I am having my reception at the Living Seas this fall and my group is the same size is yours. It *is* a bit dark in there, but this gave me the opportunity to use candles on the tables (I love candles). It is such a unique venue with the fish swimming by, and it's kind of cool to have the reception in a place you wouldn't normally be allowed in. I don't think the room will swallow a group of 40. There are six people to a table, so right there you are at 6-7 tables. Floral is also covering the tables we don't use with a floor length ivory table cloth to help the fade into the background. Also, a portion of the room will be used for our cocktail hour. I'm biased, but I love the location. If you can do a site visit to see it, that would be best to make up your mind.
Hope this helps!!