First of all we have to take into account the different phyla, and then give an example with a short explanation to go with each.
Mammals use blubber at times for minor buoyancy, but this primarily comes from the air stored in their body.
Fish on the other hand have what's called an air bladder which receives air from the blood; the amount of air is constantly regulated according to pressure and depth. How air, mainly oxygen because of nitrogen's volatility, is removed by the hemoglobin by a gas gland that produces lactic acid allowing the absorption of air into the swim bladder. It's placed near the spine; if the fish rushes to the surface, it risks bursting its bubble.
Most cephalopods have what's called a septa that's incorporated into their internal shell containing nitrogen and slime in a coiled fashion.
Birds such as penguins are buoyant due to the air in their body.
Reptiles float similar to a human's backstroke, but on their belly, keeping their head and back above the water.
Insects for another matter either use surface tension such as pond skippers or setae (dense, thick, bunch of hair) and possibly a plastron.
Finally, some amphibians' weight allows the lungs to keep the body afloat at the water's surface.
Post script
Any other interpretation or edit of this is answer is in direct violation of the answer's true meaning. Other than having knowledge of biology, one also needs knowledge of chemistry and perhaps the meanings of English words before attempting to clean up after another's mistakes.
An Marine Biologst works with animals, also where animals are,such as sea world
well they float coz they would have no holes in the body so it could float
Marine animals breathe through the nose by inhaling and exhaling. :)
Animals that live in the oceran are called marine animals. Animals that live in water that's not the ocean are called freshwater/aquatic animals.
animals in the ocean/sea
Sea lions float at the surface with one or more flippers raised out of the water. It is believed that this behavior prevents them from losing too much body heat in the water. Sea lion and other marine animals float because of their tender or light bones
the name given to tiny sea animals and plant that float in the sea.they form the main food of many sea animal
marine animals are sea toads & more!
marine animals fyi
Marine vessel float in water because of it's hollow shape and that enable it displace an amount of water which is equal to it's wiegth or volume.
In a marine environment.
Not all marine mammals float, but the ones that do float because the body of the animal is sitting on the surface of the water and that makes the pressure of the body of the animal float because the body is rising from all the pressure. Hope this helped -stupid factory
because oil is lighter than water it will float, blocking all sunlight to the marine animals. this has nothing to do with the hydrosphere i was just bored
An Marine Biologst works with animals, also where animals are,such as sea world
well they float coz they would have no holes in the body so it could float
Personally i wouldn't kill marine animals, but some people will to get food or to have fun
what are marine animals with piny rough surfaces called