Anthropogenic - Environmental change, usually pollution, that is man-made in origin.

C:

Cacophony - A 'mash' of sounds all together.

Cetacean - The taxonomic order comprising of whales, dolphins and porpoises.

D: 

Decompression sickness - When excess nitrogen occurs as bubbles within the blood. This can lead to paralysis and death if not treated, which is difficult to do with marine animals.

E:

Echolocation - The use of sound waves to determine the location of objects.

H:

Haemorrhaging - The loss of blood from damaged blood vessels in vast quantities, either internally or externally.

Hydrophones - A microphone which detects sound waves under water.

M:

Mesopelagic - Mesopelagic animals are organisms that live in the mesopelagic zone, which is the depths of the ocean between 200 and 1,000 meters below sea level.

N:

Nautical mile - A nautical mile is a unit of distance that is equal to 1,852 meters.

O:

Oceanographic Events - Ranges from waves and tides (usual) to meteotsunamis and marine heatwaves (unusual).

Odontocetes - The clade of cetaceans including the toothed whales: dolphins, porpoises, and all whales with teeth.

P:

Physiology - How cells, tissues, and organisms function.

Pinnipeds - The taxonomic order comprising of seals and sea lions.

Predation - Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey.