This year the Guardian picture desk has chosen Yannis Behrakis of Reuters as our agency photographer of the year. Here are the most astonishing moments he captured in two of the biggest stories of 2015 – the refugee crisis and the financial implosion in his home country Greece.

''I have been covering refugees and migrants for over 25 years, but this year has been different: migrants are arriving in my homeland. A couple of boats came every night. Everybody aboard was scared because they didn’t know how the police and locals would react. Small dinghies kept on coming, even when the weather was rough. The Turkish coast is just 4-5 km away''.

Last year, I was in Suruc on the Turkish-Syrian border documenting the thousands of Kurdish refugees fleeing the town of Kobani. This year on Lesbos, a man I met in Suruc recognised me. 'I made it, man! I made it,' he said.

The least challenging part of this year was taking pictures. The biggest struggle was the emotional involvement ... it was so sad to see the same thing again and again.

One day I was photographing a raft when I noticed movement in the water. I thought someone had jumped overboard. I focused using a long lens – then saw a fin. A dolphin jumped almost in front of the raft. It was a truly magical moment. It was as if the dolphin was showing the way and welcoming the people.

No one expected there to be so many of them. But most Greeks have some refugee blood, and locals realised these people only wanted to use Greece as a stepping stone to go north.

I want to express my gratitude to all the Greek and foreign volunteers who helped in the islands and the northern border. You prove that humanity is alive!

Photography can leave people speechless with its power and beauty. It can send a message to the audience, make people cry or laugh or both. It can make people feel guilty – or give money for a good cause. And it can make people think twice before pulling the trigger ...''