AT RHODE ISLAND’s Weekapaug Point, sea boulders stand stout in the spray, while low tide lingers in pools piled with life. Green crabs dip under drying red seaweed, while sea squirts slouch and sway over the stones. A stripe-legged shore crab scurries, stops, and pinches angrily at me. Periwinkles line the rocks like rough wallpaper, ingrained, it seems, into the very structure of the shoreline.
It may come as a shock to some, as it did to me during my trip to Weekapaug this February, that not one of these creatures is native to New England. Such is the nature of many marine species introductions, which have impacted nearly every coastline in the world for at least the last 500 years: Organisms find their way into waters far beyond their native ranges, often aided by human activities, and establish populations well below the surface of common cultural awareness. These organisms — from the smallest of diatoms and shellfish to sizable salmon and gigantic white-spotted jellyfish — can devastate local ecosystems, destroy coastal infrastructure, and cost billions of dollars to combat every year.
According to a Pew Oceans Commission report, “Bioinvasions is a broad term that refers to both human-assisted introductions and natural range expansions,” though the typology and terminology of these invasions are often as complex as the issues they attempt to describe. The long history of marine bioinvasions is enmeshed with travel and trade, colonization and war, fisheries and aquaria, and the countless physical means of carriage, called vectors, that allow humans — and the organisms we bring with us — to reach oceanic habitats all around the globe. Exploratory, military, and cargo vessels, which have crossed the sea daily for centuries, are the most infamous vectors. A single ship can harbor hundreds of “fouling” species on its hull, each with the potential of establishing an invasive population in the region where that ship is headed. Ballast water, stored as a stabilizing mechanism in huge tanks belowdecks, can take up entire communities of organisms at one port and release them thousands of miles later in another where they are not naturally found. While seemingly innocuous, other vectors like scuba fins and wetsuits can hide and transport tiny hitchhikers in their creases and fibers. Fishermen, too, feeling sorry for their leftover live-bait, may release hundreds of worms — as well as the non-native snails, crabs, and algae they were packaged with — into new habitats every year.
Today, modern material technology has the capacity to facilitate more marine bioinvasions than the world has ever known, and the number of non-native species reaching new shores is increasing exponentially. Furthermore, anthropogenic climate change has already expedited the poleward movement of marine creatures from their native ranges to new and previously uninhabitable regions, often with unknown consequences. As these trends continue, marine bioinvasions will only increase so long as they remain under the radar of both public and governmental attention.
A few remarkable modern case studies illustrate how pervasive and unpredictable marine bioinvasions are likely to become this century. So too do they indicate the urgency of researching and responding to species introductions across the contemporary world ocean.
IN JUNE 2012, a massive dock encrusted with marine life washed ashore on Oregon’s Agate Beach. A little more than a year earlier, the dock floated in Miwasa, Japan, until a tsunami following the 9.0 magnitude Tōhoku earthquake tore it from its harbor and sent it out to sea. The dock’s extruded polystyrene foam structure remained intact, providing an artificial oasis for ocean life as it followed the currents towards North American shores.
Beachgoers and researchers still find Japanese debris like buoys and boats washing ashore an astonishing nine years after the tsunami in places as diverse as Hawaii, California, and even parts of Alaska. Nearly all of this debris harbors a remarkable richness of living marine organisms.
For millennia, species have crossed seas and established new populations via various short-lived “rafts,” such as storm-cast seeds and trees, in a biogeographic process called transoceanic rafting. Yet today, nonbiodegradable plastic materials like polyethylene, polystyrene, and fiberglass provide durable, pervasive rafts that can keep creatures alive and reproducing across unprecedented stretches of time and distance. As storms increase in frequency and severity, human-made debris will continue washing away, underscoring not only coastal development as a major facilitator of modern marine bioinvasions, but also anthropogenic climate change.
IN 2005, OFF SOUTH CAROLINA’S Folly Beach, the warm blue sea made its daily retreat from a breakwater during an afternoon low tide. Shoals of small fish swam around the half-submerged stones, while snails slid down their sides, trying to keep pace with the sinking water. Then, a titan acorn barnacle, 100 times more massive than any indigenous barnacle species in the area, appeared like a giant pink sore on the breakwater’s worn face. Then another appeared, and another, until the whole structure seemed to break out in clusters of Megabalanus coccopoma.
Titan acorn barnacles, native to the coastal eastern Pacific from Baja California to Ecuador, were first reported in the Gulf of Mexico in 2001 and have since spread up into the southern US Atlantic. In places like South Carolina, they now dwarf and may outcompete indigenous barnacles for space and food. They’ve also become notable features on human infrastructure, like docks, pilings, and buoys. More frightening, as the sea warms, they threaten to continue their northward march into currently uninvaded waters.
