ClearBridge Investments LLC, a New York City-based investment management firm, will manage part of the $11.9 billion Vanguard Explorer Fund, Vanguard announced Monday.

Granahan Investment Management Inc. and Kalmar Investment Advisors will no longer serve as advisors to the fund.

ClearBridge’s seven-member small and mid-cap team has an investment strategy that focuses on identifying companies that are category leaders or have potential to become category leaders, and display capital allocation discipline aimed at fueling long-term, sustainable growth, Vanguard says.

Jeffrey Russell, Derek Deutsch, Brian Angerame and Aram Green will serve as portfolio managers to the Explorer Fund. The expense ratios for Explorer Fund’s Investor Shares and Admiral Shares are not expected to increase, and the investment objective and principal investment strategies for the fund will remain the same, the company says.