Mercury can be found in many different types of marine life/seafood, including squid. Sometimes squid can have significant amounts of mercury in them because of the heavy contamination which is associated with sea life. It is recommended that you in squid as well as other types of seafood in moderation, about 3 to 6 oz. per week.
It is especially important for women who are pregnant to avoid eating too much seafood, especially certain kinds like squid because of the potential threat of mercury. Although seafood is definite good for you and is an important part of a healthy balanced diet, you will want to get certain types of it in moderation.