This is a free set of seaside lesson plans ... only pages 1 - 14 are free the remaining have to be purchased but there are some great ideas in there.
http://www.funlessonplans.com/aSea/seashore.htm
From Silkysteps there is a page of
free resource links to look through, the
summer preschool store and from Amazon
lower case letter moulds for sand,
sea creatures for role play