Why do populations in the deep sea tend to have longer life spans than those in the higher layers?

The one of the marine creature named Mediterranean red coral lifespan is capable of covering nearly 500 years and challenge human age with full spirit, also observed that the patterns of sessile or immobile species like other corals, macroalgae, sponges and gorgonians have boon of long life under deep sea water.

One of the most basic reason behind their healthy life is the stability of environment which is favorable for deep-dwelling species, they get shielded from temperature changes and severe storms in such location. Pollution, poaching, contamination, human activities, etc are not that effective in deep sea, natural selection favors long lifespans in stable environments.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.