chapter 14 a coral reefs you can think of a coral reef as a wall of mouths what you're looking at are stony corals and all of these corals have used calcium carbonate to make their calcareous skeleton okay or the structure of the reef and they all have they're made up of polyps and each polyp is is capable of eating something now there's not a lot of nutrients in the water here but they get there's enough to get by not all of it is from eating things a lot of where they get their nutrients a lot of their nutrients comes from symbiotic relationships with an algae or dinoflagellate that lives in the tissues of the corals called zooxanthellae you can see the coral reefs lit are on the continental shelf uh where it's not too deep the sunlight has to be able to hit the bottom or at least reach down deep enough for the coral supporters for this the coral symbians to photosynthesize a coral coral reefs are made up of calcium carbonate secreting animals and plants this is where they're what created the limestone that we find around here we actually had reefs right around here at one time so here are some pictures of limestone wall and if you look very closely you can see fossils all through the limestone uh here's a limestone core in the top left corner and you can find many of the types of corals that you see in this picture here and uh brachiopods and so forth shells from bio by valves some fossiliferous limestone coral belonged to the phylum night area we've discussed this before and they are made up of polyps a polyp is an individual coral which secretes this protective exoskeleton of calcium carbonate called a coralite the polyps may be solitary so one individual polyp could be the entire animal or they could be colonial and colonial species give rise to the coral reefs on the right side you see an example of colonial coral here's the side view of the coralite you can see the individual polyps growing in the coral light there they have tentacles the individual palp has a tentacle uh has a mouth there's a gut cavity and has mesenterial filaments this is we'll explain those in a few minutes the some more colonial coral this one's called ganopor there are hermitivity corals and a hermitivic corals hermatipic corals have zozan belly in their tissues and these are the reef builders they are colonial corals that are found in shallow and tropical seas a hermotypic corals are non-reef building they don't have the zooxanthellae they don't have those symbians they're in the because of that they're not limited to shallow or warm water they can be found in polar seas in very deep water core reproduction they will reproduce by releasing their gametes all the same time how do they time this out we're not really sure but when they do it looks like it's snowing upwards on the reef we think it might have something to do with the phases of the moon uh once you have a fertilized zygote it it's what we call it a planular larvae and it'll metamorphose into the adult form and start to grow once it finds a hard place to settle sometimes under particularly poor conditions a coral may produce what's called bailout polyp that can leave the colony and go find try to find a new place to live and once it finds a new place it'll settle and grow and start growing into a new colony but finding a place to settle may not always be easy and notice this reef here every place that's habitable has been taken by somebody else so if you watch a coral reef very slow in time lapse uh you can see that what is happening is it's just a huge war going on all the corals are eating and fighting each other but it just happens in slow motion crawl nutritions a lot of corals eat well they have tentacles which can capture prey they have the pneumaticists or little little stinging cells that that they can use to capture food items zooplankton and so forth and then they'll take it into the gut digested there but that's not the only way that they can get their nutrition they also have symbiotic zooxanthellae we've talked about this before they have cytophotosynthetic dinoflagellates which photosynthesize the byproducts feed the coral they also provide the zocentili also provide oxygen and organic materials and they help remove the corals waste products and they enhance the skeleton formation corals also have these mesenterial filaments which they're long needle they're long thread like filaments which excrete digestive enzymes and they can be extended through the the mouth or the body wall and what they'll do is they can they can just drape it over their neighbor and try to digest their neighbor but they they they absorb food um so some other coral defenses are shading a lot of corals will grow up and try to fan out and out and shade over the corals below them to out-compete them that way and i mentioned before the tentacles which can sting each other mesenterious filaments which can they can uh they'll try to digest their neighbors many will produce toxins particularly the soft corals that don't lay down that calcium carbonate skeleton a lot of those have a lot of toxins associated with them to try to poison their neighbors another way that corals can take in food is from dissolved organic matter just things in the water that they can just take in right through the membrane cell membranes now reefs themselves are areas are found in areas where the nutrient levels are very very low if there are lots of nutrients in the water there would be a lot of algae and algae grows a lot faster than coral does so it would help complete it and smother it so corals like areas that are very devoid of nutrients however coral reefs are highly productive environments the reason is because of the zooxanthellae they're the reason why the corals can exist in these nutrient poor waters so here's some more pictures of some sea anemones and coral poly tentacles and zozanthali another reef builder that i want to talk about is coraline red algae which grows in over reef rubble and it binds and stabilizes the reef uh it's grazed extensively by some organisms but the corollary coralline algae uh helps provide this soap this solidarity so when reef gets rubble gets smashed to pieces and it's this coral analogy that cements it all together so coral reefs are complex structures that provide many many different types of ecological niches for many types of animals so you can see on the left there are some encrusting in platelight corals and on the right you can see some branching coral stag horns and alcorns so here's a drawing of the different types of corals you can see in crusting growing over a rock you can see the plate like in the folacious and the free living corals columnars massives or like the big brain corals and boulder corals and the branching corals such as the acroporas and elkhorn and staghorn coils this is just showing the hard substrate which is being filled with rubble brief rubble and other different sand uh loose sediment and coral rubble and so the reefs the reef animals continually grow upwards to stay above the sediment so here's the complex food web you don't have to memorize this but at the bottom you have your producers so your seaweeds coralline algae photosynthetic bacteria your corals zooxanthellae and you can see the relationships between the grazers detritus feeders coral and coral mucus feeders plankton feeders and then your top predators fish squids snails that sort of thing um and also detritus okay so this is waste is also a valuable resource some colonial coral have polyps that are fused together in this type in this coral you see here here's two coral heads on the right side is the coral with the living tissue surrounding it giving it that darker color and the skeleton underneath is white so you can see this the white skeleton on the coral head on the left with no with the the animals gone you