The open ocean may seem like a vast, featureless wasteland to us outsiders, but its inhabits are intrepid navigators that use its structures to embark on some of the most epic journeys known to science. Leatherback turtles have been shown to migrate across the entire Pacific Ocean. Two hatchling leatherbacks were once tracked moving 39km in 34 hours and 82km in 39 hours, an extraordinary distance for a baby weighing less than 40g in one of the first days of its life. Blue whales travel pole to pole to exploit seasonal plankton near the poles and reproduce and raise offspring in the tropics. In the open ocean, animals live on scales that we would not naturally consider a single habitat.
Huge shoals of plankton move from the deep sea and back every day as the sun rises and sets. There are massive migrations of small fish and squid that follow them to exploit this resource, as well as larger predators which hunt them. This enormous movement of biomass from the deep sea to surface and back happens every single day.
Despite the colossal size of this environment, Attenborough very rightly points out that it is still by no means hugely separated from human life. As well as the famous Pacific Garbage Patch that Elin talked about in another post, there is plastic and other marine waste in the most pristine and remote coral reefs. I have heard stories from fellow divers in the Indo-west Pacific about seeing used nappies floating past on dives. I was lucky enough to be involved with a school trip to Baubau near Sulawesi in Indonesia, and we spent a few hours on an uninhabited island cleaning up trash. On another island in Malaysia I found a DVD player and a washing machine on the beach. These are unusual exceptions – polystyrene, plastic bags and straws are ubiquitous in the ocean anywhere in the world. It’s no different in the UK – the Marine Conservation Society at Southampton spend hundreds of hours removing rubbish from beaches on the South coast. When we see pollution in an area we can all agree it is unpleasant, but as a scientist we understand it in context of this colossal, global and unprecedented problem.
This affects all levels of the marine food web. We tend to think of the deep sea as being this remote alien world, but it is still inextricably linked to human life. Microplastics accumulate in deep sea sediments – at 10,000 times higher concentrations than at the surface. Up to 90% of seabirds have plastic in their guts. Another aspect not explored in the programme is that other pollutants dissolved in water – fouling paint, oil and other contaminants – accumulate on plastics, and so make plastic even more toxic to marine life. Pollution becomes more concentrated in higher levels of the food chain in a process known as ‘biomagnification’, where smaller fish with some pollution in them are eaten in large quantities by larger fish. This means that top predators like tuna, sharks and marine mammals are the most contaminated. And as well as being concerning for environmental reasons, the seafood we eat are no exception – plastic has been found in a third of UK-caught fish, and shellfish lovers may consume up to 11,000 plastic particles per year.
Biodegradable plastic is not biodegradable in the sense one might think. These plastics are held together with degradable fibres, so they break down into smaller components. Eventually, they break down into ‘microplastics’, which then spread into every corner of the ocean. It has been suggested that a layer of plastic will be what will distinguish the human era in the fossil record of the future.
It is extremely heartening to see the reactions to this problem, and some countries (most recently Kenya) have even completely banned plastic bags outright. Hopefully Blue Planet will encourage more people than ever to think twice about whether they need that straw or bag, and eventually encourage governments and large companies to move away from the excessive use of this material.