Instruct: Given a question, retrieve relevant documents that can help answer the question.
Query: How many species of sea urchin are there?
Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to . Their tests (hard shells) are round and spiny, typically from across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Starfish are marine invertebrates. They typically have a central disc and five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. They are opportunistic feeders and are mostly predators on benthic invertebrates. Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding. They have complex life cycles and can reproduce both sexually and asexually. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence. The Asteroidea occupy several significant ecological roles. Starfish, such as the ochre sea star ("Pisaster ochraceus") and the reef sea star ("Stichaster australis"), have become widely known as examples of the keystone species concept in ecology. The tropical crown-of-thorns starfish ("Acanthaster planci") is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world's 100 worst invasive species.
Atlantic wolffish use their strong jaws to eat hardshell molluscs, crustaceans, and echinoderms. They do not eat other fish. They are known to frequently eat large whelks ("Buccinum"), cockles ("Polynices", "Chrysodomus" and "Sipho"), sea clams ("Mactra"), large hermit crabs, starfish, sea urchins. They are an important predator of sea urchins and green crabs, whose populations escalate rapidly and can negatively affect the health of a marine system.
Houtman Abrolhos has an extremely high diversity of echinoderms, with 172 species having been recorded there. 63% of these are tropical species, 14% are temperate, and 22% are endemic to Western Australia. None is endemic to the Houtman Abrolhos. Published surveys have not included observations of the crown-of-thorns starfish ("Ananthaster planci"), but individuals have occasionally been observed there. For a complete list of species, see list of echinoderms of the Houtman Abrolhos.
Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera.
Marine biota in the region have representatives of both the Indian and Pacific oceans which were caught in the Caribbean before the emergence of the Isthmus of Panama four million years ago. In the Caribbean Sea there are around 1,000 documented species of fish, including sharks (bull shark, tiger shark, silky shark and Caribbean reef shark), flying fish, giant oceanic manta ray, angel fish, spotfin butterflyfish, parrotfish, Atlantic Goliath grouper, tarpon and moray eels. Throughout the Caribbean there is industrial catching of lobster and sardines (off the coast of Yucatán Peninsula).
The largest marine algae are kelp species, which include bull kelp ("Durvillaea antarctica"), which can reach over long and is thought to be the strongest kelp in the world. As many as 47 individual plants can live on , and they can grow at a day. Kelp that is broken off its anchor provides a valuable food source for many animals, as well as providing a method of oceanic dispersal for animals such as invertebrates to travel across the Southern Ocean by riding floating kelp.
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish), although no species has yet been documented in the deepest 25% of the ocean. With 33,600 described species, fish exhibit greater species diversity than any other group of vertebrates.
The American oystercatcher feeds almost exclusively on shellfish and other marine invertebrates. Oysters are a staple of their diet, as their name suggests, but they also eat mussels, clams, limpets, sea urchins, starfish, crabs, and worms. In general, they use their bills to catch shellfish. As they walk across a shellfish bed, they look for a mollusk with a partially opened shell. When they find one, they jab their bill into the shell and sever the muscle that causes the shell to clamp shut. This can be dangerous, however, as they are sometimes drowned when they don't completely severe this muscle and the shell clamps down on their bill. A strong, tightly rooted mollusk can hold the bird in place until the tide comes in. They also feed by carrying loose shellfish out of the water and hammering at the shell or by probing the sand for soft-shell or razor clams.
Cranchia scabra is a species of glass squid. It is the only species in the genus, and is fairly small (about 150 mm). The mantle is covered by large, multi-pointed cartilagenous tubercles. When disturbed, the squid often pulls its head and arms into the mantle cavity and folds its fins tightly against the mantle to form a turgid ball. The tubercules, presumably, provide some type of protection, but it is unclear what predators are affected and how. In addition, the squid may ink into the mantle cavity, making the ball opaque. This was thought to be an aberrant behavior due to stress and confinement of shipboard aquaria until the same inking behavior was seen in cranchiids from submersibles. The function of this behavior is unknown.
