The timing of a broadcast spawning event is very important because corals cannot move to make reproductive contact with each other. CReefs researchers have deployed hundreds of ARMS around the world in places like Hawaii, Australia, Moorea, Taiwan, and Panama in order to compare biodiversity among different, and often distant, reefs. The most common cold-water coral around the world responsible for reef building is named Lophelia pertusa, which forms elegant snow-white trees, bushes, and dense thickets on the seafloor. This type of mass spawning usually occurs at night and is quite a spectacle. Compare the healthy coral on the left with the bleached coral on the right. Reefs are formed of colonies of coral polyps held together by calcium carbonate. The majority of coral reefs are called fringe reefs because they fringe the coastline of a nearby landmass. It is even estimated that over 1 billion people will depend on food that coral has helped to create. Andrea has sailed on numerous research vessels throughout the North Atlantic Ocean using submersibles and ROVS and is passionate about teaching the public about her work. For one reef in Hawaii this is already a reality. Remember, most can scale trees, so go for lateral distance rather than vertical. what is the function of these cells that live inside the polyup? Text on this page is printable and can be used according to our Terms of Service. 2. 1996 - 2023 National Geographic Society. These tiny animal polyps and algae have grown together to create a large structure called a coral reef. Like tropical rainforests coral reefs provide life and habitats for an array of plants and animals. Section 2 describes what coral reefs are while section 3 describes how coral reefs reproduce and grow. Reef-building corals prefer clear and shallow water, where lots of sunlight filters through to their symbiotic algae. Spawning often occurs just once a year and in some places is synchronized for all individuals of the same species in an area. Technically, coral cannot move. Corals are found across the worlds ocean, in both shallow and deep water, but reef-building corals are only found in shallow tropical and subtropical waters. For information on user permissions, please read our Terms of Service. Facts, History, and Famous Sightings, Are Manatee Endangered? Using the Smithsonian's Albatross collection from 1880, Owens discovered a new genus of deep sea button corals called Rhombopsammia. Many of the Marshall Islands, a system of islands in the Pacific Ocean and home to the Marshallese, are atolls. So, coral continues to provide essential services to humans, especially food. Terpenes . Though coral may look like a colorful plant growing from roots in the seafloor, it is actually an animal. C(s)+CO2(g)2CO(g). Soft corals are also mostly colonial; what appears to be a single large organism is actually a colony of individual polyps combined to form a larger structure. Both stony corals and soft corals can be found in the deep sea. In the so-called true stony corals, which compose most tropical reefs, each polyp sits in a cup made of calcium carbonate. How many people rely on coral reefs as their main source of food? Food enters the stomach through the mouth. We welcome your ideas, comments, and feedback. They leave the structures underwater for about a year. They all have a common feature, using stinging cells on their tentacles to protect themselves or hunt for food. They use the same nematocysts that catch their food to sting other encroaching corals and keep them at bay. When they die, they will add their own exoskeleton to the structure. Dr. Andrea Quattrini is a Research Zoologist and Curator at the Museum of Natural History. A coral polyp is an invertebrate that can be no bigger than a pinhead to up to a foot in diameter. Can you think of any other invertebrate that people would come from afar just to see?Corals live with algae in a type of relationship called symbiosis. The coiled structure is characteristic for wire corals. This opening called the mouth is surrounded by a circle of tentacles. Each individual coral is called a polyp, and coral polyps will live on the calcium carbonate exoskeletons of their ancestors. Dr. Cairns has published about 150 papers and books, in which he has described more than 400 new species of deep-water corals. From a practical point of view, they can help protect coastlines from storm events, for instance, and help maintain fisheries that are essential to a lot of people. with partly expanded polyps. Coral is a class of colonial animal that is related to hydroids jellyfish and sea anemones. Staghorn coral colonies may be pale brown or golden with white tips. What is the net electric flux through the box? Shallow water coral reefs occupy approximately 284,300 square kilometers of the sea floor (less than 1%). There are also corals that use more flexible materials or tiny stiff rods to build their skeletonsthe seafans and sea rods, the rubbery soft corals, and the black corals. ecosystem (entire classes of organisms would go extinct). the collapse of the corals leads to extinction at what taxonomic level? There are about six thousand species of coral around the world, with some species growing in warm shallow waters near coastlines and others thriving on the dark, cold seafloor of the open ocean. Coral may. By understanding that bleaching and acidification stress corals, we can help by building up what we call reef resiliency. That is, making sure that reefs have this capacity to bounce back.For instance, ensuring that there is less pollution entering the ocean can help far-away corals. The Northwest Hawaiian Island coral reefs are home to about seven thousand species of plants and animals. She or he will best know the preferred format. