Marine Species are Using Plastic Waste for Intrepid Global Voyages

We all see plastic in many ways. It’s the easy to buy, easy to throw water bottles and coffee cups. It’s the durable, cheap material we use to decorate the inside of our homes. Today it also becomes the evil of the world, turning our shores to eyesores and entangling innocent marine beings. Yet many of you, up until now, may never have thought about plastic as a method of transport; a way for our marine counterparts to hop aboard a slow-moving vessel and begin their round the world trip of a lifetime.

Until 2011, scientists didn’t consider plastic a mode of transport either until an earthquake struck 70 kilometres from the coast of Japan, triggering a 40 metre tsunami wave which tore shellfish cages, fishing vessels and even whole docks away from their harbours. Due to the nature of the ocean’s circular currents, scientists knew the large fragments of Japanese infrastructure were making their way towards America but until a whole pier washed ashore in Oregon, they did not know about the 60 Asian marine species which were also heading for land. This one pier was found to be carrying 400 pounds of biological life including organisms such as shore crabs, urchins and sea stars. Now more time has passed, other pieces of debris from toilet seats to footballs have washed up on America’s west coast with an estimated 289 Japanese species brought with them. Initially, this might sound quite exciting as we head out to the intertidal zone ready to spot exotic new creatures, yet these invasive species can drastically alter our environments.

An invasive or alien species is one which is found outside of its natural home range and they can cause significant damage to their new environments, be that ecological disruption, problems for human health or hits to local economies. Several years ago, Wales forked out £250,000 to eradicate Japanese sea squirts which had made a new home on the harbour walls in Anglesey which threatened the mussel population and subsequent industry. These individuals may carry new parasites which native species are simply unable to protect their bodies against while new arrivals could also be more efficient predators, feeders and reproducers, making this one of the greatest threats to global biodiversity. In Dorset, on one beach alone, 20 foreign species were found including goose barnacles from The Azores and Columbus crabs from Bermuda.

To help you understand how this might play out in the future, grey squirrels are an invasive species in the UK after being introduced in 1870. These non-natives carry a disease which is fatal to red squirrels which subsequently don’t reproduce when they are stressed. Today, 150 years later, red squirrels who were previously found throughout the whole of Britain, are rarely found south of the Lake District except on islands which greys have yet to reach. A similar scenario could play out in our oceans as plastic becomes increasingly pervasive and the oceanic transport network grows. Luckily, many conditions have to align for invaders to successfully colonise. For example, the climate must suit them, there must be plentiful food sources and there must be both males and females of reproductive age to expand the population numbers. Yet how on earth do they survive at sea in the first place?

Organisms using plastic as a hop on hop off bus is not unique to the Japanese tsunami disaster. Long distance travel has previously taken place on pieces of driftwood, jumbles of seaweed or animal carcasses. However, all these natural hosts quickly decompose and it is only since the introduction of our famously durable plastic that species have been able to travel up to six times further. While ships still provide a common source of invasive species on their hulls or contained in ballast water, these trips often only last for a few weeks or months, not the years that mussels, barnacles and crabs now spend on our synthetic waste. Scientists still aren’t sure exactly how these vagrants feed on their voyages but it is thought that 70% of travellers are suspension feeders who feed on passing floating particles in seawater. Rafting communities often form in the open ocean which contain all manner of crustacean, fish and algae all together on colourful chunks of plastic with the odd fish dipping in and out to take advantage of easy prey and a good hiding spot from predators. These flotillas can, unbelievably, actually change the environmental conditions in tiny tiny areas of the ocean to create a perfect microhabitat for small fish which use it to cross previously uncrossable deep-water barriers in the ocean. Unfortunately though, they can also carry the organisms which cause harmful algal blooms such as the Florida red tide and bacteria which induces coral diseases. Too many rafting organisms can also weigh down the plastic and cause it to sink to the ocean depths where it accumulates on top of our unmoving deep-sea dumpsite.

So all these years while we have been heralding the rise of globalisation, allowing us to move more freely around the planet, these opportunistic critters have also been enjoying their newfound freedom. While most species currently identified have used plastic to travel a relatively short distance which simply allows them to expand their territory, the durability of plastic and the slow moving currents of the ocean could mean foreign invaders are already leisurely on their way to our shores. Work is underway to reduce the invasive species brought in on ships or via dumped fishing gear while scientists working on natural disasters are hoping to target large lost items, such as the Japanese dock, after future storm events. By using our knowledge of the ocean currents, we hope to find their location before removing them from the ocean or tracking their course with GPS to make sure we are ready on the shore to combat any invaders. If you want to keep your local area with its natural ecosystem intact, you can volunteer with regional organisations to help remove any invasive species you find or to report new arrivals to help keep local much loved organisms thriving.

By Neve McCracken-Heywood