26/12/2014

Macroplastics

Continuing with plastic pollution, I wanted to bring your attention to macroplastics - and as you've probably guessed, these are simply larger pieces of plastic when compared to microplastics. Most authors refer to macroplastics as those that aren't microplastics i.e. anything bigger than between 1-5mm depending on the author (see my first post on microplastics), although Gregory and Andrady (2003) also include another class of plastics identified as mesoplastics. These include plastics such as virgin resin pellets. For the purpose of this post, I will consider macroplastics to be anything that can be seen with the naked eye. Examples include bottles and caps, cups, rope and beer can rings (Andrady 2011).

Much like microplastics, effects of macroplastics include ingestion and contamination. However, macroplastics also cause entanglement. Below is a review of these three effects:

1. Ingestion

The results of the ingestion of macroplastics are clearly seen in the Midway video in the first post [Figure 1]. Indeed, according to Rios et al. (2007), nearly half of all marine bird species are known to ingest plastic.
Animals consume plastic either directly, by mistaking it for prey, or indirectly when they consume prey that has ingested plastic. Among the problem associated with the ingestion of macroplastics are satiation and malnutrition, blockage of the intestine and internal wounding from sharp objects, all of which may be fatal to the animal (Gregory 2009).


Figure 1. Photo showing the stomach contents - most of it plastic -
of a decaying albatross found on Midway Atoll (Daily Telegraph Australia)

However, not all ingestion from macroplastics leads to death. Tomás et al. (2002) looked at 54 juvenile loggerhead turtles in the Mediterranean. They found that despite plastics accounting for 3/4 of all debris found and low feeding discrimination among the turtles, there was no clear evidence of intestine blockage or them dying because of plastic ingestion (Tomás et al. 2002).

2. Contamination

This is the same issue with microplastics (again see post below) - toxic compounds dissolved in the ocean may adsorb onto the surface of plastic and depending on the compound, may cause severe health issues, and may also make their way up through the food chain (Cole et al. 2011).

3. Entanglement


Figure 2. A selection of photos depicting various forms of entanglement; clockwise from top left: green sea turtle entangled in a gillnet (National Geographic); seal with a deep cut around its neck from a fishing line (BBC); turtle with a six-pack ring around its middle (Ocean Crusaders); another entanglement in a gillnet, but this time the victim is a grey whale (Oceana)

Turtles, some pinnipeds (seals, sea lions and fur seals), cetaceans and birds have all been affected by entanglement. This is usually due to the nets but can also be with smaller items such as bottle cap or six-pack rings [Figure 2 and references therein].
Entanglement causes limited movement and thus a reduction in how well the animal can travel and hunt/find food. This may lead to starvation and inability to feed their young (Gregory 2009).

I hope those images don't upset you too much, but I thought the best way to convey the gravity of marine pollution and the effects of entanglement was to approach it using photos. After all, an image is worth a thousand words...


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