Coral Reefs

Location of Reefs

Found between 30°north and 30°south Reason: coral reefs do not thrive in areas where the surface

temperature is below 70°F

Two areas of coral reefs– Continental– Oceanic

• Indian• Pacific

Types of Reef

Barrier– Offshore, and separated by a lagoon

Atol– Deep ocean, volcanic foundations

Fringing– Simplest – built upwards and outwards in shallow seas,

beside islands or continents

Formation of Reefs

Built of entirely marine plants and animals Material is calcium carbonate: limestone derived from the

surrounding waters by reef organisms Reef is a veneer on which new limestone can attach The sea level limits the upward growth of the reef Reefs have only existed for a relatively short amount of time in

geological terms

Corals

Both living and dead, they form a framework Solid and unyielding or soft but firmly attached Form into mounds, plates, branches or crusts Are coelenterata along with jellyfish and sea anemones

– Special prey catching cells - nematocysts Colonial – single founder individual, dividing to replicate itself

over and over again Zooxanthellae – tiny single celled photosynthesising plants

amongst within coral tissues

Plankton

Too small to be seen, and are transparent

ZOOPLANKTON– Gelatinous– Some predators, others produce fine mesh for collecting

food, some produce mucus ‘house’

PHYTOPLANKTON– Microscopic in size– Photosynthetic

Algae and Seagrasses

Important biological component of coral reefs 500 species of seaweed and 12 species of sea grasses in the

Great Barrier Reef All marine flowering plants are known as sea grasses They have male and female parts Able to pollinate while submerged in sea

– Known as hydrophilous pollination Non-flowering marine plants are known as algae/seaweed

Sponges

Important role in complex structural processes Chemically digest the limestone skeletons which go on to form

the base of the coral reef Efficient ‘vacuum cleaners’ Filter out bacteria, detritis and coral mucus

Marine Worms

Brightly coloured, voracious jaws, well developed eyes Exist within dead coral skeleton Bore by chemically dissolving coral Range from microscopic to several cms in length

Molluscs

4 major groups– Gastropods – seasnails, slugs– Bivalves – oysters, scallops, clams– Cephalopods – octopus, squid– Chitons – molluscan equivalent of

terrestrial armadillo Soft bodied with a hard outer shell Found in coastal ‘zones’

Crustaceans

Reefs abound with brilliantly coloured crustaceans Most live in hiding only come out at night to feed Exoskeleton gives protection Female lays eggs which remain attached until developed Live in permanent symbiotic relationship with coral

– Provides shelter, protection and food

Bryozoans

Hidden areas of reef encrusted with moss-like bryozoans Often most dominant life form Grow on rigid surfaces, moving objects or are free living in the

water

Echinoderms

Most conspicuous creatures on the reef E.g. sea urchins, starfish, cucumber 6000 species Almost all bottom dwelling Have a sessile lifestyle, and are suspension feeders, but some

are carnivorous

Ascidians

Filtering water bags E.g. seasquirts Two important roles:

– Feed in the water around the reef and keep it clean– Concentrate the plankton in the water making it available for

other animals Sessile lifestyle fixed firmly to substrate Cilia set up water current to allow filter feeding

Fishes

Diverse range Many have evolved with the coral As size of fish increases the number of species increases and

the number of individuals decreases Many territorial Adapted in shape and behaviour depending on food source

4 types:– Grazers– Plankton feeders– Mollusk, crab, shrimp feeders– Predators

Dangerous Animals on the Reef

Many use chemical defences Bacterial attack can be countered by development of

bacteriocides Mechanical and chemical offensive weapons also abundant

Example – Portuguese Man o’ War Have toxin loaded cells And needle sharp barbs at end of coiled spring

Example –Sea Urchins Have sharp spines Can have a coating of venomous mucus

Example –Sea Snakes Have small fangs But with deadly venom Are more dangerous than land snakes

Example –Puffer Fish Puff up and produce strong poison Is called tetrodoxin

Example –Moray Eels Have large, hooked, razor sharp teeth