Seaweed or macroalgae refers to several species of macroscopic, multicellular, marine algae. The term includes some types of red, brown, and green macroalgae. Marine algae species such as kelps provide essential nursery habitat for fisheries and other marine species and thus protect food sources; ocean algae species from seaweeds to planktons play a vital role in carbon capture, producing up to 90 percent of the planet's oxygen. Understanding these roles provides guiding principles for conservation and sustainable use of seaweeds to take precedence over industrial exploitation. Mechanical dredging of kelp, for instance, destroys the resource and dependent fisheries. Certain species of seaweed are valuable for nutrition, biomedicine, bioremediation, and other uses.
The shark is seen by divers in many places, including the Bay Islands in Honduras, Thailand, Indonesia, the Philippines, the Maldives close to Maamigili (South Ari Atoll), the Red Sea, Western Australia (Ningaloo Reef, Christmas Island), Taiwan, Panama (Coiba Island), Belize, Tofo Beach in Mozambique, Sodwana Bay (Greater St. Lucia Wetland Park) in South Africa, the Galapagos Islands, Saint Helena, Isla Mujeres (Caribbean Sea), La Paz, Baja California Sur and Bahía de los Ángeles in Mexico, the Seychelles, West Malaysia, islands off eastern peninsular Malaysia, India, Sri Lanka, Oman, Fujairah, Puerto Rico, and other parts of the Caribbean. Juveniles can be found near the shore in the Gulf of Tadjoura, near Djibouti, in the Horn of Africa.
There is currently no robust estimate of the global whale shark population. The species is considered endangered by the IUCN due to the impacts of fisheries, bycatch losses, and vessel strikes, combined with its long lifespan and late maturation. In June 2018 the New Zealand Department of Conservation classified the whale shark as "Migrant" with the qualifier "Secure Overseas" under the New Zealand Threat Classification System.
The knifetooth sawfish ("Anoxypristis cuspidata"), also known as the pointed sawfish or narrow sawfish, is a species of sawfish in the family Pristidae, part of the Batoidea, a superorder of cartilaginous fish that includes the rays and skates. Sawfish display a circumglobal distribution in warm marine and freshwater habitats. Their extant biodiversity is limited to five species belonging to two genera (Pristis and Anoxypristis). The sawfishes are characterised by the long, narrow, flattened rostrum or extension on their snout. This is lined with sharp transverse teeth, arranged in a way that resembles the teeth of a saw. It is found in the shallow coastal waters and estuaries of the Indo-West Pacific, ranging from the Red Sea and the Persian Gulf to southern Japan, Papua New Guinea and northern Australia. It is the only living member of the genus Anoxypristis, but was previously included in the genus "Pristis". Compared to that genus, "Anoxypristis" has a narrower rostral saw with numerous teeth on the distal part and no teeth on the basal one-quarter (toothless section about one-sixth in juveniles). This endangered species reaches a length of up to .
The brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Most brown algae live in marine environments, where they play an important role both as food and as habitat. For instance, "Macrocystis", a kelp of the order Laminariales, may reach 60 m (200 ft) in length and forms prominent underwater kelp forests. Kelp forests like these contain a high level of biodiversity. Another example is "Sargassum", which creates unique floating mats of seaweed in the tropical waters of the Sargasso Sea that serve as the habitats for many species. Many brown algae, such as members of the order Fucales, commonly grow along rocky seashores. Some members of the class, such as kelps, are used by humans as food.
Atlantic herring ("Clupea harengus") is a herring in the family Clupeidae. It is one of the most abundant fish species in the world. Atlantic herrings can be found on both sides of the Atlantic Ocean, congregating in large schools. They can grow up to in length and weigh up to . They feed on copepods, krill and small fish, while their natural predators are seals, whales, cod and other larger fish.
