Soft corals & their ecology
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Soft corals produce a flexible skeleton composed of small calcium carbonate structures called sclerites. They have 8 tentacles and live in colonies. Their skeleton is smaller and contains more protein than hard corals. They come in many shapes and colors and play an important role in reef ecosystems by providing habitat for other organisms. Soft corals reproduce both sexually through broadcast spawning and larval development, and asexually through budding and fragmentation.
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Soft corals & their ecology
- 2. • Produce a flexible skeleton • Composed of sclerites (small fragments of skeleton) • Tentacles are emplaced in sets of 8; thus octacorals
- 3. • A few species, such as the the blue coral (Heliopora) or the red organ-pipe coral (Tubipora) have a solid skeleton • Superficially resembling that of hard corals
- 4. • Sclerites can strengthen the base of the soft coral • Assist in the identification of the soft coral species
- 5. Different types of sclerites • Sclerite: A calcareous solid mineral element within the soft coral tissue • Spindle: A straight or curved elongated sclerite pointed at both ends. • Club: A sclerite that has a short stem leading to only one bulbous end. • Capstan: A sclerite, like a short rod with two whorls of warts • Dumb-bell: A sclerite with two warty heads connected by a narrow wartless bar.
- 6. • Tentacles also posses small pinnate fringes • Live in areas of realtively high current strength • Have stinging cells, a gastrovascular cavity, and are radially symmetrical
- 7. Difference between hard corals and soft corals Taxon Hexicorallia Octocorallia Common name Stony corals Soft corals Polyp size Small to large Small Body form Solitary to colony Colony Number of tentacles Many (in sixes) Eight Tentacle shape Simple to highly modified Pinnate *Skeleton size Massive Small *Skeleton’s mineral composition Calcium carbonate Calcium carbonate *Organic composition Less protein A lot of protein *Overall amount of organic material Two thin tissue layers Thin tissue layers plus large amounts of organic material *Nitrogen need Small Large *Properties reflecting different metabolic needs.
- 8. Scientific classification Kingdom: Animalia Phylum: Cnidaria Class: Anthozoa Subclass: Octocorallia Order: Suborders: Alcyoniina Calcaxonia Holaxonia Protoalcyonaria Scleraxonia Stolonifera Alcyonacea
- 9. Life cycle • Begins as small, free-swimming larvae called planulae • Hard, solid substrates are preferred • Metamorphoses into a founder polyp • Develop eight tentacle buds
- 10. • Soft coral development from planulae (48 hours) through one-polyp stage (two weeks) to four-polyp stage (three months)
- 11. • Some of the soft corals acquire their algal symbionts, also called zooxanthellae • Algae enter the polyp’s tissues from the environment through the mouth
- 12. Physiology • Sac-like body with radial symmetry • Gastrovascular cavity- one opening into their digestive sac that serves as both a mouth and an anus
- 14. • Autozoid polyps and siphonozoid polyps • Autozoid's tentacles gather food and make sure it gets to the mouth of the coral • Siphonozoids are responsible for pumping and distributing water throughout the coral colony
- 16. • Have both a muscular and a nervous system • Do not have hard calcium carbonate skeletons; supported by hydrostatic skeletons • The larger species, however, often have spicules; arranged individually in the body wall, also found in clumps near the colony’s base
- 17. Feeding • Most of them are filter feeders • They also possess stinging cells • Feed on plankton and the larvae of other invertebrates • Some soft coral species contain symbiotic association with zooxanthellae
- 18. Excretion • They do not any specialised organ • Have simple body plan; perform many vital functions through diffusion • Nitrogenous wastes diffuse through the body wall as ammonia; gas exchange takes place in this manner
