The Ocean has many different "climates" within it.  These climates have terrestrial counterparts; coral reefs are the rain forests of the ocean accounting for a huge percentage of its biodiversity, and dead zones are deserts - a harsh barren climate with little food, and in the case of the ocean, little oxygen.  This means, dead zones, quite literally are dead areas of the ocean that species cannot survive in for long periods of time due to the lack of oxygen.

Scientists have been observing dead zones, and have noticed they are expanding at an alarming rate, shrinking liveable habitats.  NOAA Fisheries biologist, Eric Prince, Ph.D., and a team of eight scientists are combining oceanography and fishery biology to determine how climate change is expanding dead zones.  Prince states that by using his knowledge of fishery biology, and the NOAA oceanography team they can create "...a clearer picture"

By tagging blue marlin with satellite tracking devices, Prince will record their horizontal and vertical movement throughout the ocean.  By comparing the travel of the marlin to maps detailing locations of low dissolved oxygen, Prince and his team were able to make sense of the movement.

Blue marlin, like many other marine predatory species, are high dissolved-oxygen consumers because they utilize a lot of energy to move, feed and reproduce.  The team has learned that blue marlin venture deep when dissolved-oxygen levels are high and remain shallow when dissolved-oxygen levels are low.  This is a result of the water column with low dissolved-oxygen caging the marlin near the surface where it can obtain sufficient oxygen. 

This is one of the most important discoveries in billfish conservation.  Recently some population assessments reflected an increase in billfish populations, but this research gives evidence to simply why more billfish are being seen.  If marlin are being pushed up near the surface then they are more likely to be caught, sighted or hungry for a fishing lure due to displaced food sources.  Without taking dissolving oxygen levels into account one could seriously misinterpret blue marlin numbers and cause irreparable damage by over estimating fishing quotas. 

The main way of assessing sea turtle populations is nest counts.  This is simply counting how many turtles come to a specific area to nest, and how many hatchlings are observed entering the ocean.  Over the past two decades, leatherback turtles have been increasing in numbers and Floridians are more likely to see these turtles than in the past.

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.

Recently, massive jellyfish blooms have become a more common occurrence around the world.  Some cases the blooms were so large and included many different species, even foreign ones.  An example of this was Memorial Day weekend (2011) when muave stingers, a deep-ocean jellyfish commonly found in the Mediterranean were spotted off Cocoa Beach, Florida.

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.