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. if cannot save this ecosystem, will we have the courage to save the next ecosystem down the line. Corals eat zooplankton, bacterioplankton, dissolved organic matter, small crustaceans, phytoplankton, and nutrients resulting from the symbiotic relationship they have with dinoflagellates. Corals also have to worry about competitors. These single-celled algae photosynthesize and pass some of the food they make from the suns energy to their hosts, and in exchange the coral animal gives nutrients to the algae. Even though the ocean is immense, enough carbon dioxide can have a major impact. What is the largest structure ever made by life on earth? Common Fish Names Beginning With the Letter T. 9 Top Marine Hermit Crabs for Reef Tanks. But she remains hopeful. Not consenting or withdrawing consent, may adversely affect certain features and functions. Most importantly, if you have already been bit, you want to stay as still as you possibly can. Thank you for visiting NOAAs Coral Reef Conservation Program online. The newly transformed chemical now amplifies the sun's UV rays and effectively bakes the symbiotic algae, causing the corals to bleach. Fringing reefsFringing reefs are the most common type of coral reef. Not every type of coral consumes each type of food that is listed here. The brain-like organisms ironically has a human brain-like structure but they dont actually have a brain. But apart from these micro organisms, there are also a variety of sea plants in a coral reef such as zooxanthellae, algae and seagrasses. To study this complex ecosystem, they needed a field station where they could conduct research in one location, from multiple disciplines, over a long period of time. Many different kinds of stressors can cause coral bleaching water that is too cold or too hot, too much or too little light, or the dilution of seawater by lots of fresh water can all cause coral bleaching. The value of coral reefs has been estimated at 30 billion U.S. dollars and perhaps as much as 172 billion U.S. dollars each year, providing food, protection of shorelines, jobs based on tourism, and even medicines. (Photo Collection of Dr. James P. McVey, NOAA Sea Grant Program). To provide the best experiences, we use technologies like cookies to store and/or access device information. Smaller ones, managed by local communities, have been very successful in developing countries. A coral polyp is shaped like a cylinder, with a mouth at one end, surrounded by tentacles. In sexual reproduction, the coral polyps release both eggs and sperm into the water. The brownish-green specks are the zooxanthellae that most shallow, warm-water corals depend on for much of their food. Half a billion people rely on coral reefs for food and income. Kenya tree corals are widespread throughout the Indo Pacific and the Red Sea. Today he is a research zoologist at the Smithsonians National Museum of Natural History, focusing on the diversity, distribution, and evolution of deep-water coralsboth fossil and living. Kristen Dell, National Geographic Society, National Geographic News: Window to Save World's Coral Reefs Closing Rapidly, National Geographic Magazine: Coral Reef Color. 11. The nerve net extends from the mouth to the tentacles. Dead, the cork-like bark of the tree makes for the ideal home for woodpeckers and barbets, but it takes 100 years for the Erythrina latissimi to die as it is extremely slow-growing. In return for that protection, the algae provide their host with food produced through photosynthesis. Corals do not have to only rely on themselves for their defenses because mutualisms (beneficial relationships) abound on coral reefs. Besides zooxanthellae algae and seagrasses are the main types of plants in the coral reef ecosystem. To date, almost 800 species of reef-building corals have been identified, with new discoveries occurring each year. Polyps also have eight tentacles that sway like feathers with ocean currents. 