The service, at Portsmouth Cathedral in Old Portsmouth, also commemorated the life of Admiral Lord Nelson.
The service was led by the Dean of Portsmouth, the Very Reverend Dr Anthony Cane.
Senior officers from the Royal Navy attended the cathedral service, as well as representatives of community, military and charitable organisations.
A collection was taken for the Seafarers' Charity.
Prior to the service, The Lord Mayor led a short civic procession along St Thomas's Street to the cathedral. After the service the same procession took attendees to the statue of Admiral Lord Nelson in Grand Parade, Old Portsmouth, where the Lord-Lieutenant led the laying of wreaths.
The Lord Mayor said: "It is important, as a port city, that we take the time to be thankful for seafarers and remember those who have lost their lives at sea.
"I am honoured to be part of this poignant service to honour seafarers."
The service took place just a few days after Lord Nelson’s birthday, which was on September 28 1758.
1. The procession along Oyster Street in Old Portsmouth. Picture: Mike Cooter (011023)
The procession along Oyster Street in Old Portsmouth. Picture: Mike Cooter Photo: Mike Cooter
2. Standards lowered during the national anthem at Portsmouth Cathedral. Picture: Mike Cooter (011023)
Standards lowered during the national anthem at Portsmouth Cathedral. Picture: Mike Cooter Photo: Mike Cooter
3. Tom and Nikki Coles, Lord Mayor and Lady Mayoress of Portsmouth, head the procession at the Service For Seafarers at Portsmouth Cathedral. Picture: Mike Cooter (011023)
Tom and Nikki Coles, Lord Mayor and Lady Mayoress of Portsmouth, head the procession at the Service For Seafarers at Portsmouth Cathedral. Picture: Mike Cooter Photo: Mike Cooter
4. A final prayer before the committal of the wreath into the Solent. Picture: Mike Cooter (011023)
A final prayer before the committal of the wreath into the Solent. Picture: Mike Cooter Photo: Mike Cooter