Corals are marine ANIMALS belonging to the invertebrate phylum Cnidaria.
Corals most basic structure is the POLYP, a cylindrical tube with only one opening surrounded by tentacles. Some corals consist of solitary polyps, but most of the ~1000 species are COLONIAL, where several polyps clustered together to form an individual coral colony.
Corals have been in the oceans for millions of years (~300 to 500 MYA) and they can be found in tropical seas and cold temperate areas of the planet, as well as, in deeper basins. Modern shallow tropical corals form a symbiotic association with a dinoflagellate alga from the genus Symbiodinium. This mutualism, allowed the coral-algae holobiont (= all living organisms that constitute a coral colony) to live in areas that are not accessible for each of the components.
Adjacent growth of coral colonies in a single area transforms the seascape. Coral Reefs are invaluable marine ecosystems that affect the dynamics of the oceans as well as our day-to-day activities.
Types of Corals
Corals can be solitary (a single polyp) or colonial (several polyps). The latter constitutes coral colonies. Among the colonial corals, there are four "basic" morphologies: massive, branching, leaf-like and encrusting.
Massive coral colonies are boulder-shaped. They tend to be stronger against wave action and other environmental stressors than other corals. These corals are usually located in shallow to deep areas within the reefs.
Branching colonies are characterized by having many interconnected branches. They are usually weak and prone to breakage due to impacts. These corals inhabit the more exposed areas of the reefs where waves can break their branches and help them spread, a process called fragmentation.
Leaf-like corals growth in thin layers, they are usually flat to expose their tissue to as much light as it is possible. They inhabit deeper areas in the reefs.
Encrusting corals do not have a defined morphology, they just cover the substrate and acquire that particular shape.
Solitary corals are usually form by a single large polyp. They can be found alone or in small groups.
While most corals are attached to the substrate, some live in soft sandy to muddy bottoms where hard substrate is scarce. These coral are, therefore, not attach to the substrate and are called "free-living."
Coral Reefs are magnificent marine ecosystems. They barely cover 1/10th of the tropical oceans, but harbor an immense biodiversity.
Corals and Coral Reefs are found in tropical areas of the planet. As a group, corals are very diverse and usually where the species diversity is high, the structure of Coral Reefs is more impressive. Areas where Coral Reefs are imposing include the Caribbean, The Central Pacific Ocean, The Great Barrier Reef and the Coral Triangle.
Coral Reefs ecosystems provide many important ecological and economical services:
Coral Reefs are incredibly diverse with an estimate of ~9 million different species from different groups living within them. This vast biodiversity includes many economically important species like mollusks (snails, clams and octopi) and fish (groupers).
Massive colonies growing together form barriers against natural disturbances such as hurricanes giving protection to many coastal communities, the largest being the Great Barrier Reefs. In the Caribbean, the Florida Reef Tract and the Mesoamerican Barrier Reef are also good examples of barrier reefs systems.
The intricate three-dimensional structure of Coral Reefs allows for formidable seascapes with a myriad of forms and colors, attracting tourists and generating a lucrative activity in many tropical countries.
Several compounds produced by organisms living in Coral Reefs, such as medicines, can also be valuable to humans. ( more information )
Animals that live on coral reefs
Many animals take advantage of the three dimensional structure of the reefs. Some spend all their lives in the reefs, while others used it for shelter or nursing or as hunting grounds.
The reef in this image may look fine at first, but a careful look revealed most of the substrate is not covered by corals.
This reef was once covered with living coral colonies.
Unfortunately, human and non-human related activities are affecting the health of the corals and, therefore, the stability of coral reefs.
Many stressors are causing health issues to corals including coral diseases and bleaching.
There are between 27 and 30 coral disease/syndromes reported. Diseases have driven some coral species close to extinction and are affecting the structure and dynamics of Coral Reefs.
Usually coral diseases are named after a particular characteristic, such as color, therefore, most are known as: black band disease, white band disease, yellow band disease, white pox and so on...
To determine the relation between the causative microorganism or pathogen and a disease, scientists need to prove a set of preconceived steps called “Koch’s postulates.” These are:
1. The microorganism should be found in abundance in all diseased organisms, but not in healthy.
2. The microorganism should be isolated from disease organisms.
3. The isolated microorganism should produce the same disease symptoms to healthy organisms after inoculation.
4. The microorganism must be re-isolated from the inoculated organisms.
Only few coral diseases have fulfilled Koch’s postulates, but this does not necessarily means corals are fine, diseases/syndromes cause high levels of mortality and reductions in the number of individuals on several coral species.
