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Montastraea cavernosa are gonochoric broadcast spawners, which means polyps have either male or female sex cells but not both like many other species of coral do. Spawning occurs once a year about a week after the full moon in August or September. Male colonies spawn first, an hour or two after sunset, followed by female colonies and both shallow and deep water colonies will spawn synchronously. Once fertilised the larvae become planulae which will travel in the water column before settling onto suitable substrate and developing into a polyp. This polyp will then initiate the growth of a colony.
Asexual reproduction occurs by extratentacular budding where new corallites will form and grow between the walls of existing corallites. As corallites form, polyps will deposit calcium carbonate beneath them allowing the structure of the colony to grow into massive domes.
Due to the competition for space on reefs Montastraea cavernosa has long sweeper tentacles that it uses to protect itself and the space around it. Montastraea cavernosa also has long mesenterial filaments that are extensions of their digestive systems so that they literally eat other coral species that are encroaching on their space. The sweeper tentacles are extended at night time and are usually found on the outer edges of a colony.
Montastraea cavernosa is often a dominant species in areas that are highly sedimented and it is thought that is this due to their shape and ability to remove sediment that settles onto the tissue surface. The shape of the polyps and steep sides of the colony mean that sediment tends to roll off the colony rather than settle and waves of movement by the polyps will lift and remove larger particles of sediment. Montastraea cavernosa will also secrete mucus to help remove sediment that has settled on the polyp surface.
The primary anthropogenic threats facing coral reefs are coral bleaching and ocean acidification. Although Montastraea cavernosa is not as vulnerable to bleaching as some other species but it is possible that the frequency of bleaching events will increase as sea temperatures continue to rise. When sea temperatures are higher than normal the coral can respond to this stress by expelling its symbiotic zooxanthellae, its usual energy source. The expulsion of zooxanthellae leaves the coral with a white, bleached appearance and if the bleaching is extensive or prolonged it can be fatal.
Ocean acidification is a result of the rising levels of atmospheric CO2 which means more carbon dioxide is dissolving into the ocean and lowering the pH of the water. This presents a problem to organisms that have calcium carbonate in their shells and skeletons as it makes the structures more brittle and slows growth. Current CO2 levels are approximately 387 ppm but if they are allowed to rise to 450ppm, which is predicted to happen in 20 to 30 years time, the growth of corals will be severely impacted.
Montastraea cavernosa is particularly susceptible to black band disease, white plague type I and II and dark spots. Black band disease, which is visible as black bands on coral, is caused by a collection of different types of bacteria which results in the death of coral tissue. White plague disease was also found to be caused by a bacterial pathogen and this disease is indentified by the distinct white line that forms between healthy and diseased tissue. The cause of dark spots is not yet understood but is characterised by irregular shaped dark spots on healthy tissue.
Corals are also at threat from human activities. Some threats are the same globally such as pollution, over-fishing and destruction of the reef due to dynamite fishing or boat damage. Over-fishing is a common problem because many coastal communities rely on fishing as a source of protein and income. However removal of herbivorous reef fish can lead to a phase shift where algae become the dominant species on the reef to the detriment of coral.
Deforestation is an additional threat to Montastraea cavernosa populations on the coast of Brazil and Costa Rica. The removal of terrestrial forests increases sediment runs offs from the land onto the reef, via rivers and streams, reducing light availability and covering coral in a blanket of sediment that can lead to suffocation. Mangroves and sea grasses play a crucial function in bio-stabilising sediments and preventing reefs being smothered in debris. The removal of either of these vital habitats results in the greater deposition of sediment and silt onto coral reefs.
The West African Regional MPA Network (RAMPAO) was created in 2007 to support and establish a regional network of marine protected areas in West Africa. They hope to do this by exchanging knowledge and improving the effectiveness of MPA management. So far five countries are participating in the network and about 70% of the area protected by RAMPAO is marine. Additional conservation measures in West Africa are led a by a program called the Regional Coastal and Marine Conservation Program for West Africa (PRCM) which is a venture of international non-governmental organizations and the governments of nine west African countries. This program has developed marine management plans and community based protected areas in Cape Verde, the Gambia, Guinea, Guinea Bissau, Mauritania, Senegal, and Sierra Leone
Within the Caribbean, conservation is underway following the launch of the Caribbean Challenge in 2008 when the leaders of five Caribbean nations including the Bahamas, Jamaica, Grenada, the Dominican Republic and St. Vincent and the Grenadines, pledged to protect 20% of their marine and coastal habitats by 2020. As a result of this pledge the Bahamas have so a far added 3.2 million acres of terrestrial and marine habitats to their network of MPAs.
To address the threats that result from the global change in climate, international governments need to agree to and comply with recommendations to reduce carbon emissions, but these actions need to be taken quickly before it is too late for the coral reefs to recover from the damage that has already been caused. Individuals can contribute to the conservation of coral reefs by adapting their behaviour to reduce their own carbon footprint.
Research into the ecology of Montastraea cavernosa and the causes of coral disease may also aid the creation of species specific conservation action plans.
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Vize, P.D. 2006. Deepwater broadcast spawning by Montastraea cavernosa, Montastraea franksi and Diploria strigosa at the Flower Garden Banks, Gulf of Mexico. Coral Reefs 25:169-171
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Distribution map based on data provided by the IUCN Spatial Data Collection.
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