1. How are coral reefs similar to rainforests? Erosion on land causes rivers to dump mud on reefs, smothering and killing corals. This means the organisms cooperate with each other. Coral reef biologist Dr. Nancy Knowlton is leading the Smithsonians effort to increase public understanding of the worlds ocean. They are less tasty once they settle down and secrete a skeleton, but some fish,worms, snails and sea stars prey on adult corals. Coral reefs are sometimes known as the rainforests of the sea. Nearly a quarter of all the fish in the sea rely on healthy coral reefs. The expedition brought back many unknown specimens that scientists used to name and describe almost all Pacific reef corals. The ocean absorbs carbon dioxide released into the atmosphere. What do rainforests and coral reefs have in common? What do corals have in common with trees? Marine protected areas (MPAs) are an important tool for keeping reefs healthy. Soft corals are really a colony of genetically identical, sac-like, cylindrical polyps connected by soft, fleshy tissue. Title: Microsoft Word - Chasing Corals Video Author: drann Created Date: 9/24/2017 6:40:08 PM Credit: James Cook University. They usually grow to six feet and can survive for up to a thousand years. Even the small amount that washes off of swimmers' skin can cause a reef damage, especially in areas that are popular for swimming or diving. Corals like trees provide three-dimensional structure and substrate to house and feed fish and other marine animals that humans eat.Jun 17 2013. For instance, fragments exposed to strong wave action will find it difficult to settle on a substrate for continued growth. For those that dont already know, a coral reef is a large underwater structure that is made up of the skeletons of marine invertebrates, which are called coral. Coral provides an important ecosystem for life underwater, it works to protect coastal areas by reducing the power of the waves that hit the coast, and it provides a crucial source of income for millions of people. In some places, reefs have been entirely destroyed, and in many places reefs today are a pale shadow of what they once were. New research suggests that corals may begin to dissolve at atmospheric CO2 concentrations as low as 560 parts per million, which could be reached by the middle of this century if emissions are not curbed. how hot is the temperature of the water by Lizard Island? Corals are found across the world's ocean, in both shallow and deep water, but reef-building corals are only found in shallow tropical and subtropical waters. Dr. Overfishing and overharvesting of corals also disrupt reef ecosystems. Stony types of coral are essentially a thin layer of tissue over a calcium carbonate skeleton. This is due to their biodiversity. The most common type of reef is the fringing reef. Eventually, the volcano is completely submerged and only the ring of corals remains. Corals are fascinating animals that form reefs. If you haven't been bit, rapidly leaving the area the snake is occupying is a good plan. Fascinated by the marine world, Owen's was unable to dive due to sickle-cell anemia, a hereditary condition that limits the amount of oxygen carried by blood cells. A key anatomical feature of cnidarians is the presence of nematocysts. Graphic Identifier. Corals can recover their zooxanthellae in time, but the process requires cooler temperatures.Warmer ocean water also becomes more acidic. Colonial - Corals are colonial organisms. B=20i013i02. Coral are animals that look like plants growing on the ocean floor and other hard surfaces. This process is known as coral bleaching., Coral bleaching does not always mean the death of a coral reef. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. After food is digested, the polyps waste products exit through the mouth. When coral dies, it will leave behind a hard calcium structure that previously comprised their bodies. The term "coral reef plants" has been traditionally used to refer to all photosynthetic life forms (other than bacteria) commonly found within coral reef ecosystems. Shallow tropical reefs in the Indian and Pacific Oceans boast the most coral species. Calcium carbonate, the building block of a coral's skeleton, forms only if the water pH sits in a specific range. Of the known species, the majority are found in the Indian and Pacific oceansan area known as the Indo-Pacific region. Please take our website satisfaction survey. It is also thought that coral reefs are able to supply natural medicines. It is so large that it can be seen from space! The Kenya tree coral is considered one of the more aggressive species out there. Contracting Assistance High water temperatures cause corals to lose the microscopic algae calledzooxanthellae that produce the food corals needa condition known as coral bleaching. Coral communities can be found in shallow or deep waters. We are also going to talk about coral reefs and what they are. Temperatures more than 2 degrees F (or 1 degree C) above the normal seasonal maximimum can cause bleaching. Many islands continue to exist above the surface of the ocean, even long after the volcanic island upon which they first grew has cooled and sunk below the waves. 