Invasive Species Hitch Rides on Ships, Ecological Study Finds

Report finds that spread of mollusks through shipping endangers ecological systems and disrupts marine traffic, and is only expected to increase unless counter-measures are taken

Barnacles attached to the hull of a boat
Svetlana Yudina / Shutterstock.c

The spread of invasive species through shipping endangers ecological systems and disrupts marine traffic, and is only expected to increase unless counter-measures are taken, according to a report published this month by the International Council for the Exploration of the Sea.

More than half of the invasive species in some of the world’s oceans – all of them invertebrates such as mollusks and tunicates — travel by clinging to boat exteriors, the report found. It was written by a group of scientists led by Bella Galil, a marine biologist at Tel Aviv University’s Steinhardt Museum of Natural History.

The authors examined the scope and the implications of the adhesion of plant and animal species to boats and marine structures, known as biofouling, and the subsequent spread of invasive species. In the past, hazardous materials were often used to combat biofouling, but in many countries the use of poisons for this purpose has been outlawed, and new methods are needed.

According to the report, biofilms composed of microalgae adhering to boats can increase vessel surface-friction by up to 70 percent, requiring an increase in energy use of between 1.5 and 10.1 percent to maintain pre-fouling speeds. The decrease in fuel efficiency is a significant cost burden to operators and also raises concerns about increased emission of greenhouse gases, particularly in light of the highly polluting nature of the heavy fuel oil used by the shipping industry.

The spread of invasive species through the biofouling of ships is a clear threat to the world’s aquatic environments. The authors of the report describe the effects of vessel biofouling by the colonial tunicate Didemnum vexillum (the carpet sea squirt). One of the most aggressive and rapidly spreading fouling-transported species, this organism has spread with fouled shellfish and vessels to Europe, North America and New Zealand, fouling artificial submerged structures and overgrowing natural habitats. Eradication attempts in New Zealand and in Wales ultimately failed.

In 2014, a marine animal called Zoobotryon verticillatum, commonly known as the spaghetti bryozoan and native to shallow temperate and warm waters in the western Atlantic Ocean and the Caribbean Sea, was found in the Ashdod marina. Its environmental impact locally is as yet undetermined, but in other parts of the world, invasive species introduced as a result of the biofouling of ships have completely changed local marine ecosystems.

The rise in the number of boats around the world poses a risk of increased introduction of invasive species. As of January 1, 2017, the total number of vessels in the world commercial fleet (comprising oil tankers, bulk carriers, general cargo ships, container ships, gas and chemical tankers, offshore vessels and ferries and passenger ships) was 93,161. In 2014, there were 64,000 fishing vessels of 24 meters or longer in operation (FAO 2016). Currently there are also between 9,000 and 10,000 naval vessels around the globe and around 1,000 offshore rigs. In 2015, there were 11 million registered recreational boats in the United States. In Europe there were 6 million, served by 4,500 marinas. “Small boats contribute to the problem because they frequently travel between ports,” Galil says, adding, “That is especially true in the Mediterranean Sea, a relatively small body of water that is nearly closed on all sides.”

Galil notes that the opening of new shipping routes as a result of climatic change is likely to add to the spread of invasive species, “with the most dramatic and direct changes occurring in the polar and sub-polar regions. Sea ice coverage across the Arctic has declined since the 1980s, and trans-Arctic shipping routes between Asia and ports in Europe and eastern North America, once thought impossible, may become economically feasible by mid-century.... Increasing maritime traffic in the waters around Antarctica may also increase risk of introduction [of invasive species to the sub-polar and polar regions,” the report said.

Galil added that Israel must deal with the problem too, and the first step is to do tests at ports and marinas to determine which invasive species have already arrived. She also calls for adopting the biofouling management guidelines of the International Maritime Organization.