Abiotic Factors:

-Water (H20) is naturally a very important abiotic factor in coral reefs as all of the inhabitants have adapted to saltwater life. Water is necessary for all life and coral reefs need it in abundance.

-Sunlight is very important, corals cannot live without a certain amount of light, due to their dependence on photosythesizing zooxanthellae.

-Currents often affect the location of coral reefs. For example, some new species will be brought to coral reefs because of currents. Currents also affect water temperature, the next factor on our list.

-Temperature is important because coral reefs cannot survive if the water is too cold and dramatic changes in temperature can lead to coral bleaching.

-Salinity (the level of salt in the water) affects the creatures that live there. Since corals are saltwater animals, the water must have a high enough salinity level.

-The ocean substrate (the surface of the ocean) is a barrier, because corals are not adapted to living above the water.

-The ocean floor provides a clear barrier for how deep a coral reef can go, provided the other factors do not stop it earlier.

-Turbidity (how opaque the water is) is directly related to the amount of sunlight a reef is getting. Turbidity is another reason that reefs do not form near the deltas of rivers, too much silt is deposited and not enough light can get through.

Biotic Factors

Biotic factors can generally be split into groups divided by kingdoms.

-Animals are probably the biotic factors you hear about the most. They are living organisms that have these characteristics:

    - They are heterotrophic. Heterotrophic means that they cannot get their energy directly from the sun. They must get it from an autotroph (an organism with the ability to photosynthesize). Normally this is done by eating the autotroph, or another heterotroph which eats an autotroph. For more information on this, check out energy pyramids and food webs.

    -Animals are multicellular. Some living organisms are only one cell, but animals are ot only are they multicellular, those cells are eukaryotic cells. Eukaryotic cells are more complex cells than prokaryotic cells, the only cells in existence when life first emerged. Eukaryotic cells contain little separated parts within, called organelles. These organelles have specific jobs, such as containing the code for how the cell is supposed to form and behave, or dealing with energy in the form which animals get it. Prokaryotic cells are lacking in organelles. Eukaryotic cells are also the cells that make up plants, fungi, and protists.    

    -Animals’ eukaryotic cells do not have cell walls. Cell walls are a sort of protective layer found in other eukaryotic cells like plant cells. The cells of say, a fish, do not need this cell wall.

Lots of different animals can be found in coral reefs. In fact, there are thousands and thousands of different species living in most every reef. But these species can be generally grouped together, so these are some of those groups.

• -Phylum Porifera (Sponges), is one such group found in coral reefs. Sponges are easily identifiable despite the fact that they come in different shapes and sizes. They are a very simple animal, and their cells are more independent than our cells. That being said, poriferan cells do have specialized jobs, and they work together to draw food and oxygen from the water around them. Sponges come in different colors and shapes, but they all have at least one excurrent opening, out of which the water sucked in through poriferans pores exits. A few specific examples of poriferans include tube sponges and barrel sponges.

• Phylum Cnidaria, which includes jellyfish, anemones, corals, gorgonians and hydroids, is very important to coral reefs, particularly the corals. Many cnidarians (such as corals) form colonies and attach themselves to rocks where they live, although others (like jellyfish) are live alone. When a cnidarian attaches itself to a hard surface like a rock, it is called a polyp. Often, we will refer to coral polyps on this site. When cnidarian is swimming around, it is called a medusa. Cnidarians have stinging nematocysts normally found on tentacles, which is why you get stung by a jellyfish or most fish avoid sea anemones.

• Phylum Ctenophora (comb jellies) are bioluminescent creatures often mistaken for jellyfish. They have either few tentacles or none at all and move by beating their celia, hairlike “combs” which enable them to move. These celia often look like little lights. Ctenophores cannot sting, and are very fragile. You may have seen some small ones washed up on a beach, but they are almost transparent, so they can be hard to spot.

• Phylum Platyhelminthes (flatworms) are thin oval shaped animals which look similar to nudibranchs. They move by means of celia along their undersides. Though flatworms are unsophisticated, they were some of the first animals to have a difference in their left and right sides and their front and back, so their existence is a sort of evolutionary landmark.

• Phylum Rhynchocoela (ribbon worms) are mostly found in reef habitats and are often very colorful. They are more slender than flatworms and more highly organized, but are otherwise rather similar. They are not uncommon at reefs, but are rarely seen swimming around in the open.

• Phylum Annelida (segmented worms) are found not only in reefs but also here in Kansas. Earthworms belong to this phylum. Marine worms, their coral reef counterparts are often at least partially covered in feather like bristles. Annelids are called segment worms because their bodies are made up of identical repeating segments.

• Phylum Arthropoda class Crustacea are shrimps, lobsters, crabs, and barnacles. Arthropods are the largest animal phylum in the world, as they include insects and spiders as well as crustaceans, but only mostly crustaceans live in coral reefs. The group has exoskeletons like their land counterparts, and jointed legs. Crustaceans molt occasionally, as their exoskeleton does not provide room for the animal to grow. Their bodies are made up of three sections, head, thorax, and abdomen.

• Phylum Ectoprocta (Bryozoans) are zooids which grow in many different shapes and colors. They have tentacles around their mouths which are similar to polyps, but they are not the same. Bryozoans have a sophisticated digestive system. They look very different, and can grow to look like fans, tubes, or a colorful crust.

• Phylum Mollusca (snails, bivalves, octopii, squid, etc.) are a fairly well known phylum. They are varied in appearance, but most form shells out of secreted calcium carbonate.

• Phylum Echinodermata (sea stars, sea urchins, and sea cucumbers) have an internal skeleton, but it is very different from ours. Their skeletons are made up of tiny hard plates called ossicles. Echinoderm bodies have five sections, and these are arranged around a center point. Most of them have lots of tiny feet which they use to move around.

• Phylum Chordata (fish, reptiles, and marine mammals) are the phylum that humans belong to. All animals with a backbone are in this group, and it has lots of variation. This is probably the first phylum you think of when you think of animals, and yet it is much smaller than the number of arthropods. Most of the top predators in the coral reef are chordates.

There are also other kingdoms in the coral reef. Algae for example, formerly considered part of Kingdom Plantae but now considered protists, are common in coral reefs. Seaweed is the giant of the algae, and there are three main types, green algae, red algae, and brown algae. All three can be found in coral reefs. The other types of algae are microscopic algae, like zooxanthellae. Though they are tiny, the microscopic algae plays a monumental part in the function of coral reefs. Fungi are multicellular organisms who decompose and absorb nutrients. Fungi can be found on land and in coral reefs. Bacteria also seem to have a close relationship with corals, but scientists are still a bit unsure exactly how they are working together.