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The cuttlefish’s respiratory system consists of gills, which are the primary location of respiration. Through contraction of the muscles of the cuttlefish’s body, water is able to enter the mantle cavity through the pallial aperture. 

 

For most aquatic species, they depend on the oxygen content in the body of water they live in to breathe. The cuttlefish’s respiratory system also depends on the quantity of oxygen in the ocean water, which dictated the depths at which they swim and habitat. 

 

The mechanism in which oxygen in the ocean water is picked up through the gills is called gas exchange. Inside of the gills, there are microscopic structures called lamellae, and they are very close in proximity to blood vessels that also sun through the gills. The figure below depicts what a singular gill looks like. It is attached along a long axis down the middle that attached to the wall of the mantle cavity posteriorly to the gills. These lamellae are the location where gas exchange occurs, and minute vessels in the lamellae are able to receive oxygen picked up from the water. Then the oxygen-poor water is pushed out of the cuttlefish.

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Global warming and an increase in ocean acidification have led some populations of cuttlefish to experience worsening hypoxic conditions. An increase of carbon dioxide concentration in ocean waters where cephalopods are spawning can affect embryogenesis of egg formation, and energy spending rates after hatching. Metabolic rate has been shown to slow in cephalopods that habitat ocean waters that are increasing in temperature and oxygen concentration. 

 

The threshold of hypoxic conditions for cephalopods is decreasing, as populations have been exposed to unhealthy conditions for so long. It is very important for embryonic cephalopods to have access to enough oxygen inside of the fluid in eggs (perivitelline fluid). The partial pressure for this hypoxic threshold of  PVF is measurably higher in warmer waters that have been affected by climate change. Cuttlefish and other cephalopod eggs are experiencing a rise in the rate of hypercapnic egg conditions, meaning there is an increase in carbon dioxide buildup in the circulatory system in the embryonic stage.