu archipelago, with an additional 2,000 speakers in Tahiti. The Pa‘umotu people today refer to their islands as Tuamotu wh ...

, and as far south as

Port Jackson Port Jackson, commonly known as Sydney Harbour, is a natural harbour on the east coast of Australia, around which Sydney was built. It consists of the waters of Sydney Harbour, Middle Harbour, North Harbour and the Lane Cove and Parramatta ...

. It also occurs at

Shark Bay Shark Bay () is a World Heritage Site in the Gascoyne region of Western Australia. The area is located approximately north of Perth, on the westernmost point of the Australian continent. UNESCO's listing of Shark Bay as a World Heritage S ...

on the west coast of

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and have been found in the waters of Governor's Harbor, Eleuthera Island, Bahamas. Mature collector urchins prefer open sea bottoms with some cover, but the young prefer rocky areas for concealment. Collector urchins inhabit depths of .

Relationship to humans

Collector urchins are economically important in some parts of the world. They are edible and sometimes exploited by humans; as a result, they have become less abundant. Over the past ten years,

overexploitation Overexploitation, also called overharvesting or ecological overshoot, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to ...

has caused a sharp decline in the collector urchin population.

Removing invasive algae

Hawaii state aquatic biologists, working with divers from the Hawaii Division of Aquatic Resources placed 1,000 native collector urchins on a area of reef in Kaneohe Bay on January 29, 2011. The urchins were released to help control the invasive

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), '' Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

'' Kappaphycus'', also known as "smothering seaweed," which has overrun local

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

. Tripneustes gratilla stays on the reef and is an effective algae grazer. The urchins were bred at Anuenue Fisheries Research Center from about a million

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

. The larvae produced 25,000 specimens that reached at least in diameter in about five months. The delicate young had to be kept suspended in the

water column The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...

for weeks after hatching. The project intends to release 10,000 to 25,000 urchins per month. Kaneohe Bay is the only

barrier reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

system in the United States. The alien seaweed was brought to Hawaii for commercial applications such as keeping ice chunks out of

ice cream Ice cream is a frozen dessert typically made from milk or cream that has been flavoured with a sweetener, either sugar or an alternative, and a spice, such as Chocolate, cocoa or vanilla, or with fruit, such as strawberries or peaches. Food ...

. It escaped when the industry failed. For years, the state used a marine vacuum pump to remove the algae, at one time removing . In 2009, the scientists gathered urchins from other parts of the state and released them at Kaneohe Bay. A year later, they found the urchins had successfully kept the seaweed down.

References

External links