When the tsunami waters withdrew from the devastated coast of Japan in March 2011 they took with them a vast amount of debris consisting of potentially millions of objects, and sent it rafting across the Pacific Ocean.

On this debris came a host of Japanese marine animals and plants – in fact, more than 300 living species have so far been found to have washed ashore in North America and Hawaii. Astonishingly, after an ocean journey of more than 5,000 km and nearly five years, these species continue to arrive in the United States and Canada.

The 300 species that made the tsunami-induced voyage arrived primarily on docks, boats, buoys and totes, which survive at sea far longer than natural rafts such as trees.

While marine life has floated across oceans since time began, the 2011 earthquake and tsunami revealed what we are now just beginning to understand: human-made debris such as plastic has vastly increased the numbers of marine species crossing the oceans.

Some of these species will be bad. Alongside pollution and the huge expansion of global trade and travel, the number of marine “bioinvaders” (the ocean equivalent of cane toads in Australia) has grown exponentially.

Lee Pickett/John Chapman

A more connected world

The world’s shipping fleets carry 90% of global trade and are said to be increasing at 10% per year. In and on the tens of thousands of ships that sail the seas daily are potentially thousands of species of marine animals, plants and microbes.

Ballast water, used to keep ships balanced, is taken up and then discharged in ports worldwide. This water hosts not only the microscopic larvae of clams, worms, crabs and seastars, but schools of adult fish as well. Via the shipping industry Australia has gained vast zoological and botanical gardens of global marine invaders, ranging from the European green crab to the infamous North Pacific seastar that first appeared in Tasmania.

Shipping is not the only carrier of alien species. Also growing worldwide is the ornamental aquarium industry. Each day many thousands of fish are flown around the world. Marine aquaculture industries are expanding and the live bait and live seafood trade are globally increasing.

Marine species are also finding themselves in a new world: climate change has altered the potential new homes of non-native species, now arriving in regions of the world once much too cold to accommodate them. A quickly warming world is now itching with new invasions.

Introduced species have substantial economic, social, industrial and environmental impacts. On land these species cost billions of dollars every year in management and eradication efforts.

But it has proven much harder to manage and eradicate ocean invasions – which means we have to stop them gaining a foothold in the first place.

Stemming the flow

Calls to manage ballast water began more than 25 years ago. It is now compulsory in many countries, including Australia, New Zealand, the US and Canada, for ships to exchange their water at sea before arriving in port. Coastal species are released on the high seas where they cannot survive, and ocean species are taken up but do not survive when later released into ports and harbours.

But the United Nations International Maritime Organisation call for mandatory global ballast water management remains unratified. In many countries ballast water exchange has yet to be rigorously assessed, and widespread installation of treatment systems appears to be on a longer rather than shorter agenda.

And challenges with ship hulls and sea chests remain. Strict protocols for hull cleaning and inspection should be required for ships and international yachts, as well as for recreational vessels and slow-moving barges that stick to the coast.

Australia has had national guidelines for this in place for some years, but they remain voluntary as ports and state and federal governments argue over who is to bear the cost. The strategy has yet to be fully implemented.

Building better in the ocean

The way we build and manage our environment can help marine invaders. We have the knowledge and the tools to address this.

Australian research has demonstrated that metal contamination in our ports and harbours can facilitate invasion. Cleaning up contaminants left over from the past and reducing current metal inputs from stormwater run-off or antifouling paints are low-hanging fruit and should be a priority.

Artificial structures can be built to discourage introduced species. Considering eco-engineering principles before construction could dramatically reduce the capacity of our built marine environment to harbour invasives and act as stepping stones for their spread.

Building stronger and better infrastructure will help ease the toll of monsoons and tsunamis, helping ecosystems and people, and stopping debris washing out to sea. Environmental and habitat disturbance can notably increase the likelihood of invasion: by reducing local human impacts, the greater the resistance will be of our native marine communities.

Early detection vital

Finally, when invasions do occur, early detection and rapid responses are crucial. We cannot prevent marine debris generated by tsunamis from drifting across the oceans, but we can put in place measures to detect invasions.

In this regard, a global standard was the early discovery of the black striped mussel in a Darwin marina. Detected within six months of its arrival, chemical treatment eradicated the population, followed by the tracing and inspection of every yacht that had entered and left the marina in the previous six months. It wasn’t cheap, but it taught us that eradication was not hopeless in the ocean, and helped inspire a successful eradication effort in California of an alien seaweed.

The societal, economic and ecological disasters of marine bioinvasions are not natural ones, and they are becoming more common. Our knowledge of how, why and when species can and are invading is expanding rapidly, as is our awareness that there is much that we can do to stem the rising tide.

The 9th International Conference on Marine Bioinvasions will be held in Sydney this week.