The Lightning on Monday signed defenseman Slater Koekkoek, a first-round draft pick in 2012, to a one-year contract worth $865,000.Koekkoek, 24, was a restricted free agent who has spent parts of the last four seasons with the Lightning. He had four goals and four assists in 2017-18, but saw his playing time decrease late in the season and did not dress for any playoff games.Koekkoek (pronounced koo-koo) was active for 32 of the Lightning's first 63 games, but played in just three of the final 19 after the acquisition of veteran Ryan McDonagh. After splitting time between the Lightning and the AHL's Syracuse Crunch in his first three seasons, he stayed with Tampa Bay throughout last season.The Lightning just signed McDonagh to a seven-year extension, so he and Victor Hedman are locked up longterm. Mikhail Sergachev, who played extensively as a rookie last season, is also a major part of Tampa Bay's blue-line plans.Three other defensemen — Anton Stralman, Braydon Coburn and Dan Girardi, all in their 30s — are all unrestricted free agents after next season, so Koekkoek is vying to step into a larger role left by one of their departures.Tampa Bay addressed another RFA by signing C J.T. Miller to a longterm extension last week. Cedric Paquette and Adam Erne remain unsigned.