NOAA's Coral Reef Information System (CoRIS) - About Coral Reefs This Site NOAA Home Data & Publications Regional Portal About Coral Reefs Professional Exchanges Activities Glossary Home / About Coral Reefs About Coral Reefs Coral reefs are complex, biologically diverse ecosystems. Countless studies, books and papers have been devoted to exploring and understanding the nature of these unique marine environments. These four essays discuss some of the most important aspects of coral reefs. Many of their physical and biological characteristics are discussed in detail. Coral reef threats, both natural and anthropogenic, also are explored. These essays are not meant to be exhaustive. For more information, the reader can refer to the literature cited at the end of each essay. What are Coral Reefs Coral Reef Biology Deep Water Corals Major Reef-building Coral Diseases Hazards to Coral Reefs Coral Reefs Ecosystem Essays About CoRIS Data | Retired Pages | User Survey | Report Web Page Error | Privacy Policy Revised August 14, 2014 by Webmaster Site hosted by NOAA Coral Reef Conservation Program National Oceanic and Atmospheric Administration U.S. Department of Commerce http://coris.noaa.gov/about/welcome.html http://www.coris.noaa.gov/about/[12/1/2014 2:46:05 PM] NOAA's Coral Reef Information System (CoRIS) - Coral Reefs Biology This Site NOAA Home Data & Publications Regional Portal About Coral Reefs Professional Exchanges Activities Glossary Home / About Coral Reefs / Coral Reef Biology Content on this page was last updated in February 2012. Some of the content may be out of date. For more information: Read About: http://coralreef.noaa.gov/. Reproductive Behavior Coral Reef Biology Spawning Events There are over a thousand coral species exist worldwide. Stony (hermatypic) corals are the best recognized because of their Feeding Behavior and elaborate and colorful formations. One trait of stony corals is their Reef Productivity capacity to build reef structures that range from tens, to thousands of Competitive Behavior meters across. As they grow, reefs provide structural habitats for many different vertebrate and invertebrate species – a single reef Aggressive Behavior may host tens of thousands different species. Disturbances Although corals are found throughout the world, reef-building corals References are confined to waters that exhibit a narrow band of characteristics. The water must be warm, relatively clear, and saline. These waters are almost always nutrient-poor as well. Physiologically and behaviorally, corals have evolved to take advantage of this unique environment and thrive. Not only are reef-building corals confined by a specific range of environmental conditions, but as adults, almost all of them are sessile. This means that for their entire lives, they remain on the same spot of the sea floor. Thus, reef-building corals have developed reproductive, feeding, and social behaviors that allow them to gain the maximum survival benefit from their situation. Reproductive Behavior Over the eons many corals have evolved with the ability to reproduce both asexually and sexually. In asexual reproduction, new clonal polyps bud off from parent polyps to expand or begin new colonies (Sumich, 1996). This occurs when the parent polyp reaches a certain size and divides. The process continues throughout the animal's life, forming an ever-expanding colony (Barnes and Hughes, 1999). It is worth noting that it is a judgement call whether to call this reproduction, since that implies that a polyp is an individual. In a coral, an individual could be either a polyp or the whole colony, and some lines of evidence indicate that the colony is the individual, not A spreading colony of asexually the polyp. Evidence for coral as the individual argument includes the reproducing coral polyps polyps of a colony being connected by a nervous system and provide shelter for a moray eel. gastrovacular cavity, and becoming sexually reproductive when a colony reaches a certain size, not when a polyp reaches a certain size (D. Fenner, personal communication, Jan 6, 2012). Corals can also reproduce asexually by fragmentation – that is, when a portion of the colony (say, a branch), is detached from the rest and falls in suitable substrate. This can happen either naturally, when perhaps wave action from a storm breaks off a coral piece and settles it elsewhere, or when humans purposely take coral fragments and place them in other substrate areas (Highsmith, 1982). http://www.coris.noaa.gov/about/biology/[12/1/2014 2:47:14 PM] NOAA's Coral Reef Information System (CoRIS) - Coral Reefs Biology The nature of sexual reproduction among corals varies by species. About three-quarters of all stony corals form hermaphroditic colonies. These colonies have