Colder temps will certainly affect the yeast activity. This is not necessarily a bad thing. Depending on the strain of yeast you are using, many yeasts perform better at cooler temps. For example, I fermented my first batch way too warm. The yeast stressed a bit and it threw some esters that are still aging out.
Get as much info as you can on your particular yeast strain and try to keep the temps within its optimal temperature range. Your yeast will be happier and your mead will taste better for it. You can get off flavors when the yeast are stressed by too cold, too warm, and not enough nutrient.
Good luck!
David