The DoI was unaware that part of Marine Drive fell within an Area of Special Scientific Interest before carrying out unintended resurfacing works.
The works, which it told Manx.News it did by mistake, involved road resurfacing and vegetation removal.
The area is designated as Marine Drive ASSI, recognised for its species-rich coastal grassland and hard cliffs with nesting birds.
The department’s FOI response said: “The department was not aware that the Area of Special Scientific Interest (ASSI) extended over the footway. Once made aware we have been in correspondence with DEFA.”
The vegetation removal varied from 30cm to one metre in width, with cut material deposited into the verge.
DEFA has indicated a preference for the deposited material to be removed by hand, though some may be left where it has landed on invasive Montbretia to avoid spreading the plant.
DEFA has suggested the department could submit an ASSI notice form for ongoing verge management, with consent potentially granted for five years, provided works are conducted outside nesting bird season.