- 19. Defence mechanism • Produce terpenoids and other toxic chemicals which make them free of parasites • Added benefit of killing other nearby sessile organisms • Might otherwise block the soft coral’s sunlight
- 20. • These toxins make the tissues of soft corals either distasteful or toxic to fish • Soft corals are able to move very slowly by extending the tissues at their base
- 21. Ecology • Some mollusks and fish feeds on soft corals • Planulae easily forms the food of filter feeding invertebrates • Newly formed founder polyps are easy meals for grazing fish or sea urchins
- 22. • Face competition for light, substrates and food • They cover about 37% of the reef area in the Great Barrier Reef • They are sessile filter feeders
- 23. • Prefer water with a relatively high pH, from 8.2-8.4 • Found fairly close to the surface • Rely on ocean currents to bring them food, nutrients, and oxygen
- 24. • Ideal substrate-rocks, hard corals, and crustose coralline algae • Prefer temperatures between 70 and 85 degrees Fahrenheit
- 25. • Overall feeding pressure on corals appear to be very low • Toxic or allelopathic secondary metabolites keep away most of the predators • Provide shelter to a range of other reef inhabiting organisms • Brittle star (Ophiuroidae), feather star (Crinoidea), shrimps, ctenophores and fish (gobies and pygmy sea horses)
- 26. • Few of these associates appear to also feed on the mucus of the octocorals • Mean octocoral cover of the GBR regions ranges from 3% to 35% on outer reef slopes
- 27. Reproduction • Reproduce both sexually and asexually • Sexual reproduction include both broadcasting & brooding • Usually they time their broadcastings according to the phases of the moon (alcyoniid corals )
- 29. • In brooding corals sperm alone are released into the water • Usually a few hours after sunset • Brood larvae internally by holding a small number of fertilized eggs inside the female polyp
- 30. • They hold until the offspring are almost ready to metamorphose(eg: Xenia and Heteroxenia ) • Some are external brooders (eg: Clavularia, Briareum, Rhytisma, and Efflatounaria) • Specialized structures on the outside of the polyps
- 31. • Hold fertilized eggs until a later developmental stage • Some species entangle the eggs in mucus on the surfaces of female colonies • Some have brooding sites formed by invaginations of the epidermis
- 32. • Some have brooding pouch that consists of an expansion of the pharynx (eg: Anthelia glauca) • Almost all octocoral species are gonochoric • Some Xeniidae species are hermaphroditic
- 33. Asexual reproduction • Some form runners, also called stolons, from the base of a colony to a new substrate (eg:Efflatounaria ) • Stolon reaches about 3 to 5 times the length of the colony • Moves some of its own body mass through the stolon to form a daughter colony • The stolon is reabsorbed, forming two unconnected colonies.
- 34. • Budding occurs when an individual polyp splits • Effectively growing a new polyp from the base • This method is used by all soft coral species use to enlarge a colony
- 35. • Creats buds made up of several polyps that eventually drop off of the parent colony and grow separately • Pieces are broken off of large colonies can regenerate into new colonies (fragmentation)
- 36. Types of soft corals • Gorgonian soft corals, which have fanlike structure • Carnation corals are ultrasensitive to changes in the water and water chemistry • Toadstool corals resemble mushrooms
- 37. • Tree corals, like their name, look like tiny trees in the ocean • Sea pens have a featherlike appearances • Bubble corals boast water-filled bubbles covered in bright hues
- 38. Commercially important soft corals Puple Colt Cladiella sp. Mushroom Leather Sarcophyton sp. Devils's Hand Lobophytum sp. Toadstool Leather Sarcophyton glaucum Finger Leather Sinularia polydactyla Fiji Yellow Sarcophyton sp. Gorgonian sp Pulsing Coral Xenia sp.
- 39. Mushroom corals Tongan Purple Actinodiscus sp. Purple Actinodiscus sp. Pink & Green Actinodiscus sp. Violet Actinodiscus sp. Blue Actinodiscus sp. Elephant Ear Mushroom Rhodactis mussoides Assorted Ricordea Ricordea florida Green Striped Actinodiscus sp.