by Piter Kehoma Boll
Plastic pollution is a popular topic recently and it is not rare to find pictures of animals that died due to plastic ingestion or other complications, such as asphyxia, caused by plastic pieces. However, the cause of plastic ingestion by most species is yet unknown.
The leatherback turtle, Dermochelys coriacea, is often mentioned as a species that suffers from plastic ingestion due to its diet composed primarily by jellyfish, which floating plastic bags can be mistaken for. However, another widespread sea turtle, the green turtle, Chelonia mydas, is also a common victim of plastic ingestion and amounts as small as 1 g are enough to kill juvenile specimens by blocking their guts. The diet of juvenile and adult green turtles is composed mainly by seagrass and algae, so the ingestion of plastic must be the result of another cause and not its similarity to jellyfish.
Despite being almost strictly herbivorous, green turtles ingest animal matter when they are very young and can eventually consume animals as adults too, probably as a strategy to survive when their main food source is scarce. The ingestion of animal matter is usually done by scavenging, and a common scavenged item in their diet are dead squids.
A recent study has investigated the relationship between scavenging behavior and plastic consumption in the green turtle and found out that the amount of plastic ingested by individuals feeding on dead squids is much higher than that ingested by individuals that do not present a scavenging behavior. In Brazil, plastic ingestion accounts for about 10% of the deaths of green turtles but this number may be as high as 67% among green turtles that feed on squid carcasses.
The ingestion of dead animals used to be an efficient way for green turtles to gain high amounts of protein. However, the fact that, currently, most floating material in the ocean is plastic and not dead animals turned a successful strategy into a deadly trap. If humans do not start controlling plastic waste production there will be only two possible outcomes for the green turtles in face of this new selective pressure: adaptation or extinction.
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Andrades R, Santos RA, Martins AS, Teles D, Santos RG (2019) Scavenging as a pathway for plastic ingestion by marine animals. Environmental Pollution 248: 159–165. doi: 10.1016/j.envpol.2019.02.010
Mrosovsky N, Ryan GD, James MC (2009) Leatherback turtles: the menace of plastic. Marine Pollution Bulletin 58(2): 287–289. doi: 10.1016/j.marpolbul.2008.10.018
Santos RG, Andrades R, Boldrini MA, Martins AS (2015) Debris ingestion by juvenile marine turtles: an underestimated problem. Marine Pollution Bulletin 93(1–2): 37–43. doi: 10.1016/j.marpolbul.2015.02.022
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