Merce is from the Catalan Mercè — from the Latin merces (mercy, reward) — referring to the devotion to Our Lady of Mercy. Merce is one of the Catalan feminine names.
Merce does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Merce reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.