Re: what are the primary, secondary etc. producers and consumers in the GBR?

Wow what a big quesiton, let me have a go at this one.
At the base of the trohpic pyramid on the Great Barrier Reef we have all 
the plants.  But not just the macroalgae like seaweed, the bulk of the 
primary production is produced by phytoplankton.  In fact, phytoplankton is 
the largest primary producer for the whole planet.  Anyway moving on.. then 
we have everything herbivorous.  Herbivorous fish, filter feeding 
crustaceans and gastropods, zooplankton, a whole array of animals that are 
predominately small, and lots of corals.  The only exception to the rule of 
small herbivores are the baleen whales, which kind of throws out the 
biomass of secondary producers a bit, but makes for an interesting pyramid.
Then, the next trophic pyramid, that would be the tertiary level, are 
carnivores that feed on the herbivores.  These are difficult to define as 
one group because they come in all manner of sizes.  Some zooplankton are 
carnivorous, octopus, other fish, sharks, rays, all kinds of things, 
basically anything that eats other animals.  The Great Barrier Reef isn't 
that dissimilar to other marine environments when it comes down to trophic 
levels.  
The answer to your question on predator-prey relationships can be adapted 
to any environment, terrestrial or aquatic.  The Great Barrier Reef doesn't 
have any predator-prey relationships that fail to conform to theory.  
Generally, predator-prey relationships are pretty complex.  Lets use an 
example.  Lets say sharks predating on smaller fish.  If there is a high 
abundance of smaller fish, the sharks will eat well, reproduce more, and 
subsequently eat more, reducing the population of the smaller fish to such 
a level that the sharks don't have enough food to support the population 
and their density will dwindle back to a normal level.  Meanwhile the 
smaller fish replenish their population, then the sharks eat more and it 
all happens again.  This kind of yo-yo effect happens all the time in all 
kinds of predator-prey interactions.  Another interesting component of this 
interation is co-evolution, otherwise known as the arms race.  What happens 
is a predator will get better at finding it's prey, then the prey will 
adapt to become better at hiding, then the predator will become better at 
find it, and so on and so forth.  Kind of like the flu, we identify it and 
design an vaccination for it, then it changes a bit to overcome antibiotics 
to survive, then we identify it and it all happens again. 
Grab a text book on population dynamics, there will certainly be a few 
pages, if not a chapter an density dependent and independent dynamics of 
populations and predator-prey relationships, really interesting stuff.
Phew, I hope I answered your question :).
Rochelle.