Argentinian photographer Matias Alexandro grew up afraid of open water. Now, he’s learnt to freedive (a type of diving that relies on controlling your breathing rather than on scuba-diving equipment) and has travelled across the world to capture the most incredible marine wildlife. From sharks in the Bahamas to Ibiza’s otherworldly jellyfish and the surprising animals found off the coast of Scotland, he shares his top tips on how to master underwater photography, and his favourite images from oceans across the planet.