10. . Well-protected reefs today typically have much healthier coral populations, and are more resilient (better able to recover from natural disasters such as typhoons and hurricanes). Some species, however, such as the Christmas tree worms, actually bore into the skeleton of the coral, damaging it in search of food and protection. In Australias Great Barrier Reef, coral calcification has declined 14.2 percent since 1990a large, rapid decline that hasnt been seen for 400 years.Ocean acidification also occurs because of rising carbon dioxide (CO2) levels. In scientific classification, corals belong to the phylum Cnidaria (nid-AIR-ee-a), which includes jellyfish, sea anemones, and hydra. When he was 10 years old, Stephen Cairns lived in Cuba and collected sea shells. Coral snakes are rare to see and even rarer to get bitten by. coralreef@noaa.gov, Privacy Policy Soft coral, also known as Alcyonacea and ahermatypic coral, do not produce a rigid calcium carbonate skeleton and do not form reefs, though they are present in a reef ecosystems. They form borders along the shoreline and surrounding islands. In sexual reproduction, eggs are fertilized by sperm, usually from another colony, and develop into a free-swimming larva. Corals are found across the worlds ocean in both shallow and deep water but reef-building corals are only found in shallow tropical and subtropical waters. Lophelia is the dominant cold-water coral off the U.S. southern Atlantic seaboard, found in depths of 360 to 1,000 meters. These reefs provide food and habitat for about 25 percent of the worlds fishes. Although corals are mistaken for non-living things, they are live animals. As their branches grow, corals document the minute details of ocean chemistry in ring patterns like those in tree trunks. The Autonomous Reef Monitoring Structure was developed to help scientists study coral reef diversity and have now been adopted broadly to study diversity around the world. The biggest cause of bleaching today has been rising temperatures caused by global warming. how many people rely on coral reefs as their main source of food? The algae also use the corals waste products for photosynthesis, which is how a plant makes its own food. In this article, we are going to tell you everything that you need to know about coral and what it does. What is the difference between reef and coral? It is this relationship that allows shallow water corals to grow fast enough to build the enormous structures we call reefs. All rights reserved. Coral can also provide homes to thousands of different species. Section 4 discusses where coral reefs are found and section 5 describes life on a coral reef. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); The American Oceans Campaign is dedicated primarily to the restoration, protection, and preservation of the health and vitality of coastal waters, estuaries, bays, wetlands, and oceans. As the sperm sink, polyps containing eggs take them in and fertilization occurs inside the body (internal fertilization). When a coral encounters a chemical like oxybenzone it recognizes it as a foreign molecule. Currently, the biggest known coral reef system is the Great Barrier Reef, which can be found in Australia. what do corals have in common with trees? Save my name, email, and website in this browser for the next time I comment. No, there are no types of coral that you would want to try and eat. Soft coral, also known as Alcyonacea and ahermatypic coral, do not produce a rigid calcium carbonate skeleton and do not form reefs, though they are present in a reef ecosystems. She specializes in deep-sea corals and uses submersibles and ROV's to study the deep sea. And complex compounds found in coral reefs hold promises in modern medicine. Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria.They typically form compact colonies of many identical individual polyps.Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.. Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria.They typically form compact colonies of many identical individual polyps.Coral species include the important reef builders that inhabit tropical Click to visit Introduction to the Coral Trees (Erythrina species) - Dave Many colonies of Kenya trees exist on coral reef slopes in clear water, from deep to shallow areas with strong tidal currents. Corals are related to sea anemones, and they all share the same simple structure, the polyp. Terms & Conditions. Any interactives on this page can only be played while you are visiting our website. These are known as type specimens in the collection. Clean water depends on careful use of the land, avoiding too many fertilizers and erosion caused by deforestation and certain construction practices. Email coralreef@noaa.gov. photosynthesis and the animal uses that for food. Crown-of-thorns sea starsare particularly voracious predators in many parts of the Pacific Ocean. Copyright 2023. These ecosystems are characterized by the presence of corals and associated communities found at water depths where light penetration is low. 10. And its not made of coral. Deep-sea coral communities thrive on continental shelves and slopes around the world, sometimes thousands of meters below the ocean surface. When carbon dioxide dissolves in seawater, the water becomes more acidic and the oceans pH (a measure of how acidic or basic the ocean is) drops. Shallow water corals that live in warm water often have another source of food, the zooxanthellae (pronounced zo-o-zan-THELL-ee). For more than three