the ability to produce both male and female gametes. The remainder form gonochoristic colonies which can produce either male or female gametes, but not both. The sexuality of corals';whether hermaphroditic or gonochoristic—tends to be consistent within species and genera, although there are exceptions (Veron, 2000). As a predominantly sessile group of organisms, about three-quarters of all stony corals employ broadcast spawning to distribute their offspring over a broad geographic area. These corals release massive numbers of eggs and sperm into the water column (Veron, 2000). The gametes fuse in the water column to form planktonic larvae (planulae). A moderately-sized colony may produce up to several thousand planulae per year (Barnes and Hughes, 1999). Large numbers of planulae are produced to compensate for the many hazards they inevitably will encounter as they are carried through the water. The time between planulae formation and settlement is a period of exceptionally high mortality among corals (Barnes and Hughes, 1999). In contrast, some coral species brood planulae within their bodies after internal fertilization. While spawning is associated with high numbers of eggs and planulae, brooding results in fewer, larger and better-developed planulae (Veron, 2000). Planulae swim upward toward the light (positive phototaxis) to enter the surface waters and be transported by the current. This behavior is observed not only in nature but in laboratory experiments as well (Jones and Endean, 1973). After floating at the surface for some time, the planulae swim back down to the bottom, where, if conditions are favorable, they will settle and begin a new colony (Barnes and Hughes, 1999). In most species, the larvae settle within two days, although some will swim for up to three weeks, and in one known instance, two months (Jones and Endean, 1973). A male star coral (Montastraea cavernosa) releases sperm into Once the planulae settle, mortality rates drop steadily as they the water column. metamorphose into polyps and form colonies which increase in size. The new colony becomes sexually mature at a minimum size, depending on the species. Some massive species, like those in the genus Favia, reach sexual maturity when the colony grows to about 10 cm in diameter, which occurs when they are about eight years old. However, some faster-growing, branching corals, including species of Acropora, Pocillipora, and Stylophora, reach sexual maturity at a younger age (Barnes and Hughes, 1999). (top) Spawning Events Among sessile corals, the timing of the mass release of gametes into the water column (broadcast spawning event) is very important because males and females cannot move into reproductive contact. Spawning species must release their gametes into the water simultaneously. Because colonies may be separated by wide distances, this release must be both precisely and broadly synchronized, and is usually done in response to multiple environmental cues (Veron, 2000). The long-term control of spawning (control of the maturation of gonads) may be related to temperature, day length and/or rate of A star coral (Montastraea temperature change (either increasing or decreasing). The short-term franksi), releasing egg and (getting ready to spawn) control is usually based on lunar cues. The sperm bundles, with a feeding brittle star (Ophioderma final release, or spawn, is usually based on the time of sunset. Cues rubicundum). also may be biological (involving chemical messengers) or physical (Veron, 2000). Brooding species can store unfertilized eggs for weeks, and thus, require less synchrony for fertilization. Spawning species require synchrony within a time frame of hours (Veron, 2000). This http://www.coris.noaa.gov/about/biology/[12/1/2014 2:47:14 PM] NOAA's Coral Reef Information System (CoRIS) - Coral Reefs Biology regional synchrony varies geographically. In Australia’s Great Barrier Reef, more than 100 of the 400 plus species of corals spawn simultaneously within a few nights during spring or early summer (Willis, B.L. et al., 1997). Studies have shown that coral species can form hybrids through mass spawning (Hatta et al., 1999). Such observations have led to the theory of reticulate evolution (Veron, 1995) whereas modern coral species came about not through the separation of new species along different lineages, but rather through a continual process of separation and fusion. In western Australia and the Flower Garden Banks of the northern Gulf of Mexico, spawning occurs in late summer or fall (Levinton, 1995), and not necessarily simultaneously. In the northern Red Sea, none of the major coral species reproduce at the same time. In addition, individual corals do not necessarily breed every year (Sumich, 1996). Evidence indicates