Habitat-Builders: Coral

2017 is drawing to a close, which means our field course is just a flip of the calendar away!  Some students are already in the Caribbean, bringing in the New Year with style – wherever you are, I wish you a happy one!  If all the celebrations have left you little time for research, I’ve done some of the legwork for you – my next few posts will be about the plants and animals which help make the Bahamas so special.  Starting off under the sea, let’s look at some coral reefs!

Famously as diverse as rainforests and yet made up of tiny animals called polyps, coral reefs form one of the most important ecosystems in the Bahamas.  Besides drawing in tourists with their beauty, they also create the limestone base on which an abundance of reef creatures build their homes.  One of their many benefits for humans is that reefs act as a natural breakwater around the shore.  For more on their importance and how to help protect them, check out this blog post from last year.

 

 

Corals are divided into those with hard and soft bodies; the hard corals are those which build the calcareous base of the reef, while soft corals are delicate and plant-like.

Identifying corals to a species level can be difficult without a microscope, but are usually categorised by the shape formed by the colony.  Here are a few found around the Bahamas:

‘Massive’ corals are so named because they form boulder-like masses, not necessarily due to their size!  Having said that, brain corals can live for 900 years and grow as tall as a person.   The above grooved brain coral is often associated with long-spined sea urchins, grazers which eat algae which may otherwise smother the coral.

Another ‘massive’ coral is the great star coral (below), which truly deserves its title – its polyps, while tiny in most coral species, are the size of a human thumb!

‘Encrusting’ corals creep along the rocks on which they first settled, forming an uneven coral blanket – often with strange projections sticking out!  This mustard hill coral (above) is home to an alien-looking bristle worm.

Confusingly, mustard hill corals can also take the shape of ‘massive’ corals.  Lack of fidelity to one form is common in corals as it enables them to capitalise on the amount of sunlight they receive.  Massive corals, for example, often are flatter in deep, dimly-lit water.  This gives them a greater surface area turned to the sun, which their zooxanthellae (tiny plants within the coral polyps) use to photosynthesise energy for the coral.

A third category describing the shape of coral is ‘columnar’.  Demonstrating this is a mass of finger coral, a slow-growing and one of the longest-lived species.  Its columns may also form stubby branches.  This species isn’t fussy as to where it calls home and sometimes even grows on mangrove roots (more on them next time!).  Happily, it is also somewhat resistant to bleaching, a phenomenon caused by rising ocean temperatures which threatens many coral species.

A true ‘branching’ species is the magnificent elkhorn coral.  This species is fast-growing thanks to its lightweight skeleton.  Once abundant, they were hit hard by disease in the 1980s and are now listed as critically endangered on the IUCN Red List.  The Cape Eleuthera Institute is involved in conservation work for this species, attempting to re-grow some of their elkhorn using coral fragments and a structure made from recycled materials.  Read more about this project here.

Finally, an example of a soft coral – this waffle-like creature is a gorgonian, similar to sea plumes and sea whips.  In front of it are some fabulously-named social feather dusters, or ‘cluster dusters’, a type of bristle worm and another animal species which looks deceptively like a plant!

This should give you some pointers on how to describe corals seen on a dive – searching for a ‘columnar’ coral will probably get you further than a ‘blobby’ one!  For more corals found in the Bahamas, check out Arkive‘s amazing directory of marine invertebrates.

Next I’ll be looking at the plant life which constructs Bahamian habitats – until then, happy new year!

eo271    December 31st, 2017    Bahamas    , , , ,

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