Macrocystis pyrifera, commonly known as giant kelp or giant bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus "Macrocystis". Giant kelp is common along the coast of the eastern Pacific Ocean, from Baja California north to southeast Alaska, and is also found in the southern oceans near South America, South Africa, Australia, and New Zealand. Individual algae may grow to more than long at a rate of as much as per day. Giant kelp grows in dense stands known as kelp forests, which are home to many marine animals that depend on the algae for food or shelter. The primary commercial product obtained from giant kelp is alginate, but humans also harvest this species on a limited basis for use directly as food, as it is rich in iodine, potassium, and other minerals. It can be used in cooking in many of the ways other sea vegetables are used, and particularly serves to add flavor to bean dishes.
Crown-of-thorns starfish ("Acanthaster planci") is the major predator of the reefs, as it preys upon coral polyps by climbing onto them, extruding its stomach over them, and releasing digestive enzymes to absorb the liquefied tissue. An individual adult can eat up to 6 m of reef per year. In 2000, an outbreak of crown-of-thorns starfish contributed to a loss of 66% of live coral cover on sampled reefs. Changes in water quality and overfishing of natural predators, such as the Giant Triton, may have contributed to an increase in the number of crown-of-thorns starfish.
The leatherback sea turtle ("Dermochelys coriacea"), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtles and is the fourth-heaviest modern reptile behind three crocodilians. It is the only living species in the genus Dermochelys and family Dermochelyidae. It can easily be differentiated from other modern sea turtles by its lack of a bony shell, hence the name. Instead, its carapace is covered by skin and oily flesh. "Dermochelys" is the only extant genus of the family Dermochelyidae.
At last count, a total of 389 species of fish have been recorded from the Houtman Abrolhos. 16 species occur in very large numbers; in decreasing order of abundance, these are:
Commercially important species include "Pagrus auratus" (pink snapper), "Choerodon rubescens" (baldchin groper), "Glaucosoma hebraicum" (westralian dhufish) and "Plectropomus leopardus" (coral trout). For a complete list of fish species recorded at the Houtman Abrolhos, see List of fishes of the Houtman Abrolhos.
Seaweed farming is the practice of cultivating and harvesting seaweed. In its simplest form, it consists of the management of naturally found batches. In its most advanced form, it consists of fully controlling the life cycle of the algae. The main food species grown by aquaculture in Japan, China and Korea include "Gelidium", "Pterocladia", "Porphyra", and "Laminaria". Seaweed farming has frequently been developed as an alternative to improve economic conditions and to reduce fishing pressure and over exploited fisheries. Seaweeds have been harvested throughout the world as a food source as well as an export commodity for production of agar and carrageenan products.
Loxechinus albus is an echinoderm of the family Parechinidae, native to coastal southern South America, ranging from Ecuador, along the entire coasts of Peru and Chile, to Argentina, as well as the Falkland Islands. It is known as the Chilean sea urchin or red sea urchin, but the latter name is typically used for the North Pacific "Mesocentrotus franciscanus" and it is not the only species of sea urchin in Chile (although it is the most common and widespread large sea urchins in that country). "L. albus" is found on rocky reefs and shores in the intertidal and subtidal zones to a depth of .
Sea urchins can be found in all climates, from warm seas to polar oceans. The larvae of the polar sea urchin "Sterechinus neumayeri" have been found to use energy in metabolic processes twenty-five times more efficiently than do most other organisms. Despite their presence in nearly all the marine ecosystems, most species are found on temperate and tropical coasts, between the surface and some tens of meters deep, close to photosynthetic food sources.
Toxopneustes is a genus of sea urchins from the tropical Indo-Pacific. It contains four species. They are known to possess medically significant venom to humans on their pedicellariae (tiny claw-like structures). They are sometimes collectively known as flower urchins, after the most widespread and most commonly encountered species in the genus, the flower urchin ("Toxopneustes pileolus"). Species included in the genus are the following:
Despite their name, urchin barrens are usually abundant with marine invertebrate life, echinoderms in particular. Species such as the sunflower starfishes, brittle stars, and the purple sea urchin are common. Although macrofauna such as these are aplenty,
there is little primary productivity among microorganisms. This makes it difficult for newly settled sea urchins (juveniles) to survive, making barrens more dangerous for juveniles than for adults. Once having wiped out a kelp forest, the environment becomes unsupportive of new sea urchin settlement and adults are forced to find a new resource.