Many credit this resurgence to the massive jellyfish blooms that have been hitting the coast of Florida in the summer months. The counties of Volusia and Brevard were hit the hardest. But even my dives off Fort Lauderdale (Broward County) had a lot of jellyfish and I was warned by the DMs to wear a fully-piece wetsuit for protection from jellies, even though the water was 86 degrees. Some moon jellyfish were so large, I was able to notice them from the fly-bridge of a boat cruising 38kts from Key West to Fort Lauderdale!
Jellyfish are not actually fish - they are more closely related to corals than anything else. They are a gelatinous species and the preferred prey of leatherback turtles, and also loggerhead turtles. These species of sea turtles have adapted to become immune to the venomous tentacles of jellyfish.
Many scientists will attest that jellyfish blooms are increasing in size and frequency. Although there has not been much research on this in the past so it is hard to say for sure. One thing they believe is there is a definite correlation between the jellyfish blooms and increasing numbers of leatherback turtles.
Scientists know that the nesting cycles of sea turtles can be reduced if their food is limited. Reproduction takes a lot of energy, and when sea turtles can live for so long, they will store and save their energy to reproduce at a better time. If there's more jellyfish, there's more food to be eaten, more energy can be spent and reproduction happens more often.