Great. In case you change your mind I have been noodling on this and have a full blown idea that I will write out in full to get it out of my head . If I was doing this I would have used a large series of isopods and set the following systems around them.

In my head the chains of islands would have a slow but consistent current that allows for some boats to just float between islands. These boats would be slow and completely uncontrolled. In order to move faster the isopod ships would capture a swarm of isopods in low nets which would allow the boat to move faster in the opposite direction of the current since the isopods are moving towards new detritus. (This allows for interesting travel decisions since going each direction has a different type of ships and different travel speeds).

As the isopods ships gets to a new island they would need to pull up their nets to slow down. They would then harvest the isopods and start selling to refuel their water supplies. They would open the larger ones and sell their meat either raw or cook. They would also sell the cleaned shells from sizes of a pumpkin down to a few inches. In order to clean the shells they would throw them in a large vat alongside any isopods to small to harvest to ferment for months. This alcoholic fermented isopod meat would make a stew like drink which is what the crew primarily lives off of. All of the leftover meat and guts would be preserved this way for years. Once this raw meats have fermented long enough they can open it off the harvest the cleaned and bleached shells.

In order to catch a new swarm they will need some waste to attract them. After each island they would drop off the entire crew's collected excrement before they pull up the net to get them moving. That way the party will need to pay to travel and promise their excrement along the journey to the ship. Sure to get the party questioning and throw the players off.