Introduce guests to an "Under the Sea" baby shower with some cute invitations that display your theme. You can purchase Under the Sea baby shower invitations that are already filled out, you may choose under the sea themed fill-in type invitations, or you can create handmade invitations that coordinate with your theme and color scheme! Personalized invitations may be a bit more expensive, but they are great if you are short on time and want something that just needs to be stuffed into an envelope and be mailed out. The handmade invitations will be more labor intensive, but they are fun to design and you can include specific ocean items that your guest of honor loves.
If you choose to create your own invitations, it's a great idea to include a catchy phrase or poem that includes shower details. Some examples include: "Swim over to Kayla's Reef and celebrate the arrival of a new little guppy!", "Under the Sea with baby and me, join us with glee for a ocean party!"
Make sure your invitations include the basics such as mom's name, the shower date, time and location. If you have the information, it is also a good idea to include baby's due date, the sex of the baby (if known), and any nursery theme mom will be using, as well as where mom is registered for baby gifts. You may want to let guests know if a light lunch or dessert only will be served, as well as if the shower is for adults only or if children are welcome. Some hosts choose a couples baby shower which works quite well with an Under the Sea baby shower theme because of the fun games and interesting ocean tidbits that you can include to keep the men entertained!
More fun ideas at this post, Under The Sea Baby Shower.