In addition to diseases, coral bleaching is largely the single most traumatic stressor for corals.
Bleaching has been defined in several ways and it basically is the loss of coloration in the coral colony due to either loss or expel of the symbiotic algae or its pigments.
Coral bleaching has been associated with several environmental anomalies, being increased temperatures the most common cause of these phenomena.
As water temperatures are predicted to increase with climate change, it is likely bleaching will become more common and more stressful for corals. Some current observations suggest this is already the case.
Losing the symbiont for the corals is like losing the main source or energy, the power plant. During bleaching, energy is not produced and corals are force to use the energy stored within the polyp's tissue. If the symbiosis is not reestablished colonies can experience partial (some areas of the colony) to total (the whole colony) mortality.
The effects of bleaching go beyond the actual event, with some evidence indicating that bleached corals tend to grow and reproduce less and be more affected by diseases a year after the bleaching occurred.
One of the most heavily affected areas in the planet is the Caribbean Sea, with reports of most of the known diseases and where bleaching events are becoming more frequent and more devastating.
In nature, all organisms need to build defenses against biological and environmental stressors.
Evidence indicates that corals do have several innate immune mechanisms to protect themselves from pathogens and changes habitat conditions.
The mechanisms include:
1. Melanin production
2. Antioxidant activity
3. Antimicrobial activity
Recently, the use of next generation sequencing techniques have provided the possibility to study changes in the levels of expression in genes, allowing to understand more the mechanisms involve in the immune system of corals. We now know that several genes are affected by thermal stress, as well as, by the presence of pathogens. These studies will improve our understanding of how corals cope with stressors. Additionally, they will provide resources to help these important animals overcome climate change.
How to help save corals and Coral Reefs ... and other ecosystems
Support conservation Donate/volunteer for associations involved in Coral Reef research and conservation.Reusable Grocery BagsUse them, this reduces the use of plastic bags, which are a big contaminant. Batteries Use rechargeable batteries, and dispose them in the appropriate places help reduce the dangerous substances on them that reach the ocean. Reusable water bottles Reduce the amount of plastic.LightsSwitch off lights and turn air conditioning down help reduce carbon emissions, which means less coral bleaching in the future. Sustainable foodAsk where your fish is from - eating sustainably-harvested fish means, healthy reefs and we will have fish to eat for a long time. Collect your trashSpecially in the beach, put your trash where it belongs - marine debris like plastic bags and fishing line endangers turtles, dolphins, seabirds and many other marine organisms. Responsible snorkeling and diving Watch your fins when you snorkel - corals are fragile and take a long time to grow.Don't feed the fish Human food is bad for fish and fish have to play their role in the marine food web. ONLY take memories and photographs Coral Reef are constantly changing, removing things could be doing more damage than we think. Send words not balloons Send homemade cards, balloons are one of the most frequently found forms of marine debris. Leave the shells Sea shells could be hermit crab homes, the rubble zones for fish to live in, and contribute to beach formation. Clean-ups Specially coastal cleanups help reduce debris in the ocean and Coral Reefs. Learn Education reduces divers and snorkelers physical impacts, and help people understand these ecosystems. Natural products Use of natural products helps reduce contaminants in the water. Bike/walk to work Helps reduce carbon emissions. Less water The more water we use, the less it reaches the ocean affecting the salinity and the health of the marine ecosystems. Less fertilizers Large amounts of nutrients reaching the ocean can cause harmful algae blooms and poison animals and favor pathogens. Native plants Use them in your garden, they are naturally adapted to that environment, requiring less pesticides and fertilizers. Recycle This not only helps the ocean but all earth ecosystems. Re-use This not only helps the ocean but all earth ecosystems.Get involved Participate in local environmental programs/events
Long-lasting bulbs Reduce the amount of chemicals that can reach the oceans and the reefs.
Mooring buoys DO NOT ANCHOR ON REEFS!! Anchors and anchor chains, literarily kill corals and other organisms.Reefs clean-ups This activities reduce the amount of trash in the reefs.
Get politicians involvedAsk your public representatives to create plans to protect the environment.
Carpool Reduced fuel emissions.
I am very thankful with the people in the coral-list that helped put this list together.