Range expansion is a growing trend in twenty-first century marine bioinvasions. Cimate change causes ocean water to heat up and alter chemically; as a result, some creatures leave their current low-latitude ranges and head poleward to where environmental conditions, such as temperature, have become hospitable. Examples of this include “Caribbean Creep,” or the movement of West Indian organisms into Mid-Atlantic waters, as well as many instances of marine invertebrates shifting up the American west coast. As a result of human activity, some species like M. coccopoma may find themselves in a new region, out of which they may eventually disperse and thus compound the effects of their original invasion. In other cases, a species simply moves out of its native range into a region in which it had never previously lived. Both scenarios present planning concerns.
Some range expansions may prove harmless; therefore, it is not necessarily defenses scientists are after, but rather knowledge, of what species are on the move. Such knowledge is crucial in understanding whether or not a species is likely to cause damage, or if it can coexist agreeably in the present ecosystem. Unfortunately, “a major issue here is that it’s nearly impossible to predict which species will be moving north” — or south, depending on the point of origin — notes Dr. Jim Carlton, professor emeritus of marine sciences at Williams College. This makes it exceptionally difficult to forecast new introductions or prepare for their possible consequences. Additionally, because receiving regions are warming at different rates, it can be challenging to tell which currently uninvaded habitats or regions may soon prove hospitable to nonindigenous populations.
A variety of pre-invasion detection methods, however, are being explored in labs and harbors around the world, perhaps most prominently in New Zealand and Australia.
IN THE SPRING OF 2015, Bonamia ostreae, a devastating, non-native oyster parasite, was discovered in Marlborough Sound, off the coast of New Zealand’s South Island. To protect shellfish populations, the Ministry for Primary Industries (MPI) — a public service agency charged with addressing New Zealand’s biosecurity breaches — established zones of containment for the parasite and began surveillance efforts to detect further outbreaks. When farmed oysters around Stewart Island began to die off two years later, MPI identified B. ostreae as the culprit early on and halted its spread by culling all aquacultured oysters in the region. Oyster farmers were compensated for their losses by MPI; today, aquaculture practices are reestablished in the area with little sign of further parasite infestation.
New Zealand is a world leader in marine biosecurity practices, due in part to its dedicated marine pest management system. This system, run by MPI, implements preventative measures like biofouling and ballast water controls on foreign vessels to stop invasions before they occur. It also establishes baseline ecological surveys all around the islands, against which unfamiliar or nonindigenous species can be compared.
Dr. Ulla von Ammon, Postdoc of the biosecurity team at the Cawthron Institute in Nelson, attributes the country’s biosecurity success to modern genetic surveillance techniques as well. By using molecular methods such as monitoring environmental DNA (eDNA) in harbors and other busy waterways, researchers may be able to accurately target, detect, and potentially stop the spread of non-native marine organisms before they become established. These genetic approaches, which include analyzing water samples by techniques such as high-throughput sequencing and real-time polymerase chain reaction (PCR) — the same techniques used to detect coronaviruses — are often more sensitive and less time consuming than traditional diver surveillance, especially when the species in question arrive as larvae or are microscopic like B. ostreae, von Ammon says.
Additionally, she notes that New Zealand’s biosecurity public awareness programs seek to make responses to marine bioinvasions “more stringent, reliable, and easy for people to understand.”
PERHAPS OTHER NATIONS can learn from New Zealand. The US has made numerous attempts to combat non-native marine species, including the use of machinery like fish screens and seaweed mowers to address past invaders Chinese mitten crabs and Atlantic cordgrass along the Pacific coast. Over the years, such attempts have achieved varying levels of success. Yet, because there is no comprehensive review of US efforts to control marine bioinvasions, researchers are unable to determine the overall degree of success to date. Moreover, maintaining an effective federal bioinvasion program has proven strugglesome in recent years; in 2019, the Trump Administration halved the US National Invasive Species Council’s already meager $1.2 million annual budget and completely eliminated its Invasive Species Advisory Committee in the process.
Yet, in spite of these deregulations, experts like Dr. Carlton remain hopeful that with frequent media coverage of species invasions, including recent reports on deadly murder hornets as well as non-native mussels in Antarctica, the public is catching on to threats posed by both terrestrial and marine non-indigenous species. As a result, Carlton notes that there is now a “growing army of ‘citizen scientists’ who are our eyes and ears and voices on the ground,” alerting researchers to the presence of alien species before they become established. This active public understanding of marine bioinvasions, combined with the potential of new genetic surveillance methods, is, at least, a step in the right direction.
Dominick Leskiw’s research this summer was supported by the Buck Lab for Climate and Environment.
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