and their backyard ichchanging draticalally two years s ago, this aqaquatic parase w was igood c contion, its blue lagooprisisne and betifuful. but catastrophe has struck. the ter r is wming a at alarming r rate, bleachihing e corals. first they l lose their cocol, then they didie off. anne n now dives a world devd df lilife. nothing g but grey -- - a saddg sighght. dr. hoggetett: lots of d dead c. we sawaw two living g branching corals -- two. anlolots andots s of dd coraral. reporter: dedespite the bebeaul blue skikies and wondederful we sands, thehe great barririer res fightiting for its s survival. anne has no o doubt that c clie change is s responsible e fore bleaching. dr. hohoggett: it's devastatin, it's heartbreaking, absolutely heartbreaking. in the l last four yeaears we e had twtwo major cyclclones ando coral l bleaching epepisode. and thosose have realllly damd the coralsls. anand that's goioing to take ay long time fofor it to recocoverm th. rereport: therere'color everywhere here. thgrgreat rrier r ef is more an 2 200kilometers long. 's theheorld's largest cor reef e ecoste