Marine animals use their senses to find food and mates, as well as to avoid predators. An animal will become much more vulnerable to harm if one of its senses are not working properly. This goes double for the sense of smell, which fish use a lot.
A research team from the Florida Atlantic University (FAU) studied the physiological effects of crude oil on the olfactory sense of the Atlantic stingray (Hypanus sabinus). They simulated the levels of oil pollution found in coastal waters during the Deepwater Horizon crisis and exposed animals to the toxic pollutant for different lengths of time.
Based on the results of their experiment, it only took 48 hours of exposure to the oil before the stingray's sense of smell suffered severe degradation. The researchers concluded that crude oil harmed the health of stingrays, which would in turn affect the marine ecosystem that it is a part of. (Related: Sunlight triggers chemical reactions that make the Deepwater Horizon oil spill unlikely to degrade.)
FAU researcher Dr. Stephen M. Kajiura oversaw the study on the sense of smell of stingrays. He and his research team tested the olfactory reactions of the animals to both clean water and crude oil-tainted water.
Electro-physiological assays showed that stingrays exposed to oil reacted much more weakly to important scents like food and predators. The affected animals took much longer to detect a smell, recognize it, and take the appropriate response.
"Unlike other sensory systems in which the receptor cells are not in immediate contact with the environment such as the eye, inner ear, lateral line, and electroreceptors, the chemo-sensory cells of the olfactory organ are directly exposed, through the mucus, to the seawater," explained Kajiura.
Th exposed receptor cells of the olfactory system can be directly injured by crude oil and other water pollutants that come into contact with it. This could lead to stingrays suffering earlier deaths and reduced population levels.
H. sabinus lives in the shallow waters of coastal areas. However, its deep-water cousins are potentially more vulnerable to crude oil due to several factors.
Benthic or deep-sea fish have much slower metabolic rates due to the cold temperature of their home waters. Their slower-working bodies could take much longer to purge crude oil from their tissues. That gives the toxic chemical much more time to accumulate in the body and harm important cells and organs.
Furthermore, skates and other oviparous species of elasmobranchs (sharks, rays, etc.) reproduce by laying fertilized egg cases on the seafloor. The embryos in these eggs take a long time to grow before hatching.
The immature embryos are highly sensitive to environmental conditions. So if the sediment around them contains a lot of crude oil, the toxic chemical will affect their growth and development.
Of the numerous chemical compounds in crude oil, the heavy metals are perhaps the most dangerous. Aluminum, cobalt, copper, manganese, mercury, and zinc can disrupt the ion channels that link together the parts of the olfactory system.
There are also fractions of crude oil that can dissolve in water. These water-soluble compounds are known to injure olfactory epithelium cells.
FAU researcher Kajiura warned that crude oil exposure does not have to kill an animal outright to be considered dangerous. Its crippling effects on the sense of smell of marine animals should be considered a long-term threat to the ecosystem.