EOSC 315 - Module F - Instructor: Michael Lipsen PDF

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Instructor: Michael Lipsen...

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EOSC 315 – Notes on Module F – The Mesopelagic

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Also called the twilight zone Depth from 200m to 1000m below water surface

Fishes which live in the mesopelagic can be categorized as non-migrators and vertical migrators. Non-migrators and their distinct adaptations -

Have no swim bladder because it is not needed as the organism stays at the same depth most of the time Have weak bones and flabby muscles due to limited movement necessary for survival

Vertical migrators and their distinct adaptations -

Swim bladder is needed due to frequent movement Well-developed and strong bones and muscles for energy needs during migration

Similarities between non-migrators and migrators -

Large eyes and mouth to spot prey of any size and shape and feed on them Small body size as food is scarce and to conserve energy Photophores on body which give off light and brightness to break the silhouette of their bodies which is used to confuse predators (and sometimes, preys as well)

Adaptations for avoidance of predation -

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Transparent bodies so as not to be easily spotted and caught by predators Red/black coloration to blend in with the dark environment of the deep Thin/flattened bodies to reduce silhouette and appear smaller when seen from below by other organisms Counterillumination as camouflage using photophores found on the animal’s underside which blur their silhouette and confuse predators which cannot clearly distinguish their prey’s body shape in the dark Upper side of body is darker because water appears darker when viewed from above Ventral side of body is bright and silvery as water is bright when viewed from below...