This blue male was once a pink female..... here Scarus gibbus is being cleaned by two little Cleaner Wrasse who perform the job of dentist/parasite removalist for most of the reef's fish.  They set up cleaning stations on prominent coral outcrops where they advertise their services with a distinctive wagging dance.  A great spot to hang out and watch the queue of fish lining up for their appointment! 

This lady here is a first stage female Scarus gibbus - in the next image is a male so you can see the difference! 

Starting life as females, Maori Wrasse have spectacular tatoos around their eyes..... some will change sex to become male at about 9 years of age at which point they boss the younger females around as they patrol their territory on the back edge of the reef. 

Lives amongst the tentacles of its host anemone as a family group usually of 3 or more individuals.  There is only one breeding female in each group.  They start life as male.  If the large dominant female is removed or dies, the largest remaining male will change sex and become the breeding female. This particular anemone fish  Amphiprion melanopus  is nearly always with one species of anemone (Entacmaea quadricolour)

...a voracious predator with highly poisonous spines flared in warning to approaching fish. 

Spectacularly coloured Scarus spinus is found on shallow reef tops where it grinds the surface of corals with its parrot like beak to scrape of the algae that grows on most non-coral hard surfaces on a reef. 

The genus name is Fungia - a good name for a Mushroom Coral. These are one of the few corals that live as solitary large polyps and do not become colonies as most corals do.  Because they are large (up to 20cm across) looking at them is a great way to learn about corals.  They have the mouth in the centre - you can see it here - with the septa (structural walls of the coral) radiating outwards.  Like all corals it has symbiotic zooxanthellae in its tissues as well as tentacles that catch passing prey such as plankton (mainly by night). As juveniles they are attached to the substrate (the reef surface) by a little stalk just like a mushroom.  As the coral grows, the stalk falls off and the weight of the coral keeps it on the bottom. 

Tiny but very beautiful, this coral forms small rounded or encrusting colonies with often flurorescent green tentacles that are frequently open and feeding during the day. The high and pointed septa give the corallites a star-like appearance. 

Probably Lobophyllia, you can see the tissue covering the skeleton of the coral quite clearly.  Each corallite (the cup containing each polyp) is about 3-4cm across, and the colony as a whole can grow up to 1m or so across. 

While they don't have a hard internal skeleton, the soft corals are an important part of reef life - providing habitat and food for many reef animals.  The tentacles on soft corals are usually fringed, and in groups of 8 (hence the name of their subclass is Octocorals), whereas hard corals have simple tentacles on the polyps and are in groups of 6 (hence their name is Hexacorals). 

Forming round colonies of various sizes, the corallites look like round honeycomb shaped dents, the mouth in the centre.  Again the tentacles come out at night to feed, with daytime being when zooxanthellae (the microscopic plants) produce nutrition as proteins and carbohydrates for the coral.  Honeycomb corals are identified to species by the way the corallites join onto each other - forming ridges or valleys and the way the septa are laid out.  This one is probably Favia rotundata. 

Reefs don't grow into mountains or hills. Why?  Corals are living animals as we know, and they dry out if they are exposed to the air for too long.  So how long is too long?  While corals produce a remarkable mucous that lubricates them and has a high level of coral "sunscreen" this mechanism can only work for a short period.  Low spring tides expose the top of the reef for a few hours just a few days a year.  Growth that has occurred over the past year may be killed off with this extended exposure to air and sun.  Sometimes we see the top of a reef appearing white as snow a few days after the low spring tide - especially if it has been a bright sunny and hot day. 

Corals expand their colony by reproducing asexually and budding off more polyps along their branches for example.  But each year, they produce eggs and sperm for a single night of a coral sexual explosion when these gametes mix like a pink soup in the water.  Indeed, it is a fabulous soup for predators such as fish - which is why the spawning is at night when fish sleep and is synchronous within a coral species on a particular reef so that there is a good chance of fertilisation in the vast ocean.  Any predators that are around for it (such as night feeding plankton and fish) have a complete feast but can only eat a limited amount in one go - maximising survival for the corals.  The fertilised egg becomes a planktonic larva until it becomes heavy and settles on a reef to become a new coral where it asexually reproduces to form a colony. 

Pseudoceros dimidiatus - advertising its poisonous flesh to potential predators with its bright stripes. 

Close up of the tentacles of Entacmaea quadricolour - an anemone that is often host to several species of Anemone Fish. 

One of the many worms that burrow into coral for its home... feeding on suspended matter on the water with its fine blue gills that act like a net. 

One of the many animals that buries itself into coral by secreting a mild acid that allows the coral to grow around it but not over it, forming a secure and safe niche that makes it difficult for marauding large jawed fish - such as Buffalo Fish or Triggers, to extract them. 

These little creatures are indeed an animal.  They are a sea squirt and so are filter feeders - simple examples have one hole where water comes in, a basket inside that filters food, then waste water is pumped out through a second hole.   Compound ascidians are many "individuals" joined together basically, with many incurrent holes (the little dots) and one large excurrent siphon (the green hole in the middle).  This example Didenum molle, is one of the most common found on our Great Barrier Reef.  This one was at Opal Reef off Port Douglas. 

All the Echinoderms (meaning spiny skin) have a pattern of radial symmetry - usually with 5 points.  Starfish, sea urchins, sea cucumbers, sand dollars and feather stars are examples.  Starfish usually feed by crawling over the bottom using the hydrostatically operated tube feet on the underside of their arms, and everting their stomachs over their prey. Most are carnivores or feed on detritus. This one is Nardoa novaecaledoniae. 

A perfect blue star - Linckia laevigata - unfortunately one of the most frequently harvested in the Indo Pacific as a souvenir.  These starfish are usually found on the tops of reefs where they feed primarily on algae and detritus on the reef floor. 

Another relative of the starfish, Feather Stars are living relatives of the ancient Sea Lilies that were one of the first forms of life in ancient seas.  They are suspension feeders and filter water in their arms, moving it with tiny "podia" on a mucous trail that leads down to the central mouth. 

On the edge of the continental shelf, north from Port Douglas is a linear chain of reefs know as The Ribbons.  Steep dropoffs on the windward side, oceanic clear water and an aura of adventure and wilderness make this special area a drawcard for even the most experienced of underwater explorers. 

At the northern end of the Ribbon Reefs, a series of mountainous islands perch not far from the outer reefs.  The largest of these is Lizard Island - also home to the renown luxurious Lizard Island Lodge and a world class research station. 

Only 8 nautical miles from Port Douglas, this jewel of an island sand cay is visited by several operators each day.  Its the perfect spot  to snorkel from a beach for your first coral reef exploration, and as an added bonus, there is a remarkable range of undersea life to discover; a wide variety of corals, giant clams, very friendly turtles and remarkable macro (ie small critters) life. 

Surprising pockets of unusual underwater life is a feature of the very accessible, yet very beautiful Low Isles.