Everybody that hear a Mayday cannot respond to the ships that is in distress. If you hear distress traffic where somebody already have responded you listen in and when suitable contact MRCC or the responding vessel and report your position and how quick you can get to the position. On he YouTube clips you can hear other ships report to Silja Europa that they are available.
After some time MRCC will designate one ship as OSC, on scene commander (today called on scene coordinator), and they act as an extension to MRCC making decisions and communication locally. Usually multiple VHF channels are setup for different traffic. For example search vs rescue vs helicopter operations.
First contact was with Viking Mariella at 1:21:55
Ainsalu: Mayday Mayday Estonia please (unclear)
(This seems to indicate some impatience? Perhaps had called before?)
There was a brief exchange.
The first contact with Silja Europe was at 01:23.11, over a minute later.
Ainsalu: Europa, Estonia, Silja Europa, Estonia
This indicates he had Europa showing on his network, to know the name.
Europa takes eight seconds to respond: Estonia, this is Silja Europa replying on channel 16.
Seven seconds later, Estonia repeats, as though not heard:
Ainsalu: Silja Europa
Seven seconds later, Europa repeats:
Estonia, this is Silja Europa on channel 16
No response. 21 seconds later Estonia broadcasts:
Silja Europa,Viking, Estonia
Viking Mariella replies four seconds later: Estonia, Estonia
This is a gap of 24 seconds since it last spoke to Estonia, with: Estonia, Mariella over.
This indicates a lack of communication due to a lack of response. Two seconds later, Estonia states: Mayday Mayday.
Europa calls Estonia two more times and then 31 seconds later without reply, it is now Third Officer, Tammes for Estonia
Tammes: This is Estonia. Who is it there? Silja Europa, Estonia.
In the meantime, Turku MRCC, the operator/communication officer, Ilkka Jouko Kalevi Kärppälä, who was on duty, says he got the Mayday at 1:24. At Nagu MRCC the operator/communication officer, Rauli Tapio Winberg, states he heard the Mayday at 1:23.
This is a whole one minute after Ainsalu called: Mayday Mayday Estonia please (unclear)
For Turku MRCC two minutes later.
The Nagu MRCC officer Winberg also says he didn't have Estonia on his radar but did have Mariella, Europa and Isabella. He says in his police statement, there was interference here.