It is now very common for plastic debris to get mixed into the foods of marine animals. The number of marine animals that are victims of eating plastic is increasing (Kühn et al. 2015).
The accidental consumption of plastic is well documented among seabirds (Yamashita et al. 2016). It is reported that 40% of seabirds, 104 out of the 406 species of seabirds, have eaten marine debris (Kühn et al. 2015). In particular, the Procellariiformes, which includes albatrosses, are well known eaters of plastic.
The frequency and the extent of plastic eating depends on the type of seabird (Ryan 2015). Generally speaking, eating plastic causes stomach ulcers or a decreased ability to digest (Yamashita et al. 2016).
When the digestive tube is clogged with plastic, this leads to starvation (Pierce et al. 2004). When the stomach is filled with plastic, the seabirds believe in error that they are full and stop looking for food (Hoss & Settle 1990).
If they have eaten a sharp piece of plastic, their digestive tract will be damaged. Furthermore, by eating plastic, they bring toxic chemical substances into their bodies (Yamashita et al. 2011, Tanaka et al. 2013).
Then, their nutritional status significantly worsens. They are deprived of the chance to reproduce and end up dying. Only the bones and feathers, and the plastic, remain.
Although plastic debris can be found everywhere in the ocean, it tends to be accumulated in those places where marine animals gather to seek food (Howell et al. 2012). For example, seabirds come together at oceanic fronts to forage, but the drifting plastic waste is also concentrated there.
An oceanic front is the line where two different types of water masses, such as with different water temperatures or salt densities, meet. Because of the difference in the density, they don’t merge immediately, and the speed of the current becomes slower at the border between the water masses. Therefore, quantities of floating things, such as plankton, become piled up there.
Because lots of small fishes come for this plankton, an oceanic front is an ideal feeding place for seabirds as well. However, these plankton and small fish are not the only ones to gather around the front; so does the floating plastic waste.
Thus, seabirds encounter lots of plastic debris when they catch their food. There are numerous reports of plastic eating incidents by Procellariiformes, such as Procellariidae and Diomedeidae, which seek food on the surface of the water (Yamashita et al. 2016).
It appears that these seabirds eat the floating plastic, either with their food or because they mistake it for food. The reason for this misunderstanding is that the plastic has a similar scent to that of plankton (Savoca et al. 2016).
Procellariiformes have a strong sense of smell and use it to find plankton . The source of this scent is dimethyl sulfide （DMS) (Nevitt et al. 2002), which is exactly the smell of the ocean.
There are several steps in the formation of DMS. First, DMSP （dimethylsulfoniopropionate), the precursor of DMS, is created inside the body.
When phytoplankton are eaten by zooplankton, their cells are crushed and DMSP from inside their cells spills into the ocean. Then, the spilled DMSP is eaten by bacteria, whereby there is decomposition by enzymes and DMSP is turned into DMS (Nagao 2012).
DMS in the ocean is released into the air. The more phytoplankton and zooplankton there is, the greater the amount of DMS is released into the air. Thus, the DMS lets the seabirds know where the plankton is.
However, in actual fact, lots of bacteria also stick to plastic debris. Because these bacteria also turn DMSP to DMS, plastic becomes impregnated with the same smell of the ocean (Savoca et al. 2016).
Therefore, Procellariiformes most likely eat plastic waste without realizing it (Savoca et al. 2016).
The parent birds return to the nest, where the hungry chicks are waiting. They regurgitate the food from their stomachs and give it to their offspring, thus passing on the plastic.
In the Midway atolls, almost all of the chicks of the Lausanne albatross, that is, more than 97% of the chicks checked, had large amounts of plastic in their stomachs (Auman et al. 1997).
The chicks of Procellariiformes, including the Lausanne albatross, cannot regurgitate the plastic that has accumulated in their stomachs and they die even before they have left their parents (Auman et al. 1997, Lavers et al. 2014).
When the plastic accumulates in their stomach, they cannot eat their real food. They will suffer from malnutrition or dehydration and end up starving to death (Auman et al. 1997).