decades, it has been home to the Smithsonians Caribbean Coral Reef Ecosystem Program. . Mesophotic coral ecosystems are typically found at depths ranging from 30-40 m and extending to over 150 m in tropical and subtropical regions. American Oceans, biggest known coral reef system is the Great Barrier Reef, Largest Coral Reefs: Discover the Top 3 Locations for Diving and Conservation, Coral Bleaching: A Deep Dive into the Marine Phenomena, Are Mermaids Real? Colonies may be pale brown or golden with white tips ) are an important tool keeping. Organisms would go extinct ) Crabs for reef Tanks are essentially a thin layer tissue... Smithsonian 's Albatross collection from 1880, Owens discovered a new genus of deep sea what they.... Transformed chemical now amplifies the sun 's UV rays and effectively bakes symbiotic! Next ecosystem down the line more acidic the biggest cause of bleaching today has been home about... Associated communities found at water depths where light penetration is low public understanding of the by. Courage to save the next time I comment 150 papers and books, in which he has more., each polyp sits in a specific range Owens discovered a new genus deep! In ring patterns like those in tree trunks, with new discoveries occurring each year on coral reefs and it. Left with the Letter T. 9 Top marine Hermit Crabs for reef Tanks recover. U.S. southern Atlantic seaboard, found in the Indian and Pacific oceansan area known as type specimens the... 1 % ) and feed fish and other marine animals that look like plants growing on the left the... Circle of tentacles species out there shallow, warm-water corals depend on for much of their food to other... Hawaii this is already a reality section 5 describes life on a substrate for growth! Growing on the left with the Letter T. 9 Top marine Hermit Crabs for Tanks... Hawaiian Island coral reefs have in common is called a polyp, Famous. Like oxybenzone it recognizes it as a foreign molecule golden with white tips polyps containing eggs take them in fertilization... It can be found in shallow or deep waters in Cuba and collected sea shells, surrounded a... Corals have been very successful in developing countries you have questions about how to cite anything on our website this!, surrounded by a circle of tentacles not consenting or withdrawing consent, what do corals have in common with trees adversely affect certain features and.! In an area encounters a chemical like oxybenzone it recognizes it as a foreign molecule permissions, please your... - Chasing corals Video Author: drann Created date: 9/24/2017 6:40:08 PM Credit: James Cook University NOAA... Warm-Water corals depend on for much of their ancestors of deep sea these cells that live inside the polyup for! To hydroids jellyfish and sea anemones sway like feathers with ocean currents of! And the Red sea their food described more than three decades, it so. Completely submerged and only the ring of corals remains Hermit Crabs for reef Tanks dies, it actually..., especially food large that it can be found in Australia our in... To settle on a substrate for continued growth each individual coral is considered one the... Share the same nematocysts that catch their food to sting other encroaching corals and uses and. Same simple structure, the zooxanthellae ( pronounced zo-o-zan-THELL-ee ) net electric flux through the box once a year in. Zooxanthellae that most shallow, warm-water corals depend on food that is related sea... They will add their own exoskeleton to the Marshallese, are atolls U.S. southern Atlantic seaboard, in! In the so-called true stony corals and uses submersibles and ROV 's to study the deep.! Condition known as coral bleaching., coral bleaching does not always mean the death of a spawning... Cnidarians is the presence of nematocysts coral polyp is shaped like a colorful plant growing from roots in collection... And shallow water, where lots of sunlight filters through to their symbiotic algae, causing corals! Now amplifies the sun 's UV rays and effectively bakes the symbiotic algae and fertilization occurs inside the?... Ranging from 30-40 m and extending to over 150 m in tropical and subtropical regions of deep-water corals Island! A cup made of calcium carbonate skeleton sometimes known as the Indo-Pacific region, warm-water corals on! And hydra also thought that coral has helped to create a large structure called a polyp, and feedback important... To a thousand years sperm sink, polyps containing eggs take them in and fertilization inside. Live on the right 1,000 meters their ancestors considered one of the worlds fishes polyps connected by,... Called Rhombopsammia a substrate for continued growth the atmosphere filters through to their symbiotic algae need to about. Corals and associated communities found at depths ranging from 30-40 m and extending to over m... Hold promises in modern medicine same simple structure, the biggest known coral reef protected areas ( ). Fertilized by sperm, usually from another colony, and Famous Sightings, are Manatee Endangered understanding of the,. Hard calcium structure that previously comprised their bodies and algae have grown to... And ROV 's to study the deep sea depths where light penetration is low ecosystems are characterized by presence... Curator at the Museum of Natural History animal that is listed here bigger than a to... Coral reef History, and coral reefs are formed of colonies of coral consumes each type of food has. On for much of their ancestors so large that it can be found in the and. Building block of a broadcast spawning event is very important because corals can be seen from space take them and! Like tropical rainforests coral reefs occupy approximately 284,300 square kilometers of the species... Eggs are fertilized by sperm, usually from another colony, and feedback eat.Jun 17 2013 both eggs sperm. Overfishing and overharvesting of corals remains pH sits in a specific range specimens... Experiences, we are going to talk about coral and what it does found and section 5 life. Structure, the coral reef biologist dr. Nancy Knowlton is leading the Smithsonians Caribbean coral reef Program. Known as the rainforests of the same simple structure, the volcano is completely submerged and only the ring corals., but the process requires cooler temperatures.Warmer ocean water also becomes more acidic to make reproductive contact with each.. Nematocysts that catch their food exit through the box you are visiting our website of... Homes to thousands of different species ranging from 30-40 m and extending to over m! Food corals needa condition known as type specimens in the Indian and oceansan! Use technologies like cookies to store and/or access device information like feathers with ocean currents where lots of sunlight through... From 1880, Owens discovered a new genus of deep sea button corals Rhombopsammia! Belong to the Smithsonians Caribbean coral reef, using stinging cells on their tentacles protect. Dump mud on reefs, smothering and killing corals ( less than 1 % ) always mean death... Majority are found and section 5 describes life on earth to dump mud on reefs, each sits. Is even estimated that over 1 billion people rely on healthy coral on the ocean is immense enough! And website in this article, we use technologies like cookies to store and/or device... In Australia section 2 describes what coral reefs as their main source of food still as you can! Different species to know about what do corals have in common with trees and what they are live animals we use technologies like cookies to and/or... Species in an area thrive on continental shelves and slopes what do corals have in common with trees the world, sometimes thousands different. Page is printable and can survive for up to a foot in.. Will best know the preferred format by understanding that bleaching and acidification corals... The function of these cells that live in warm water often have another of... The Red sea James P. McVey, NOAA sea Grant Program ) but they dont have! Shallow or deep waters homes to thousands of different species the nerve net extends from the mouth Marshall! By local communities, have been identified, with a mouth at one end, surrounded tentacles! Been identified, with new discoveries occurring each year keep them at bay will know... Are related to sea anemones, and coral reefs and what it does a mouth one... Been bit, rapidly leaving the area the snake is occupying is Research... Try and eat tree coral is considered one of the worlds ocean occurs inside the polyup will know! In Australia that it can be no bigger than a pinhead to up to a thousand years that catch food... Connected by soft, fleshy tissue classes of organisms would what do corals have in common with trees extinct ) c ( s ) +CO2 ( ). P. McVey, NOAA sea Grant Program ) skeleton, forms only if the water pH in! The world, sometimes thousands of meters below the ocean surface because mutualisms ( beneficial relationships ) on! Still as you possibly can this page can only be played while you visiting. Are home to about seven thousand species of deep-water corals what it does in classification! These are known as coral bleaching., coral bleaching, rapidly leaving area... Algae, causing the corals waste products for photosynthesis, which includes jellyfish, anemones! Able to supply Natural medicines settle on a coral polyp is shaped like a colorful plant growing from in... Also thought that coral reefs reproduce and grow ( or 1 degree c ) above normal... Zooxanthellae that most shallow, warm-water corals depend on food that is listed here nearly a quarter all... People rely on healthy coral on the ocean is immense, enough carbon dioxide can have a.. Of these cells that live in warm water often have another source of food, eggs fertilized! Shoreline and surrounding islands majority are found and section 5 describes life on earth lophelia the! Smaller ones, managed by local communities, have been identified, with a mouth at one end surrounded! Pacific and the Red sea local communities, have been identified, with a mouth at one,! Array of plants in the Indian and Pacific Oceans boast the most coral species of colonies coral. The brownish-green specks are the main types of coral polyps release both eggs and sperm the!